Upregulation of Matrix Metalloproteinase-2 in the Arterial Vasculature Contributes to Stiffening and Vasomotor Dysfunction in Patients With Chronic Kidney Disease
Background— Cardiovascular disease is the leading cause of mortality in chronic kidney disease patients on maintenance dialysis. Given the importance of matrix metalloproteinase-2 (MMP-2) in matrix integrity, vascular cell function, and structural stability, we hypothesized that MMP-2 was elevated in the macrovasculature in dialyzed chronic kidney disease patients compared with chronic kidney disease patients not on dialysis and kidney donors.
Methods and Results— Arteries from live kidney donors (Adonor; n=30) and recipients (nondialysis [Anondialyzed], n=17; dialysis [Adialyzed], n=23 [peritoneal dialysis, n=10; hemodialysis, n=13]) were harvested during the transplantation procedure. Compared with Adonor, MMP-2 upregulation was evident in both recipient groups. Protein expression of latent plus active MMP-2 in Adialyzed was 2-fold that in Anondialyzed. MMP-2 activity increased with length of dialysis (r=0.573, P=0.004). In Adialyzed, medial elastic fiber fragmentation was pronounced, and the ratio of external elastic lamina to media was negatively correlated with MMP-2 activity (r=−0.638, P=0.001). Adialyzed was 25% stiffer than Anondialyzed; this increased stiffness correlated with MMP-2 activity (r=0.728, P<0.0001) and the severity of medial calcium deposition (r=0.748, P=0.001). The contractile function and endothelium-dependent relaxation were reduced by 35% to 55% in Adialyzed and were negatively associated with MMP-2 activity (r=−0.608, P=0.002; r=−0.520, P=0.019, respectively). Preincubation with MMP-2 inhibitor significantly improved contractility and relaxation in Adialyzed.
Conclusions— We describe a strong correlation between MMP-2 activation and elastic fiber disorganization, stiffness, calcification, and vasomotor dysfunction in the arterial vasculature in dialyzed chronic kidney disease patients. These findings may contribute to an improved understanding of mechanisms important in vascular health in chronic kidney disease patients.
Received January 6, 2009; accepted June 15, 2009.
Mortality from cardiovascular disease is 15 to 30 times higher in patients with chronic kidney disease (CKD) compared with the general population1–3 and is even higher in patients on peritoneal dialysis (PD) and hemodialysis (HD) therapy. These observations suggest that the disease manifestations of CKD are not only limited to the glomerulus but also generally affect the vascular system. Critical changes in vasomotor function and vessel structure could explain the propensity of cardiovascular disease in association with CKD progression.3
Clinical Perspective on p 801
Vascular function is determined by a set of factors that include endothelial secretion, smooth muscle contractility, and structural integrity. Vascular abnormalities develop early in CKD in parallel with cardiac abnormalities and become more severe as end-stage disease is reached. Endothelial dysfunction and reduced nitric oxide (NO) bioavailability are implicated as the initial steps in the vascular damage in CKD. Exaggerated production of vasoconstrictors (eg, norepinephrine, endothelin-1, and angiotensin) has been suggested to be associated with uremia.4–6 Several studies report decreased vascular responsiveness to adrenergic agonists in CKD and that this factor contributes to the hemodynamic instability and autonomic disturbances.7–9 It is generally accepted that structural alterations, including nonocclusive vascular remodeling, are prevalent in CKD.10,11 Increased aortic stiffness, as measured by pulse-wave velocity (PWV), and vascular calcification have been shown to be associated with unfavorable cardiovascular outcomes such as left ventricular hypertrophy, decreased coronary perfusion, and isolated systolic hypertension in dialyzed patients.10 A recent study has shown that medial calcification was evident in both predialyzed and dialyzed children, but factors specific to dialysis may be responsible for the extremely rapid calcification accompanied by extensive vascular remodeling.11
Vascular remodeling represents any enduring change in the size and/or composition of an adult blood vessel. The processes permit blood vessels to adapt to stressors but paradoxically may underline the pathogenesis of cardiovascular disease.12 Physiological and pathological vascular remodeling entails degradation and reorganization of extracellular matrix, explaining the recent great interest in matrix metalloproteinases (MMPs). The gelatinase MMP-2 is of particular importance in vascular biology because it is expressed abundantly in arterial vasculature and its activity is markedly modified during disease progression.12 In addition to the matrix-degrading property, MMP-2 has been shown to inhibit smooth muscle contraction, which could be associated with the development of aortic aneurysm and venous dilatation.12–15 MMPs are known to be activated in a cellular environment under oxidative stress and with reduced NO bioavailability.16 Inflammatory cells in the adventitia or smooth muscle cells in the media secrete MMP-2, and the release of degraded elastic fiber highly induces calcium deposition.17 Elastinolysis is the primary event impairing the arterial mechanical properties,15 and serum MMP-2 is associated with arterial stiffness.18 Serum MMP-2 has been suggested to be one of the strong independent variables linked to intima-media thickness in dialyzed patients.19 Recently, we have demonstrated that the upregulation of MMP-2 in human internal mammary artery is associated with reduced kidney function, ie, declining estimated glomerular filtration rate.20
We hypothesized that MMP-2 would be upregulated in the artery from dialyzed patients compared with nondialyzed CKD patients and kidney donors. Appreciating the potential different impacts that dialysis procedures themselves would have, we also compared arteries from PD and HD patients to determine whether they differ in MMP-2 activation and vascular function. We demonstrate that elevated MMP-2 in the artery from dialyzed patients is strongly associated with the degeneration of elastic fibers, arterial stiffening, calcification, and vasomotor dysfunction compared with arteries from nondialyzed patients. Given the known biological functions of MMP-2 in vascular health and disease progression, we suggest that the upregulation of MMP-2 may be one of the important pathological mechanisms by which the presence of CKD with and without dialysis exposure exacerbates vascular dysfunction.
Study Population Selection
Patients who were to undergo live donor kidney transplantation at St Paul’s Hospital (Vancouver, British Columbia, Canada) were approached for participation in the study, which was approved by the ethics boards of Providence Health Care and the University of British Columbia. Written informed consent was obtained from donors (n=30) and recipients (n=40) before surgery.
All patients consented to noninvasive measurements of vascular stiffness (PWV measurements)21 and the use of the discarded inferior epigastric artery (from recipients) and renal artery (from donors). Harvested vessels were placed in ice-cold RPMI in the presence of heparin and delivered to the laboratory for functional experiments within 1 hour. Medical records were used to obtain demographic data and information on cardiovascular risk factors and renal function at the time of transplantation. The estimated glomerular filtration rate was calculated from the Modification of Diet in Renal Diseases formula. We use Anondialyzed to denote the artery harvested from the patient who had not been on dialysis at the time of transplantation and Adialyzed to denote the artery from the patient who had been on either PD (n=10) or HD (n=13).
Note that a “ring” artery is needed for the functional and mechanical experiments. Because of this technical limitation, we were able to collect only 5 renal arteries from the donor group. However, for the molecular biology experiments, renal arterial segments could be used; thus, more donor samples were available.
Additional experiments performed included Western immunoblotting, gelatinolytic zymography, reverse zymography, Movat staining, von Kossa staining, in vivo PWV, isometric force measurement, and mechanical properties of artery.15,20,22,23 The specifics of these procedures are available in the online-only Data Supplement.
Data are reported as mean±SD. Comparisons between 2 groups were performed by unpaired t test. Comparisons of ≥3 groups were performed with 1-way ANOVA (with Bonferroni posthoc analysis for multiple comparisons). Differences between concentration-response curves (involve multiple parameters per patient) were analyzed by a linear mixed-effects model that accounted for correlated data using individual patient random effects. Correlations between MMP-2 activity and the vascular functional/ structural parameters were calculated with Spearman rank correlation. Correlations were studied when all data points were combined and in subgroups (ie, PD and HD). To investigate whether 2 regression lines were significantly different, we tested the equality of slopes and intercepts by using general linear models. If 2 linear regression lines had neither a different slope nor a different intercept, a common regression coefficient and the y intercept were used to describe the whole population. When ≥3 regression lines were compared, we tested for equality of all or just some of the lines by using general linear models. Construction of concentration-response curves and statistical analysis were performed with GraphPad Prism (version 4.03, GraphPad, San Diego, Calif) software and SPSS version 14.0 (SPSS Inc, Chicago, Ill).
Thirty donors and 40 transplant recipients consented to participate in the study. Of the recipients, 23 were on dialysis, and 17 were not. Table I of the online-only Data Supplement describes the demographics of the study groups. Among the recipients, the only difference was in medication use. More of the nondialysis patients than dialysis patients used calcium channel blockers, but there were no significant differences between these 2 cohorts in any other parameters. Note that the duration of exposure to CKD, defined as number of months since first nephrologist consult to dialysis start date or transplantation, is comparable between the 2 groups, as is the prevalence of diabetes mellitus and hypertension. On average, the dialysis group had been exposed to 37.6 months of dialysis treatment. Importantly, the donor and recipient ages were not different. We also describe the differences between the 10 PD and 13 HD patients. The only significant difference between those 2 groups was female gender.
Elevated Activation of MMP-2 in Adialyzed
The protein expression of latent MMP-2 in Adialyzed was greatly increased compared with that in Adonor and Anondialyzed (P<0.0001). Active MMP-2 expression in Anondialyzed and Adialyzed was 3.5-fold higher than that in Adonor. The PD group was not significantly different from the HD group with respect to latent (P=0.09) and active (P=0.23) MMP-2 expression (Figure 1A and 1B). Expression of tissue inhibitor of metalloproteinase (TIMP) -1 and TIMP-2, the major endogenous inhibitors of MMP-2 activation,12 was not different among all groups. However, the activities of TIMP-1 and TIMP-2 in Adonor were significantly higher than those in Adialyzed (P=0.038 and P=0.007, respectively). TIMP-1 and TIMP-2 activities in Adialyzed were only 75% and 64%, respectively, of those of Anondialyzed. There was no difference in TIMP activity between the PD and HD groups (Figure 1C through 1E).
Activities of latent and active MMP-2 were significantly (P<0.001) less in Adonor compared with the recipient groups. Latent and active MMP-2 activities were upregulated in Adialyzed by 43% and 146%, respectively, compared with Anondialyzed (Figure 2A and 2B). We pooled the activities of the latent and active forms of MMP-2 and observed a positive correlation with the length of CKD before renal replacement therapy (transplantation or dialysis) in the nondialyzed group (r=0.713, P=0.001). This correlation was absent in the PD (P=0.227) and HD (P=0.521) groups, which were not significantly different from each other in slope (P=0.720) and intercept (P=0.969) (Figure 2C). The total MMP-2 activity formed a positive correlation with length of dialysis (r=0.573, P=0.004) when all data were combined. In the subgroup analysis, the linear regression lines between the PD and HD groups were not significantly different in slope (P=0.555) and intercept (P=0.187) (Figure 2D).
Although the total MMP-2 activity was comparable between the PD and HD groups (Figure 2A), of interest, there appeared to be a difference in the increase in MMP-2 level as a function of exposure time to different dialysis modalities. A pronounced increase in MMP-2 activity (ie, >325 arbitrary units, the averaged value from all dialyzed subjects) was seen in HD patients earlier in the course of their treatment (ie, after 29.5±6.2 months of exposure; n=8) than in the PD patients (ie, after 145±65 months of exposure; n=5; P=0.05).
Degradation of Elastic Fiber in the Media of Adialyzed Correlates With MMP-2 Activity
On Movat histology, elastic fiber was present in the internal elastic lamina, tunica media, and external elastic lamina (EEL) of the artery (Figure 3). Within the tunica media, a uniformly long and continuous structure of elastic fiber was found in both Adonor and Anondialyzed (Figure 3D and 3F). However, elastic fiber in the tunica media of Adialyzed was thinner and appeared fragmented (Figure 3H and 3J). Along the EEL, a disintegrated organization of elastic fiber was evident in recipient groups, whereas in Adonor, it presented as a continuous and intact structure (Figure 3E). Although the intima-media thickness among Adonor (0.508±0.024 mm), Anondialyzed (0.502±0.028 mm), and Adialyzed (0.500±0.025 mm) was not significantly different, the ratio of EEL to medial thickness in Anondialyzed was only 77% of that in Adonor (P=0.01). This ratio was further decreased in Adialyzed by 35% compared with that in Anondialyzed (Figure 3L). Intimal thickening was detected in 46% of Adialyzed but absent in Anondialyzed (Figure 3A through 3C).
There was a negative correlation between the activity of MMP-2 and the ratio of EEL to media in Adialyzed (r=−0.638, P=0.001; Figure 3M). This correlation was weaker in Anondialyzed (r=−0.42, P=0.05).
Increased Stiffness in Adialyzed Is Associated With MMP-2 Activity
Arterial stiffness was evaluated in vitro from the J-shaped stress-strain curve (Figure 4A). Measurement of arterial stiffness (the K value) indicated that Adialyzed was 25% and 30% stiffer than Anondialyzed and Adonors (P=0.02) (Figure 4B). When all data points were combined, the K value demonstrated a strong correlation with the in vivo PWV (r=0.728, P<0.0001). In the subgroup analysis, this strong correlation was seen in the nondialyzed (r=0.722, P=0.002), PD (r=0.913, P=0.002), and HD (r=0.783, P=0.013) groups (Figure 4C). These 4 linear regression lines were not different in slope (P=0.157) but intercept (P=0.039).
To investigate the structural stability, we measured the breaking stress, which represents the breakage of elastic fiber and smooth muscle association, the point at which the vessel could no longer maintain the stable resting tension. The breaking stress was >50% lower in Adialyzed than in Adonor and Anondialyzed; the ease with which preservation of stable tension was lost suggested the structural weakening in Adialyzed (Figure 4D).
The K value positively correlated with MMP-2 activity in Adialyzed (r=0.678, P=0.001) but not in Anondialyzed (r=0.326, P=0.218). In the subgroup analysis, the PD and HD linear regression lines were significantly different in slope (P=0.05) (Figure 4E).
Increased Calcium Deposition in Adialyzed Is Associated With Increased MMP-2 Activity
From the von Kossa staining, calcium/ phosphate deposition was evident, to various degrees, in 74% of CKD patients. In Adialyzed, calcium deposition was more severe than in Anondialyzed (Figure 5A through C). The semiquantified calcium deposition positively correlated with the K value in Adialyzed (r=0.748, P=0.001) but not in Anondialyzed (r=0.16, P=0.54; Figure 5D).
Because vascular smooth muscle cells release not only calcium but also MMPs during the process of calcification,24 we sought to determine whether the increased MMP-2 was a result of the greater calcification in Adialyzed or whether it was associated with exposure to dialysis. We compared Anondialyzed and Adialyzed with similar graded calcium deposition. Significantly more MMP-2 was present in Adialyzed (Figure 5E). We also observed an increase in calcification severity with length of dialysis (Figure 5F).
Vascular Dysfunction in Adialyzed Correlates With MMP-2 Activation
Vasoconstriction in response to KCl in Adialyzed was only 30% and 50% of that in the nondialyzed and donor groups, respectively (Figure 6A). The maximal force (Emax) induced by 50 μmol/L phenylephrine in Adialyzed was 65% of that in Anondialyzed (Figure 6B), although the pEC50 values were not significantly different between 2 groups (nondialyzed, 5.42±0.26; dialyzed, 5.39±0.46). We also stimulated vasoconstriction with angiotensin, serotonin, and endothelin-1, and Adialyzed developed 45% to 55% less force regardless of the means of stimulation (Figure 6B).
The KCl-stimulated contraction was negatively correlated with MMP-2 activity in Adialyzed (r=−0.608, P=0.002; Figure 6C) but not in Anondialyzed (r=−0.22, P=0.65). When Adialyzed was preincubated with specific MMP-2 inhibitor, the phenylephrine-induced contraction was significantly (P=0.02) improved (Figure 6D).
The maximal response of acetylcholine-stimulated endothelium-dependent relaxation in Adonor was 48% greater than that in Adialyzed (P=0.04). The acetylcholine response in Adialyzed was only 66% of that in Anondialyzed despite the similar pEC50 (nondialyzed, 6.88±0.25; dialyzed, 6.81±0.47; Figure 7A). In Adialyzed and Anondialyzed, the expression of phosphorylated endothelial NO synthase (eNOSSer1177), which indicates the activation of endothelial NO synthase, was only 50% of that in Adonor (Figure 7B). The endothelium-dependent relaxation in the Adialyzed was negatively correlated with MMP-2 activity (r=−0.520, P=0.019; Figure 7C), but this relation was absent in Anondialyzed (P=0.55). Preincubation with specific MMP-2 inhibitor improved the acetylcholine relaxation by 247% in Adialyzed with severely deteriorated endothelial function (<30% relaxation). However, MMP-2 inhibitor did not improve relaxation in the vessel with better endothelial function (Figure 7D).
Patients with CKD at any stage are at increased risk of cardiovascular complications, with the highest risk being in the dialysis group.1–3 Various hypotheses and observational studies suggest that dialysis procedures per se may be responsible for detrimental changes in vascular function and structure, although how this occurs remains an area of active investigation. This study explores the hypothesis that MMP-2 upregulation may be one of the key processes explaining the aberrations in structure and function seen in CKD. We have used a cross-sectional study design to examine human tissue from donors and recipients at the time of kidney transplantation. Living kidney transplantation represents a unique opportunity to examine vessels and clinical status in a controlled situation. We describe a number of novel findings that support the hypothesis that CKD patients, more notably those on dialysis, have alterations in structural and functional properties of the arterial vasculature. In Adialyzed, the upregulation of MMP-2 is strongly associated with length of dialysis, elastic fiber degradation and arterial stiffening, medial calcification, and impaired vasocontraction and endothelium-dependent relaxation. Upregulation of MMP-2 appears to begin in the predialysis stage, and those exposed to PD and HD appear to exhibit further activation of MMP-2. Given the variety of events that occur during the dialysis procedure that may influence MMP-2 levels (detailed more fully below), the results also suggest that MMP-2 could be one of the plausible causal mechanisms that contribute to structural remodeling, vascular dysfunction, and ultimately the enhanced cardiovascular burden in adult CKD patients receiving maintenance dialysis.
We have described upregulation of MMP-2 in CKD in general relative to donors and, within the recipient population, differential upregulation between those on and not on dialysis. MMPs play diverse roles in arterial pathological processes during restenosis, calcification, atherosclerosis, and aneurysmal degeneration.12 The altered regulation of MMPs in the vasculature may be a critical component in linking CKD to vascular changes that cause both microvascular and macrovascular disease and ultimately cardiovascular disease. We have previously demonstrated that MMP-2 activity is associated with reduced renal function in the human internal mammary artery.20 The present data extend our previous findings (which were in early CKD patients) and show that along a continuum, dialyzed patients have greater activation of MMP-2 activity than the nondialyzed group. Nevertheless, in the nondialyzed group, arterial MMP-2 activity appears to be correlated with the duration of CKD, whereas in the dialyzed group, arterial MMP-2 activity does not relate to the duration of CKD before dialysis initiation. Importantly, MMP-2 activation was associated with the duration of dialysis, thus leading to the hypothesis that the dialysis procedure may promote MMP-2 activity. Exposure to dialysis treatments would lead to abnormalities in metabolic, humoral, inflammatory, and hemodynamic factors (eg, chronic volume overload, oxidative stress, vitamin D deficiency, hyperphosphatemia, hyperhomocysteinemia, and upregulation of cytokines, growth factors, and C-reactive protein), which are known to be promoters of MMP-2 activation.1,12,25–28 Moreover, our observation suggests that MMP-2 may be more profoundly and quickly upregulated by the HD procedure. However, future studies need to measure MMP-2 activity from tissue and blood at the beginning of dialysis in different modalities (eg, HD and PD) and follow those levels over time before definite statements can be made. Taken together, the upregulation of MMP-2 and the downregulation of TIMPs in Adialyzed indicate a favorable proteolytic activity in the vasculature.
The strong correlation between MMP-2 activity and elastic fiber degeneration and arterial stiffness in Adialyzed supports the hypothesis that MMP-2 would be a crucial dialysis-related factor modifying the matrix component and leading to arterial stiffness. MMPs are secreted by smooth muscle cells and inflammatory cells in the adventitia or media, which consequently leads to degradation of medial elastic fiber.12 Elastic fiber is essential for arterial elasticity; therefore, the fragmentation seen in Adialyzed may explain the structural weakening and reduction of elasticity. Our observation of an increased incidence of neointimal formation is concordant with the current literature that suggests that MMP-2 activation is a strong independent variable linked to intima-media thickness in dialyzed patients.11,12,19,25
The significant correlation between arterial stiffness and calcium deposition in the Adialyzed is also concordant with other investigations. It has been shown that vascular calcification in dialyzed patients was associated with increased stiffness of large-capacity, elastic-type arteries like the aorta, brachial artery, and common carotid artery.1,11,21,24,29 We suggest, on the basis of published literature, that there may be a potential relationship between MMP-2 and calcification, given that MMP-2 causes elastinolysis and disrupts arterial elasticity. During vascular calcification, smooth muscle cells undergo apoptosis and phenotypic transformation and release a variety of proteinases, including MMPs.24 The present data demonstrate that the increased MMP-2 activity in Adialyzed is associated with exposure to dialysis, not calcification per se. Our observations complement the current literature and suggest the detrimental roles of MMP-2 in vascular remodeling and functional aberration during the osteogenic and matrix degenerative processes.15,17,22,30
We performed a comprehensive set of functional experiments to elucidate how the structural deterioration in the vasculature influences the vasomotor function in patients with various degrees of CKD. The decreased response to KCl may be explained by the clinical observation that dialyzed patients have an elevated total body potassium and serum potassium, likely causing some degree of desensitization. The reduction of agonist-induced contraction could be due to the paucity of α-smooth muscle actin expression in the arteries11,31 and the increased levels of vasoconstrictors4–6 causing receptor downregulation and desensitization. Calcium entry for contraction could also be inhibited by the decreased Na+/K+-ATPase activity in muscle cells32 and the upregulation of MMP-2 in Adialyzed,13,14 which indicates its nonproteolytic property in the vasculature.12–14 Patients on dialysis have been reported to exhibit indicators of endothelial injury and reduction of NO synthesis.33 The reciprocal relation between NO bioavailability and MMP activation16 corroborates the association between endothelium-dependent relaxation and MMP-2 activity in the dialyzed group. Nevertheless, from this systematic and comprehensive set of functional experiments, we have demonstrated the improvement in contraction and relaxation by antagonizing MMP-2 activity, which strongly supports our hypothesis that MMP-2 plays a critical role in CKD- and dialyzed-associated vasomotor dysfunction.
This study has limitations. First, the exploration of a single set of hypotheses related to MMP-2 means that we may miss the opportunity to examine other MMPs (eg, MMP-9, MMP-1, and MMP-3) that are important in vascular remodeling. From our preliminary observation, there was a moderate increase in arterial MMP-9 activity in the dialyzed group, but it did not reach statistical significance (P=0.19). Second, the exposures of patients to CKD care were not identical (eg, dialysis and nondialysis; PD and HD). However, we have attempted to analyze the data with appropriate separation of those factors that were overtly different between the groups. Given that this cohort includes only patients receiving live kidney transplantation who were demographically and clinically similar, the issue of “selection of the fittest” arises. The lesions described would likely represent the least severe of all CKD populations, given that they are well enough to undergo transplantation. Thus, the signal we have demonstrated herein may be much more profound if we were to study long-term dialysis patients not eligible for transplantation because of high cardiovascular disease burden or those who were receiving cadaveric transplantation with longer dialysis exposure. Third, the cross-sectional nature of the study does not allow us to confirm or refute that the dialysis procedure leads to worsening of vascular function because it is confounded by time, eg, longer total duration of CKD exposure in those who undergo dialysis before preemptive transplantation. Nonetheless, our results raise interesting questions for further testing using more sophisticated and appropriate methodology. Given that access to tissue at different stages of disease in 1 individual may be difficult, the present study design is appropriate for exploratory and pragmatic purposes. Thus, this is a relative limitation and gives us a conservative estimate of the possible effect of time, dialysis, or both on vascular health. Fourth, in an adult study, all patients have some degree of preexisting confounders for vascular disease (eg, diabetes mellitus, dyslipidemia, and hypertension). However, the incidence of these concomitant diseases was not significantly different between the 2 recipient groups. Note again that all of these individuals had been screened and found to be of sufficiently good cardiovascular health to proceed with transplantation. Ideally, tissue in pediatric patients may lead to further insights because young patients tend to have less vascular disease burden. Finally, the relatively small number of patients in the subgroups limits our ability to infer any statistical difference between groups because of power to detect true differences of moderate magnitude.
In this unique study using human vessels from healthy live kidney donors and transplant recipients, we have described an interesting relationship between MMP-2 activation and elastic fiber degeneration, stiffening, medial calcification, and vasomotor dysfunction in macroarterial vasculature. From described pathophysiological mechanisms, it is possible to postulate that the activation of MMP-2 and the resulting structural and functional changes in the vasculature may be accelerated by the PD and HD procedures. Loss of structural and functional integrity as a result of differences in arterial MMP-2 activity may be an important component in understanding the susceptibility of vascular disease in CKD patients. Furthermore, it may be that the manipulation of MMP-2 activity could be a potential therapeutic strategy for controlling vascular function, calcification, and arterial stiffening in patients with kidney disease. We offer this set of experiments in human tissue as evidence to support further exploration of disease mechanisms, and the possible role of MMP-2 in the pathobiology of vascular disease in CKD warrants serious consideration in future studies.
Sources of Funding
This study was funded by the Kidney Foundation of Canada. Dr Chung is a recipient of the Michael Smith Foundation for Health Research/St Paul Hospital Foundation Trainee Award. H.H.C. Yang is a recipient of the Michael Smith Foundation for Health Research Junior Trainee Award and NSERC: Alexander Graham Bell Canada Graduate Scholarship.
Schiffrin EL, Lipman ML, Mann JF. Chronic kidney disease: effects on the cardiovascular system. Circulation. 2007; 116: 85–97.
Sarnak MJ, Levey AS, Schoolwerth AC, Coresh J, Culleton B, Hamm LL, McCullough PA, Kasiske BL, Kelepouris E, Klag MJ, Parfrey P, Pfeffer M, Raij L, Spinosa DJ, Wilson PW, for the American Heart Association Councils on Kidney in Cardiovascular Disease, High Blood Pressure Research, Clinical Cardiology, and Epidemiology and Prevention. Kidney disease as a risk factor for development of cardiovascular disease: a statement from the American Heart Association Councils on Kidney in Cardiovascular Disease, High Blood Pressure Research, Clinical Cardiology, and Epidemiology and Prevention. Circulation. 2003; 108: 2154–2169.
Shichiri M, Hirata Y, Ando K, Emori T, Ohta K, Kimoto S, Ogura M, Inoue A, Marumo F. Plasma endothelin levels in hypertension and chronic renal failure. Hypertension. 1990; 15: 493–496.
Safar ME, Benetos A. Factors influencing arterial stiffness in systolic hypertension in the elderly: role of sodium and the renin-angiotensin system. Am J Hypertens. 2003; 16: 249–258.
Blacher J, Guerin AP, Pannier B, Marchais SJ, Safar ME, London GM. Impact of aortic stiffness on survival in end-stage renal disease. Circulation. 1999; 99: 2434–2439.
Shroff RC, McNair R, Figg N, Skepper JN, Schurgers L, Gupta A, Hiorns M, Donald AE, Deanfield J, Rees L, Shanahan CM. Dialysis accelerates medial vascular calcification in part by triggering smooth muscle cell apoptosis. Circulation. 2008; 118: 1748–1757.
Galis ZS, Khatri JJ. Matrix metalloproteinases in vascular remodeling and atherogenesis: the good, the bad, and the ugly. Circ Res. 2002; 90: 251–262.
Chung AW, Au Yeung K, Sandor GG, Judge DP, Dietz HC, van Breemen C. Loss of elastic fiber integrity and reduction of vascular smooth muscle contraction resulting from the upregulated activities of matrix metalloproteinase-2 and -9 in the thoracic aortic aneurysm in Marfan syndrome. Circ Res. 2007; 101: 512–522.
Basalyga DM, Simionescu DT, Xiong W, Baxter BT, Starcher BC, Vyavahare NR. Elastin degradation and calcification in an abdominal aorta injury model: role of matrix metalloproteinases. Circulation. 2004; 110: 3480–3487.
Yasmin, McEniery CM, Wallace S, Dakham Z, Pulsalkar P, Maki-Petaja K, Ashby MJ, Cockcroft JR, Wilkinson IB. Matrix metalloproteinase-9 (MMP-9), MMP-2, and serum elastase activity are associated with systolic hypertension and arterial stiffness. Arterioscler Thromb Vasc Biol. 2005; 25: 372–378.
Chung AW, Yang HHC, Radomski MW, van Breemen C. Long-term doxycycline is more effective than atenolol to prevent thoracic aortic aneurysm in Marfan syndrome through the inhibition of matrix metalloproteinase-2 and -9. Circ Res. 2008; 102: e73–e85.
Chung AW, Hsiang YN, Matzke LA, McManus BM, van Breemen C, Okon EB. Reduced expression of vascular endothelial growth factor paralleled with the increased angiostatin expression resulting from the upregulated activities of matrix metalloproteinase-2 and -9 in human type 2 diabetic arterial vasculature. Circ Res. 2006; 99: 140–148.
Giachelli CM, Speer MY, Li X, Rajachar RM, Yang H. Regulation of vascular calcification: roles of phosphate and osteopontin. Circ Res. 2005; 96: 717–722.
Annuk M, Zilmer M, Lind L, Linde T, Fellström B. Oxidative stress and endothelial function in chronic renal failure. J Am Soc Nephrol. 2001; 12: 2747–2752.
Vlachopoulos C, Dima I, Aznaouridis K, Vasiliadou C, Ioakeimidis N, Aggeli C, Toutouza M, Stefanadis C. Acute systemic inflammation increases arterial stiffness and decreases wave reflections in healthy individuals. Circulation. 2005; 112: 2193–2200.
Guérin AP, London GM, Marchais SJ, Metivier F. Arterial stiffening and vascular calcifications in end-stage renal disease. Nephrol Dial Transplant. 2000; 15: 1014–1021.
Qin X, Corriere MA, Matrisian LM, Guzman RJ. Matrix metalloproteinase inhibition attenuates aortic calcification. Arterioscler Thromb Vasc Biol. 2006; 26: 1510–1516.
Schildmeyer LA, Braun R, Taffet G, Debiasi M, Burns AE, Bradley A, Schwartz RJ. Impaired vascular contractility and blood pressure homeostasis in the smooth muscle alpha-actin null mouse. FASEB J. 2000; 14: 2213–2220.
Cardiovascular disease is the leading cause of mortality in chronic kidney disease (CKD) patients on maintenance dialysis. Given the known biological functions of matrix metalloproteinase-2 (MMP-2) in vascular cell function and structural stability, we hypothesize that MMP-2 upregulation may be responsible for the vascular dysfunction and remodeling seen in CKD and describe differential regulation according to dialysis status. Using a cross-sectional study, we examine human vessels obtained from donors and recipients at the time of kidney transplantation. We demonstrate the pronounced MMP-2 upregulation in the arteries from dialyzed patients, and the results suggest that MMP-2 activation may be an important causal mechanism by which structural remodeling and vascular dysfunction occur in adult CKD patients receiving dialysis. Although numerous animal studies have examined the pathological modifications in the vasculature during CKD development, many have demonstrated inconsistent results in different models and strains and thus may be of limited applicability to the human condition. The complex vascular pathology in CKD seen in middle-aged and elderly patients is impossible to reproduce in laboratory animals. Therefore, this translational study has the advantage of examining human vessels; in doing so, we may begin to characterize some of the fundamental mechanisms of vascular disease in CKD. Given the importance of MMP-2 in maintaining vascular integrity, our findings are highly clinically relevant, and with the increasing interest in linking basic science and clinical science, we believe that the observed MMP-2 upregulation and its association with vascular dysfunction will stimulate others to explore this avenue of research further.
The online-only Data Supplement is available with this article at http://circ.ahajournals.org/cgi/content/full/CIRCULATIONAHA.109.862565/DC1.