Abstract 13617: Protein Disulfide Isomerase is a Key Regulating Factor of Cardiac Stem Cell Function During Hypoxia
The human heart is a self-renewing organ characterized by the presence of c-kit-positive cardiac stem cell (hCSC) stored in niches and widespread within the myocardium. Stem cell niches are exposed to low oxygen tension and this metabolic adaptation offers a selective advantage to CSC compared to terminally differentiated cells, such as myocytes, during hypoxia. However, the molecular mechanisms are poorly understood. Protein disulfide isomerase (PDI), is a member of the unfolded protein response, which is activated to prevent protein misfolding during stress, as occurs during ischemia. The objective of this work was to determine whether PDI is present and functional in CSC and it is involved in the preservation of the stem cell pool during hypoxia.
Surgical specimens were collected from the atrial and ventricular myocardium of 21 patients and hCSCs and myocuted were isolated. This cohort of patients included 11 women and 10 men affected by ischemic cardiomyopathy; 11 patients also had diabetes. Age was comparable in women and men. The yield of CSCs harvested from each sample did not vary with age or diabetes The PDI was very low expressed in the myocytes, sampled from the ventricle and atria of the patients investigated. Interestingly, by qRT-PCR, a 2000-fold difference was found in PDI expression comparing CSC and myocytes . Subsequently, the effects of hypoxia (1% O2) were studied in hCSCs in vitro and analyzed at 12, 24, 48 and 96 hours. With respect to cells cultured in normoxia, 1% O2 led to upregulation of PDI and HIF1α transcripts in a time dependent manner. This results were coupled with an increase of the transcripts for the stemness associated genes c-kit, Oct4, Nanog and IGF-1R. Moreover, a high correlation was found between the expression of PDI in the CSC and the infarct size evaluated 5 months after revascularization. A highly significant direct correlation between improvement of ejection fraction at FU and hCSC length of telomeres (p<0.01; R2 0.358) telomerase activity (p<0.05; R2 0.34) and PDI expression was observed (p<0.05; R2 0.44).
In conclusion, our data indicate PDI is a key regulator of CSC response to hypoxia and favors the conservation of their undifferentiated phenotype and most importantly their potential activation after injury.
- © 2013 by American Heart Association, Inc.