Abstract 3870: Microtubule Affinity-Regulating Kinase (MARK)-2 Down-Regulation in Pressure-Hypertrophied Myocardium Promotes Microtubule Network Densification
The MARK family of protein kinases phosphorylate the microtubule-associated proteins (MAPs) that bind to and stabilize microtubules (MTs), causing MAP release from microtubules and microtubule depolymerization. In neurons, this plays a critical role in the formation of neurofibrilatory tangles in Alzheimer’s disease. However, the role of MARKs in the dense microtubule network in some forms of heart disease has been unknown. Since changes in cardiac MTs in hypertrophy are the opposite of those in neurons in Alzheimer’s, we hypothesized that MARKs might be down-regulated in hypertrophy and promote MT polymerization. The activity and protein levels of MARK2, the most abundant cardiac MARK isoform, were measured in the feline models of pathological right ventricular (RV) pressure overload (PAB) and physiological RV volume overload (ASD). MARK2 activity and protein were decreased within 48 hours in the PAB RV and remained downregulated for at least 4 weeks, whereas MARK2 activity and protein were unchanged in the 4 week ASD RV. To test the potential of MARK as a therapeutic agent in preventing the development of the abnormal MT network seen in severe pressure overload hypertrophy, HA-tagged human MARK2 and MARK4 cDNA (gifts from Dr. Drewes (J. Biol. Chem., Vol. 279, Issue 7, 5915, 2004) were used to generate recombinant adenoviruses of MARK2 (AdMARK2) and MARK4 (AdMARK4). AdMARK2 and AdMARK4 were then used for adenovirus-mediated expression of MARK2 and MARK4 in isolated normal and 4 week PAB RV adult feline cardiocytes. The cardiocytes overexpressing MARK2 and MARK4 were normal in shape and size. The polymerized fraction of cardiac α β-tubulin heterodimers was decreased by about 70% in the cardiocytes overexpressing MARK2 or MARK4 compared with those infected with β-gal adenovirus. Consistent with this, the MT network seen via confocal microscopy was substantially depolymerized in normal and hypertrophied cardiocytes overexpressing MARK2 or MARK4. These results provide the first evidence that MARK2 is downregulated in pressure-hypertrophied myocardium, which in turn promotes a dense MT network. They also show that overexpression of MARKs may correct this abnormality, such that MARKs may represent a novel therapeutic target for heart failure treatment.