Regulation of autophagy in cardiomyocytes by Ins(1,4,5)P3 and IP3 -receptors

• Published in: Journal of molecular and cellular cardiology 2013-01, Vol.54, p.19-24
• Main Authors: Wong, Albert, Grubb, David R, Cooley, Nicola, Luo, Jieting, Woodcock, Elizabeth A
• Format: Article
• Language: English
• Subjects: Autophagosome; Beclin-1; Cardiovascular; FoxO1; Ins(1,4,5)P3; IP3-5-phosphatase; IP3-R
• ISSN: 0022-2828; 1095-8584
• DOI: 10.1016/j.yjmcc.2012.10.014

Abstract Autophagy is a process that removes damaged proteins and organelles and is of particular importance in terminally differentiated cells such as cardiomyocytes, where it has primarily a protective role. We investigated the involvement of inositol(1,4,5) tris phosphate (Ins(1,4,5)P3 ) and its receptors in autophagic responses in neonatal rat ventricular myocytes (NRVM). Treatment with the IP3 -receptor (IP3 -R) antagonist 2-aminoethoxydiphenyl borate (2-APB) at 5 or 20 μmol/L resulted in an increase in autophagosome content, defined as puncta labeled by antibody to microtubule associated light chain 3 (LC3). 2-APB also increased autophagic flux, indicated by heightened LC3II accumulation, which was further enhanced by bafilomycin (10 nmol/L). Expression of Ins(1,4,5)P3 5-phosphatase (IP3 -5-Pase) to deplete Ins(1,4,5)P3 also increased LC3-labeled puncta and LC3II content, suggesting that Ins(1,4,5)P3 inhibits autophagy. The IP3 -R can act as an inhibitory scaffold sequestering the autophagic effector, beclin-1 to its ligand binding domain (LBD). Expression of GFP-IP3 -R-LBD inhibited autophagic signaling and furthermore, beclin-1 co-immunoprecipitated with the IP3 -R-LBD. A mutant GFP-IP3 -R-LBD with reduced ability to bind Ins(1,4,5)P3 bound beclin-1 and inhibited autophagy similarly to the wild type sequence. These data provide evidence that Ins(1,4,5)P3 and IP3 -R act as inhibitors of autophagic responses in cardiomyocytes. By suppressing autophagy, IP3 -R may contribute to cardiac pathology.