UPREGULATION OF CD38 AND DOWNREGULATION OF NAD IN MITOCHONDRIA OF LEFT VENTRICULAR MYOCARDIUM OF DOGS WITH HEART FAILURE: A CELLULAR ENERGY-LIMITING MALADAPTATION

Background: Nicotinamide adenine dinucleotide (NAD) is a crucial regulator of signaling pathways important in the generation cyclic-ADP-ribose and the regulator of the NAD-dependent deacetylases sirtuins. NAD itself is regulated by CD38, a 45-kD transmembrane glycoprotein ubiquitously distributed and has multifunctional enzyme activity including a major NADase activity. Studies have shown that NAD depletion is associated with increased oxidative stress and opening of the mitochondrial (MITO) permeability transition pores, maladaptations that limit cellular energy-dependent functions and promotes cellular injury and death. This study tested the hypothesis that protein levels of CD38 are elevated in MITO of LV myocardium of dogs with heart failure (HF) and leads to downregulation of NAD. Methods: Studies were performed in LV tissue obtained from 7 HF dogs (LV ejection fraction ≤35% and 6 normal (NL) dogs. MITO were isolated from LV tissue and used to prepare SDS-extract. Protein level of CD38 and porin, a MITO protein used as an internal loading control, were determined using Western blotting coupled with chemiluminescence detection and band intensities expressed in densitometric units (du). CD38 was normalized to porin. NAD levels were determined in isolated MITO using an NAD+/NADH quantitation kit and expressed as pmols/mg protein. Results: Protein levels of porin in MITO of LV were similar between NL and HF dogs (0.66 ± 0.02 vs. 0.64 ± 0.04 du). CD38 normalized to porin was significantly increased in dogs with HF compared to NL dogs (2.64 ± 0.30 vs. 1.05 ± 0.06, p\u3c0.05) whereas NAD levels were markedly and significantly reduced in HF compared to NL dogs (7.9 ± 0.9 vs. 34.2 ± 1.8, p\u3c0.05). Conclusion: CD38 protein levels are markedly elevated and NAD levels markedly downregulated in MITO of LV myocardium of dogs with chronic HF. Therapies that normalizes CD38 and/or NAD levels may prove beneficial in HF by eliciting improved cellular energetics and by limiting cellular injury and ongoing cell death