Abstract 1912: Neural Cell Adhesion Molecule is a Cardioprotective Factor Upregulated by Metabolic Stress
Purpose: The failing heart is characterized by alterations in energy metabolism. To screen for cell-surface proteins showing enhanced expression under metabolic stress, we performed a signal sequence trap in combination with a functional cloning method.
Methods and results: We screened for cell-surface proteins showing enhanced expression using oligomycin, a mitochondorial inhibitor in H9C2 rat cardiac myoblasts. One of the identified genes was neural cell adhesion molecule (NCAM). In H9C2 and primary rat cardiac myocytes, oligomycin treatment significantly upregulated the mRNA and protein level of NCAM in a p38-dependent manner, whereas phenylephrine and AT-II did not. To analyze the expression pattern of NCAM in diseased hearts in vivo, we examined the NCAM expression in a mouse MI model. mRNA was upregulated 15.2±0.20 fold in the infarcted area (P<0.01). Immunohistochemical analysis demonstrated that NCAM was strongly expressed in residual cardiac myocytes inside and adjacent to infarcted scars at both the acute and chronic phase, whereas it was detectable only at the intercalated discs in the non-infarcted area and sham-operated model. We also examined the NCAM expression pattern in Dahl salt-sensitive (DS) rats during LVH and CHF periods. NCAM expression was enhanced by 3.0±0.48 fold in the LVH stage (P<0.01) and further increased by 24.1±2.34 fold (P<0.001) in the heart failure stage. Immunohistochemical analysis demonstrated that strong NCAM staining was observed in the subendomyocardium surrounding the fibrotic area. To investigate the role of NCAM in cardiac cells, we introduced siRNA against NCAM by lentivirus. Proliferation of H9C2 was significantly reduced when NCAM was knocked down. The survival rate of cardiac myocytes treated with oligomycin was significantly reduced when NCAM was knocked down (86±0.02% vs. 54.6±0.11%, P<0.05), suggesting the protective role of endogenous NCAM. However, stimulation of NCAM with synthetic peptide activated AKT and increased the survival rates of cardiac myocytes dose dependently, but this effect was abolished by treatment with PI3K inhibitor.
Conclusion: NCAM may play a protective role in the metabolically stressed heart and may be available as a new therapeutic target.