Abstract Or113: Identification of Newly Synthesized Protein in Cardiomyocytes after Myocardial Infarction

Abstract

Compared to mRNA, proteins perform ultimate functions in the heart and can be rapidly upregulated or downregulated in response to environmental inputs. Identifying how the proteome is altered in cardiomyocytes (CMs) after myocardial infarction (MI) will improve our understanding of the stress response signaling after MI and contribute to developing new therapeutic strategies. Here, we developed a method for determining which proteins in CMs are newly synthesized after MI by using mice expressing a mutant methionyl-tRNA synthetase that incorporates the non-canonical amino acid azidonorleucine into the newly synthesized peptides of CMs. We found that the proteins synthesized at the highest levels in homeostasis are involved in sarcomere structure and metabolism, which aligns with immunofluorescence staining results that showed enrichment of newly synthesized proteins localized at the sarcomere and intercalated disc. We showed that α-actin, a critical component of the sarcomere, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), an enzyme for glucose metabolism, are highly dynamic and require constant protein synthesis for maintenance. After MI, protein synthesis in CMs within the infarct area is halted, and the border zone CMs showed reduced protein synthesis. Most notably, proteins associated with mitochondrial oxidative phosphorylation are reduced compared with sham. By integrating with spatial transcriptomics, we also discovered that the MI-induced genes are enriched in CMs within the infarcted areas. These CMs exhibit decreased general protein synthesis, indicating a decoupling of transcriptional and translational regulation following MI. Collectively, our findings revealed that CMs rapidly respond to injuries by controlling protein synthesis, which is independent of the expression of mRNAs.