Summary Alternative splicing greatly expands the coding capacity of the human genome, but how many alternative transcripts are translated as proteins or carry functional importance remains unknown and awaits experimental verification. Here, we describe a protocol that combines transcriptomics (RNA-seq) and proteomics (mass spectrometry [MS]) analyses to identify alternative isoforms in proteomes. This workflow is applicable to custom-generated RNA-seq and MS data from matching samples, as well as the reanalysis of existing transcriptomics and proteomics datasets in public repositories. For complete details on the use and execution of this protocol, please refer to Lau et al. (2019) .

The risks of heart diseases are significantly modulated by age and sex, but how these factors influence baseline cardiac gene expression remains incompletely understood. Here we used RNA sequencing and mass spectrometry to compare gene expression in female and male young adult (4 months) and early aging (20 months) mouse hearts, identifying thousands of age and sex dependent gene expression signatures. Sexually dimorphic cardiac genes are broadly distributed, functioning in mitochondrial metabolism, translation, and other processes. In parallel, we found over 800 genes with differential aging response between male and female, including genes in cAMP and PKA signaling. Analysis of the sex-adjusted aging cardiac transcriptome revealed a widespread remodeling of exon usage patterns that is largely independent from differential gene expression, concomitant with upstream changes in RNA-binding protein and splice factor transcripts. To evaluate the impact of the splicing events on cardiac proteoform composition, we applied an RNA-guided-proteomics computational pipeline to analyze the mass spectrometry data, and detected hundreds of putative splice variant proteins that have the potential to rewire the cardiac proteome. Taken together, the results here suggest that cardiac aging is associated with (1) widespread sex-biased aging genes, and (2) a rewiring of RNA splicing programs, including sex- and age- dependent changes in exon usages and splice patterns that have the potential to influence cardiac protein structure and function. These changes contribute to the emerging evidence for considerable sexual dimorphism in the cardiac aging process that should be considered in the search for disease mechanisms.

No abstract

The risks of heart diseases are significantly modulated by biological age and sex, but how these factors influence baseline cardiac gene expression remains incompletely understood. Here we characterized young adult and early aging mouse hearts using proteogenomics to identify age and sex dependent gene expression signatures in the mouse heart. RNA sequencing from 4 months old and 20 months old female and male C57BL/6J hearts identified thousands of genes with differential transcript abundances both between sexes (male vs. female) and across age groups (20 mo. vs. 4 mo.). Sex-associated cardiac genes are broadly distributed, functioning in the TCA cycle, mitochondrial translation, autophagy, and other processes. In addition, we found over 800 genes with differential aging response between male and female, which are enriched in calmodulin signaling and cell cycle regulations. Comparison with mass spectrometry data shows a cluster of metabolism genes with up-regulated transcripts but down-regulated protein levels in aging hearts, consistent with an uncoupling of transcriptional regulations in the genetic program with protein compositions. An analysis of sex-adjusted aging cardiac transcriptomes further revealed widespread remodeling of exon usage patterns that is largely independent from differential gene expression, concomitant with upstream changes in RNA-binding protein and splice factor transcripts. To evaluate the potential impact of the splicing events on proteoform composition in the heart, we applied an RNA-guided-proteomics computational pipeline to analyze the mass spectrometry data, and putatively identified hundreds of splice events with the potential to rewire the cardiac proteome through producing detectable splice isoform specific peptides. Taken together, this study contributes to emerging evidences for considerable sexual dimorphism in the cardiac aging process involving sex-biased aging genes and regulatory networks. Aging hearts are associated with a rewiring of RNA splicing programs, including sex- and age-dependent changes in exon usages and splice patterns that have the potential to influence cardiac protein structure and function. These changes represent an under-investigated aspect of cardiac aging that should be considered in the search for disease mechanisms.