Faculty Bibliography

Aims/UNASSIGNED:Previous studies in murine hearts and in cell systems have shown that modifications in the expression or sequence integrity of the desmosomal molecule plakophilin-2 (PKP2) can alter the downstream expression of transcripts necessary for the electrical and mechanical function of the heart. These findings have provided support to mechanistic hypotheses that seek to explain arrhythmogenic right ventricular cardiomyopathy (ARVC) in humans. However, the relation between PKP2 expression and the transcriptome of the human heart remains poorly explored. Furthermore, while a number of studies have documented the clinical similarity between familial ARVC in humans and inheritable ARVC in boxer dogs, there is a puzzling lack of convergence as to the possible genetic causes of disease in one species vs. the other. Methods and results/UNASSIGNED:We implemented bioinformatics analysis tools to explore the relation between the PKP2-dependent murine and human transcriptomes. Our data suggest that genes involved in intracellular calcium regulation, and others involved in intercellular adhesion, form part of a co-ordinated gene network. We further identify PROX1 and PPARA (coding for the proteins Prox1 and PPAR-alpha, respectively) as transcription factors within the same network. Conclusion/UNASSIGNED:On the basis our analysis, we hypothesize that the molecular cascades initiated by the seemingly unrelated genetic mutations in humans and in boxers actually converge downstream into a common pathway. This can explain the similarities in the clinical manifestation of ARVC in humans and in the boxer dogs.

Background: Genetic/genomic research has greatly advanced our understanding of heart disease. Yet a comprehensive map of the protein landscape of living human hearts is still lacking. Since cardiac protein degradation progresses rapidly post-mortem, it is essential to limit studies to samples collected from live individuals and immediately process these for data acquisition. Objective: To defne the human cardiac chamber-specifc proteome from samples collected in vivo. Methods: Cardiac biopsies of right atria (RA), left atria (LA) and left ventricle (LV) were collected from seven humans undergoing open chest surgery and analyzed by high-resolution mass spectrometry. Results: We identifed 7314 proteins across cardiac chambers. Proteome-wide analysis revealed hundreds of proteins differentially expressed between RA and LA, and between atria and LV with high statistical signifcance. We found over-representation of: a) fbrosis-related proteins in LA, b) autonomic regulation-related proteins in RA, and c) sarcomeric and intercalated disc proteins in LV. We used our data to advance disease-related leads obtained via genetics/genomics. Specifcally, previous GWA studies identifed six loci associated with mitral valve prolapse (MVP). We queried our dataset for abundance of proteins coded by all genes within those 6 loci, recovering gene candidates for fve of these: two genes previously associated with MVP and four new ones. Separately, we found signifcant chamber-specifc over-representation of disease-causing dilated cardiomyopathy variants in LV, with the corresponding observation that protein abundance in LV is signifcantly higher for high-confdence variants. Conclusion: We present the frst comprehensive atlas of chamber-specifc human cardiac protein expression obtained from samples collected in vivo. We identify hundreds of proteins with chamber-specifc expression; some correspond to known functional characteristics and others to novel chamber-specifc identifers, with potential as drug targets. Our studies offer a crucial link between genomic data and the mechanisms of disease

Connexins are integral membrane building blocks that form gap junctions, enabling direct cytoplasmic exchange of ions and low-molecular-mass metabolites between adjacent cells. In the heart, gap junctions mediate the propagation of cardiac action potentials and the maintenance of a regular beating rhythm. A number of connexin interacting proteins have been described and are known gap junction regulators either through direct effects (e.g., kinases) or the formation of larger multifunctional complexes (e.g., cytoskeleton scaffold proteins). Most connexin partners can be categorized as either proteins promoting coupling by stimulating forward trafficking and channel opening or inhibiting coupling by inducing channel closure, internalization, and degradation. While some interactions have only been implied through co-localization using immunohistochemistry, others have been confirmed by biophysical methods that allow detection of a direct interaction. Our understanding of these interactions is, by far, most well developed for connexin 43 (Cx43) and the scope of this review is to summarize our current knowledge of their functional and regulatory roles. The significance of these interactions is further exemplified by demonstrating their importance at the intercalated disc, a major hub for Cx43 regulation and Cx43 mediated effects.