Chaperone-Mediated Autophagy in Cardiac Fibrosis

ABSTRACT Repair of the infarcted heart is dependent on timely activation and de-activation of fibroblasts and myofibroblasts. In the infarcted myocardium, fibroblasts undergo dynamic phenotypic transitions that require rapid turnover of their intracellular proteins. This constant renewal of the proteome involves not only transcriptionally-driven activation of protein synthesis, but also selective patterns of protein degradation. Chaperone-Mediated Autophagy (CMA) can selectively remove specific proteins to terminate their function, regulating a range of cellular processes, including survival, proliferation and differentiation. Our preliminary data show that myofibroblast-specific disruption of CMA perturbs repair following myocardial infarction, reducing recruitment of activated myofibroblasts, and that fibroblast CMA stimulated migration and collagen lattice contraction. The cardiac reparative defects of myofibroblast-specific CMA loss are similar to the adverse consequences of aging, which also impairs myofibroblast infiltration and is associated with attenuated CMA activity. Accordingly, we hypothesize that CMA is dynamically regulated in fibroblasts undergoing phenotypic transitions in infarcted hearts, and plays a central role in repair, by modulating the proteomic profile, phenotype and function of reparative fibroblasts and myofibroblasts. The hypothesis will be tested in 4 specific aims: Aim 1: to study the role of fibroblast and myofibroblast CMA in repair and remodeling of the infarcted heart, using mice with cell-specific disruption of lysosomal-associated membrane protein type 2A (LAMP2A), the critical lysosomal membrane protein involved in binding and internalization of CMA substrates. Aim 2: to study the role of CMA in regulating the phenotypic transitions of infarct fibroblasts and to explore the link between CMA activation and infarct fibroblast heterogeneity. Aim 3: to study the effects of CMA in regulation of fibroblast responses and to identify specific CMA substrates that may be implicated. Aim 4: to examine whether accentuation of CMA in infarct fibroblasts and myofibroblasts improves repair and attenuates adverse remodeling and to explore the effectiveness of therapy with CMA activators in healing infarcts in both young and old mice. Effects of genetic overexpression of LAMP2A in infarct fibroblasts and myofibroblasts will be studied. Moreover, the effects of treatment with first-in-class small molecule CMA activators in young and old mouse infarcts will be investigated. The proposed studies will provide the first evidence on the role of CMA in repair and fibrosis of the infarcted heart and may suggest novel therapies targeting CMA in order to improve cardiac repair.