The impact of autophagy modulation on phenotype and survival of cardiac stromal cells under metabolic stress

LDHA contributes to nicotine induced cardiac fibrosis through autophagy flux impairment

Cardiac fibrosis is a typical feature of cardiac pathological remodeling, which is associated with adverse clinical outcomes and has no effective therapy. Nicotine is an important risk factor for cardiac fibrosis, yet its underlying molecular mechanism remains poorly understood. This study aimed to identify its potential molecular mechanism in nicotine-induced cardiac fibrosis. Our results showed nicotine exposure led to the proliferation and transformation of cardiac fibroblasts (CFs) into myofibroblasts (MFs) by impairing autophagy flux. Through the use of drug affinity responsive target stability (DARTS) assay, cellular thermal shift assay (CETSA), and surface plasmon resonance (SPR) technology, it was discovered that nicotine directly increased the stability and protein levels of lactate dehydrogenase A (LDHA) by binding to it. Nicotine treatment impaired autophagy flux by regulating the AMPK/mTOR signaling pathway, impeding the nuclear translocation of transcription factor EB (TFEB), and reducing the activity of cathepsin B (CTSB). In vivo, nicotine treatment exacerbated cardiac fibrosis induced in spontaneously hypertensive rats (SHR) and worsened cardiac function. Interestingly, the absence of LDHA reversed these effects both in vitro and in vivo. Our study identified LDHA as a novel nicotine-binding protein that plays a crucial role in mediating cardiac fibrosis by blocking autophagy flux. The findings suggest that LDHA could potentially serve as a promising target for the treatment of cardiac fibrosis.

Progressive stages of dysmetabolism are associated with impaired biological features of human cardiac stromal cells mediated by the oxidative state and autophagy

Cardiac stromal cells (CSCs) are the main players in fibrosis. Dysmetabolic conditions (metabolic syndrome—MetS, and type 2 diabetes mellitus—DM2) are strong pathogenetic contributors to cardiac fibrosis. Moreover, modulation of the oxidative state (OxSt) and autophagy is a fundamental function affecting the fibrotic commitment of CSCs, that are adversely modulated in MetS/DM2. We aimed to characterize CSCs from dysmetabolic patients, and to obtain a beneficial phenotypic setback from such fibrotic commitment by modulation of OxSt and autophagy. CSCs were isolated from 38 patients, stratified as MetS, DM2, or controls. Pharmacological modulation of OxSt and autophagy was obtained by treatment with trehalose and NOX4/NOX5 inhibitors (TREiNOX). Flow‐cytometry and real‐time quantitative polymerase chain reaction (RT‐qPCR) analyses showed significantly increased expression of myofibroblasts markers in MetS‐CSCs at baseline (GATA4, ACTA2, THY1/CD90) and after starvation (COL1A1, COL3A1). MetS‐ and DM2‐CSCs displayed a paracrine profile distinct from control cells, as evidenced by screening of 30 secreted cytokines, with a significant reduction in vascular endothelial growth factor (VEGF) and endoglin confirmed by enzyme‐linked immunoassay (ELISA). DM2‐CSCs showed significantly reduced support for endothelial cells in angiogenic assays, and significantly increased H₂O₂ release and NOX4/5 expression levels. Autophagy impairment after starvation (reduced ATG7 and LC3‐II proteins) was also detectable in DM2‐CSCs. TREiNOX treatment significantly reduced ACTA2, COL1A1, COL3A1, and NOX4 expression in both DM2‐ and MetS‐CSCs, as well as GATA4 and THY1/CD90 in DM2, all versus control cells. Moreover, TREiNOX significantly increased VEGF release by DM2‐CSCs, and VEGF and endoglin release by both MetS‐ and DM2‐CSCs, also recovering the angiogenic support to endothelial cells by DM2‐CSCs. In conclusion, DM2 and MetS worsen microenvironmental conditioning by CSCs. Appropriate modulation of autophagy and OxSt in human CSCs appears to restore these features, mostly in DM2‐CSCs, suggesting a novel strategy against cardiac fibrosis in dysmetabolic patients. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.