Comprehensive methodological evaluation of V-ATPase assembly in the context of cardiac lipid overload: implications for (endo)lysosomal function and autophagy

The vacuolar-type H+-translocating ATPase (V-ATPase) plays a pivotal role in cellular homeostasis by acidifying endosomes and lysosomes, regulating key processes such as autophagy and membrane trafficking. While the importance of V-ATPase in these functions is well-established, the methodologies for studying its assembly and function remain varied and under-characterized. In this study, we systematically validated and compared methodologies for assessing V-ATPase assembly and endo/lysosomal acidification under physiological and high-fat conditions, both in vitro and in vivo. Various techniques, including fractionation, immunoprecipitation, immunofluorescence microscopy, and proximity ligation assays, were evaluated using cardiomyocyte cell lines, rat models of lipid overload, and two heart-specific V-ATPase-knockout mouse models (V-ATPase subunits ATP6V1G1 and ATP6V0D2). High palmitate (HP) and bafilomycin A1 (BafA) were used to manipulate v-ATPase function, while a colorimetric assay assessed proton-pumping activity. Results consistently showed that HP and BafA induced V-ATPase disassembly and inhibited proton-pumping activity, leading to impaired endo/lysosomal acidification and autophagy inhibition upon fusion of autophagosomes with lysosomes. Similar findings were observed in vivo, where a high-fat diet (HFD) reproduced the effects of HP on cardiac tissue. The methodologies were further validated in two heart-specific V-ATPase-knockout mouse models, demonstrating consistent outcomes across different experimental approaches. This study establishes a robust framework for evaluating V-ATPase assembly and function. The validated methodologies reveal that lipid overload inhibits autophagy and contributes to insulin resistance by inducing V-ATPase disassembly and subsequent lysosomal dysfunction. These findings offer insights into the molecular mechanisms underlying metabolic diseases and provide valuable tools for further research.