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 <i>in vitro</i> and <i>in vivo</i>. 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 <i>in vivo</i>, 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.