Von Willebrand factor a domain containing 8 (VWA8) is a mitochondria–ER spacer that restrains β-adrenergic–induced cardiac hypertrophy

Background Mitochondria–sarco/endoplasmic reticulum contact sites (MSRCs) contribute to the pathological progression of heart failure. However, the dynamic alterations of MSRCs and their underlying molecular mechanisms during cardiac hypertrophy are not understood. Purpose To identify molecular mechanisms driving MSRC dynamic remodeling in β-adrenergic agonist–induced cardiac hypertrophy. Methods We integrated proteomic and transcriptomic analyses to identify differentially expressed MSRC-resident proteins in hypertrophic hearts. Electron microscopy and fluorescence resonance energy transfer (FRET) imaging were employed to assess changes in MSRC formation. Proteinase K protection and sodium carbonate extraction assays were used to determine submitochondrial protein localization. Mitochondrial calcium homeostasis and substrate utilization capacity were evaluated using calcium sensors and Seahorse metabolic flux analysis. Transgenic mouse models and isoproterenol-infused Alzet osmotic minipumps were used to assess cardiac phenotypes under β-adrenergic stress in vivo. Results The β-adrenergic agonist isoproterenol increased MSRC formation in cardiomyocytes both in vitro and in vivo. This effect was accompanied by downregulation of the previously poorly characterized protein von Willebrand factor A domain-containing 8 (VWA8) in hypertrophic hearts (GSE195466). Proteomic analyses revealed that VWA8 is enriched at MSRCs, where it integrates in the outer mitochondrial membrane with its C-terminus exposed to the cytoplasm. Genetic deletion of VWA8 resulted in ejection fraction–preserved cardiac hypertrophy and exacerbated isoproterenol-induced cardiac dysfunction in mice. Acting as a novel spacer at MSRCs, loss of VWA8 increased mitochondria–sarco/endoplasmic reticulum proximity both in vitro and in vivo. This was associated with enhanced mitochondrial calcium uptake and increased glucose-dependent respiration, alongside impaired fatty acid-dependent respiration. Re-expression of full-length VWA8, but not the short isoform, or expression of engineered ER–mitochondrial spacers, rescued morphological and functional defects in VWA8-/- differentiated AC16 cardiomyocytes. Conclusion VWA8 functions as an MSRC spacer protein that protects against cardiac hypertrophy by limiting excessive MSRC formation during β-adrenergic stimulation.