KLHL24 mutation drives intermediate filament degradation, mitochondrial dysfunction and fibrosis in heart failure patients

A striking aspect of epidermolysis bullosa patients with a mutation in KLHL24 (KLHL24^mut) is their life-threatening deterioration of heart function. KLHL24 is a component of the ubiquitin-proteasome system and acts as a substrate-specific adaptor protein for E3 ubiquitin ligase. KLHL24^mut is thought to represent a gain-of-function mutation, with associated cardiac and skin pathologies arising from the excessive degradation of its target proteins. Although reduced desmin levels in cardiomyocytes (CMs) have already been documented, the potential involvement of additional mechanisms in KLHL24^mut -driven heart pathology remains unexplored.

We report on two patients with KLHL24^mut who recently manifested heart failure. To gain insights into their physiopathology, we integrated clinical data with proteomic analyses of heart tissue as well as human induced pluripotent stem cell (hiPSC) models carrying KLHL24^mut. Mass spectrometry analysis of CMs differentiated from patient-derived hiPSCs mirrored the proteomic profile of their corresponding left ventricle tissue samples. KLHL24^mut resulted in a reduction of several intermediate filaments (IF), mitochondrial and muscle fibre proteins as well as the emergence of an early fibrotic signature. By utilising various hiPSC-derived cardiac models along with flow cytometry, immunofluorescence, and western blot analyses, we confirmed that the excessive proteasomal activity of endogenous KLHL24^mut caused a decrease in levels of desmin, synemin and vimentin, IF proteins of CMs and cardiac fibroblasts. Moreover, KLHL24^mut led to mitochondrial mislocalization and increased mitophagy, reduced PKA activity, and sarcomere shortening in CMs.

The deterioration of heart function in patients with KLHL24^mut is driven by excessive proteasome-dependent degradation of multiple IF proteins across various cardiac cell types. Monotypic hiPSC-derived CMs and end-stage patient-derived cardiac explants from patients exhibit similar features, uncovering early pathological mechanisms and identifying a list of potential novel KLHL24^mut target proteins. Finally, our findings validate that hiPSC-derived CMs represent a relevant model for future studies.