Abstract Body (Do not enter title and authors here): Introduction: Mitochondrial abnormalities are a characteristic of heart failure leading to energy deprivation and disease worsening. The mitochondrial deubiquitinating enzyme USP30, removes ubiquitin and represses PINK1/PARKIN-mediated mitophagy leading to accumulation of dysfunctional mitochondria. In this study we investigated the role of MTX652, a clinical stage USP30 inhibitor, in a mouse model of cardiac hypertrophy using transverse aortic constriction (TAC).

Hypothesis: Inhibition of USP30 will promote mitophagy resulting in clearance of dysfunctional mitochondria and improved cellular health leading to cardioprotective effects.

Aims: To determine if MTX652 can protect from TAC induced cardiac hypertrophy and remodelling.

Methods: Male C57BL/6 mice, 8 weeks old, were subjected to sham surgeries or TAC using a 26G needle to induce cardiac pressure overload. MTX652 (1.5 or 5 mg/kg, n=12-13) or vehicle (n=11) was administered orally, twice daily, starting 2 days post-surgery. Captopril (30 mg/kg/d, n=13) was also included as a positive control. After 4 weeks, echocardiography assessed left ventricle (LV) function and morphology. Cell based assays assessed MTX652 target engagement and TOM20 ubiquitination in vitro.

Results: LV hypertrophy and wall thickening was observed in TAC animals. Treatment with MTX652 decreased systolic LV volume (1.5 mg/kg p<0.05 and 5 mg/kg p<0.01) and diameter (1.5 mg/kg p<0.01 and 5 mg/kg p<0.05,) demonstrating comparable effects to Captopril. A reduction in anterior wall thickness in diastole was also observed with MTX652 (5 mg/kg, p<0.01). Cardiac dysfunction was also evident in TAC animals with MTX652 showing improvements in both ejection fraction (1.5 mg/kg and 5 mg/kg, p<0.0001) and fractional shortening (1.5 mg/kg and 5 mg/kg, p<0.0001).

Cellular target engagement for MTX652 was confirmed in HeLa-YFP-Parkin cells with an EC₅₀ of 2.7 nM (n=2). Furthermore, the USP30 substrate TOM20 was ubiquitinated following MTX652 treatment in vitro (EC₅₀=6.1 nM, n=4) providing evidence of mitophagy activation, a finding also confirmed in mouse heart tissue (MTX652, 5mg/kg).

Conclusions: The USP30 inhibitor, MTX652 significantly protected mice from TAC induced cardiac hypertrophy and LV dysfunction. Furthermore, MTX652 potentiates ubiquitylation of TOM20 as a mechanism to promote mitophagy. These data suggest our clinical stage molecule could provide a novel therapeutic approach for the treatment of cardiac hypertrophy and heart failure.