To explore the potential of UCH-L1 as a novel therapeutic and diagnostic target in heart failure

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Heart failure (HF) is the number one reason for admission among patients in the Veteran (VA) health system, consuming a significant portion of VA medical resources. However, the molecular mechanism of HF is poorly understood and the treatment of HF still remains at the level of controlling symptom and reducing risk factors without a cure. Hence, further research into developing pathogenic mechanism-specific novel therapies for HF is an urgent need. Our pilot studies have demonstrated that a deubiquitinating enzyme, ubiquitin carboxyl- terminal hydrolase L1 (UCH-L1) is upregulated in the cardiomyocytes of mouse and human failing hearts. In addition, cardiomyocyte-restricted (CR) transgenic overexpression of UCH-L1 (CR-UCH-L1 Tg) exaggerates cardiac pathological remodeling and dysfunction in a mouse model of pressure overload (PO)-induced cardiomyopathy and HF, and the CR-UCH-L1 Tg-induced adverse phenotypes could be rescued by the treatment with a reversible, competitive, act-site directed inhibitor of UCH-L1, LDN-57444. Moreover, UCH-L1 is capable of suppressing autophagy in PO-hearts, which serves as crucial adaptive mechanism to protect against PO-induced cardiomyopathy and HF. At the molecular level, it is most likely that UCH-L1 facilitates mTORC1 (mechanistic target of rapamycin complex 1) dependent inactivation of ULK1 (uncoordinated-51-like kinase 1)-mediated autophagy induction and the activation of DAP1 (death-associated protein 1)-mediated inhibition of autophagy flux in cardiomyocytes. Interestingly, the circulating level of exosomal UCH-L1 is elevated conceivably via a mechanism of autophagy inhibition (AI)-induced increases in exosomal loading and secretion of UCH-L1 in cardiomyocytes of PO-hearts. Collectively, our findings compellingly support the hypothesis that targeting UCH-L1 is a novel approach for the treatment of HF and circulating exosomal UCH- L1 serves as novel biomarker of HF. This hypothesis will be tested by three specific aims in mouse models as well as in VA HF patients as follows: Aim 1 is to determine the therapeutic potential of targeting UCH-L1 in HF in mice. The impact of CR-UCH-L1 knockout (KO) and the efficacy of UCH-L1 inhibitor, LDN-57444 on PO- induced cardiomyopathy and HF will be investigated. Aim 2 is to determine the molecular mechanism by which UCH-L1 mediates HF, testing the hypothesis that UCH-L1 controls the assembly of mTORC1 in favor of increasing the access of mTOR to ULK1 for phosphorylation of ULK1 at S757 while decreasing the association of mTOR with DAP1 for dephosphorylation of DAP1 to enhance AI in cardiomyocytes, thereby exaggerating cardiac pathological remodeling and dysfunction. We will determine whether CR-UCH-L1 Tg-induced adverse phenotypes are rescued by additional enhancement of cardiac autophagy via CR overexpression of autophagy related gene (Atg)7 or autophagy activator, rapamycin. Also, we will dissect the signaling mechanism by which UCH-L1 inhibits autophagy with an initial focus on the regulation of mTORC1 assembly thereby inhibiting ULK1-mediated autophagy induction while enhancing DAP1-mediated suppression of autophagy flux in cardiomyocytes. Aim 3 is to define PO-induced upregulation and release of cardiac UCH-L1 with a focus on the molecular mechanism for exosomal release of UCH-L1 into circulation in animal models and the diagnostic and/or prognostic value of circulating exosomal UCH-L1 in VA HF patients. While a critical role of AI in driving cognate of heat shock protein 70 (HSC70)-mediated exosomal loading of UCH-L1 and secretory carrier membrane protein 5 (SCAMP5)-mediated exosomal release of UCH-L1 in cardiomyocytes with accumulated UCH-L1 will be dissected, the concept that circulating exosomal UCH-L1 is a novel biomarker for evaluating HF in VA patients will be tested. The outcome will pave the way for translational studies of targeting UCH-L1 to treat and manage cardiac disease and HF. Thus, this proposal outcome will, in addition to establishing a unique and independent research program relevant to the VA medical research mission, result in a mechanistically based therapeutic approach for reducing the HF burden within the VA patient population.