Fortilin, CTNNA3, and the Heart

Project Summary The main goal of this grant proposal titled “Fortilin, CTNNA3, and the Heart” is to test the central hypothesis that the inability of the failing heart to maintain fortilin expression leads to decreased CTNNA3 transcription, increased CTNNA3 protein degradation, and lethal heart failure (HF). Nearly 6

million Americans live with HF, with about 670,000 new cases diagnosed each year. HF is a relentlessly progressive disease that is associated with an unacceptably high death rate—about 40% of patients with severe HF die within a year. The attempts to slow HF progression by overexpression of sarcoplasmic reticulum

calcium ATPase (SERCA2a), stromal cell-derived factor-1 (SDF-1), or adenylyl cyclase type 6 (AC6) in humans using adeno associated virus (AAV) have been unsuccessful. New molecular targets for development of HF therapeutics must be identified. Although fortilin, a multifunctional 172-amino acid protein, is one of the most

abundantly expressed proteins in the hearts, its role in the heart remained unknown when we found that the myocardial samples from HF patients expressed significantly less fortilin than in those from control patients. To test whether decreased fortilin levels in the failing hearts is the cause or effect of HF, we generated heart-

specific fortilin knockout (KO) mice. These mice rapidly develop severe HF and die within 9 weeks of age. Non- biased systematic microarray analyses from KO and wild-type mouse hearts showed that the expression of CTNNA3, which encodes a protein also known as α-T-catenin that is a component of the intercalated disc (ID),

was severely decreased in the hearts of KO mice. Transmission electron microscopy showed disrupted IDs in the hearts of KO mice. Strikingly, further molecular analyses revealed that fortilin binds CTNNA3 and that fortilin transcriptionally activates the CTNNA3 gene. We have assembled a team with all expertise needed

to test the hypothesis that fortilin prevents HF by maintaining CTNNA3 expression and the integrity of ID in the heart. We will first confirm that fortilin positively regulates CTNNA3 at both protein and mRNA levels using cell-based assays. Additionally, using at least 300 de-identified human heart lysates from HF patients

and healthy hearts, we will evaluate the correlation between fortilin and CTNNA3 protein expression (Aim 1). We will then attempt to rescue the HF phenotype of the KO mice by replenishing fortilin or CTNNA3 by either AAV-mediated delivery or by crossing the KO mice with CTNNA3 transgenic mice (Aim 2). Finally, we will test

if the transgenic overexpression of fortilin in the hearts of mice protects them against ischemia-induced and pressure-overload-induced through CTNNA3 (Aim 3). Upon completion of the project, we will have fully evaluated the role of fortilin in HF, elucidated the mechanism by which fortilin deficiency causes the

heart to fail, and established a sound strategy to reverse the progression of HF by replenishing fortilin and/or CTNNA3 in the failing heart.