Whole exome sequencing reveals UNC45B as a novel candidate gene functionally associated with Dilated Cardiomyopathy

Abstract

UNC45B, a UCS class myosin chaperone that facilitates Hsp90-myosin interactions, plays a crucial role in early myofibrillogenesis, though its specific function sustaining cardiac contractility remains obscure. Here we identified seven non-synonymous (p.L486F, p.C487Y, p.A492T, p.D496Y, p.R721Q, p.A780V and p.C786Y) and two synonymous (p.Y769= and p.A780=) variants in UNC45B through whole-exome sequencing (WES) and subsequent genetic screening of Dilated Cardiomyopathy (DCM) patients by Sanger sequencing. The majority of the variants (77.7%) are localized within the highly conserved UCS domain of UNC45B, a critical region for chaperone-like property, also known for myosin binding site. In-vitro analysis by immunofluorescence revealed cytoplasmic mislocalization of mutant UNC45B and pronounced hypertrophic morphology, most evident in p.R721Q and p.A780V mutants. Nuclear fragmentation, a hallmark of cellular stress and apoptosis, was also prominently detected in these variants. Complementary ultrastructural analysis by TEM further substantiated these observations, revealing nuclear deformation, increased cytoplasmic vacuolation, and marked chromatin disorganization. To assess the downstream molecular consequences, qRT-PCR was performed which revealed robust up-regulation of hypertrophic markers (Nppa, Mef2c, Myh6, Myh7, Actc1, Ttn, Nfatc1, and Nfatc2), with Nppa and Mef2c showing >12-fold induction in p.R721Q, p.A780V and p.C786Y variants. Additionally, an increased apoptosis marker Bax/Bcl2 ratio, particularly in p.R721Q (=27.6) and p.A780V (=18.3), confirmed activation of apoptotic signalling pathways. Additionally, 2D and 3D in-silico modeling revealed notable conformational changes which strongly corroborate in-vitro findings. Collectively, these variants weaken the structure and function of UNC45B, causing disrupted sarcomeric organization, pronounced cellular hypertrophy, and subsequent activation of apoptotic pathways leading to cardiac dysfunction.