A novel αB-crystallin R123W variant drives hypertrophic cardiomyopathy by promoting maladaptive calcium-dependent signal transduction

Abstract

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disorder affecting 1 in 500 people in the general population. Characterized by asymmetric left ventricular hypertrophy, cardiomyocyte disarray and cardiac fibrosis, HCM is a highly complex disease with heterogenous clinical presentation, onset and complication. While mutations in sarcomere genes can account for a substantial proportion of familial cases of HCM, 40%–50% of HCM patients do not carry such sarcomere variants and the causal mutations for their diseases remain elusive. Recently, we identified a novel variant of the alpha-crystallin B chain (CRYABR123W) in a pair of monozygotic twins who developed concordant HCM phenotypes that manifested over a nearly identical time course. Yet, how CRYABR123W promotes the HCM phenotype remains unclear. Here, we generated mice carrying the CryabR123W knock-in allele and demonstrated that hearts from these animals exhibit increased maximal elastance at young age but reduced diastolic function with aging. Upon transverse aortic constriction, mice carrying the CryabR123W allele developed pathogenic left ventricular hypertrophy with substantial cardiac fibrosis and progressively decreased ejection fraction. Crossing of mice with a Mybpc3 frame-shift model of HCM did not potentiate pathological hypertrophy in compound heterozygotes, indicating that the pathological mechanisms in the CryabR123W model are independent of the sarcomere. In contrast to another well-characterized CRYAB variant (R120G) which induced Desmin aggregation, no evidence of protein aggregation was observed in hearts expressing CRYABR123W despite its potent effect on driving cellular hypertrophy. Mechanistically, we uncovered an unexpected protein-protein interaction between CRYAB and calcineurin. Whereas CRYAB suppresses maladaptive calcium signaling in response to pressure-overload, the R123W mutation abolished this effect and instead drove pathologic NFAT activation. Thus, our data establish the CryabR123W allele as a novel genetic model of HCM and unveiled additional sarcomere-independent mechanisms of cardiac pathological hypertrophy.

Role of the Alpha-B-Crystallin Protein in Cardiomyopathic Disease

“…A recently identified mutation in CRYAB by Maron et al, the CRYAB R123W mutation, was discovered through genetic analysis in twins that developed hypertrophic cardiomyopathy with temporal concordance [ 35 , 36 ]. Follow-up mouse studies revealed that, unlike the previous two mutations, CRYAB R123W does not cause desmin aggregation but rather leads to cardiac dysfunction through sarcomere-independent mechanisms [ 36 ].…”

“…A recently identified mutation in CRYAB by Maron et al, the CRYAB R123W mutation, was discovered through genetic analysis in twins that developed hypertrophic cardiomyopathy with temporal concordance [ 35 , 36 ]. Follow-up mouse studies revealed that, unlike the previous two mutations, CRYAB R123W does not cause desmin aggregation but rather leads to cardiac dysfunction through sarcomere-independent mechanisms [ 36 ]. Knock-in mice with the CRYAB R123W mutation do not develop hypertrophic cardiomyopathy spontaneously but undergo a distinct remodeling process upon pressure overload via transverse aortic constriction [ 36 ].…”

“…Follow-up mouse studies revealed that, unlike the previous two mutations, CRYAB R123W does not cause desmin aggregation but rather leads to cardiac dysfunction through sarcomere-independent mechanisms [ 36 ]. Knock-in mice with the CRYAB R123W mutation do not develop hypertrophic cardiomyopathy spontaneously but undergo a distinct remodeling process upon pressure overload via transverse aortic constriction [ 36 ]. Wild-type CRYAB has been previously reported to play a protective role against the development of pathological hypertrophy in pressure-overloaded hearts [ 10 ].…”

“…Wild-type CRYAB has been previously reported to play a protective role against the development of pathological hypertrophy in pressure-overloaded hearts [ 10 ]. As for the mechanism behind the protective effects of wild-type CRYAB in this setting, it has been proposed that CRYAB prevents the interaction between calcineurin and NFAT and inhibits the subsequent downstream activation [ 36 ]. The CRYAB R123W mutant is unlikely to block that interaction as efficiently, therefore leading to aberrant activation [ 36 ].…”

“…As for the mechanism behind the protective effects of wild-type CRYAB in this setting, it has been proposed that CRYAB prevents the interaction between calcineurin and NFAT and inhibits the subsequent downstream activation [ 36 ]. The CRYAB R123W mutant is unlikely to block that interaction as efficiently, therefore leading to aberrant activation [ 36 ]. Crossing of Cryab R123W mice with NFAT-luciferase reporter mice resulted in an increase in NFAT-luciferase reporter activity, while overexpression in H9c2 cells also led to increased NFAT-luciferase reporter activity [ 36 ].…”