Heterogeneous Distribution of Genetic Mutations in Myosin Binding Protein-C Paralogs

Bringing into focus the central domains C3-C6 of myosin binding protein C

Myosin binding protein C (MyBPC) is a multi-domain protein with each region having a distinct functional role in muscle contraction. The central domains of MyBPC have often been overlooked due to their unclear roles. However, recent research shows promise in understanding their potential structural and regulatory functions. Understanding the central region of MyBPC is important because it may have specialized function that can be used as drug targets or for disease-specific therapies. In this review, we provide a brief overview of the evolution of our understanding of the central domains of MyBPC in regard to its domain structures, arrangement and dynamics, interaction partners, hypothesized functions, disease-causing mutations, and post-translational modifications. We highlight key research studies that have helped advance our understanding of the central region. Lastly, we discuss gaps in our current understanding and potential avenues to further research and discovery.

Hypertrophic cardiomyopathy in MYBPC3 carriers in aging

Hypertrophic cardiomyopathy (HCM) is characterized by abnormal thickening of the myocardium, leading to arrhythmias, heart failure, and elevated risk of sudden cardiac death, particularly among the young. This inherited disease is predominantly caused by mutations in sarcomeric genes, among which those in the cardiac myosin binding protein-C3 (MYBPC3) gene are major contributors. HCM associated with MYBPC3 mutations usually presents in the elderly and ranges from asymptomatic to symptomatic forms, affecting numerous cardiac functions and presenting significant health risks with a spectrum of clinical manifestations. Regulation of MYBPC3 expression involves various transcriptional and translational mechanisms, yet the destiny of mutant MYBPC3 mRNA and protein in late-onset HCM remains unclear. Pathogenesis related to MYBPC3 mutations includes nonsense-mediated decay, alternative splicing, and ubiquitin-proteasome system events, leading to allelic imbalance and haploinsufficiency. Aging further exacerbates the severity of HCM in carriers of MYBPC3 mutations. Advancements in high-throughput omics techniques have identified crucial molecular events and regulatory disruptions in cardiomyocytes expressing MYBPC3 variants. This review assesses the pathogenic mechanisms that promote late-onset HCM through the lens of transcriptional, post-transcriptional, and post-translational modulation of MYBPC3, underscoring its significance in HCM across carriers. The review also evaluates the influence of aging on these processes and MYBPC3 levels during HCM pathogenesis in the elderly. While pinpointing targets for novel medical interventions to conserve cardiac function remains challenging, the emergence of personalized omics offers promising avenues for future HCM treatments, particularly for late-onset cases.

Fast and slow skeletal myosin binding protein-C and aging

Aging is associated with skeletal muscle strength decline and cardiac diastolic dysfunction. The structural arrangements of the sarcomeric proteins, such as myosin binding protein-C (MyBP-C) are shown to be pivotal in the pathogenesis of diastolic dysfunction. Yet, the role of fast (fMyBP-C) and slow (sMyBP-C) skeletal muscle MyBP-C remains to be elucidated. Herein, we aimed to characterize MyBP-C and its paralogs in the fast tibialis anterior (TA) muscle from adult and old mice. Immunoreactivity preparations showed that the relative abundance of the fMyBP-C paralog was greater in the TA of both adult and old, but no differences were noted between groups. We further found that the expression level of cardiac myosin binding protein-C (cMyBP-C), an important modulator of cardiac output, was lowered by age. Standard SDS-PAGE along with Pro-Q Diamond phosphoprotein staining did not identify age-related changes in phosphorylated MyBP-C proteins from TA and cardiac muscles; however, it revealed that MyBP-C paralogs in fast skeletal and cardiac muscle were highly phosphorylated. Mass spectrometry further identified glycogen phosphorylase, desmin, actin, troponin T, and myosin regulatory light chain 2 as phosphorylated myofilament proteins in both ages. MyBP-C protein-bound carbonyls were determined using anti-DNP immunostaining and found the carbonyl level of fMyBP-C, sMyBP-C, and cMyBP-C to be similar between old and adult animals. In summary, our data showed some differences regarding the MyBP-C paralog expression and identified an age-related reduction of cMyBP-C expression. Future studies are needed to elucidate which are the age-driven post-translational modifications in the MyBP-C paralogs.