Mechanistic and Translational Investigations of HSPB8-associated dominant rimmed vacuolar myopathy

Mechanistic and Translational Investigations of HSPB8-associated dominant rimmed vacuolar myopathy. Autosomal dominant mutations in the heat shock protein family B member 8 (HSPB8) have been associated with (i) distal hereditary motor neuropathy; (ii) axonal Charcot-Marie-Tooth disease; and (iii) most

recently autosomal dominant rimmed vacuolar myopathy (RVM). Patients with HSPB8 RVM primarily develop a distal myopathy in their 30s-40s, with proximal limb girdle weakness in their 40s-50s, and eventually become wheelchair-bound. Muscle biopsy shows fatty replacement, fibrosis, and rimmed vacuoles. HSPB8 is involved in

chaperone-assisted selective autophagy (CASA), and in conjunction with BAG3, recognizes and promotes the autophagy-mediated removal of misfolded proteins. Our long-term goal is to develop a potent therapy to stop/reduce the progression of HSPB8-associated dominant-rimmed vacuolar myopathy. Major gaps: The

mechanisms through which mutant HSPB8 results in aggregation, and the availability of treatments that preserve or restore proteostasis by enhancing autophagy for HSPB8-rimmed vacuolar myopathies. Preliminary results: To investigate, in vitro and in vivo, the molecular mechanism of HSPB8-associated myopathy, and to assess the

potential of new treatments, we generated: (i) patient myoblasts derived from induced pluripotent cell lines (iPSCs); and (ii) a clinically relevant C57BL/6NJ-Hspb8 knock-in mouse model with the c.515dupC variant using CRISPR/Cas9 technology which manifests myopathic weakness starting at 6 months. We demonstrated that the

HSPB8 fs mutant is associated with: (A) increased TDP-43 and autophagy markers in the patient muscle, fibroblasts, and myoblasts. (B) The Hspb8 knock-in mouse muscle histology revealed central nuclei and muscle degeneration with fibrous and adipose replacement; and immunohistochemical and biochemical studies

revealed aggregates, increased TDP-43, and autophagy pathology resembling human pathology. Our group performed two high-throughput drug screenings and identified colchicine and trehalose to reduce the aggregates, additionally, trehalose benefitted a mouse model of neurodegeneration. Hypothesis: Based on both in vitro and

in vivo studies, our central hypothesis is that mutated HSPB8 exerts a toxic gain of function, and leads to HSPB8 mutant aggregation. Our current results support the hypothesis that compounds that stimulate autophagy favor the removal of protein aggregates related to HSPB8 fs mutations. Specific Aims: To test our hypothesis, we

propose three specific aims: Aim 1: To investigate the molecular mechanism of pathogenesis of HSPB8- associated myopathy in vitro patient iPSC-derived myoblasts and the Hspb8515dupC mouse model. Aim 2: To reverse the mutant HSPB8 pathology in vitro in patient myoblasts with an autophagy inducer trehalose. Aim 3:

To stop or reduce the HSPB8-associated myopathy by upregulating autophagy in the mutant mouse model. Based on our previous studies, we will use trehalose in vivo in the Hspb8515dupC mouse model. Successful completion of the present mechanistic and translational study will pave the way for the treatment of HSPB8-

associated dominant-rimmed vacuolar myopathy, and will also benefit other related disorders.