DNAJB6 isoform specific knockdown: Therapeutic potential for limb girdle muscular dystrophy D1.

Dominant missense mutations in DNAJB6, a co-chaperone of HSP70, cause limb girdle muscular dystrophy (LGMD) D1. No treatments are currently available. Two isoforms exist, DNAJB6a and DNAJB6b, each with distinct localizations in muscle.

Distinctive chaperonopathy in skeletal muscle associated with the dominant variant in DNAJB4.

DnaJ homolog, subfamily B, member 4, a member of the heat shock protein 40 chaperones encoded by DNAJB4, is highly expressed in myofibers. We identified a heterozygous c.270 T > A (p.

Neuronal VCP loss of function recapitulates FTLD-TDP pathology.

The pathogenic mechanism by which dominant mutations in VCP cause multisystem proteinopathy (MSP), a rare neurodegenerative disease that presents as fronto-temporal lobar degeneration with TDP-43 inclusions (FTLD-TDP), remains unclear. To explore this, we inactivate VCP in murine postnatal forebrain neurons (VCP conditional knockout [cKO]). VCP cKO mice have cortical brain atrophy, neuronal loss, autophago-lysosomal dysfunction, and TDP-43 inclusions resembling FTLD-TDP pathology.

Inhibition of DNAJ-HSP70 interaction improves strength in muscular dystrophy.

Dominant mutations in the HSP70 cochaperone DNAJB6 cause a late-onset muscle disease termed limb-girdle muscular dystrophy type D1 (LGMDD1), which is characterized by protein aggregation and vacuolar myopathology. Disease mutations reside within the G/F domain of DNAJB6, but the molecular mechanisms underlying dysfunction are not well understood. Using yeast, cell culture, and mouse models of LGMDD1, we found that the toxicity associated with disease-associated DNAJB6 required its interaction with HSP70 and that abrogating this interaction genetically or with small molecules was protective.

Desmin forms toxic, seeding-competent amyloid aggregates that persist in muscle fibers.

Desmin-associated myofibrillar myopathy (MFM) has pathologic similarities to neurodegeneration-associated protein aggregate diseases. Desmin is an abundant muscle-specific intermediate filament, and disease mutations lead to its aggregation in cells, animals, and patients. We reasoned that similar to neurodegeneration-associated proteins, desmin itself may form amyloid.

Lithium chloride corrects weakness and myopathology in a preclinical model of LGMD1D.

Objective: To understand DNAJB6's function in skeletal muscle and identify therapeutic targets for limb-girdle muscular dystrophy 1D (LGMD1D).

Methods: DNAJB6 knockout (KO) myoblasts were generated with Crispr/cas9 technology, and differentially accumulated proteins were identified using stable isotope labeling, followed by quantitative mass spectrometry. Cultured KO myotubes and mouse muscle from DNAJB6b-WT or DNAJB6b-F93L mice were analyzed using histochemistry, immunohistochemistry, and immunoblot.

VCP maintains lysosomal homeostasis and TFEB activity in differentiated skeletal muscle.

Differentiated tissue is particularly vulnerable to alterations in protein and organelle homeostasis. The essential protein VCP, mutated in hereditary inclusion body myopathy, amyotrophic lateral sclerosis and frontotemporal dementia, is critical for efficient clearance of misfolded proteins and damaged organelles in dividing cells, but its role in terminally differentiated tissue affected by disease mutations is less clear. To understand the relevance of VCP in differentiated tissue, we inactivated it in skeletal muscle of adult mice.

Loss of lipin 1-mediated phosphatidic acid phosphohydrolase activity in muscle leads to skeletal myopathy in mice.

Lipin 1 regulates glycerolipid homeostasis by acting as a phosphatidic acid phosphohydrolase (PAP) enzyme in the triglyceride-synthesis pathway and by regulating transcription factor activity. Mutations in human lipin 1 are a common cause of recurrent rhabdomyolysis in children. Mice with constitutive whole-body lipin 1 deficiency have been used to examine mechanisms connecting lipin 1 deficiency to myocyte injury.

Keap1/Cullin3 Modulates p62/SQSTM1 Activity via UBA Domain Ubiquitination.

p62/SQSTM1 (p62) is a scaffolding protein that facilitates the formation and degradation of ubiquitinated aggregates via its self-interaction and ubiquitin binding domains. The regulation of this process is unclear but may relate to the post-translational modification of p62. In the present study, we find that Keap1/Cullin3 ubiquitinates p62 at lysine 420 within its UBA domain.

TMEM184b Promotes Axon Degeneration and Neuromuscular Junction Maintenance.

Unlabelled: Complex nervous systems achieve proper connectivity during development and must maintain these connections throughout life. The processes of axon and synaptic maintenance and axon degeneration after injury are jointly controlled by a number of proteins within neurons, including ubiquitin ligases and mitogen activated protein kinases. However, our understanding of these molecular cascades is incomplete.

Myofibrillar disruption and RNA-binding protein aggregation in a mouse model of limb-girdle muscular dystrophy 1D.

Limb-girdle muscular dystrophy type 1D (LGMD1D) is caused by dominantly inherited missense mutations in DNAJB6, an Hsp40 co-chaperone. LGMD1D muscle has rimmed vacuoles and inclusion bodies containing DNAJB6, Z-disc proteins and TDP-43. DNAJB6 is expressed as two isoforms; DNAJB6a and DNAJB6b.

SQSTM1 splice site mutation in distal myopathy with rimmed vacuoles.

Objective: To identify the genetic etiology and characterize the clinicopathologic features of a novel distal myopathy.

Methods: We performed whole-exome sequencing on a family with an autosomal dominant distal myopathy and targeted exome sequencing in 1 patient with sporadic distal myopathy, both with rimmed vacuolar pathology. We also evaluated the pathogenicity of identified mutations using immunohistochemistry, Western blot analysis, and expression studies.

Targeted sequencing and identification of genetic variants in sporadic inclusion body myositis.

Sporadic inclusion body myositis (sIBM) has clinical, pathologic and pathomechanistic overlap with some inherited muscle and neurodegenerative disorders. In this study, DNA from 79 patients with sIBM was collected and the sequencing of 38 genes associated with hereditary inclusion body myopathy (IBM), myofibrillar myopathy, Emery-Dreifuss muscular dystrophy, distal myopathy, amyotrophic lateral sclerosis and dementia along with C9orf72 hexanucleotide repeat analysis was performed. No C9orf72 repeat expansions were identified, but; 27 rare (minor allele frequency <1%) missense coding variants in several other genes were identified.

Autophagic vacuolar pathology in desminopathies.

Autophagic vacuolar myopathies are an emerging group of muscle diseases with common pathologic features. These include autophagic vacuoles containing both lysosomal and autophagosomal proteins sometimes lined with sarcolemmal proteins such as dystrophin. These features have been most clearly described in patients with Danon's disease due to LAMP2 deficiency and X-linked myopathy with excessive autophagy (XMEA) due to mutations in VMA21.

Increased autophagy accelerates colchicine-induced muscle toxicity.

Colchicine treatment is associated with an autophagic vacuolar myopathy in human patients. The presumed mechanism of colchicine-induced myotoxicity is the destabilization of the microtubule system that leads to impaired autophagosome-lysosome fusion and the accumulation of autophagic vacuoles. Using the MTOR inhibitor rapamycin we augmented colchicine’s myotoxic effect by increasing the autophagic flux; this resulted in an acute myopathy with muscle necrosis.

mTOR dysfunction contributes to vacuolar pathology and weakness in valosin-containing protein associated inclusion body myopathy.

Autophagy is dysfunctional in many degenerative diseases including myopathies. Mutations in valosin-containing protein (VCP) cause inclusion body myopathy (IBM) associated with Paget's disease of the bone, fronto-temporal dementia and amyotrophic lateral sclerosis (IBMPFD/ALS). VCP is necessary for protein degradation via the proteasome and lysosome.