Mouse fukutin deletion impairs dystroglycan processing and recapitulates muscular dystrophy

Abstract

Dystroglycan is a transmembrane glycoprotein that links the extracellular basement membrane to cytoplasmic dystrophin. Disruption of the extensive carbohydrate structure normally present on α-dystroglycan causes an array of congenital and limb girdle muscular dystrophies known as dystroglycanopathies. The essential role of dystroglycan in development has hampered elucidation of the mechanisms underlying dystroglycanopathies. Here, we developed a dystroglycanopathy mouse model using inducible or muscle-specific promoters to conditionally disrupt fukutin (Fktn), a gene required for dystroglycan processing. In conditional Fktn-KO mice, we observed a near absence of functionally glycosylated dystroglycan within 18 days of gene deletion. Twentyweek-old KO mice showed clear dystrophic histopathology and a defect in glycosylation near the dystroglycan O-mannose phosphate, whether onset of Fktn excision driven by muscle-specific promoters occurred at E8 or E17. However, the earlier gene deletion resulted in more severe phenotypes, with a faster onset of damage and weakness, reduced weight and viability, and regenerating fibers of smaller size. The dependence of phenotype severity on the developmental timing of muscle Fktn deletion supports a role for dystroglycan in muscle development or differentiation. Moreover, given that this conditional Fktn-KO mouse allows the generation of tissue-and timingspecific defects in dystroglycan glycosylation, avoids embryonic lethality, and produces a phenotype resembling patient pathology, it is a promising new model for the study of secondary dystroglycanopathy.

Role of dystroglycan in limiting contraction-induced injury to the sarcomeric cytoskeleton of mature skeletal muscle

“…During this process and the accompanying growth, skeletal muscle fibers increase significantly in breadth (the mean diameter of hind limb muscle fibers increases fivefold) and even more in length (the average muscle fiber length for an adult is 20-30 mm, which is 1,000-fold longer than a mononucleated cell) (44). DG and the DGC are critical during this dynamic phase of sarcolemmal expansion (45)(46)(47). Contraction-induced injury before the onset of necrosis has been investigated in muscles of mouse pups deficient for both dystrophin and utrophin (48).…”

“…These systems include tamoxifen-induced disruption of fukutin (46), RNA-mediated knockdown of fukutin-related protein (49), and dystrophin knockdown using a tetracycline-responsive transactivator or RNAi system (50,51). Interestingly, knockdown of dystrophin at maturity did not result in a discernible phenotype (48).…”

Cell Receptor–Basement Membrane Interactions in Health and Disease

“…This receptor is highly expressed in the muscle and skeletal muscle-targeted deletion of dystroglycan or fukutin, an enzyme required for dystroglycan processing, results in muscular dystrophy in mice (Beedle et al, 2012; Cohn et al, 2002). Interestingly, dystroglycan is also expressed at high levels in podocytes; however, podocytes-specific deletion of this receptor does not result in significant renal abnormalities either at baseline or following injury (Jarad et al, 2011).…”

Depletion of lamina-associated polypeptide 1 from cardiomyocytes causes cardiac dysfunction in mice

“…Hence, it appears that skeletal muscle myocytes are more susceptible to damage from loss of LAP1 than cardiomyocytes. It is unlikely that this difference is originated from the timing of Cre expression as MCK-Cre is expressed at approximately embryonic day 17 in differentiating myocytes, 40,41 and Myh6-Cre is expressed from embryonic day 11.5 throughout the myocardium. 42,43 Recently, three affected members of a Turkish family with an autosomal recessive limb-girdle muscular dystrophy with joint contractures were reported to carry a mutation in TOR1AIP1 that generates a premature stop codon in the LAP1B coding sequence.…”