Background: The dystroglycan complex consists of two subunits: extracellular a-dystroglycan and membrane-spanning beta-dystroglycan, which provide a tight link between the extracellular matrix and the intracellular cytoskeleton. Previous studies showed that 43 kDa beta-dystroglycan is proteolytically cleaved into the 30 kDa fragment by matrix metalloproteinases (MMPs) in various non-muscle tissues, whereas it is protected from cleavage in muscles by the sarcoglycan complex which resides close to the dystroglycan complex. It is noteworthy that cleaved beta-dystroglycan is detected in muscles from patients with sarcoglycanopathy, sarcoglycan-deficient muscular dystrophy. In vitro assays using protease inhibitors suggest that both MMP-2 and MMP-9 contribute to the cleavage of beta-dystroglycan. However, this has remained uninvestigated in vivo. Methods: We generated triple-knockout (TKO) mice targeting MMP-2, MMP-9 and gamma-sarcoglycan to examine the status of beta-dystroglycan cleavage in the absence of the candidate matrix metalloproteinases in sarcoglycan-deficient muscles. Results: Unexpectedly, beta-dystroglycan was cleaved in muscles from TKO mice. Muscle pathology was not ameliorated but worsened in TKO mice compared with y-sarcoglycan single-knockout mice. The gene expression of MMP-14 was up-regulated in TKO mice as well as in gamma-sarcoglycan knockout mice. In vitro assay showed MMP-14 is capable to cleave beta-dystroglycan. Conclusions: Double-targeting of MMP-2 and MMP-9 cannot prevent cleavage of beta-dystroglycan in sarcoglycanopathy. Thus, matrix metalloproteinases contributing to beta-dystroglycan cleavage are redundant, and MMP-14 could participate in the pathogenesis of sarcoglycanopathy. (C) 2017 Elsevier Inc. All rights reserved.