Fibrosis and inflammation are greater in muscles of beta-sarcoglycan-null mouse than mdx mouse

Abstract

The Sgcb-null mouse, with knocked-down β-sarcoglycan, develops severe muscular dystrophy as in type 2E human limb girdle muscular dystrophy. The mdx mouse, lacking dystrophin, is the most used model for Duchenne muscular dystrophy (DMD). Unlike DMD, the mdx mouse has mild clinical features and shows little fibrosis in limb muscles. To characterize ECM protein deposition and the progression of muscle fibrosis, we evaluated protein and transcript levels of collagens I, III and VI, decorin, and TGF-β1, in quadriceps and diaphragm, at 2, 4, 8, 12, 26, and 52 weeks in Sgcb-null mice, and protein levels at 12, 26, and 52 weeks in mdx mice. In Sgcb-null mice, severe morphological disruption was present from 4 weeks in both quadriceps and diaphragm, and included conspicuous deposition of extracellular matrix components. Histopathological features of Sgcb-null mouse muscles were similar to those of age-matched mdx muscles at all ages examined, but, in the Sgcb-null mouse, the extent of connective tissue deposition was generally greater than mdx. Furthermore, in the Sgcb-null mouse, the amount of all three collagen isoforms increased steadily, while, in the mdx, they remained stable. We also found that, at 12 weeks, macrophages were significantly more numerous in mildly inflamed areas of Sgcb-null quadriceps compared to mdx quadriceps (but not in highly inflamed regions), while, in the diaphragm, macrophages did not differ significantly between the two models, in either region. Osteopontin mRNA was also significantly greater at 12 weeks in laser-dissected highly inflamed areas of the Sgcb-null quadriceps compared to the mdx quadriceps. TGF-β1 was present in areas of degeneration-regeneration, but levels were highly variable and in general did not differ significantly between the two models and controls. The roles of the various subtypes of macrophages in muscle repair and fibrosis in the two models require further study. The Sgcb-null mouse, which develops early fibrosis in limb muscles, appears more promising than the mdx mouse for probing pathogenetic mechanisms of muscle fibrosis and for developing anti-fibrotic treatments. Highlights • The Sgcb-null mouse develops severe muscular dystrophy, the mdx mouse does not. • Fibrosis developed earlier in Sgcb-null quadriceps and diaphragm than mdx. • Macrophages were commoner in mildly inflamed parts of Sgcb-null quadriceps than mdx. • The Sgcb-null model appears more useful than mdx for studying fibrotic mechanisms. • The Sgcb-null model also appears more useful for developing anti-fibrotic treatments.

Opposing roles of miR-21 and miR-29 in the progression of fibrosis in Duchenne muscular dystrophy

“…Haematoxylin and eosin (H&E), Gomori modified trichrome, acid phosphatase, and immunohistochemical stainings were performed on consecutive 6-8 μm-thick cryosections. Numbers of acid-phosphatase-positive cells from highly inflamed and mildly inflamed regions were counted on micrographs of acid phosphatase-stained sections, as described in Gibertini et al [13].…”

“…As control, sections were incubated either with rabbit non-immune serum, or isotype-specific nonimmune IgG (Dako), or the primary antibodies were omitted. The area of collagen immunostaining, as indicator of fibrosis, was determined at × 20 magnification as described [13]. Briefly, 4 randomly selected fields were photographed from each section and digitalized.…”

β-Sarcoglycan Deficiency Reduces Atherosclerotic Plaque Development in ApoE-Null Mice

“…One is that, in addition to dystrophin and β-sarcoglycan both being crucial components in a functional DGC, these 2 proteins may have equally important individual functions. Gradual differences between these 2 genotypes have been noticed in the manifestation of skeletal muscle dystrophy [17]. An explanation that cannot be excluded is that cross-breeding these mice with the ApoE-/- mice may induce altered functions of the DGC as well as of dystrophin and β-sarcoglycan.…”

“…Additional complex components in adipose tissue and in vascular smooth muscle are ζ-, δ-, and ε-sarcoglycan [15,16]. Compared with mdx mice, β-sarcoglycan-deficient (bSG-/-) mice exhibit increased fibrosis of muscle tissue, which shows an impaired capacity of glucose uptake, implicating an increased risk of cardiovascular comorbidities in patients with limb-girdle muscular dystrophy [15,17]. Regarding defects in the vasculature in bSG-/- mice, constrictions associated with pre- and poststenotic aneurysms have been observed in heart and skeletal muscle tissue.…”

Exosomes and exosomal miRNAs from muscle-derived fibroblasts promote skeletal muscle fibrosis

“…(http://rsb.info.nih.gov/nih-image/), as described (Gibertini et al, 2014). Briefly, from each section, 8 fields were selected for content of fluorescent exosomes (4 fields with more than 10 positive spots and 4 fields with less than 10 positive spots), photographed and digitalized.…”