Differential Expression of Genes Involved in the Degeneration and Regeneration Pathways in Mouse Models for Muscular Dystrophies

The genetically determined muscular dystrophies are caused by mutations in genes coding for muscle proteins. Differences in the phenotypes are mainly the age of onset and velocity of progression. Muscle weakness is the consequence of myofiber degeneration due to an imbalance between successive cycles of degeneration/regeneration. While muscle fibers are lost, a replacement of the degraded muscle fibers by adipose and connective tissues occurs. Major investigation points are to elicit the involved pathophysiological mechanisms to elucidate how each mutation can lead to a specific degenerative process and how the regeneration is stimulated in each case. To answer these questions, we used four mouse models with different mutations causing muscular dystrophies, Dmd (mdx) , SJL/J, Large (myd) and Lama2 (dy2J) /J, and compared the histological changes of regeneration and fibrosis to the expression of genes involved in those processes. For regeneration, the MyoD, Myf5 and myogenin genes related to the proliferation and differentiation of satellite cells were studied, while for degeneration, the TGF-beta 1 and Pro-collagen 1 alpha 2 genes, involved in the fibrotic cascade, were analyzed. The result suggests that TGF-beta 1 gene is activated in the dystrophic process in all the stages of degeneration, while the activation of the expression of the pro-collagen gene possibly occurs in mildest stages of this process. We also observed that each pathophysiological mechanism acted differently in the activation of regeneration, with distinctions in the induction of proliferation of satellite cells, but with no alterations in stimulation to differentiation. Dysfunction of satellite cells can, therefore, be an important additional mechanism of pathogenesis in the dystrophic muscle.

Persistence of Inflammatory Response to Intense Exercise in Diabetic Rats

In this study we evaluated the onset and resolution of inflammation in control and streptozotocin-induced diabetic rats subjected to a single session of intense exercise. The following measurements were carried out prior to, immediately after, and 2 and 24 hours after exercise: plasma levels of proinflammatory cytokines (TNF-alpha, IL-1 beta, IL-6, CINC-2 alpha/beta, MIP-3 alpha, and IL-6), immunoglobulins (IgA and IgM), acute phase proteins (CRP and C3), and creatine kinase (CK) activity. We also examined the occurrence of macrophage death by measurements of macrophages necrosis (loss of membrane integrity) and DNA fragmentation. An increase was observed in the concentration of IL-1 beta (3.3-fold) and TNF-alpha (2.0-fold) and in the proportion of necrotic macrophages (4.5-fold) in diabetic rats 24 hours after exercise, while the control group showed basal measurements. Twenty-four hours after the exercise, serum CK activity was elevated in diabetic rats but not in control animals. We concluded that lesion and inflammations resulting from intense exercise were greater and lasted longer in diabetic animals than in nondiabetic control rats.

Variable expressivity of osteogenesis imperfecta in a Brazilian family due to p.G1079S mutation in the COL1A1 gene

Osteogenesis imperfecta (OI) is a Mendelian disease with genetic heterogeneity characterized by bone fragility, recurrent fractures, blue sclerae, and short stature, caused mostly by mutations in COL1A1 or COL1A2 genes, which encode the pro-alpha 1(I) and pro-alpha 2(I) chains of type I collagen, respectively. A Brazilian family that showed variable expression of autosomal dominant OI was identified and characterized. Scanning for mutations was carried out using SSCP and DNA sequence analysis. The missense mutation c.3235G>A was identified within exon 45 of the COL1A1 gene in a 16-year-old girl diagnosed as having OI type I; it resulted in substitution of a glycine residue (G) by a serine (S) at codon 1079 (p.G1079S). The proband's mother had the disease signs, but without bone fractures, as did five of nine uncles and aunts of the patient. All of them carried the mutation, which was excluded in four healthy brothers of the patient's mother. This is the first description in a Brazilian family with OI showing variable expression; only one among seven carriers for the c.3235G>A mutation developed bone fractures, the most striking clinical feature of this disease. This finding has a significant implication for prenatal diagnosis in OI disease.