Description of Osmolyte Pathways in Maturing Mdx Mice Reveals Altered Levels of Taurine and Sodium/Myo-Inositol Co-Transporters

Abstract

Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by progressive muscle degeneration. Osmotic stress participates to DMD pathology and altered levels of osmolyte pathway members have been reported. The goal of this study was to gain insight in osmoregulatory changes in the mdx mouse model by examining the expression of osmolyte pathway members, including taurine transporter (TauT), sodium myo-inositol co-transporter (SMIT), betaine GABA transporter (BGT), and aldose reductase (AR) in the skeletal muscles and diaphragm of mdx mice aged 4, 8, 12, and 26 weeks. Necrosis was most prominent in 12 week-old mdx mice, whereas the amount of regenerated fibers increased until week 26 in the tibialis anterior. TauT protein levels were downregulated in the tibialis anterior and gastrocnemius of 4 to 12 week-old mdx mice, but not in 26 week-old mice, whereas TauT levels in the diaphragm remained significantly lower in 26 week-old mdx mice. In contrast, SMIT protein levels were significantly higher in the muscles of mdx mice when compared to controls. Our study revealed differential regulation of osmolyte pathway members in mdx muscle, which points to their complex involvement in DMD pathogenesis going beyond general osmotic stress responses. These results highlight the potential of osmolyte pathway members as a research interest and future therapeutic target in dystrophinopathy.

Exploring the Therapeutic Potential of Ectoine in Duchenne Muscular Dystrophy: Comparison with Taurine, a Supplement with Known Beneficial Effects in the mdx Mouse

“…As taurine is a known modifier of its transporter, TauT, and taurine supplementation resulted in a significant downregulation of TauT levels in vitro [ 19 ], we investigated protein expression of TauT in vivo. Similar to our previous results [ 11 ], we observed a significant downregulation of TauT protein levels in mdx mice compared to control mice. However, TauT levels did not change upon osmolyte treatment, which is in line with previous findings [ 17 , 39 ].…”

“…Histopathological characterization was carried out as described previously [ 11 ]. The amount of healthy fibers, regenerating fibers (centronucleated fibers) and necrotic fibers (macrophage invaded fibers and fibers with loss of structure and/or pale cytoplasm,) was manually counted in three whole muscle haematoxylin-eosin (H&E) stained sections of the tibialis anterior per mouse ( Figure 4 ).…”

“…However, the anti-inflammatory effect was specific for the type of treatment, with broader anti-inflammatory effects exerted by taurine. The pro-inflammatory chemokine CCL2 , also known as monocyte chemoattractant protein 1 ( MCP-1 ), is increased in the muscle of mdx mice [ 11 , 35 , 36 ]. As CCL2 recruits immune cells to sites of muscle injury, it presents a potential biomarker of disease severity in DMD [ 35 ].…”

“…In total, three sections of the tibialis anterior (>150 µm apart) were analysed. Per section, an average of 2226 fibers were counted by a blinded investigator, and analysis was carried out as described previously [ 11 ].…”

“…Taurine or 2-aminoethanesulfonic acid is a natural sulphur-containing amino acid that is either taken up from the diet or synthetized in the body from cysteine or methionine [ 9 ]. Besides its function in osmotic homeostasis, the osmolyte taurine participates in protein stabilization and muscle performance [ 10 , 11 ]. Taurine exerts anti-oxidative and anti-inflammatory actions, which is particularly of interest in conditions with an inflammatory pathogenic component, such as DMD.…”