The PKA-p38MAPK-NFAT5-Organic Osmolytes Pathway in Duchenne Muscular Dystrophy: From Essential Player in Osmotic Homeostasis, Inflammation and Skeletal Muscle Regeneration to Therapeutic Target

Variations in fluid chemical potential induce fibroblast mechano-response in 3D hydrogels

Mechanical deformation of skin creates variations in fluid chemical potential, leading to local changes in hydrostatic and osmotic pressure, whose effects on mechanobiology remain poorly understood. To study these effects, we investigate the specific influences of hydrostatic and osmotic pressure on primary human dermal fibroblasts in three-dimensional hydrogel culture models. Cyclic hydrostatic pressure and hyperosmotic stress enhanced the percentage of cells expressing the proliferation marker Ki67 in both collagen and PEG-based hydrogels. Osmotic pressure also activated the p38 MAPK stress response pathway and increased the expression of the osmoresponsive genes PRSS35 and NFAT5. When cells were cultured in two-dimension (2D), no change in proliferation was observed with either hydrostatic or osmotic pressure. Furthermore, basal, and osmotic pressure-induced expression of osmoresponsive genes differed in 2D culture versus 3D hydrogels, highlighting the role of dimensionality in skin cell mechanotransduction and stressing the importance of 3D tissue-like models that better replicate in vivo conditions. Overall, these results indicate that fluid chemical potential changes affect dermal fibroblast mechanobiology, which has implications for skin function and for tissue regeneration strategies.

Aucubin protects against retinal ganglion cell injury in diabetic rats via inhibition of the p38MAPK pathway

OBJECTIVE

To explore the role of aucubin in regard to injured retinal ganglion cells (RGCs) in diabetic rats and its mechanism.

METHODS

A rat model of diabetes mellitus was created by single intraperitoneal injection of 55 mg/kg of streptozotocin. Rats were treated with intraperitoneal injection of 1, 5, and 10 mg/kg aucubin or 5 μg/kg p38MAPK inhibitor SB203580, once a day, for 28 consecutive days. Body weight, blood glucose, morphological changes, count and apoptosis of RGCs, p38MAPK signaling pathway, apoptosis-related proteins, oxidative stress indices, and inflammatory factors were observed and compared among the groups.

RESULTS

Aucubin and SB203580 reduced the abnormality of the photoreceptor layer, bipolar cell layer and RGCs. Aucubin significantly reduced body weight, fasting blood glucose, RGC apoptosis rate, p38MAPK protein phosphorylation level, protein expression of Caspase 3 and Bax, vascular endothelial growth factors (interleukin-1β, intercellular adhesion molecule-1 and tumor necrosis factor-α) and malondialdehyde levels, and increased RGC count and protein expression of Bcl-2 and Bcl-2/Bax (P < 0.05).

CONCLUSION

Aucubin can protect RGCs in diabetic rats, inhibit RGC apoptosis, and reduce oxidative stress and inflammatory response, and 10 mg/kg aucubin showed optimal efficacy. The mechanism may be related to the inhibition of the p38MAPK signaling pathway.

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

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.