NADPH Oxidase 4 Contributes to Myoblast Fusion and Skeletal Muscle Regeneration.

Myoblast fusion is an essential step in skeletal muscle development and regeneration. NADPH oxidase 4 (Nox4) regulates cellular processes such as proliferation, differentiation, and survival by producing reactive oxygen species (ROS). Insulin-like growth factor 1 induces muscle hypertrophy via Nox4, but its function in myoblast fusion remains elusive. Here, we report a ROS-dependent role of Nox4 in myoblast differentiation. Regenerating muscle fibers after injury by cardiotoxin had a lower cross-sectional area in Nox4-knockout (KO) mice than myofibers in wild-type (WT) mice. Diameters and fusion index values of myotubes differentiated from Nox4-KO primary myoblasts were significantly lower than those of myotubes derived from WT myoblasts. However, no difference was observed in the differentiation index and expression of MyoD, myogenin, and myosin heavy chain 3 (MHC) between KO and WT myotubes. The decreased fusion index was also observed during differentiation of primary myoblasts and C2C12 cells with suppressed Nox4 expression. In contrast, in C2C12 cells overexpressing Nox4, the fusion index was increased, whereas the differentiation index and MHC and myogenin protein expression were not affected compared to control. Interestingly, the expression of myomaker (Tmem8c), a fusogenic protein that controls myoblast fusion, was reduced in Nox4-knockdown C2C12 cells. The myomaker expression level was proportional to the cellular ROS level, which was regulated by of Nox4 expression level. These results suggests that Nox4 contributes to myoblast fusion, possibly through the regulation of myomaker expression via ROS production, and that Nox4-dependent ROS may promote skeletal muscle regeneration and growth.

3'-Sialyllactose as an inhibitor of p65 phosphorylation ameliorates the progression of experimental rheumatoid arthritis.

BACKGROUND AND PURPOSE: 3'-Sialyllactose (3'-SL) is a safe compound that is present in high levels in human milk. Although it has anti-inflammatory properties and supports immune homeostasis, its effect on collagen-induced arthritis (CIA) is unknown. In this study, we investigated the prophylactic and therapeutic effect of 3'-SL on the progression of rheumatoid arthritis (RA) in in vitro and in vivo models. EXPERIMENTAL APPROACH: The anti-arthritic effect of 3'-SL was analysed with fibroblast-like synoviocytes in vitro and an in vivo mouse model of CIA. RT-PCR, Western blotting and ELISA were performed to evaluate its effects in vitro. Histological analysis of ankle and knee joints of mice with CIA was performed using immunohistochemistry, as well as safranin-O and haematoxylin staining. KEY RESULTS: 3'-SL markedly alleviated the severity of CIA in the mice by reducing paw swelling, clinical scores, incidence rate, serum levels of inflammatory cytokines and autoantibody production. Moreover, 3'-SL reduced synovitis and pannus formation and suppressed cartilage destruction by blocking secretion of chemokines, pro-inflammatory cytokines, matrix metalloproteinases and osteoclastogenesis via NF-κB signalling. Notably, phosphorylation of p65, which is a key protein in the NF-κB signalling pathway, was totally blocked by 3'-SL in the RA models. CONCLUSIONS AND IMPLICATIONS: 3'-SL ameliorated pathogenesis of CIA by suppressing catabolic factor expression, proliferation of inflammatory immune cells and osteoclastogenesis. These effects were mediated via blockade of the NF-κB signalling pathway. Therefore, 3'-SL exerted prophylactic and therapeutic effects and could be a novel therapeutic agent for the treatment of RA.

Astrocytic phospholipase A2 contributes to neuronal glutamate toxicity.

The role of astrocytes in glutamate toxicity has been controversial. Here, we show that astrocytes in neuron-astrocyte co-cultures increased neuronal sensitivity to chronic glutamate exposure but not to acute exposure. Enhanced neuronal toxicity by chronic exposure was dependent on astrocyte cell numbers. A reduced generation of extracellular H2O2 induced by glutamate was observed in co-cultures. Further, neuronal glutamate toxicity was not suppressed by NADPH oxidase (Nox) inhibitors, catalase or Nox4 knockdown in co-cultures, whereas these compounds effectively reduced the toxicity in pure neuron cultures. Instead, the intracellular scavenger of reactive oxygen species, N-acetylcysteine (NAC), reduced neuronal cytotoxicity in co-cultures, whereas catalase worked in pure neuron cultures. Lipoxygenase (LOX) inhibitors attenuated neuronal glutamate toxicity in co-cultures but not in pure neuron cultures. Neuronal 5-LOX activity was increased only in co-cultures, whereas 12-LOX activity was increased in both types of cultures. The cyclooxygenase (COX) inhibitors, indomethacin and NS-398, and the phospholipase A2 (PLA2) inhibitors, LY311727 and MAFP, more effectively reduced neuronal glutamate toxicity in co-cultures than in pure neuron cultures. However, in co-cultures, pre-treating neurons and astrocytes with the same inhibitors generated opposite results. COX inhibitors suppressed neuronal glutamate toxicity in pre-treated neurons rather than astrocytes, whereas PLA2 inhibitors reduced the toxicity in pre-treated astrocytes rather than neurons. Gene-specific knockdown of PLA2 confirmed these results. Knockdown of cPLA2α and/or sPLA2-V in astrocytes rather than in neurons more effectively reduced glutamate toxicity in co-cultures. These findings suggest that astrocytic PLA2 activity increases neuronal sensitivity to chronic glutamate exposure in neuron-astrocyte co-cultures.