褐藻醣膠改善腫瘤壞死因子-α誘導C2C12小鼠骨骼肌細胞耗損

骨骼肌質量和力量的喪失是老年人常見的問題，被稱為肌少症(Sarcopenia)，它與飲食蛋白質攝取不足及慢性發炎反應有密切相關性。研究發現，肌少症與老年人生活品質降低、身體殘疾及死亡率有密切相關，故如何預防與減少老化造成的肌肉蛋白質耗損，逐漸受到重視。小分子褐藻醣膠(Fucoidan)是由棕色海藻中萃取的一種分子量<10 kDa的水溶性多醣，具有抗發炎和抗癌等功能。本研究室之前研究發現，補充褐藻醣膠可能經由減少骨骼肌肉中腫瘤壞死因子-α (Tumor necrosis factor-α , TNF-α)濃度，改善餵食低蛋白質飲食老化小鼠骨骼肌肉流失。本實驗以C2C12小鼠骨骼肌細胞模式，評估褐藻醣膠調控促發炎物質TNF-α誘發蛋白質分解的功效與相關機制。結果顯示，C2C12肌肉細胞給予低分子量褐藻醣膠顯著改善TNF-α造成C2C12肌肉細胞肌凝蛋白重鏈(Myosin heavy chain, MyHC)蛋白質表現降低。此外，低分子量褐藻醣膠減少TNF-α誘發C2C12肌肉細胞與蛋白質異化相關訊息傳遞因子GDF-8/Myostatin蛋白質、促發炎細胞激素Interleukin-6 (IL-6) mRNA表現、泛素-蛋白酶路徑(ubiquitin-proteasome pathway, UPP)及自噬作用-溶酶體路徑 (autophagy-lysosome pathway, ALP)相關指標MuRF1、Atrogin-1、p62、Beclin-1及LC3Ⅱ等蛋白質表現來達到改善作用。此外，低分子量褐藻醣膠減少TNF-α誘發C2C12肌肉細胞與肌肉蛋白質分解相關轉錄因子NF-kB p65、C/EBP-ß核蛋白表現量及增加p-FoxO3a細胞質蛋白表現量。綜合以上研究結果推論，低分子量褐藻醣膠可經由降低TNF-α誘發C2C12肌肉細胞蛋白質異化相關訊息傳遞因子表現與轉錄因子活性，進而降低促發炎細胞激素IL-6 mRNA及蛋白質降解UPP與ALP路徑相關分子蛋白質表現，改善TNF-α減少肌肉細胞MyHC蛋白質表現。此實驗結果可作為未來進一步評估補充褐藻醣膠改善疾病與老化誘發肌肉萎縮相關臨床前研究的參考數據。

Sarcopenia characterized by the gradual and universal loss of skeletal muscle mass and function is a common problem in the elderly and is associated with dietary protein deficiency and chronic inflammation. Studies have found that sarcopenia is closely related to poor quality of life, physical disability, and mortality in the elderly. Therefore, how to prevent and reduce muscle protein loss has gained much recognition. Low molecular weight fucoidan is a natural sulfated polysaccharide of <10 kDa molecular wight and is isolated from the brown algae. Low molecular weight fucoidan(<10 kDa) exhibits anti-inflammatory and anti-cancer activities. Previous studies from our laboratory found that the supplementation of fucoidan may through reduction of tumor necrosis factor-α level in skeletal muscle improve skeletal muscle loss in aging mice fed with a low-protein diet. In this experiment, C2C12 mouse skeletal muscle cell model were used to evaluate the effects and related mechanisms of low molecular weight fucoidan on TNF-α induced myotube protein loss. The results showed that Myosin heavy chain (MyHC) was significantly increased by pretreated with low molecular weight fucoidan in TNF-α treated C2C12 muscle cells. In addition, low molecular weight fucoidan reduces TNF-α-induced GDF-8/Myostatin protein and the pro-inflammatory cytokine Interleukin-6 (IL-6) mRNA expression as well as markers of ubiquitin-proteasome pathway (UPP) and autophagy-lysosome pathway (ALP) such as MuRF1, Atrogin-1, p62, Beclin-1 and LC3Ⅱ protein expression. Moreover, low molecular weight fucoidan reduces TNF-α-induced expression of NF-kB p65, C/EBP-ß nuclear protein and of phosphorylated FoxO3a which are main transcription factors induced protein catabolism related factor expression. In summary, low-molecular-weight fucoidan may through reduced TNF-α-induced protein degradation signaling factors and transcription factors activation which is resulted in a decline of the expression of UPP and ALP-related factors and an increase of MyHC expression in C2C12 myotubes. The results of this experiment can be used as a preclinical data for further evaluation of the efficacy of fucoidan supplementation on improving diseases and aging induced muscle atrophy.