越來越多的證據表明，運動可以刺激骨骼肌釋放蛋白質（稱為肌肉因子），這些蛋白質以類似荷爾蒙的方式發揮作用，並對遠端器官產生特定的內分泌影響。在我們的研究過程中發現MyoD促使 FNDC5（irisin）和纖維母細胞生長因子21 (FGF21)基因表現量上升。N-lactoyl-phenylalanine（N-LP）是一種新型運動代謝物，在劇烈運動後由多種細胞中的carnosine dipeptidase 2（CNDP2）合成，由乳酸和苯丙胺酸合成，N-LP對於脂肪細胞的氧化代謝等作用與irisin/FGF21相似。在本研究中，我們想要探討骨骼肌中鳶尾素/FGF21和N-LP之間的關係以及它們對肌肉骨骼系統的相互作用。首先我們發現 FGF21 啟動子的活性被 MyoD、N-LP 和神經傳導物質乙醯膽鹼 (Ach) 激活，但被細胞因子 TNFα 和 IL-1β 抑制，結果顯示FGF21啟動子透過分化和運動訊號活化。此外，雖然 Ach 或 N-LP 能夠在GM或DM環境中促使FGF21 啟動子活化，但它們共處理下會抑制 DM環境中的FGF21啟動子，這意味著拮抗途徑參與了它們的訊號傳導。使用N-LP 和Irisin/FGF21 處理骨源細胞（MC3T3），分析它們對於骨生成的作用。我們發現N-LP從早期就增強了骨生成作用，但irisin/FGF21的效果只能在晚期才能看到，特別是成骨相關基因Osteopontin(OPN)的活化。我們的研究結果提供了肌肉因子與N-LP之間的新關係，N-LP可能成為骨質疏鬆症或相關疾病的新療法。;A growing body of evidence has shown that exercise can stimulate the release of proteins from skeletal muscle, termed myokines, that work in a hormone-like fashion and exert specific endocrine effects on distant organs. In our study, we have found that FNDC5 (irisin) and fibroblast growth factor 21 (FGF21) were up-regulated by MyoD. N-lactoyl-phenylalanine (N-LP) is a newly identified metabolite synthesized from lactate and phenylalanine by the enzyme carnosine dipeptidase 2（CNDP2）in various cells after strenuous exercise, and it share similar effect with irisin/FGF21 on adipocytes, such as oxidative metabolism enhancement. In this study, we aim to investigate the relationship between irisin/FGF21 and N-LP in skeletal muscle and their synergistic effect on the musculoskeletal system. We found that the promoter activity of FGF21 was activated by MyoD, N-LP, and the neurotransmitter acetylcholine (Ach) but repressed by cytokines TNFα and IL-1β, suggesting its activation by differentiation and exercise signals. Additionally, although either Ach or N-LP can enhance FGF21 promoter activity in GM or DM, together they repressed FGF21 promoter in DM, implying antagonistic pathways are involved in their signaling. MC3T3 osteoblast cells were treated with N-LP and irisin/FGF21 to analyze their distinct and synergistic effect on osteogenesis. We found that N-LP enhanced osteogenesis starting from early stage but the effect of irisin/FGF21 could only be seen at late stage, especially the activation of the osteogenic gene Osteopontin. Our results provide new relationship between myokines and the exercise metabolite N-LP, and N-LP might become a new therapy for osteoporosis or related diseases.
