Grässel Susanne, Opolka Alfred, Anders Sven, Straub Rainer H, Grifka Joachim, Luger Thomas A, Böhm Markus
Department of Orthopaedic Surgery and Centre for Medical Biotechnology, University of Regensburg, Regensburg, Germany.
Arthritis Rheum. 2009 Oct;60(10):3017-27. doi: 10.1002/art.24846.
The pro-opiomelanocortin (POMC)-derived neuropeptide alpha-melanocyte-stimulating hormone (alpha-MSH) mediates its effects via melanocortin (MC) receptors. This study was carried out to investigate the expression patterns of the MC system and the effects of alpha-MSH in human articular chondrocytes.
Articular chondrocytes established from human osteoarthritic joint cartilage were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting for the expression of MC receptors, POMC, and prohormone convertases (PCs). MC-1 receptor (MC-1R) expression in articular cartilage was further studied by immunohistochemistry. Ca(2+) and cAMP assays were used to monitor alpha-MSH signaling, while studies of alpha-MSH function were performed in cultures with chondrocyte micromass pellets stimulated with alpha-MSH. Expression of cytokines and extracellular matrix (ECM) components was determined by real-time RT-PCR, Western immunoblotting, and enzyme-linked immunosorbent assays.
MC-1R expression was detected in articular chondrocytes in vitro and in articular cartilage in situ. In addition, expression of transcripts for MC-2R, MC-5R, POMC, and PCs was detected in articular chondrocytes. Stimulation with alpha-MSH increased the levels of intracellular cAMP, but not Ca(2+), in chondrocytes. Both messenger RNA and protein expression of various proinflammatory cytokines, collagens, matrix metalloproteinases (MMPs), and SOX9 was modulated by alpha-MSH.
Human articular chondrocytes are target cells for alpha-MSH. The effects of alpha-MSH on expression of cytokines and MMPs suggest that this neuropeptide plays a role in inflammatory and degenerative processes in cartilage. It is conceivable that inflammatory reactions can be mitigated by the induction of endogenous MCs or administration of alpha-MSH to the affected joints. The induction pattern of regulatory and structural ECM components such as collagens as well as SOX9 and anabolic and catabolic cytokines points to a function of alpha-MSH as a trophic factor in skeletal development during endochondral ossification rather than as a factor in homeostasis of permanent cartilage.
源自阿黑皮素原（POMC）的神经肽α-黑素细胞刺激素（α-MSH）通过黑素皮质素（MC）受体介导其作用。本研究旨在探讨MC系统在人关节软骨细胞中的表达模式以及α-MSH的作用。
采用逆转录-聚合酶链反应（RT-PCR）和蛋白质印迹法分析从人骨关节炎关节软骨分离培养的关节软骨细胞中MC受体、POMC和激素原转化酶（PCs）的表达。通过免疫组织化学进一步研究关节软骨中MC-1受体（MC-1R）的表达。采用钙离子（Ca²⁺）和环磷酸腺苷（cAMP）检测法监测α-MSH信号，同时在用α-MSH刺激的软骨细胞微团培养物中研究α-MSH的功能。通过实时RT-PCR、蛋白质免疫印迹法和酶联免疫吸附测定法检测细胞因子和细胞外基质（ECM）成分的表达。
在体外关节软骨细胞和原位关节软骨中均检测到MC-1R的表达。此外，在关节软骨细胞中检测到MC-2R、MC-5R、POMC和PCs转录本的表达。α-MSH刺激可增加软骨细胞内cAMP水平，但不增加Ca²⁺水平。α-MSH可调节多种促炎细胞因子、胶原蛋白、基质金属蛋白酶（MMPs）和SOX9的信使核糖核酸和蛋白质表达。
人关节软骨细胞是α-MSH的靶细胞。α-MSH对细胞因子和MMPs表达的影响表明，这种神经肽在软骨的炎症和退变过程中起作用。可以设想，通过诱导内源性MCs或向受影响关节施用α-MSH可减轻炎症反应。胶原蛋白以及SOX9等调节性和结构性ECM成分以及合成代谢和分解代谢细胞因子的诱导模式表明，α-MSH在软骨内骨化过程中的骨骼发育中作为一种营养因子发挥作用，而不是在永久性软骨的稳态中发挥作用。
