作者:Thierry Thomas、Bartolome Burguera
DOI:10.1359/jbmr.2002.17.9.1563
日期:——
Recently, leptin has emerged as a potential candidate responsible for protective effects of fat on bone tissue. However, it remains difficult to draw a clear picture of leptin effects on bone metabolism because published data are sometimes conflicting or apparently contradictory. Beyond differences in models or experimental procedures, it is tempting to hypothesize that leptin exerts dual effects depending on bone tissue, skeletal maturity, and/or signaling pathway. Early in life, leptin could stimulate bone growth and bone size through direct angiogenic and osteogenic effects on stromal precursor cells. Later, it may decrease bone remodeling in the mature skeleton, when trabecular bone turnover is high, by stimulating osteoprotegerin (OPG) expression. Leptin negative effects on bone formation effected through central nervous system pathway could counterbalance these peripheral and positive effects, the latter being predominant when the blood‐brain barrier permeability decreases or the serum leptin level rises above a certain threshold. Thus, the sex‐dependent specificity of the relationship between leptin and bone mineral density (BMD) in human studies could be, at least in part, caused by serum leptin levels that are two‐ to threefold higher in women than in men, independent of adiposity. Although these hypotheses remain highly speculative and require further investigations, existing studies consistently support the role of leptin as a link between fat and bone.
最近,瘦素成为脂肪对骨骼组织保护作用的潜在候选因子。然而,由于已发表的数据有时相互矛盾或明显冲突,因此很难明确瘦素对骨骼代谢的影响。除了模型或实验程序的不同外,我们倾向于假设瘦素根据骨骼组织、骨骼成熟度和/或信号传导途径发挥双重作用。在生命早期,瘦素可通过直接对基质前体细胞产生血管生成和成骨作用来刺激骨骼生长和骨骼大小。在成熟骨骼中,当小梁骨更新率高时,瘦素可能会通过刺激骨保护素(OPG)的表达来减少骨骼重塑。瘦素通过中枢神经系统途径对骨形成产生的负面影响可能会抵消这些外周和积极影响,当血脑屏障通透性降低或血清瘦素水平超过一定阈值时,后者占主导地位。因此,在人类研究中,瘦素与骨矿物质密度(BMD)之间关系的性别依赖性特异性可能至少部分是由血清瘦素水平引起的,女性血清瘦素水平比男性高两到三倍,与肥胖无关。尽管这些假设仍然具有高度的推测性,需要进一步研究,但现有研究一致支持瘦素作为脂肪和骨骼之间的联系。