铁调素降低“铁过载”预防“绝经后骨代谢异常”的机理研究

Abnormal bone metabolism after menopause is caused by several risk factors. Estrogen deficiency is considered one of the most important risk factors. However, hormone replacement therapy (HRT) is only partially effective in slowing down bone loss in post-menopausal women. Recently, iron overload has been recognized as another risk factor independent of estrogen deficiency. It has been found that there is concurrent but inverse changes of ferritin versus estrogen during menopausal transition. Iron overload has been demonstrated to inhibit bone formation and promote bone resorption, not only in vitro, but also in vivo, thus leading to osteoporosis.Oxidative stress has been widely accepted as the mechanism of iron overload-induced osteoporosis..Based on above findings, our previous studies confirmed the association of iron overload with post-menopausal bone metabolism, and investigated the effects of desferrioxamine (DFO) on bone metabolism of ovariectomized (OVX) rats. The results was promising that the abnormal bone metabolism of OVX rats could be prevented by DFO, which is known to chelate iron.Meanwhile, DFO reduced oxidative stress of OVX rats significantly. .Hepcidin is a newly discovered endogenous hormone and known to inhibit iron absorption and thereby decrease body iron overload through inhibiting ferroportin, which transports the iron out of the cells. Our pre-experimental results showed that hepcidin could up-regulate bone formation markers of osteoblasts and down-regulate bone resorption markers of osteoclasts. This study will explore whether hepcidin could improve abnormal bone metabolism of OVX rats through decreasing iron overload and oxidative stress..Hepcidin is different from DFO as it is an endogenous hormone. Recent studies have found that hepcidin inhibits ferroportin through activating JAK2/STAT3 signaling pathway. Coincidently, both IL-3 and IL-6 have been reported to promote bone formation through stimulating JAK2/STAT3 signaling pathway. Therefore, this study will investigate the effects of hepcidin on osteoblasts and osteoclasts in vitro through co-culture system of osteoblasts and osteoclasts, and further explore the role of JAK2/STAT3 pathway in the effects using gene silencing technology. Therefore, this study will also provide the cellular evidence for future clinical application of hepcidin in post-menopausal osteoporosis in addition to decreasing iron overload and oxidative stress, and further enrich the concept of the prevention and treatment of abnormal bone metabolism in postmenopausal women.

我们的细胞、动物实验提示：绝经后骨代谢异常与"铁过载"密切相关；降低铁过载（去铁胺）可明显预防骨代谢异常。那么，"铁调素"作为降低铁过载的新物质（内源性类激素），是否可以改善骨代谢异常？预实验中我们观察到：铁调素可以上调骨形成指标、下调骨吸收指标；成骨细胞上存在铁调素作用靶点（膜铁转运蛋白）。.本项目将对绝经后大鼠（去势模型）进行铁调素干预；同时在"成骨细胞-破骨细胞共育体系"也进行铁调素干预，成骨细胞采用基因沉默技术处理。研究主要观察动物、细胞干预后的骨代谢指标和细胞生物活性指标变化，并结合铁代谢、JAK2-STAT3细胞信号、氧化应激等不同指标间变化；了解不同剂量铁调素降低铁过载对实验大鼠骨代谢的影响，分析这一影响与JAK2/STAT3信号通路改变、氧化应激改变的关联，提出铁调素（类激素：小剂量大作用）防治绝经后骨代谢异常的实验依据和相关机理，丰富绝经后骨代谢异常的防治理念和干预方法。

本项目通过"内源性及外源性铁调素变化的干预"研究了其对铁代谢及骨代谢的影响，主要观察在体、成骨、破骨细胞干预后的骨代谢和细胞生物活性指标变化，并结合铁代谢、BMP-Smad信号通路等不同指标间变化，了解铁调素对铁蓄积动物模型骨代谢的影响。结果提示，铁调素有利于降低体内的铁离子水平，并能够促进成骨细胞的分化发育。另外铁调素过表达小鼠呈现骨量增加的表型，铁调素敲除的小鼠则相反。利用铁调素敲除斑马鱼进行深度测序分析，结果显示BMP-Smad信号通路基因表达差异显著，提示铁调素的变化通过成骨相关的代谢通路调节骨量。该研究为铁调素通过降铁机理预防绝经后女性骨质疏松症打下基础，并对后期的临床试验及新药研制意义深远。