背景:人类的先前数据表明,极端的身体不活动(EPI)对性别之间的铁代谢有不同的影响。我们的目标是通过研究暴露于后肢卸载(HU)的两性大鼠来加深潜在的机制,模拟EPI的参考实验模型。
方法:将8周龄雄性和雌性Wistar大鼠分配到对照(CTL)或后肢卸载(HU)条件(n=12/组)。经过7天的HU,血清,肝脏,脾,脾比目鱼肌被切除.在血清样本中测量铁参数,和ICP-MS用于定量组织中的铁。通过RT-qPCR和Western印迹分析铁代谢基因和蛋白质。
结果:与对照男性相比,对照雌性在血清中表现出较高的铁浓度(+43.3%,p<0.001),肝脏(LIC;+198%,P<0.001),脾脏(SIC;+76.1%,P<0.001),血清转铁蛋白饱和度(TS)(+53.3%,P<0.001),与以前在人类中的观察结果相反。HU鼠雄性,但不是女性,表现出LIC(+54%P<0.001)和SIC(+30.1%,P=0.023),随着H-铁蛋白蛋白水平的上升(+60.9%和+134%,分别,在肝脏和脾脏中;P<0.05)和TFRC蛋白水平降低(-36%;-50%,分别,P<0.05)。HU男性也表现出脾HO-1和NRF2mRNA水平的增加,(p<0.001),以及HU女性(P<0.001)。伴随着在HU动物中观察到的肌肉萎缩,女性比目鱼肌中的铁浓度增加(+26.7,P=0.004),而男性仅观察到一种趋势(+17.5%,P=0.088)。此外,男性比目鱼中的H-铁蛋白和肌红蛋白水平增加(+748%,P<0.001,+22%,分别为P=0.011)和女性(+369%,P<0.001,+21.9%,分别为P=0.007),而TFRC和铁转运蛋白(FPN)蛋白水平在男性中降低(-68.9%,P<0.001,-76.8%,分别为P<0.001)和女性(-75.9%,P<0.001,-62.9%,分别为P<0.001)。有趣的是,在两性中,血红素出口商FLVCR1mRNA在比目鱼中增加,而蛋白质水平下降(男性为-39.9%P=0.010,女性为-49.1%P<0.001)。
结论:综合来看,这些数据支持,在大鼠中(1)极端的体力活动不同地影响铁在两性中的分布,(2)脾红吞噬作用可能在这种铁的错误分布中起作用。两性萎缩的比目鱼肌中较高的铁浓度与铁储存蛋白的增加之间的解耦有关(即,铁蛋白和肌红蛋白)和铁出口蛋白水平的降低(即,FPN和FLVCR1),从而支持在极度缺乏体力活动的情况下骨骼肌中的铁螯合。
BACKGROUND: Previous data in humans suggest that extreme physical inactivity (EPI) affects iron metabolism differently between sexes. Our objective was to deepen the underlying mechanisms by studying rats of both sexes exposed to hindlimb unloading (HU), the reference experimental model mimicking EPI.
METHODS: Eight-week-old male and female Wistar rats were assigned to control (CTL) or hindlimb unloading (HU) conditions (n = 12/group). After 7 days of HU, serum, liver, spleen, and soleus muscle were removed. Iron parameters were measured in serum samples, and ICP-MS was used to quantify iron in tissues. Iron metabolism genes and proteins were analysed by RT-qPCR and Western blot.
RESULTS: Compared with control males, control females exhibited higher iron concentrations in serum (+43.3%, p < 0.001), liver (LIC; +198%, P < 0.001), spleen (SIC; +76.1%, P < 0.001), and transferrin saturation (TS) in serum (+53.3%, P < 0.001), contrasting with previous observations in humans. HU rat males, but not females, exhibited an increase of LIC (+54% P < 0.001) and SIC (+30.1%, P = 0.023), along with a rise of H-ferritin protein levels (+60.9% and +134%, respectively, in liver and spleen; P < 0.05) and a decrease of TFRC protein levels (-36%; -50%, respectively, P < 0.05). HU males also exhibited an increase of splenic HO-1 and NRF2 mRNA levels, (p < 0.001), as well as HU females (P < 0.001). Concomitantly to muscle atrophy observed in HU animals, the iron concentration increased in soleus in females (+26.7, P = 0.004) while only a trend is observed in males (+17.5%, P = 0.088). In addition, the H-ferritin and myoglobin protein levels in soleus were increased in males (+748%, P < 0.001, +22%, P = 0.011, respectively) and in females (+369%, P < 0.001, +21.9%, P = 0.007, respectively), whereas TFRC and ferroportin (FPN) protein levels were reduced in males (-68.9%, P < 0.001, -76.8%, P < 0.001, respectively) and females (-75.9%, P < 0.001, -62.9%, P < 0.001, respectively). Interestingly, in both sexes, heme exporter FLVCR1 mRNA increased in soleus, while protein levels decreased (-39.9% for males P = 0.010 and -49.1% for females P < 0.001).
CONCLUSIONS: Taken together, these data support that, in rats (1) extreme physical inactivity differently impacts the distribution of iron in both sexes, (2) splenic erythrophagocytosis could play a role in this iron misdistribution. The higher iron concentrations in atrophied soleus from both sexes are associated with a decoupling between the increase in iron storage proteins (i.e., ferritin and myoglobin) and the decrease in levels of iron export proteins (i.e., FPN and FLVCR1), thus supporting an iron sequestration in skeletal muscle under extreme physical inactivity.