Supplementary Material for: Jak1/Stat3 Activation Alters Phosphate Metabolism Independently of Sex and Extracellular Phosphate Levels

<b><i>Introduction:</i></b> Phosphate homeostasis is regulated by a complex network involving the parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), and calcitriol acting on several organs including the kidney, intestine, bone, and parathyroid gland. Previously, we showed that activation of the Janus kinase 1 (Jak1)-signal transducer and activator of transcription 3 (Stat3) signaling pathway leads to altered mineral metabolism with higher FGF23 levels, lower PTH, and higher calcitriol levels. Here, we investigated if there are sex differences in the role of Jak1/Stat3 signaling pathway on phosphate metabolism and if this pathway is sensitive to extracellular phosphate alterations. <b><i>Methods:</i></b> We used a mouse model (<i>Jak1</i>^S645P+/−) that resembles a constitutive activating mutation of the Jak1/Stat3 signaling pathway in humans and analyzed the impact of sex on mineral metabolism parameters. Furthermore, we challenged <i>Jak1</i>^S645P+/− male and female mice with a high (1.2% w/w) and low (0.1% w/w) phosphate diet and a diet with phosphate with organic origin with lower bioavailability. <b><i>Results:</i></b> Female mice, as male mice, showed higher intact FGF23 levels but no phosphaturia, and higher calcitriol and lower PTH levels in plasma. A phosphate challenge did not alter the effect of Jak1/Stat3 activation on phosphate metabolism for both genders. However, under a low phosphate diet or a diet with lower phosphate availability, the animals showed a tendency to develop hypophosphatemia. Moreover, male and female mice showed similar phosphate metabolism parameters. The only exception was higher PTH levels in male mice than those in females. <b><i>Discussion/Conclusion:</i></b> Sex and extracellular phosphate levels do not affect the impact of Jak1/Stat3 activation on phosphate metabolism.

<b><i>引言：</i></b> 磷酸盐稳态由复杂调控网络维持，该网络涉及甲状旁腺激素（parathyroid hormone, PTH）、成纤维细胞生长因子23（fibroblast growth factor 23, FGF23）及骨化三醇（calcitriol），可作用于肾脏、肠道、骨骼与甲状旁腺等多个器官。本团队此前的研究显示，詹纳斯激酶1（Janus kinase 1, Jak1）-信号转导与转录激活因子3（signal transducer and activator of transcription 3, Stat3）信号通路的激活可改变矿物质代谢，表现为FGF23水平升高、PTH水平降低及骨化三醇水平升高。本研究旨在探讨Jak1/Stat3信号通路在磷酸盐代谢中的作用是否存在性别差异，以及该通路是否对细胞外磷酸盐水平变化具有敏感性。
<b><i>方法：</i></b> 本研究使用了模拟人类Jak1/Stat3信号通路组成型激活突变的小鼠模型（<i>Jak1</i>^S645P+/−），并分析了性别对矿物质代谢相关参数的影响。此外，本研究对<i>Jak1</i>^S645P+/−雌雄小鼠分别开展高磷（1.2% 质量分数）、低磷（0.1% 质量分数）膳食干预，以及采用生物利用度较低的有机磷膳食进行干预。
<b><i>结果：</i></b> 与雄性小鼠一致，雌性小鼠的完整FGF23水平升高，但无磷酸盐尿，血浆骨化三醇水平升高、PTH水平降低。磷负荷实验未改变两种性别小鼠中Jak1/Stat3激活对磷酸盐代谢的影响。但在低磷膳食或磷生物利用度较低的膳食干预下，小鼠均表现出低磷血症的发病倾向。此外，雌雄小鼠的磷酸盐代谢参数基本一致，仅雄性小鼠的血浆PTH水平高于雌性小鼠，为唯一差异点。
<b><i>讨论/结论：</i></b> 性别与细胞外磷酸盐水平均不会影响Jak1/Stat3激活对磷酸盐代谢的调控作用。