Department of Physiology, University of Alberta, Edmonton, Alberta, Canada; The Women's & Children's Health Research Institute, Edmonton, Alberta, Canada.
Experimentelle und Klinische Pharmakologie und Toxikologie, Saarland University, Homburg, Germany.
Cell Mol Gastroenterol Hepatol. 2019;8(4):625-642. doi: 10.1016/j.jcmgh.2019.07.005. Epub 2019 Aug 6.
BACKGROUND & AIMS: Intestinal Ca absorption early in life is vital to achieving optimal bone mineralization. The molecular details of intestinal Ca absorption have been defined in adults after peak bone mass is obtained, but they are largely unexplored during development. We sought to delineate the molecular details of transcellular Ca absorption during this critical period.
Expression of small intestinal and renal calcium transport genes was assessed by using quantitative polymerase chain reaction. Net calcium flux across small intestinal segments was measured in Ussing chambers, including after pharmacologic inhibition or genetic manipulation of TRPV6 or Ca1.3 calcium channels. Femurs were analyzed by using micro-computed tomography and histology.
Net TRPV6-mediated Ca flux across the duodenum was absent in pre-weaned (P14) mice but present after weaning. In contrast, we found significant transcellular Ca absorption in the jejunum at 2 weeks but not 2 months of age. Net jejunal Ca absorption observed at P14 was not present in either Trpv6 mutant (D541A) mice or Ca1.3 knockout mice. We observed significant nifedipine-sensitive transcellular absorption across the ileum at P14 but not 2 months. Ca1.3 knockout pups exhibited delayed bone mineral accrual, compensatory nifedipine-insensitive Ca absorption in the ileum, and increased expression of renal Ca reabsorption mediators at P14. Moreover, weaning pups at 2 weeks reduced jejunal and ileal Ca1.3 expression.
We have detailed novel pathways contributing to transcellular Ca transport across the distal small intestine of mice during development, highlighting the complexity of the multiple mechanisms involved in achieving a positive Ca balance early in life.
生命早期肠道钙吸收对于实现最佳骨矿化至关重要。在达到峰值骨量后，成年人的肠道钙吸收的分子细节已经得到了定义，但在发育过程中，这些细节在很大程度上尚未得到探索。我们试图描绘这个关键时期细胞内钙吸收的分子细节。
通过定量聚合酶链反应评估小肠和肾脏钙转运基因的表达。在 Ussing 室中测量小肠段的净钙通量，包括在 TRPV6 或 Ca1.3 钙通道的药物抑制或基因操作后。通过微计算机断层扫描和组织学分析股骨。
在未断奶（P14）的小鼠中，十二指肠的净 TRPV6 介导的钙通量不存在，但在断奶后存在。相比之下，我们发现在 2 周龄但不在 2 月龄时，空肠存在明显的细胞内钙吸收。在 Trpv6 突变体（D541A）小鼠或 Ca1.3 敲除小鼠中，观察到的 P14 时的净空肠钙吸收并不存在。我们观察到 P14 时的硝苯地平敏感细胞内吸收在回肠中存在，但在 2 月龄时不存在。Ca1.3 敲除幼鼠表现出骨矿物质积累延迟、回肠中硝苯地平不敏感的钙吸收代偿增加以及 P14 时肾脏钙重吸收介质表达增加。此外，在 2 周龄时断奶会降低空肠和回肠的 Ca1.3 表达。
我们详细描述了在发育过程中小鼠远端小肠细胞内钙转运的新途径，突出了生命早期实现正钙平衡所涉及的多种机制的复杂性。
