Defining novel transport mechanisms for volume-regulating corticosteroids in the collecting duct of the kidney

皮质类固醇是一种关键的体积调节激素，它以肾脏的收集管为目标，在那里它们迅速改变Na+和H2O的运输，这一过程巩固了全身Na+平衡的微调，并维持了我们的循环容量。在生理条件下，由于11HSD2酶的活性，矿皮质激素醛固酮在收集管中特异性地起作用，该酶将更丰富的糖皮质激素皮质醇转化为无活性的代谢物。然而，在某些条件下，糖皮质激素也可能刺激Na+运输。关于这些激素结合的类固醇受体、随后的转录事件及其对离子运输的影响，我们知道得很多。然而，对于这些激素在亲脂性之外的运动知之甚少，这赋予了它们在质膜上自由扩散的能力。Mansley实验室已经生成了转录组图谱，绘制了皮质类固醇诱导的Na+运输在集合管细胞模型中的遗传信号。这项工作确定了几个膜转运蛋白家族，其表达受皮质类固醇急性治疗的调节。初步研究表明，皮质类固醇实际上可能以定向方式主动运输，激素在单层两侧分布不对称，细胞内浓度可忽略不计。虽然关于皮质类固醇在集束管中的主动运输的研究很少，但其他研究小组已经表明，皮质类固醇可以在身体的其他部位（如大脑和脂肪组织）进行主动运输。该项目的主要研究目标如下：确定细胞和组织水平上假定的皮质类固醇转运蛋白的定位；研究哪些假定的转运蛋白能够进行皮质类固醇转运；确定在远端肾元的细胞模型中删除已识别的转运蛋白的效果

Corticosteroids are critical volume-regulating hormones which target the collecting duct of the kidney where they rapidly alter Na+ and H2O transport, a process which underpins the finetuning of total body Na+ balance and maintains our circulating volume. Under physiological conditions the mineralocorticoid aldosterone acts specifically in the collecting duct due to the activity of the enzyme 11HSD2 which converts the much more abundant glucocorticoid cortisol to an inactive metabolite. However, under certain conditions, glucocorticoids may also stimulate Na+ transport. Much is known about the steroid receptors that these hormones bind, subsequent transcriptional events and their effects upon ion transport. Little, however, is known regarding the movement of these hormones beyond their lipophilic nature, endowing them the ability to diffuse freely across plasma membranes.The Mansley lab have generated transcriptomic profiles mapping the genetic signals underpinning corticosteroid-induced Na+ transport in a cellular model of the collecting duct. This work identified several families of membrane transporters whose expression are regulated by acute treatment with corticosteroids. Preliminary studies revealed that corticosteroids may in fact be actively transported in a directed manner, with asymmetrical distribution of hormones on either side of the monolayer and negligible intracellular concentrations. Whilst little has been described in the field regarding active corticosteroid transport specifically in the collecting duct, other groups have shown that corticosteroids can be actively transported elsewhere in the body e.g. brain and adipose tissue. The key research aims of the project are as follows:To determine the localisation of putative corticosteroid transporters at cellular and tissue levelTo investigate which of the putative transporters are capable of corticosteroid transportTo determine the effects of deleting the identified transporter(s) in a cellular model of the distal nephron