Awuah Boadi Eugenia, Shin Samuel, Yeroushalmi Samuel, Choi Bok-Eum, Li Peijun, Bandyopadhyay Bidhan C
Calcium Signaling Laboratory, Research Service, Veterans Affairs Medical Center, 50 Irving Street, NW, Washington, DC 20422, USA.
Division of Renal Diseases & Hypertension, Department of Medicine, The George Washington University, Washington, DC 20037, USA.
Int J Mol Sci. 2021 Mar 17;22(6):3050. doi: 10.3390/ijms22063050.
Proximal tubular (PT) acidosis, which alkalinizes the urinary filtrate, together with Ca supersaturation in PT can induce luminal calcium phosphate (CaP) crystal formation. While such CaP crystals are known to act as a nidus for CaP/calcium oxalate (CaOx) mixed stone formation, the regulation of PT luminal Ca concentration ([Ca]) under elevated pH and/or high [Ca] conditions are unknown. Since we found that transient receptor potential canonical 3 (TRPC3) knockout (KO; -/-) mice could produce mild hypercalciuria with CaP urine crystals, we alkalinized the tubular pH in TRPC3-/- mice by oral acetazolamide (0.08%) to develop mixed urinary crystals akin to clinical signs of calcium nephrolithiasis (CaNL). Our ratiometric (λ340/380) intracellular [Ca] measurements reveal that such alkalization not only upsurges Ca influx into PT cells, but the mode of Ca entry switches from receptor-operated to store-operated pathway. Electrophysiological experiments show enhanced bicarbonate related current activity in treated PT cells which may determine the stone-forming phenotypes (CaP or CaP/CaOx). Moreover, such alkalization promotes reactive oxygen species generation, and upregulation of calcification, inflammation, fibrosis, and apoptosis in PT cells, which were exacerbated in absence of TRPC3. Altogether, the pH-induced alteration of the Ca signaling signature in PT cells from TRPC3 ablated mice exacerbated the pathophysiology of mixed urinary stone formation, which may aid in uncovering the downstream mechanism of CaNL.
近端肾小管（PT）酸中毒可使尿液滤液碱化，同时PT中的钙过饱和可诱导管腔磷酸钙（CaP）晶体形成。虽然已知此类CaP晶体是CaP/草酸钙（CaOx）混合结石形成的核心，但在pH升高和/或高钙条件下PT管腔钙浓度（[Ca]）的调节尚不清楚。由于我们发现瞬时受体电位阳离子通道亚家族C成员3（TRPC3）基因敲除（KO；-/-）小鼠可产生伴有CaP尿结晶的轻度高钙尿症，我们通过口服乙酰唑胺（0.08%）使TRPC3-/-小鼠的肾小管pH碱化，以形成类似于钙肾结石（CaNL）临床症状的混合尿结晶。我们的比率测量（λ340/380）细胞内[Ca]结果显示，这种碱化不仅会增加Ca流入PT细胞，而且Ca进入的模式会从受体介导途径转变为储存介导途径。电生理学实验表明，处理后的PT细胞中与碳酸氢盐相关的电流活性增强，这可能决定结石形成表型（CaP或CaP/CaOx）。此外，这种碱化会促进活性氧的产生，并上调PT细胞中的钙化、炎症、纤维化和凋亡，在缺乏TRPC3的情况下这些情况会加剧。总之，pH诱导的TRPC3基因敲除小鼠PT细胞中Ca信号特征的改变加剧了混合性尿路结石形成的病理生理学，这可能有助于揭示CaNL的下游机制。
