Division of Nephrology, Department of Medicine IV, University Hospital, Ludwig-Maximilians-University Munich, Munich, Germany.
Department of Nephrology and Medical Intensive Care, Charité-Universitätsmedizin Berlin, Berlin, Germany.
Front Immunol. 2021 Apr 21;12:673423. doi: 10.3389/fimmu.2021.673423. eCollection 2021.
Calcium oxalate (CaOx) crystal formation, aggregation and growth is a common cause of kidney stone disease and nephrocalcinosis-related chronic kidney disease (CKD). Genetically modified mouse strains are frequently used as an experimental tool in this context but observed phenotypes may also relate to the genetic background or intestinal microbiota. We hypothesized that the genetic background or intestinal microbiota of mice determine CaOx crystal deposition and thus the outcome of nephrocalcinosis. Indeed, , or / knockout mice on a 129/C57BL/6J (B6J) background that were fed an oxalate-rich diet for 14 days did neither encounter intrarenal CaOx crystal deposits nor nephrocalcinosis-related CKD. To test our assumption, we fed C57BL/6N (B6N), 129, B6J and Balb/c mice an oxalate-rich diet for 14 days. Only B6N mice displayed CaOx crystal deposits and developed CKD associated with tubular injury, inflammation and interstitial fibrosis. Intrarenal mRNA expression profiling of 64 known nephrocalcinosis-related genes revealed that healthy B6N mice had lower mRNA levels of uromodulin () compared to the other three strains. Feeding an oxalate-rich diet caused an increase in uromodulin protein expression and CaOx crystal deposition in the kidney as well as in urinary uromodulin excretion in B6N mice but not 129, B6J and Balb/c mice. However, backcrossing 129 mice on a B6N background resulted in a gradual increase in CaOx crystal deposits from F2 to F7, of which all B6N/129 mice from the 7 generation developed CaOx-related nephropathy similar to B6N mice. Co-housing experiments tested for a putative role of the intestinal microbiota but B6N co-housed with 129 mice or B6N/129 (3 and 6 generation) mice did not affect nephrocalcinosis. In summary, genetic background but not the intestinal microbiome account for strain-specific crystal formation and, the levels of uromodulin secretion may contribute to this phenomenon. Our results imply that only littermate controls of the identical genetic background strain are appropriate when performing knockout mouse studies in this context, while co-housing is optional.
草酸钙（CaOx）晶体的形成、聚集和生长是肾结石病和肾钙质沉着症相关慢性肾病（CKD）的常见原因。在这种情况下，通常使用基因修饰的小鼠品系作为实验工具，但观察到的表型也可能与遗传背景或肠道微生物群有关。我们假设，小鼠的遗传背景或肠道微生物群决定了 CaOx 晶体的沉积，从而影响肾钙质沉着症的结果。事实上，在 129/C57BL/6J（B6J）背景下的或 / 基因敲除小鼠，在给予富含草酸盐的饮食 14 天后，既没有发现肾内 CaOx 晶体沉积，也没有发生肾钙质沉着症相关的 CKD。为了验证我们的假设，我们用 C57BL/6N（B6N）、129、B6J 和 Balb/c 小鼠喂食富含草酸盐的饮食 14 天。只有 B6N 小鼠出现 CaOx 晶体沉积，并发展为与肾小管损伤、炎症和间质纤维化相关的 CKD。对 64 种已知与肾钙质沉着症相关的基因的肾内 mRNA 表达谱分析显示，健康的 B6N 小鼠的尿调蛋白（）mRNA 水平低于其他三种品系。用富含草酸盐的饮食喂养会导致 B6N 小鼠的尿调蛋白蛋白表达和肾内 CaOx 晶体沉积增加，以及尿调蛋白排泄增加，但 129、B6J 和 Balb/c 小鼠则不会。然而，将 129 小鼠回交至 B6N 背景上，会导致 F2 到 F7 代的 CaOx 晶体沉积逐渐增加，其中所有来自第 7 代的 B6N/129 小鼠都发展为类似于 B6N 小鼠的 CaOx 相关肾病。共笼实验测试了肠道微生物群的潜在作用，但 B6N 与 129 小鼠或 B6N/129（第 3 代和第 6 代）小鼠共笼并没有影响肾钙质沉着症。总之，遗传背景而不是肠道微生物群决定了特定品系的晶体形成，而尿调蛋白分泌水平可能与此现象有关。我们的结果表明，在这种情况下进行基因敲除小鼠研究时，只有相同遗传背景品系的同窝仔鼠是合适的对照，而共笼是可选的。
