Self-defense of the kidney: Probing monoallelic expression and functional effects of proteinuria-associated CUBN variants

二倍体的好处被认为包括掩盖部分隐性突变和增加遗传多样性，这反过来可能会促进逆境恢复和细胞可塑性。肾小球损伤，如肾病综合征和糖尿病肾病，可导致肾小管间质纤维化，这是疾病进展的主要驱动力。在这种情况下，关键的细胞类型是近端肾小管细胞(PTCs)，因为它们有很高的代谢需求，并且通过渗漏的肾小球的蛋白质和脂质的重新吸收持续超负荷。特别是，白蛋白携带的饱和脂肪酸被PTCs代谢，但在摄取时也会导致内质网应激和细胞损伤。在这里，我假设，编码摄取受体cubilin的CUBN基因座上高功能遗传多样性和单等位基因表达的组合，是预防肾脏疾病的一种古老机制。这一假说是基于我们最近的发现，即人类对CUBN突变的耐受性很好，甚至可能在进化中赋予选择性杂合子优势，尽管会导致尿蛋白丢失(或蛋白尿)。为了解决这一假设，我们将首先探讨在不同的胁迫条件下，单等位基因CUBN的表达是否会在PTCs之间产生有益的细胞竞争。为此，我们将使用杂合子CUBN-GFP细胞培养和小鼠，在其中可以产生单等位基因表达。其次，我们将在小鼠中从功能上验证已识别的CUBN变体，并测试它们在预防肾小球蛋白尿方面的效力。总之，我们的目标是建立一种新的肾脏保护模式，对蛋白尿肾病的诊断、预后和治疗具有高度的相关性。

The benefits of diploidy are considered to involve masking partially recessive mutations and to increase genetic diversity, which in turn may promote stress resilience and cellular plasticity. Glomerular injury, such as in nephrotic syndrome and diabetic nephropathy, can lead to tubulointerstitial fibrosis, a major driver of disease progression. Key cell types in this context are proximal tubular cells (PTCs), because they have a high metabolic demand and are continuously overloaded by the reabsorption of the proteins and lipids passing the leaky glomerulus. Particularly, saturated fatty acids carried by albumin are metabolized by the PTCs but can also cause ER stress and cell damage upon uptake. Here, I hypothesize that the combination of high functional genetic diversity and monoallelic expression at the CUBN locus, encoding for the uptake receptor cubilin, is an ancient mechanism for the protection against kidney disease. This hypothesis is based on our recent finding that CUBN mutations are very well tolerated by humans and may even confer selective heterozygote advantages in evolution despite causing urinary protein loss (or proteinuria). To address this hypothesis, we will first explore whether monoallelic CUBN expression generates beneficial cell competition among PTCs under different stress conditions. For this, we will use heterozygous CUBN-GFP cell culture and mice, in which monoallelic expression previously could be generated. Second, we will functionally validate the identified CUBN variants in the mouse and test their potency in protecting against glomerular proteinuria. Altogether, we aim to establish a novel paradigm for kidney protection with high relevance for the diagnosis, prognosis and treatment of proteinuric kidney disease.