Disease Pathways in Podocyte Injury - Approaching FSGS by single-nucleus RNA-sequencing

足细胞是肾滤过单元——肾小球的上皮细胞类型，足细胞疾病可导致蛋白尿和进行性肾脏疾病。进行性足细胞损伤和丢失的常见且统一的肾小球表型是局灶性和节段性肾小球硬化（FSGS）。FSGS是一种组织学模式，由各种异质性和进行性疾病过程引起，涉及足细胞病理。FSGS的一个特点是其异质性，特别是在同一组织内同时发生不同的细胞群，反映不同程度的细胞损伤和疾病特异性分子特征。这种情况与恶性肿瘤组织的异质性相当，它可能同时包含肿瘤干细胞、分化和去分化的肿瘤细胞、宿主组织的健康细胞、各种免疫细胞以及响应免疫系统攻击的肿瘤细胞。FSGS的根本原因仍然难以捉摸，导致这种组织病理学损伤模式的不同疾病实体也不清楚。在肿瘤生物学中，单细胞和单核rna测序（scRNAseq, snRNAseq）最近被证明是描述肿瘤内细胞群，表征免疫反应和了解肿瘤治疗耐药机制的强大技术。我们最近使用这种技术来阐明肾小球的细胞组成（Karaiskos等人，2018），现在将使用snRNAseq来阐明FSGS早期发病过程中的细胞特异性转录模式。由于FSGS对致病刺激反应的细胞异质性，snRNAseq有望增加对该疾病的现有知识。为了达到这一目标，我们将采用3种不同的小鼠FSGS模型(一种遗传模型（Wt1hetdel），一种毒性模型（阿霉素）和一种采用足细胞特异性表达白喉毒素受体的转基因小鼠模型。获得的数据将与现有的多层组学数据（bulkRNAseq，蛋白质组学，磷酸化蛋白质组学和代谢组学）相结合，以确定FSGS发病机制背后的细胞生物学变化，并破译肾小球中细胞类型的特异性反应。

Podocytes are the epithelial cell-type of the renal filtration unit – the glomerulus – and podocyte disease leads to proteinuric and progressive kidney disease. The common and unifying glomerular phenotype of progressive podocyte damage and loss is focal and segmental glomerulosclerosis (FSGS). FSGS is a histologic pattern resulting from various heterogeneous and progressive disease processes that involve podocyte pathology. A hallmark of FSGS is its heterogeneity, in particular the simultaneous occurrence of various cell populations reflecting different degrees of cell damage and disease-specific molecular signatures within the same tissue. This situation is comparable to the heterogeneity of malignant tumor tissues, which may simultaneously contain tumor stem cells, differentiated and de-differentiating tumor cells, healthy cells of the host tissue, various immune cells, as well as tumor cells responding to the attacking immune system. The underlying cause of FSGS has remained elusive and the different disease entities leading to this histopathological pattern of injury are not clear. In tumor biology, single-cell and single-nucleus RNA-sequencing (scRNAseq, snRNAseq) have recently proven as powerful techniques to delineate cell populations within tumors, characterize the immune response, and understand mechanisms of resistance to tumor therapy. We have recently employed this technique to elucidate the cellular composition of the renal glomerulus (Karaiskos et al. 2018) and will now use snRNAseq to elucidate cell-specific transcriptional patterns during early pathogenesis of FSGS. Due to cellular heterogenity in the response to disease-causing stimuli in FSGS snRNAseq holds the promise to add much to the current knowledge on this disease. To reach this goal, we will employ 3 different mouse models of FSGS (one genetic model (Wt1hetdel), one toxic model (adriamycin) and one transgenic mouse model employing the podocyte-specific expression of the diphtheria toxin receptor. The data obtained will be combined with available multilayered omics-data (bulkRNAseq, proteomics, phospho-proteomics and metabolomics) to take the next towards identifying the cell biological changes underlying the pathogenesis of FSGS and to decipher cell-type specific responses in the glomerulus.