Renal primary cilia lengthen in the progression of diabetic kidney disease

Impaired Glucose Metabolism, Primary Cilium Defects, and Kidney Cystogenesis in Glycogen Storage Disease Type Ia

Key Points

Metabolism adaptations due to glucose-6 phosphate accumulation in glycogen storage disease type Ia kidneys, toward a Warburg-like metabolism, promoted cell proliferation. Metabolic perturbations directly affected primary cilium structure and cystogenesis in glycogen storage disease type Ia kidneys.

Background

Glycogen storage disease type Ia (GSDIa) is a rare metabolic disorder caused by mutations in the catalytic subunit of glucose-6 phosphatase (G6PC1). This leads to severe hypoglycemia, and most young patients with GSDIa develop CKD. The kidney pathology is characterized by the development of cysts, which typically occur at an advanced stage of CKD.

Methods

To elucidate the molecular mechanisms responsible for cyst formation, we characterized renal metabolism, molecular pathways involved in cell proliferation, and primary cilium integrity using mice in which G6pc1 was specifically deleted in the kidney from an in utero stage.

Results

GSDIa mice exhibited kidney fibrosis, high inflammation, and cyst formation, leading to kidney dysfunction. In addition, the loss of G6PC1 led to the ectopic accumulation of glycogen and lipids in the kidneys and a metabolic shift toward a Warburg-like metabolism. This metabolic adaptation was due to an excess of glucose-6 phosphate, which supports cell proliferation, driven by the mitogen-activated protein kinase/extracellular signal–regulated kinases and protein kinase B/mammalian target of rapamycin pathways. Treatment of GSDIa mice with rapamycin, a target of the mammalian target of rapamycin pathway, reduced cell proliferation and kidney damage. Our results also identified lipocalin 2 as a contributor to renal inflammation and an early biomarker of CKD progression in GSDIa mice. Its inactivation partially prevented kidney lesions in GSDIa. Importantly, primary cilium defects were observed in the kidneys of GSDIa mice.

Conclusions

Metabolic adaptations because of glucose-6 phosphate accumulation in GSDIa renal tubules, toward a Warburg-like metabolism, promoted cell proliferation and cyst formation in a similar manner to that observed in various cystic kidney diseases. This was associated with downregulation of primary cilium gene expression and, consequently, altered cilium morphology.

Increased ER stress by depletion of PDIA6 impairs primary ciliogenesis and enhances sensitivity to ferroptosis in kidney cells

Primary cilia are crucial for cellular balance, serving as sensors for external conditions. Nephronophthisis and related ciliopathies, which are hereditary and degenerative, stem from genetic mutations in cilia-related genes. However, the precise mechanisms of these conditions are still not fully understood. Our research demonstrates that downregulating PDIA6, leading to cilia removal, makes cells more sensitive to ferroptotic death caused by endoplasmic reticulum (ER) stress. The reduction of PDIA6 intensifies the ER stress response, while also impairing the regulation of primary cilia in various cell types. PDIA6 loss worsens ER stress, hastening ferroptotic death in proximal tubule epithelial cells, HK2 cells. Counteracting this ER stress can mitigate PDIA6 depletion effects, restoring both the number and length of cilia. Moreover, preventing ferroptosis corrects the disrupted primary ciliogenesis due to PDIA6 depletion in HK2 cells. Our findings emphasize the role of PDIA6 in primary ciliogenesis, and suggest its absence enhances ER stress and ferroptosis. These insights offer new therapeutic avenues for treating nephronophthisis and similar ciliopathies. [BMB Reports 2024; 57(10): 453-458].

Identification of functional heterogeneity of immune cells and tubular-immune cellular interplay action in diabetic kidney disease

Background

Renal inflammation plays key roles in the pathogenesis of diabetic kidney disease (DKD). Immune cell infiltration is the main pathological feature in the progression of DKD. Sodium glucose cotransporter 2 inhibitor (SGLT2i) were reported to have antiinflammatory effects on DKD. While the heterogeneity and molecular basis of the pathogenesis and treatment with SGLT2i in DKD remains poorly understood.

Methods

To address this question, we performed a single-cell transcriptomics data analysis and cell cross-talk analysis based on the database (GSE181382). The single-cell transcriptome analysis findings were validated using multiplex immunostaining.

Results

A total of 58760 cells are categorized into 25 distinct cell types. A subset of macrophages with anti-inflammatory potential was identified. We found that Ccl3+ (S100a8/a9 high) macrophages with anti-inflammatory and antimicrobial in the pathogenesis of DKD decreased and reversed the dapagliflozin treatment. Besides, dapagliflozin treatment enhanced the accumulation of Pck1+ macrophage, characterized by gluconeogenesis signaling pathway. Cell-cross talk analysis showed the GRN/SORT1 pair and CD74 related signaling pathways were enriched in the interactions between tubular epithelial cells and immune cells.

Conclusions

Our study depicts the heterogeneity of macrophages and clarifies a new possible explanation of dapagliflozin treatment, showing the metabolism shifts toward gluconeogenesis in macrophages, fueling the anti-inflammatory function of M2 macrophages, highlighting the new molecular features and signaling pathways and potential therapeutic targets, which has provided an important reference for the study of immune-related mechanisms in the progression of the disease.

Mechanisms underlying morphological and functional changes of cilia in fibroblasts derived from patients bearing ARL3T31A and ARL3T31A/C118F mutations

ARL3 is essential for cilia development, and mutations in ARL3 are closely associated with ciliopathies. In a previous study, we observed distinct phenotypes of retinal dystrophy in patients with heterozygous ARL3T31A and compound heterozygous ARL3T31A/C118F mutations, indicating that different mutation types may exert diverse effects on their functions. Here, we generated transformed immortal fibroblast cells from patients carrying heterozygous ARL3T31A and compound heterozygous ARL3T31A/C118F mutations, and systematically evaluated their cilia morphology and function, which were further validated in ARPE-19 cells. Results showed that both ARL3T31A and ARL3T31A/C118F mutations led to a decrease in cilium formation. The ARL3T31A/C118F mutations caused significantly elongated cilia and impaired retrograde transport, whereas the ARL3T31A mutation did not induce significant changes in fibroblasts. RNA-sequencing results indicated that compared to ARL3T31A , ARL3T31A/C118F fibroblasts exhibited a higher enrichment of biological processes related to neuron projection development, tissue morphogenesis, and extracellular matrix (ECM) organization, with noticeable alterations in pathways such as ECM-receptor interaction, focal adhesion, and TGF-β signaling. Similar changes were observed in the proteomic results in ARPE-19 cells. Core regulated genes including IQUB, UNC13D, RAB3IP, and GRIP1 were specifically downregulated in the ARL3T31A/C118F group, and expressions of IQUB, NPM2, and SLC38A4 were further validated. Additionally, IQUB showed a rescuing effect on the overlong cilia observed in ARL3T31A/C118F fibroblasts. Our results not only enhance our understanding of ARL3-related diseases but also provide new insights into the analysis of heterozygous and compound heterozygous mutations in genetics.

The roles of gut microbiota and its metabolites in diabetic nephropathy

Diabetic nephropathy (DN) is a severe microvascular complication of diabetes, which increases the risk of renal failure and causes a high global disease burden. Due to the lack of sustainable treatment, DN has become the primary cause of end-stage renal disease worldwide. Gut microbiota and its metabolites exert critical regulatory functions in maintaining host health and are associated with many pathogenesis of aging-related chronic diseases. Currently, the theory gut-kidney axis has opened a novel angle to understand the relationship between gut microbiota and multiple kidney diseases. In recent years, accumulating evidence has revealed that the gut microbiota and their metabolites play an essential role in the pathophysiologic processes of DN through the gut-kidney axis. In this review, we summarize the current investigations of gut microbiota and microbial metabolites involvement in the progression of DN, and further discuss the potential gut microbiota-targeted therapeutic approaches for DN.