Skeletal muscle wasting is commonly associated with chronic kidney disease (CKD), resulting in increased morbidity and mortality. However, the link between kidney and muscle function remains poorly understood. Here, we took a complementary interorgan approach to investigate skeletal muscle wasting in CKD. We identified increased production and elevated blood levels of soluble pro-cachectic factors, including activin A, directly linking experimental and human CKD to skeletal muscle wasting programs. Single-cell sequencing data identified the expression of activin A in specific kidney cell populations of fibroblasts and cells of the juxtaglomerular apparatus. We propose that persistent and increased kidney production of pro-cachectic factors, combined with a lack of kidney clearance, facilitates a vicious kidney/muscle signaling cycle, leading to exacerbated blood accumulation and, thereby, skeletal muscle wasting. Systemic pharmacological blockade of activin A using soluble activin receptor type IIB ligand trap as well as muscle-specific adeno-associated virus–mediated downregulation of its receptor ACVR2A/B prevented muscle wasting in different mouse models of experimental CKD, suggesting that activin A is a key factor in CKD-induced cachexia. In summary, we uncovered a crosstalk between kidney and muscle and propose modulation of activin signaling as a potential therapeutic strategy for skeletal muscle wasting in CKD.

Complement factor C5a has two known receptors, C5aR, which mediates proinflammatory effects, and C5L2, a potential C5a decoy receptor. We previously identified C5a/C5aR signaling as a potent profibrotic pathway in the kidney. Here we tested for the first time the role of C5L2 in renal fibrosis. In unilateral ureteral obstruction (UUO)-induced kidney fibrosis, the expression of C5aR and C5L2 increased similarly and gradually as fibrosis progressed and was particularly prominent in injured dilated tubules. Genetic deficiency of either C5aR or C5L2 significantly reduced UUO-induced tubular injury. Expression of key proinflammatory mediators, however, significantly increased in C5L2- compared with C5aR-deficient mice, but this had no effect on the number of renal infiltrating macrophages or T cells. Moreover, in C5L2^−/−mice, the cytokine and matrix metalloproteinase-inhibitor tissue inhibitor of matrix metalloproteinase-1 was specifically enhanced. Consequently, in C5L2^−/−mice the degree of renal fibrosis was similar to wild type (WT), albeit with reduced mRNA expression of some fibrosis-related genes. In contrast, C5aR^−/−mice had significantly reduced renal fibrosis compared with WT and C5L2^−/−mice in UUO. In vitro experiments with primary tubular cells demonstrated that deficiency for either C5aR or C5L2 led to a significantly reduced expression of tubular injury and fibrosis markers. Vice versa, stimulation of WT tubular cells with C5a significantly induced the expression of these markers, whereas the absence of either receptor abolished this induction. In conclusion, in experimental renal fibrosis C5L2 and C5aR both contribute to tubular injury, and, while C5aR acts profibrotic, C5L2 does not play a role in extracellular matrix accumulation, arguing against C5L2 functioning simply as a decoy receptor.

Focal segmental glomerulosclerosis (FSGS) involves podocyte injury, potentially linked to dysfunctional nuclear pore complexes (NPCs). We show that selinexor (KPT-330), a nuclear export inhibitor, restores NPC function in vitro. In an FSGS rat model, selinexor improves kidney function, lowers serum creatinine and cystatin C levels, and reduces serum lipid levels. However, histological damage persists, indicating partial but not complete protection. These findings highlight NPC-targeted therapies as a potential strategy for treating FSGS.

Background: Activated parietal epithelial cells (PECs) and podocytes are key effector cells in the development of crescentic glomerulonephritis and focal segmental glomerulosclerosis (FSGS). Platelet-derived growth factor (PDGF)-C has been found to be important for tubulointerstitial fibrosis development, but its relevance for crescentic glomerulonephritis and FSGS was previously unknown. Methods: To address this, expression analyses for both PDGF-C and its receptor PDGFRα were carried out in mouse and human kidney tissues. To further elucidate a functional role of PDGF-C, the murine nephrotoxic nephritis model of crescentic glomerulonephritis was induced in a) Pdgfc -deficient mice, b) mice treated with a neutralizing PDGF-C antibody, and c) Pax8-cre::Pdgfc ^fl / ^fl mice with conditional Pdgfc deletion in kidney epithelial cells. We also subjected the collapsing FSGS model of the anti-Thy1.1 transgenic mouse to pharmacological PDGF-C inhibition. The studies were supplemented by PEC in vitro analyses. Results: Our data showed that PDGF-C was upregulated in PECs and expressed de novo in podocytes under disease conditions. It promoted the proliferation and activation of primary as well as conditionally immortalized PECs in vitro . In both the genetic and pharmacological PDGF-C intervention studies in murine crescentic glomerulonephritis and FSGS, significant improvements in glomerular crescent formation, glomerular sclerosis, renal inflammation and kidney function parameters were observed upon PDGF-C deficiency or antagonism. Mechanistically, transcription factor FOXM1 was identified as a mediator of disease-related PDGF-C expression in PECs. Conclusions: Our studies identified epithelial PDGF-C as a contributor to disease progression in crescentic glomerulonephritis and FSGS, acting in part through the activation of parietal epithelial cells.

Acute kidney injury is a frequent, life-threatening complication of liver disease. The stress-responsive DNA- and RNA-binding protein Y-box-binding protein 1 (YB-1) regulates gene expression and modulates liver-kidney crosstalk, with partial systemic YB-1 deficiency protecting the liver but worsening kidney injury in a murine bile duct ligation (BDL) model. To further define cell-specific roles of YB-1, its expression was selectively reduced in kidney and immune cells, and the effects on primary liver and secondary kidney injury were evaluated. Conditional Ybx1 knockout mice targeting tubular ( Pax8 ^cre xYbx1 ^fl ) and myeloid ( LysM ^cre xYbx1 ^fl ) cells were used to study YB-1 function during BDL-induced cholestasis and kidney damage. Organ injury and fibrosis were evaluated by histology, gene expression, and serum markers. Tubular YB-1 deficiency was associated with reduced kidney injury and fibrosis. This was accompanied by a decreased expression of the bile acid uptake transporter ASBT and an increased expression of the efflux transporter OSTβ. These changes are consistent with a coordinated detoxification response limiting intracellular bile acid accumulation. However, this deficiency aggravated liver damage after BDL. In contrast, myeloid YB-1 deficiency reduced serum markers of liver injury but worsened renal inflammation and injury, mirroring findings in whole-body Ybx1 haploinsufficient mice. These findings identify YB-1 as a crucial regulator of organ-specific responses in cholestatic liver disease, with opposing, cell type-dependent effects on liver and kidney injury, highlighting its central role in inter-organ communication.

The nuclear envelope, with its nuclear pore complexes, establishes a selective barrier that maintains the spatial organization of the cellular proteome. Whether this barrier remains intact in long-lived postmitotic cells during aging is largely unknown. Here, we show that aging podocytes experience a progressive loss of nuclear-cytoplasmic compartmentalization. Using subcellular proteomics and quantitative imaging, we identify a global redistribution of proteins between the nucleus and cytoplasm, affecting key regulators of RNA processing, chromatin organization, and cellular metabolism. Loss of compartmentalization is accompanied by mitochondrial dysfunction, increased reactive oxygen species production, and aberrant nuclear accumulation of YAP1, linking nuclear barrier failure to metabolic and transcriptional dysregulation. These findings identify nuclear envelope dysfunction as a driver of proteome disorganization and cellular decline in aging podocytes and suggest that loss of nuclear-cytoplasmic compartmentalization represents a general mechanism contributing to dysfunction in long-lived cells.