Deciphering the Cell-Specific Specificity of the α-Klotho–Cellular Inhibitor of Apoptosis Protein 1 Axis in Autosomal Dominant Polycystic Kidney Disease

In a recent article published in JASN, Li et al. elegantly elucidate the role of αKlotho in autosomal dominant polycystic kidney disease, identifying a TNF-dependent mechanism by which αKlotho interacts with and destabilizes cellular inhibitor of apoptosis protein 1 (cIAP1), thereby promoting cystic epithelial cell death and suppressing inflammation.1 The integration of single-cell RNA sequencing (scRNA-seq) with mechanistic validation substantially advances understanding of how aging-associated molecules influence cyst progression. While the study convincingly demonstrates the proapoptotic effects of the αKlotho–cIAP1 axis in cystic epithelial cells, the basis of the anti-inflammatory phenotype warrants further discussion. Li et al. attribute reduced macrophage recruitment primarily to suppression of NF-κB signaling in epithelial cells and the consequent decrease in cytokines such as monocyte chemoattractant protein-1.1 However, given systemic administration of recombinant αKlotho and the ubiquitous expression of cIAP1, αKlotho may also directly modulate immune cells, independently of epithelial-derived signals. cIAP1 is a critical regulator of innate immune responses and survival in macrophages. Under high TNF conditions—which the authors demonstrate in the cystic microenvironment—cIAP1 prevents TNF-induced necroptosis or apoptosis in macrophages and sustains canonical NF-κB activation.2,3 The scRNA-seq data (Figure 5 and Supplemental Figure 6) identify macrophage clusters and analyze cell–cell communication.1 It would be informative to know whether cIAP1 expression is reduced within these macrophage clusters in polycystic kidney disease 1 homozygous kidney-limited transgene or recombinant αKlotho-treated kidneys. If αKlotho directly destabilizes cIAP1 in macrophages, the “anti-inflammatory” phenotype could reflect not only reduced recruitment but also apoptosis of infiltrating macrophages and/or shifts in their polarization driven by altered NF-κB dynamics.4 The study further shows that soluble αKlotho interacts with the caspase activation and recruitment domain of cIAP1.1 As cIAP1 is primarily cytosolic, this implies intracellular entry of soluble αKlotho. Although the authors rule out dependence on the classical fibroblast growth factor 23–fibroblast growth factor receptor pathway, the mechanism by which soluble αKlotho gains cytoplasmic access remains unclear. Determining whether internalization is cell type–specific could explain the strong effect in the cystic milieu with limited toxicity in healthy tissue and will be crucial for defining bioavailability requirements of αKlotho-based therapeutics. In conclusion, Li et al. provide compelling evidence that αKlotho is a therapeutic candidate in autosomal dominant polycystic kidney disease. Further analysis of cIAP1 degradation in immune cell subsets using the existing scRNA-seq dataset would refine the proposed model and clarify whether αKlotho acts solely on cystic epithelium or also directly reshapes the immune microenvironment—information important for anticipating immunologic side effects and optimizing dosing in future clinical trials.