Abstract
KEY POINTS: Detrimental effects of Krüppel-like factor 4 knockdown in podocytes were eliminated with the inhibition of signal transducer and activator of transcription 3 (STAT3) signaling specifically in podocytes. Human kidney biopsies with renal vasculitis demonstrated a glomerular enrichment of STAT3 downstream genes, which negatively correlated with eGFR. Deconvolution of the bulk RNA-seq from Nephrotic Syndrome Study Network showed an enrichment of STAT3 downstream genes in podocytes as compared with other cell clusters. BACKGROUND: Podocyte loss and parietal epithelial cell activation are features of subtypes of glomerulonephritis and FSGS. We recently reported that the podocyte-specific loss of Krüppel-like factor 4 (Klf4(ΔPod)) triggers dysregulated glomerular signal transducer and activator of transcription 3 (STAT3) activation, podocyte loss with parietal epithelial cell activation and proliferation, leading to FSGS. Although pharmacologic systemic STAT3 inhibition attenuated this phenotype, it remains unclear whether the detrimental effects of Klf4 loss are primarily a result of dysregulated STAT3 activation intrinsically in podocytes. METHODS: Mice with the concurrent and conditional knockdown of Stat3 and Klf4 (Klf4(ΔPod)Stat3(ΔPod)) were generated and characterized. Expression arrays from kidney biopsies with various types of glomerular diseases, deposited in Nephroseq, were interrogated for glomerular expression of genes downstream of STAT3 signaling. Cell-specific modulation of STAT3 genes was determined using single-cell RNA sequencing–based proportional cell type deconvolution of bulk RNA-seq obtained from the Nephrotic Syndrome Study Network (NEPTUNE) FSGS and healthy controls. RESULTS: Klf4(ΔPod)Stat3(ΔPod) mice demonstrated no significant podocyte loss, parietal epithelial cell activation and proliferation, FSGS lesions, albuminuria, kidney dysfunction, and tubulointerstitial fibrosis and inflammation compared with the Klf4(ΔPod) mice. Klf4(ΔPod)Stat3(ΔPod) mice also exhibited less glomerular myofibroblasts (+α-smooth muscle actin) as compared with Klf4(ΔPod) mice. Overall survival was restored in Klf4(ΔPod)Stat3(ΔPod) mice as compared with Klf4(ΔPod) mice. Interrogation of expression arrays from human kidney biopsies with renal vasculitis demonstrated a glomerular enrichment of genes involved in canonical STAT3 signaling as compared with healthy controls, which negatively correlated with eGFR. Deconvolution of the bulk RNA-seq data from NEPTUNE showed an enrichment of these STAT3 genes in podocytes as compared with other glomerular cell clusters. CONCLUSIONS: Collectively, these data demonstrate that inhibiting podocyte-specific STAT3 signaling was sufficient to counter the detrimental effects of Klf4 loss in podocytes and prevented albuminuria, accelerated podocyte loss, activation and proliferation of parietal epithelial cells, FSGS lesions, and kidney failure.