Single-cell RNA sequencing of skin and kidney cells in lupus nephritis provides insights into pathogenesis and indicates novel potential biomarkers

Classification and treatment decisions in lupus nephritis (LN) are largely based on renal histology. Single-cell RNAseq (scRNAseq) analysis may accurately differentiate types of renal involvement at the transcriptomic level, and better inform treatment decisions and prognosis. scRNAseq was performed on kidney and non-lesional skin tissue collected from clinically indicated renal biopsies, and skin biopsies obtained at the time of renal biopsies, in 20 systemic lupus erythematosus (SLE) patients. Cell-types were determined using principal component analysis and tSNE plotting, resulting in the definitive identification of keratinocytes, tubular cells, mesangial cells, fibroblasts, endothelial cells, and leukocytes. Tubular cells in patients with proliferative nephritis demonstrated upregulated TNF signaling compared with membranous nephritis. Interestingly, keratinocytes of patients with proliferative nephritis also demonstrated upregulated TNF signaling. Furthermore, tubular cells of patients who did not respond to standard immunosuppressive treatment showed upregulation of extracellular matrix proteins and fibrotic markers at the time of biopsy. Using logistic regression analysis, a 4-gene tubular fibrosis score was created which predicted response to treatment, with an area under curve of 0.9. We conclude that scRNAseq using small amounts of renal biopsy tissue in SLE can differentiate between the different classes of LN, and provide important insights into potential pathogenic mechanisms. Further, changes in the skin of LN patients can provide a useful source of biomarkers and may reflect important information concerning concurrent kidney pathological events.

Therapeutic blockade of immune complex-mediated glomerulonephritis by highly selective inhibition of Bruton’s tyrosine kinase

Lupus nephritis (LN) is a potentially dangerous end organ pathology that affects upwards of 60% of SLE patients. Bruton’s tyrosine kinase (BTK) is important for B cell development, Fc receptor signaling, and macrophage polarization. In this study, we investigated the effects of a novel, highly selective and potent BTK inhibitor, BI-BTK-1, in an inducible model of LN in which mice receive nephrotoxic serum (NTS) containing anti-glomerular antibodies. Mice were treated once daily with vehicle alone or BI-BTK-1 (0.3–10 mg/kg, n=16/group), either prophylactically or therapeutically.

When compared with control treated mice, NTS-challenged mice treated prophylactically with BI-BTK-1 exhibited significantly attenuated disease which was dose dependent, as measured by proteinuria, serum creatinine, and serum BUN. Histological assessment confirmed marked renal protection in the BI-BTK-1 treatment groups. BI-BTK-1 treatment resulted in decreased recruitment of inflammatory monocytes from the splenic reservoir, and a decrease in infiltrating IBA-1+ cells, as well as C3 deposition, within the kidney. RT-PCR on whole kidney RNA and serum profiling indicated that BTK inhibition significantly decreased levels of LN-relevant inflammatory cytokines and chemokines. Renal RNA expression profiling by RNA-seq revealed that BI-BTK-1 dramatically modulated pathways related to inflammation and glomerular injury. Importantly, when administered therapeutically, BI-BTK-1 reversed established proteinuria and improved renal histopathology.

Our results highlight the important role for BTK in the pathogenesis of immune complex-mediated nephritis, and BTK inhibition as a promising therapeutic target for LN.