Podocyte injury is the causative event in all proteinuric kidney diseases including minimal change disease (MCD) and FSGS. Glucocorticoids (GCs) are often the initial and preferred treatment for these conditions. The beneficial effects of GCs are not caused by immunomodulation, but are mediated by their direct effects on podocytes. Unfortunately, GC therapy is riddled with severe systemic toxicities that limit their use. Identification of essential salutary GC-induced targets in podocytes might allow for new therapeutic approaches that can minimize toxicity but maintain efficacy. In the current proposal, we identified diminished expression of the transcription factor dachshund1 (DACH1) in a large-scale mutagenic screen designed to identify mutations that restored injury susceptibility to genetically injury-resistant podocytes. We found DACH1 to be essential to podocyte function in both novel global and podocyte-specific knock out mouse models. Importantly, podocyte- specific DACH1 heterozygous mice, which have reduced glomerular DACH1 expression levels similar to human MCD and FSGS patients, were remarkably susceptible to adriamycin nephropathy, and this phenotype was ameliorated by GC therapy. We found that GC administration caused early and significant induction of DACH1 expression, and we confirm binding of GC receptor to the DACH1 promoter by ChIP assay. Moreover, the protective allele of a DACH1 intronic SNP (rs626277), which has been identified in genome-wide association studies as linked to incident and prevalent CKD, introduced a GC-alpha transcription factor-binding site that was abrogated in the presence of the risk allele. When we tested these alleles in reporter studies, the protective allele dramatically augmented DACH1 promoter activity in response to GCs, consistent with GC- potentiated enhancer function. In GC treated kidney transplant patients, the protective rs626277 allele correlated closely with increased glomerular DACH1 expression and improvement in proteinuria. Furthermore, in a cohort of MCD and FSGS patients, protective and risk alleles correlated with GC responsiveness and resistance respectively. We hypothesize that DACH1 is a central transcriptomic regulator of the salutary glomerular GC response and that rs626277 genotype status, which modulates podocyte DACH1 transcription in the setting of GC therapy, is an important determinant of GC-responsiveness in nephrotic syndrome patients. Our proposal includes three specific aims: i) demonstrate that DACH1 over-expression is protective using a novel inducible podocyte-specific DACH1 transgenic mouse model ii) show that the beneficial effects of GCs in podocytes are mitigated in the absence of DACH1 expression using novel inducible podocyte-specific knockout mice iii) correlate rs626277 genotype status with clinical outcomes in GC-treated MCD and FSGS patients in NEPTUNE and cross-examine mechanistic and transcriptomic data obtained from the first two aims in these patients. If validated, rs626277 genotype status could serve to individualize risk-benefit stratification of GC therapy in nephrotic syndrome patients PRIOR to treatment initiation.
Because glucocorticoids, the main therapeutic option for most primary glomerular diseases, are limited by severe systemic toxicities, there is an urgent need in nephrology to replace their use with novel podocyte-targeted therapies or at the very least, to identify in advance of their administration, the subset of patients who are likely be glucocorticoid responsive. This project identifies the essential podocyte gene DACH1 as a central transcriptomic regulator of the salutary glomerular glucocorticoid response and analyzes involved mechanisms with the goal of identifying novel therapeutic approaches. This work will also correlate a prevalant intronic locus, which our data show augments DACH1 transcription in the setting of glucocorticoid therapy, with clinical outcomes in glucocorticoid-treated primary glomerular disease patients, a clinically important observation that may allow for better individualized risk-benefit stratification prior to initiating glucocorticoid therapy.
