Mechanisms of the development of mesangial proliferative glomerulonephritis via constitutive-active expression of IKK2 in juxtaglomerular renin precursor cells

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Extra-/juxtaglomerular renin lineage cells (RLC) are mesangial precursor cells migrating into the glomerulus to replace mesangial cells after glomerular injury. Hereby, the RLC must receive signals from the intraglomerular processes (injury, cell death, inflammation) and react by loss of renin production, immigration, proliferation and mesangial differentiation / myofibroblast activation. It is unclear which extracellular and intracellular signals are essential for this phenotypical change of the RLC and whether this primarily regenerative mechanism can also lead pathogenetically to a mesangial proliferative glomerulonephritis. To solve this question experimentally, in an unbiased approach we differentially characterized the RLC before and during our murine mesangiolytic glomerulonephritis model in vivo before and during the glomerular repair reaction by transcriptome analysis. An early TNF-α and continuing nuclear factor κB (NF-κB) stimulation were shown during immigration. In in vitro studies using the renin lineage cell line As4.1, it was already demonstrated that the TNF-α/NF-κB system shuts down renin production and causes a phenotypical change towards activated mesangial cells/myofibroblasts. By creating a novel transgene mouse line with induction of the constitutive-active expression of the NF-κB activator IKK2 specifically in RLC, not only changes of the juxtaglomerular apparatus, but also activation of macula densa cells and a mesangial proliferative glomerulonephritis were observed. NF-κB represents a ubiquitously distributed family of transcription factors that are activated especially by inflammatory signals from extracellular area in terms of a “sensor system” and particularly change the cell phenotype toward survival, proliferation, invasion/migration and myofibroblast differentiation and activation respectively. With this application, we would like to test the main hypothesis that solely the constitutive-active expression of IKK2 (via NF-κB activation) in RLC is sufficient to cause a mesangial proliferative glomerulonephritis via induction of a phenotypical change from a juxtaglomerular renin producing cell to a renin-negative, migrating, proliferative, myofibroblast-activated and mesangial differentiated intraglomerular cell. By FACS sorting, histological and intravital microscopic cell tracing methods, we will examine whether and how the selectively activated RLC actively immigrate into the glomerulus. Mechanisms and factors will be separately evaluated and cellularly characterized concerning the RLC, the glomerulus as well as the interaction with the neighboring macula densa cells. In parallel, in vitro studies using the murine renin lineage cell line As4.1 will analyze the phenotypical impact of different IKK2 constructs after transfection. In addition, we would like to explore the question whether a TNF-α/NF-κB activation in the juxtaglomerular niche is verifiable with different human renal diseases.