Innate Immune Signaling Contributes to Tubular Cell Senescence in the Glis2 Knockout Mouse Model of Nephronophthisis.

Nephronophthisis (NPHP), the leading genetic cause of end-stage renal failure in children and young adults, is a group of autosomal recessive diseases characterized by kidney-cyst degeneration and fibrosis for which no therapy is currently available. To date, mutations in >25 genes have been identified as causes of this disease that, in several cases, result in chronic DNA damage in kidney tubular cells. Among such mutations, those in the transcription factor-encoding GLIS2 cause NPHP type 7. Loss of function of mouse Glis2 causes senescence of kidney tubular cells. Senescent cells secrete proinflammatory molecules that induce progressive organ damage through several pathways, among which NF-κB signaling is prevalent. Herein, we show that the NF-κB signaling is active in Glis2 knockout kidney epithelial cells and that genetic inactivation of the toll-like receptor (TLR)/IL-1 receptor or pharmacologic elimination of senescent cells (senolytic therapy) reduces tubule damage, fibrosis, and apoptosis in the Glis2 mouse model of NPHP. Notably, in Glis2, Tlr2 double knockouts, senescence was also reduced and proliferation was increased, suggesting that loss of TLR2 activity improves the regenerative potential of tubular cells in Glis2 knockout kidneys. Our results further suggest that a combination of TLR/IL-1 receptor inhibition and senolytic therapy may delay the progression of kidney disease in NPHP type 7 and other forms of this disease.

Loss of diacylglycerol kinase epsilon in mice causes endothelial distress and impairs glomerular Cox-2 and PGE2 production.

Thrombotic microangiopathy (TMA) is a disorder characterized by microvascular occlusion that can lead to thrombocytopenia, hemolytic anemia, and glomerular damage. Complement activation is the central event in most cases of TMA. Primary forms of TMA are caused by mutations in genes encoding components of the complement or regulators of the complement cascade. Recently, we and others have described a genetic form of TMA caused by mutations in the gene diacylglycerol kinase-ε (DGKE) that encodes the lipid kinase DGKε (Lemaire M, Fremeaux-Bacchi V, Schaefer F, Choi MR, Tang WH, Le Quintrec M, Fakhouri F, Taque S, Nobili F, Martinez F, Ji WZ, Overton JD, Mane SM, Nurnberg G, Altmuller J, Thiele H, Morin D, Deschenes G, Baudouin V, Llanas B, Collard L, Majid MA, Simkova E, Nurnberg P, Rioux-Leclerc N, Moeckel GW, Gubler MC, Hwa J, Loirat C, Lifton RP. Nat Genet 45: 531-536, 2013; Ozaltin F, Li BH, Rauhauser A, An SW, Soylemezoglu O, Gonul II, Taskiran EZ, Ibsirlioglu T, Korkmaz E, Bilginer Y, Duzova A, Ozen S, Topaloglu R, Besbas N, Ashraf S, Du Y, Liang CY, Chen P, Lu DM, Vadnagara K, Arbuckle S, Lewis D, Wakeland B, Quigg RJ, Ransom RF, Wakeland EK, Topham MK, Bazan NG, Mohan C, Hildebrandt F, Bakkaloglu A, Huang CL, Attanasio M. J Am Soc Nephrol 24: 377-384, 2013). DGKε is unrelated to the complement pathway, which suggests that unidentified pathogenic mechanisms independent of complement dysregulation may result in TMA. Studying Dgke knockout mice may help to understand the pathogenesis of this disease, but no glomerular phenotype has been described in these animals so far. Here we report that Dgke null mice present subclinical microscopic anomalies of the glomerular endothelium and basal membrane that worsen with age and develop glomerular capillary occlusion when exposed to nephrotoxic serum. We found that induction of cyclooxygenase-2 and of the proangiogenic prostaglandin E2 are impaired in Dgke null kidneys and are associated with reduced expression of the antithrombotic cell adhesion molecule platelet endothelial cell adhesion molecule-1/CD31 in the glomerular endothelium. Notably, prostaglandin E2 supplementation was able to rescue motility defects of Dgke knockdown cells in vitro and to restore angiogenesis in a test in vivo. Our results unveil an unexpected role of Dgke in the induction of cyclooxygenase-2 and in the regulation of glomerular prostanoids synthesis under stress.

Loss of Glis2/NPHP7 causes kidney epithelial cell senescence and suppresses cyst growth in the Kif3a mouse model of cystic kidney disease.

Enlargement of kidney tubules is a common feature of multiple cystic kidney diseases in humans and mice. However, while some of these pathologies are characterized by cyst expansion and organ enlargement, in others, progressive interstitial fibrosis and kidney atrophy prevail. The Kif3a knockout mouse is an established non-orthologous mouse model of cystic kidney disease. Conditional inactivation of Kif3a in kidney tubular cells results in loss of primary cilia and rapid cyst growth. Conversely, loss of function of the gene GLIS2/NPHP7 causes progressive kidney atrophy, interstitial inflammatory infiltration, and fibrosis. Kif3a null tubular cells have unrestrained proliferation and reduced stabilization of p53 resulting in a loss of cell cycle arrest in the presence of DNA damage. In contrast, loss of Glis2 is associated with activation of checkpoint kinase 1, stabilization of p53, and induction of cell senescence. Interestingly, the cystic phenotype of Kif3a knockout mice is partially rescued by genetic ablation of Glis2 and pharmacological stabilization of p53. Thus, Kif3a is required for cell cycle regulation and the DNA damage response, whereas cell senescence is significantly enhanced in Glis2 null cells. Hence, cell senescence is a central feature in nephronophthisis type 7 and Kif3a is unexpectedly required for efficient DNA damage response and cell cycle arrest.

Epithelial innate immunity mediates tubular cell senescence after kidney injury.

Acute kidney injury (AKI) is a common clinical condition of growing incidence. Patients who suffer severe AKI have a higher risk of developing interstitial fibrosis, chronic kidney disease, and end-stage renal disease later in life. Cellular senescence is a persistent cell cycle arrest and altered gene expression pattern evoked by multiple stressors. The number of senescent cells increases with age and even in small numbers these cells can induce chronic inflammation and fibrosis; indeed, in multiple organs including kidneys, the accumulation of such cells is a hallmark of aging. We hypothesized that cellular senescence might be induced in the kidney after injury and that this might contribute to progressive organ fibrosis. Testing this hypothesis, we found that tubular epithelial cells (TECs) in mice senesce within a few days of kidney injury and that this response is mediated by epithelial Toll-like and interleukin 1 receptors (TLR/IL-1R) of the innate immune system. Epithelial cell-specific inhibition of innate immune signaling in mice by knockout of myeloid differentiation 88 (Myd88) reduced fibrosis as well as damage to kidney tubules, and also prevented the accumulation of senescent TECs. Importantly, although inactivation of Myd88 after injury ameliorated fibrosis, it did not reduce damage to the tubules. Selectively induced apoptosis of senescent cells by two different approaches only partially reduced kidney fibrosis, without ameliorating damage to the tubules. Our data reveal a cell-autonomous role for epithelial innate immunity in controlling TEC senescence after kidney injury, and additionally suggest that early therapeutic intervention is required for effective reduction of long-term sequelae of AKI.

Antiglomerular Basement Membrane Disease in a Pediatric Patient: A Case Report and Review of the Literature.

Goodpasture's syndrome (GPS) remains a very rare disease entity in the pediatric population characterized by the presence of pulmonary hemorrhage and rapidly evolving glomerulonephritis. We hereby describe the case of a 2-year-old girl who presented with renal failure and was diagnosed with GPS. A brief review of the literature in regard to data on demographics, pathogenesis, clinical features, diagnosis, treatment, and prognosis for renal recovery is also provided.