Sparsentan is superior to losartan in the gddY mouse model of IgA nephropathy.

BACKGROUND: The mechanism leading to the development of immunoglobulin A nephropathy (IgAN) remains to be completely understood. Endothelin-1 (ET-1) as well as angiotensin II (AngII) promote glomerular injury, tubulointerstitial inflammation and fibrosis leading to chronic kidney disease. Sparsentan, a dual endothelin angiotensin receptor antagonist, recently received accelerated approval in the USA for the reduction of proteinuria in adults with IgAN at high risk of disease progression. To elucidate the mechanisms by which sparsentan is efficacious in IgAN, we examined the effect of treatment in gddY mice, a spontaneous IgAN mouse model, versus the monoselective angiotensin II type 1 receptor (AT1R) antagonist, losartan, on the development of renal injury at doses resulting in similar blood pressure lowering. METHODS: Four-week-old gddY mice were given control chow, chow containing sparsentan or drinking water containing losartan until 12 or 20 weeks old. RESULTS: Remarkably, the albumin:creatine ratio (ACR) was attenuated more rapidly and to a greater extent in mice treated with sparsentan than those treated with losartan. The decrease in ACR from baseline after 4 weeks of treatment correlated with beneficial effects of sparsentan on glomerulosclerosis and protection of podocytes and glycocalyx after 16 weeks of treatment across treatment groups; thus, sparsentan treatment delayed development of renal injury to a greater extent than losartan. Expression of mRNA for ET-1, endothelin type A receptor and AT1R and proinflammatory genes was upregulated in 12-week-old gddY mice and was prevented by sparsentan and losartan to a comparable extent. CONCLUSIONS: The results of this study, and in light of the results of the phase 3 PROTECT trial, provide a novel perspective and understanding of the mechanisms by which sparsentan has a beneficial renoprotective effect against IgAN compared with AT1R antagonism alone.

The nucleotide-sensing Toll-Like Receptor 9/Toll-Like Receptor 7 system is a potential therapeutic target for IgA nephropathy.

The progression determinants of IgA nephropathy (IgAN) are still not fully elucidated. We have previously demonstrated that the mucosal activation of toll-like receptor (TLR) 9, which senses microbial unmethylated CpG DNA, influences progression by producing aberrantly glycosylated IgA. However, numerous recent reports of patients with IgAN presenting with gross hematuria after the mRNA vaccination for coronavirus disease 2019 suggest that the RNA-sensing system also exacerbates IgAN. Here, we investigated whether TLR7, which recognizes microbial RNA, is also involved in IgAN progression using a murine model and tonsil tissue from 53 patients with IgAN compared to samples from 40 patients with chronic tonsillitis and 12 patients with sleep apnea syndrome as controls. We nasally administered imiquimod, the ligand of TLR7, to IgAN-prone ddY mice and found that TLR7 stimulation elevated the serum levels of aberrantly glycosylated IgA and induced glomerular IgA depositions and proteinuria. Co-administered hydroxychloroquine, which inhibits TLRs, canceled the kidney injuries. In vitro, stimulating splenocytes from ddY mice with imiquimod increased interleukin-6 and aberrantly glycosylated IgA levels. The expression of TLR7 in the tonsils was elevated in patients with IgAN and positively correlated with that of a proliferation-inducing ligand (APRIL) involved in the production of aberrantly glycosylated IgA. Mechanistically, TLR7 stimulation enhanced the synthesis of aberrantly glycosylated IgA through the modulation of enzymes involved in the glycosylation of IgA. Thus, our findings suggest that nucleotide-sensing TLR9 and TLR7 play a crucial role in the pathogenesis of IgAN. Hence, nucleotide-sensing TLRs could be reasonably strong candidates for disease-specific therapeutic targets in IgAN.

Identification of IgA autoantibodies targeting mesangial cells redefines the pathogenesis of IgA nephropathy.

Immunoglobulin A (IgA) nephropathy (IgAN) is the most common type of primary glomerulonephritis, often progressing to renal failure. IgAN is triggered by IgA deposition in the glomerular mesangium by an undefined mechanism. Here, we show that grouped ddY (gddY) mice, a spontaneous IgAN model, produce serum IgA against mesangial antigens, including ßII-spectrin. Most patients with IgAN also have serum anti-ßII-spectrin IgA. As in patients with IgAN, IgA+ plasmablasts accumulate in the kidneys of gddY mice. IgA antibodies cloned from the plasmablasts carry substantial V-region mutations and bind to ßII-spectrin and the surface of mesangial cells. These IgAs recognize transfected and endogenous ßII-spectrin exposed on the surface of embryonic kidney-derived cells. Last, we demonstrate that the cloned IgA can bind selectively to glomerular mesangial regions in situ. The identification of IgA autoantibody and its antigen in IgAN provides key insights into disease onset and redefines IgAN as a tissue-specific autoimmune disease.

The leukotriene B4 /BLT1-dependent neutrophil accumulation exacerbates immune complex-mediated glomerulonephritis.

Crescent formation is the most important pathological finding that defines the prognosis of nephritis. Although neutrophils are known to play an important role in the progression of crescentic glomerulonephritis, such as anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis, the key chemoattractant for neutrophils in ANCA-associated glomerulonephritis has not been identified. Here, we demonstrate that a lipid chemoattractant, leukotriene B4 (LTB4 ), and its receptor BLT1 are primarily involved in disease pathogenesis in a mouse model of immune complex-mediated crescentic glomerulonephritis. Circulating neutrophils accumulated into glomeruli within 1 h after disease onset, which was accompanied by LTB4 accumulation in the kidney cortex, leading to kidney injury. LTB4 was produced by cross-linking of Fc gamma receptors on neutrophils. Mice deficient in BLT1 or LTB4 biosynthesis exhibited suppressed initial neutrophil infiltration and subsequent thrombotic glomerulonephritis and renal fibrosis. Depletion of neutrophils before, but not after, disease onset prevented proteinuria and kidney injury, indicating the essential role of neutrophils in the early phase of glomerulonephritis. Administration of a BLT1 antagonist before and after disease onset almost completely suppressed induction of glomerulonephritis. Finally, we found that the glomeruli from patients with ANCA-associated glomerulonephritis contained more BLT1-positive cells than glomeruli from patients with other etiologies. Taken together, the LTB4 -BLT1 axis is the key driver of neutrophilic glomerular inflammation, and will be a novel therapeutic target for the crescentic glomerulonephritis.

Mucosal Immune System Dysregulation in the Pathogenesis of IgA Nephropathy.

The mucosal immune system, via a dynamic immune network, serves as the first line of defense against exogenous antigens. Mucosal immune system dysregulation is closely associated with the pathogenesis of immunoglobulin A nephropathy (IgAN), as illustrated by IgAN having the clinical feature of gross hematuria, often concurrent with mucosal infections. Notably, previous studies have demonstrated the efficacy of tonsillectomy and found that a targeted-release formulation of budesonide reduced proteinuria in patients with IgAN. However, it remains unclear how exogenous antigens interact with the mucosal immune system to induce or exacerbate IgAN. Thus, in this review, we focus on the dysregulation of mucosal immune response in the pathogenesis of IgAN.

Galactose-Deficient IgA1 as a Candidate Urinary Marker of IgA Nephropathy.

In patients with IgA nephropathy (IgAN), circulatory IgA1 and IgA1 in the mesangial deposits contain galactose-deficient IgA1 (Gd-IgA1). Some of the Gd-IgA1 from the glomerular deposits is excreted in the urine and thus urinary Gd-IgA1 may represent a disease-specific marker. We recruited 338 Japanese biopsy-proven IgAN patients and 120 patients with other renal diseases (disease controls). Urine samples collected at the time of renal biopsy were used to measure Gd-IgA1 levels using a specific monoclonal antibody (KM55 mAb). Urinary Gd-IgA1 levels were significantly higher in patients with IgAN than in disease controls. Moreover, urinary Gd-IgA1 was significantly correlated with the severity of the histopathological parameters in IgAN patients. Next, we validated the use of urinary Gd-IgA1 levels in the other Asian cohorts. In the Korean cohort, urinary Gd-IgA1 levels were also higher in patients with IgAN than in disease controls. Even in Japanese patients with IgAN and trace proteinuria (less than 0.3 g/gCr), urinary Gd-IgA1 was detected. Thus, urinary Gd-IgA1 may be an early disease-specific biomarker useful for determining the disease activity of IgAN.

Renal pathological analysis using galactose-deficient IgA1-specific monoclonal antibody is a strong tool for differentiation of primary IgA nephropathy from secondary IgA nephropathy.

In several cases with IgA nephropathy (IgAN), differential diagnosis is difficult due to the complication with other systemic diseases which can induce secondary IgAN. Recently, we demonstrated that immunostaining with galactose-deficient IgA1-specific monoclonal antibody (KM55 mAb) specifically showed positive in primary IgAN cases. Here, we report four cases which we could make definitive diagnosis by immunohistological analysis using KM55 mAb. The underlying systemic diseases are rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), hepatitis C (HCV) and Crohn's disease (CD). Renal pathological findings in the four cases revealed mesangial proliferative glomerulonephritis with IgA and C3 deposits. Immunostaining with KM55 mAb was positive for three cases complicated with RA, SLE and CD, respectively. Thus, these three cases were diagnosed as primary IgAN and treated with tonsillectomy and steroid pulse therapy. These three cases finally achieved clinical remission. On the other hand, the case with HCV showed negative for KM55. Finally, we diagnosed as HCV-related nephropathy and successfully treated by antiviral agents. These cases suggested KM55 mAb is a strong tool to differentiate primary IgAN from secondary IgAN.

Protective effects of DPP-4 inhibitor on podocyte injury in glomerular diseases.

BACKGROUND: Dipeptidyl peptidase-4 (DPP-4) is a serine protease that inhibits the degradation of glucagon-like peptide 1. DPP-4 inhibitors are used worldwide to treat type 2 diabetes mellitus and were recently shown to have pleiotropic effects such as anti-oxidant, anti-inflammatory, and anti-fibrotic actions. DPP-4 inhibitors improve albuminuria and renal injury including glomerular damage independent of its hypoglycemic effect. Although DPP-4 is mainly expressed in the kidney, the physiological function of DPP-4 remains unclear. METHODS: The localization of renal DPP-4 activity was determined in human renal biopsy specimens with glycyl-1-prolyl-4-methoxy-2-naphthylamide and the effects of a DPP-4 inhibitor were examined in human cultured podocyte. RESULTS: DPP-4 activity under normal conditions was observed in some Bowman's capsular epithelial cells and proximal tubules, but not in the glomerulus. DPP-4 activity was observed in crescent formation in anti-neutrophil myeloperoxidase cytoplasmic antigen antibody nephritis, nodular lesions in diabetic nephropathy, and some podocytes in focal segmental glomerulosclerosis. Notably, the DPP-4 inhibitor saxagliptin suppressed DPP-4 activity in podocytes and the proximal tubules. To assess the effect of DPP-4 inhibitor on podocytes, human cultured podocytes were injured by Adriamycin, which increased DPP-4 activity; this activity was dose-dependently suppressed by saxagliptin. Treatment with saxagliptin maintained the structure of synaptopodin and RhoA. Saxagliptin also improved the detachment of podocytes. CONCLUSIONS: DPP-4 activity induces degradation of synaptopodin and reduction of RhoA, resulting in destruction of the podocyte cytoskeleton. Saxagliptin may have pleiotropic effects to prevent podocyte injury.