Focal Segmental Glomerulosclerosis Pathogenesis

Diabetes, Digestive, Kidney Diseases

Investigators

Linked publications & trials

Abstract

Focal segmental glomerulosclerosis (FSGS) is a clinical-pathologic syndrome characterized by the accumulation of fibrotic proteins in glomeruli, initially involving only some glomeruli (focal) and involving portions (segments) of the affected glomeruli. FSGS can be classified as follows: idiopathic FSGS, HIV-associated FSGS, hyperfiltration FSGS (due to reduced renal mass, renal toxins, or obesity), and genetic causes. In order to define the molecular mechanisms responsible for HIV-associated FSGS, we have established a line of mice in which transgene expression can be regulated in the glomerular podocyte using an tetracycline-regulated system. We have shown that expression is tightly regulated and is restricted to the podocyte. We have used this system to express the HIV-1 accessory protein Vpr in the podocyte. These mice develop proteinuria beginning 4 weeks after treatment with tetracycline and with 95% of mice developing proteinuria by 20 weeks. FSGS appears at 8 weeks, progressing to global glomerulosclerosis and end-stage kidney disease. Podocyte phenotype is abnormal, with reduced expression of the differentiation marker synaptopodin and de novo expression of the injury marker desmin. Increased cell proliferation is present in the glomerular tuft, parietal epithelum, and tubular epithelium. These results demonstrate that Vpr is sufficient to induce HIV-associated FSGS in transgenic mice. We have recently generated mutant Vpr mice, either bearing the R80A mutation that abrogates the cell cycle arrest function of Vpr, or the L64-67-68A triple mutation that abrogates nuclear receptor binding. We are characterizing the phenotype of these mice Pirfenidone is an orally-active, small molecule inhibitor of fibrosis, whose mechanism of action has not been well-defined but might involve inhibiting production of TGF-beta. We have carried out an open label, phase II study for FSGS patients with declining renal function. The study design compares the rate of glomerular filtration rate (GFR) decline during a baseline period in which blood pressure is controlled and the patient receives angiotensin antagonist medication (ACE inhibitor or angiotensin receptor blocker) with the rate of GFR decline while on pirfenidone therapy plus angiotensin antagonist medication. We have enrolled 20 patients, who receive treatment for at least one year but may continue pirfenidone thereafter. In 16 patients who have received at least 4 months of therapy, after a mean follow-up of 19 months, the GFR decline rate improved from 0.81 +/- 0.46 (mean, SD) ml/min/mo during the baseline period to 0.55 +/- 0.40 ml/min/mo while receiving pirfenidone (P=0.03). This represents an improvement of 32%, an effect size comparable to that of ACE inhibitors in patients with diabetic nephropathy (another disease characterized by glomerulosclerosis). We are discussing with collaborator plans to carry out a multi-center, randomized, placebo-controlled phase III study to confirm efficacy. Building on our results with intermittent oral pulse dexamethasone, we have initiated a new trial comparing a more intensive steroid regimen for children and adults with minimal change disease and FSGS. We have increased the dexamethasone dose in three ways: increased duration (48 weeks versus 32 weeks), increased dose during the first 3 months (50 mg/m2 for the weeks 1-16 and 25 mg/m2 for weeks 17-48) and randomized patients to 2 doses every 2 weeks and 4 doses every 4 weeks (all patients receive 48 doses over 48 weeks). Five patients have been enrolled in this study.