Feasibility of Repairing Glomerular Basement Membrane Defects in Alport Syndrome

Abstract

Alport syndrome is a hereditary glomerular disease that leads to kidney failure. It is caused by mutations affecting one of three chains of the collagen a3a4a5(IV) heterotrimer, which forms the major collagen IV network of the glomerular basement membrane (GBM). In the absence of the a3a4a5(IV) network, the a1a1a2(IV) network substitutes, but it is insufficient to maintain normal kidney function. Inhibition of angiotensin-converting enzyme slows progression to kidney failure in patients with Alport syndrome but is not a cure. Restoration of the normal collagen a3a4a5 (IV) network in the GBM, by either cell-or gene-based therapy, is an attractive and logical approach toward a cure, but whether or not the abnormal GBM can be repaired once it has formed and is functioning is unknown. Using a mouse model of Alport syndrome and an inducible transgene system, we found that secretion of a3a4a5(IV) heterotrimers by podocytes into a preformed, abnormal, filtering Alport GBM is effective at restoring the missing collagen IV network, slowing kidney disease progression, and extending life span. This proof-of-principle study demonstrates the plasticity of the mature GBM and validates the pursuit of therapeutic approaches aimed at normalizing the GBM to prolong kidney function.

A role for genetic susceptibility in sporadic focal segmental glomerulosclerosis

“…To achieve podocyte-specific expression, our ES cells also expressed a DOX-inducible transactivator molecule (rtTA3G) under the control of a podocyte-specific promoter (nephrin) (43). shRNA oligos were embedded into a miR30 transgene (48).…”

Rac1 Activation in Podocytes Induces Rapid Foot Process Effacement and Proteinuria

“…We considered that the patchy and uneven expression of CA-Rac1 might be due to silencing of the POD-rtTA transgene. To circumvent this problem, a new transgenic mouse line expressing a modified form of rtTA (rtTA-3G) under the control of the mouse nephrin (Nphs1) promoter was generated (NEF-rtTA) (34) and was bred to our EGFP_CA-Rac1 mice. Examination of kidneys from double transgenic (NEFϫRac1) mice after 4 days of DOX treatment showed a greater proportion of glomeruli and higher numbers of podocytes expressing the transgene than those for PODϫRac1 mice (Fig.…”

“…The NPHS2-rtTA (PODrtTA) strain was obtained from Jeffrey Kopp at the NIH (22). The Nphs1-rtTA-3G (NEF-rtTA) strain will be described in detail elsewhere (34). All mice used in this study were male, and therefore, each carried only one copy of the EGFP_CA-Rac1 transgene on his single X chromosome.…”

Increasing the level of peroxisome proliferator-activated receptor γ coactivator-1α in podocytes results in collapsing glomerulopathy

“…Given the decrease in PGC1α expression in DKD, we next examined whether restoring PGC1α levels can be protective. We generated mice with podocyte-specific inducible PGC1α expression by breeding nephrin-rtTA (Nefta) mice (17), which express the rtTA transactivator specifically in podocytes, with tetO-Ppargc1a animals (18), in which the Ppargc1a gene is under the control of a doxycycline-responsive promoter element. Double-transgenic mice (Nefta-PGC1α) were born at the expected Mendelian frequency and appeared healthy without evidence of renal histological abnormalities or albuminuria.…”

“…Nefta mice carrying the nephrin-rtTA transgene were obtained from Jeffrey Miner (Washington University, St. Louis, Missouri, USA) (17). TetO-Ppargc1a-transgenic mice were purchased from The Jackson Laboratory (stock number 012387).…”