We are studying a mutant gene which when homozygous leads to a lethal kidney disease in mice. These mice undergo a spontaneous autoimmune reaction which involves multiple immune pathways. We have cloned the relevant gene, and have found that it codes for a mitochondrial protein similar to trans-prenyltransferase. This enzyme is needed for isoprenylation of coenzyme Q (CoQ), and is now known as prenyl diphosphate synthase subunit 2 (Pdss2). The mutant mice have defective mitochondria, as demonstrated by ultrastructural analysis, and we believe that this defect leads to the death of glomerular podocytes. This in turn leads to an autoimmune response which involves both the tubular interstitium and the glomeruli. The kidney disease can be prevented to some extent by CoQ supplementation, and to an even greater extent by probucol. The mechanism by which probucol does this has not been fully elucidated, but we and our collaborators (Dr. Marni Falk at CHOP and Dr. Cathy Clarke at UCLA) have demonstrated that it increases the endogenous production of CoQ.
In collaboration with Dr. Julie Blendy, Dr. Harry Ischiropoulos, and their students, we have demonstrated that these mutant mice also have neuromuscular defects that resemble Parkinson’s disease. We are currently working on several possible therapies which have the potential of treating these problems.
The human disease with the greatest similarity to this phenotype is focal segmental glomerular sclerosis, or FSGS. It is well known that there is a significant genetic component to FSGS susceptibility, and in collaboration with a group at the NIH, we have obtained evidence that PDSS2 is one of the genes that is involved in this susceptibility.
The Pdss2 mutation was targeted to hepatocytes utilizing mice homozygous for the floxed gene (B6.Pdss2loxP/loxP) crossed with partners that expressed cre under the control of an albumin/cre promoter (B6.Cg-Tg(Alb-cre)21 Mgn/J (Alb/cre)) obtained from The Jackson Laboratory.
The kd/kd mouse is homozygous for the V117M mutation in PDSS2, the “kidney disease” mutation, which occurred spontaneously in a CBA/CaH colony. These mice spontaneously develop severe and progressive nephritis leading to renal failure, characterized by cellular infiltration, tubular destruction and glomerular sclerosis.
The kd allele was transferred to the C57BL/6J (B6) background by mating a recombinant kd haplotype with B6 with selection for closely linked microsatellite markers that were studied in a mapping experiment.
Tissue-specific conditional knockouts can be generated by crossing with Cre-expressing strains.
Podocyte-specific knockouts were obtained by crossing mice homozygous for the floxed gene (B6.Pdss2loxP/loxP) with partners that expressed cre under the control of the Podocin promoter. The Pdss2 gene is targeted in the glomeruli but not the collecting tubules.