Expressionof polycystin-1 in MDCK cells promotes tubulogenesis and confersresistance to apoptosis. Boca et al. examined the mechanismunderlying these effects. They found that expression of wild-typepolycystin-1, but not mutant polycystin-1, activates phosphatidylinositol3-kinase (PI3-kinase) and stimulates the phosphorylation ofAkt (protein kinase B) and its downstream target FKRH-1. Akthas previously been shown to stimulate tubulogenesis and inhibitapoptosis. Expression of a dominant-negative Akt mutant preventsthe resistance to apoptosis conferred by polycystin-1. Treatmentwith PI3-kinase inhibitors blocks phosphorylation of Akt andinhibits tubulogenesis. Recent studies suggest that inhibitionof calcium-dependent activation of PI3-kinase and Akt leadsto activation of ERK kinases and increases cell proliferation.Taken together, these findings suggest that polycystin-1 mayexert its cellular effects by promoting calcium entry and activatingthe PI3-kinase/Akt signaling pathway. In autosomal dominantpolycystic kidney disease, loss of polycystin-1 results in inhibitionof PI3-kinase/Akt, increased ERK, and increased proliferationand apoptosis. See Boca et al., pages 637647.
A Way to Protect the Kidney from Injury Induced by Lithotripsy.
It is wellestablished that in lithotripsy shock waves of sufficient intensityto disrupt stones also induce significant renal injury and someloss of function. Several years ago, Willis et al. reportedthat application of a therapeutic dose of shock waves to onepole of the kidney seemed to protect the opposite pole frominjury when it was treated with the same dose later. In thisstudy, these observations are extended to show that this protectiveeffect is reproducible, that protection can be conferred bylower doses of shock waves that do not induce injury, and thatprotective doses can be applied prophylactically to the samearea later treated with higher therapeutic doses. The studydoes not define the mechanism of the protective effect, butit offers an excellent model in which to do that and suggeststhat lithotripsy can likely be made a much safer and less injuriousprocedure than it currently is. See Willis et al., pages 663673.
Regulatory T Cells Limit Proteinuric Renal Injury in Mice.
The pathogenesisof adriamycin nephropathy, a murine model of chronic proteinuricrenal disease, involves both chemical and immunologic mechanisms.Published studies have implicated T lymphocytes as contributingto the development of this disease. To assess whether regulatoryT cells could prevent adriamycin nephropathy, Wang et al. transducedCD4+ T cells with Foxp3, a transcription factor that is consideredthe "master switch" for induction of a regulatory T cell phenotype.The authors demonstrated that Foxp3-transduced T cells, butnot controls, indeed exhibited features of regulatory/suppressorT cells. Moreover, adoptive transfer of the ex vivotransducedregulatory T cells limited the functional and histologic manifestationsof adriamycin nephropathy. This novel effect of Foxp3-transducedregulatory T cells on the development of chronic renal diseasehas potentially important therapeutic implications. See Wanget al., pages 697706.
How Is the Glomerulus Vascularized?
Vascularendothelial growth factor (VEGF) is a secreted protein thatstimulates angiogenesis. During normal kidney development, VEGFproduced by developing podocytes is required for the migrationof endothelial cells into the glomerulus. Eremina et al. nowshow that VEGF is also required for mesangial cell migrationand survival. Mice expressing a hypomorphic allele of VEGF areborn with normal glomeruli but undergo mesangiolysis within10 to 12 d after birth. Mesangiolysis is preceded by the lossof glomerular endothelial cells. The complete absence of VEGFin podocytes prevents the migration of mesangial cells intodeveloping glomeruli. Mesangial cells do not express VEGF receptors,but they do express receptors for PDGF, a growth factor producedby endothelial cells. These findings suggest that the vascularizationof the developing glomerulus proceeds via a two-step processin which VEGF produced by podocytes stimulates endothelial cellmigration, then PDGF produced by glomerular endothelial cellsstimulates mesangial cell migration. See Eremina et al., pages724735.
Doi etal. examine polymorphisms of the vascular endothelial growthfactor (VEGF) gene in 101 male subjects with ESRD and 189 healthycontrols in this issue of JASN. They found that two single nucleotidepolymorphisms in the 3' untranslated region of the gene arelinked to each other and are significantly associated with ESRD.Sequence variation in the 3' untranslated region of a gene doesnot affect the protein sequence but can affect mRNA stability.The VEGF gene polymorphisms are associated with higher circulatingVEGF levels, which appear to be due to increased mRNA stability.Interestingly, overexpression of VEGF in mice (though to a muchgreater degree than observed in this study) results in a glomerularlesion similar to collapsing glomerulonephritis. Although thefindings need to be confirmed in a larger prospective study,this study is the first to suggest that sequence variation inVEGF may be associated with the risk of ESRD in males. See Doiet al., pages 823830.
Does Preeclampsia Increase the Risk for Later Kidney Disease?
Preeclampsiais associated with increased risk of adverse maternal outcomes,including hypertension, cardiovascular disease, and persistentmicroalbuminuria. The report by Vikse and colleagues in thisissue of JASN suggests that the kidney may not be spared thelong-term consequences of this disease. They linked >750,000women in two national registries to identify women with andwithout preeclampsia who underwent a subsequent kidney biopsy.They report that both preeclamsia and having an infant withlow birth weight were independent risk factors for subsequentkidney biopsy during the next five years. Although the possibilitythat both the preeclampsia and subsequent kidney biopsy weredue to unrecognized kidney disease cannot be totally excluded,these results emphasize the need to carefully exclude subclinicalkidney disease among women presenting with antepartum hypertensionand proteinuria both at initial evaluation and during subsequentfollow-up. See Vikse et al., pages 837845.
Toward Optimal Dosing of Mycophenolic Acid.
Mycophenolicacid (MPA) is an immunosuppressant commonly used to preventrenal transplant rejection. Large between- and within-patientvariability in the pharmacokinetics of MPA has been described,but this variability remains largely unexplained. In a retrospectivemeta-analysis of 468 renal transplant patients from 6 clinicaltrials, van Hest and colleagues explored the relationship betweenvarious clinical factors and the pharmacokinetics of MPA. Thestudy revealed that exposure to MPA independently increasedwith increasing renal function, albumin, and hemoglobin as wellas decreasing prednisone and cyclosporine levels, but was notindependently influenced by delayed graft function, recipientrace, or diabetes. The findings have clinical relevance in thata significant change in renal function or serum albumin couldbe used as an indication for therapeutic monitoring of MPA levels,in an effort to maximize efficacy and limit toxicity. See vanHest et al., pages 871880.
Should All Transplant Recipients Receive ACE/ARB Therapy?
The beneficialeffects of angiotensin-converting enzyme inhibitors (ACEI) andangiotensin receptor blockers (ARB) in reducing proteinuria,slowing progression, and reducing the risk for associated cardiovasculardisease is well established in chronic kidney disease patientsat high risk for cardiovascular disease. Similar data are notavailable for transplant recipients who also have chronic kidneydisease. This retrospective study of 2031 patients from Austrialooked at the effect of ACEI/ARB therapy on graft and patientsurvival in recipients of renal allografts, adjusting for otherrisk factors. Heinze et al. report a 20% higher 10-yr patientand graft survival rate in patients treated with ACEI/ARB therapycompared with those who were not. Although the study is retrospectiveand several important variables are not completely excludedas contributing to the findings, the magnitude of the differencesobserved are impressive and supports the use of these agentsin transplant recipients until the results of prospective trialsare available. See Heinze et al., pages 889899.
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