Risk factors for Kaposi's sarcoma-associated herpesvirus infection among HIV-1-infected pregnant women in the USA

OBJECTIVES: We sought to identify risk factors for infection with the Kaposi's Sarcoma-associated herpesvirus (KSHV) among pregnant women and to examine a reported association of KSHV with injecting drug use (IDU) and hepatitis C virus (HCV) infection. DESIGN: Cross-sectional evaluation of questionnaire data and KSHV and HCV seroprevalence in the Women and Infants Transmission Study. METHODS: In sera collected from HIV-1-infected pregnant women (n = 887) and, at age 12 months, their offspring (n = 900) at six sites in the USA and Puerto Rico, KSHV and HCV antibodies were detected with sensitive and specific enzyme immunoassays. Risk of KSHV was estimated by the unadjusted and adjusted odds ratio (OR(adj)) and 95% confidence interval (CI). The geographic referent sites were Chicago and Boston. RESULTS: Forty-seven (5.3%) of the women and three (0.3%) of the infants were KSHV seropositive. In univariate and multivariate analyses, KSHV in the women was associated with enrollment in Puerto Rico, Houston or Brooklyn (OR(adj), 4.3; 95% CI, 1.8-10.4) or Manhattan (OR(adj), 9.8; 95% CI, 3.7-25.6); non-completion of high school (OR(adj), 1.8; 95% CI, 0.9-3.4); the number of sexually transmitted diseases (OR(adj), 1.4; 95% CI, 1.0-1.9 per disease); and especially with IDU and HCV infection (OR(adj), 3.5; 95% CI, 1.5-7.9). CONCLUSIONS: Transmission of KSHV by blood inoculation may be highly inefficient, but our data support the hypothesis that it does occur. Large formal studies to evaluate whether KSHV transmission occurs via transfusion are needed to inform decisions regarding screening volunteer blood donors to protect the blood supply.     

mTORC1 activation in podocytes is a critical step in the development of diabetic nephropathy in mice

Diabetic nephropathy (DN) is among the most lethal complications that occur in type 1 and type 2 diabetics. Podocyte dysfunction is postulated to be a critical event associated with proteinuria and glomerulosclerosis in glomerular diseases including DN. However, molecular mechanisms of podocyte dysfunction in the development of DN are not well understood. Here we have shown that activity of mTOR complex 1 (mTORC1), a kinase that senses nutrient availability, was enhanced in the podocytes of diabetic animals. Further, podocyte-specific mTORC1 activation induced by ablation of an upstream negative regulator (PcKOTsc1) recapitulated many DN features, including podocyte loss, glomerular basement membrane thickening, mesangial expansion, and proteinuria in nondiabetic young and adult mice. Abnormal mTORC1 activation caused mislocalization of slit diaphragm proteins and induced an epithelial-mesenchymal transition-like phenotypic switch with enhanced ER stress in podocytes. Conversely, reduction of ER stress with a chemical chaperone significantly protected against both the podocyte phenotypic switch and podocyte loss in PcKOTsc1 mice. Finally, genetic reduction of podocyte-specific mTORC1 in diabetic animals suppressed the development of DN. These results indicate that mTORC1 activation in podocytes is a critical event in inducing DN and suggest that reduction of podocyte mTORC1 activity is a potential therapeutic strategy to prevent DN.     

Anion Exchanger 1 Interacts with Nephrin in Podocytes

The central role of the multifunctional protein nephrin within the macromolecular complex forming the glomerular slit diaphragm is well established, but the mechanisms linking the slit diaphragm to the cytoskeleton and to the signaling pathways involved in maintaining the integrity of the glomerular filter remain incompletely understood. Here, we report that nephrin interacts with the bicarbonate/chloride transporter kidney anion exchanger 1 (kAE1), detected by yeast two-hybrid assay and confirmed by immunoprecipitation and co-localization studies. We confirmed low-level glomerular expression of kAE1 in human and mouse kidneys by immunoblotting and immunofluorescence microscopy. We observed less kAE1 in human glomeruli homozygous for the NPHS1_FinMaj nephrin mutation, whereas kAE1 expression remained unchanged in the collecting duct. We could not detect endogenous kAE1 expression in NPHS1_FinMaj podocytes in primary culture, but heterologous re-introduction of wild-type nephrin into these podocytes rescued kAE1 expression. In kidneys of Ae1^−/− mice, nephrin abundance was normal but its distribution was altered along with the reported kAE1-binding protein integrin-linked kinase (ILK). Ae1^−/− mice had increased albuminuria with glomerular enlargement, mesangial expansion, mesangiosclerosis, and expansion of the glomerular basement membrane. Glomeruli with ILK-deficient podocytes also demonstrated altered AE1 and nephrin expression, further supporting the functional interdependence of these proteins. These data suggest that the podocyte protein kAE1 interacts with nephrin and ILK to maintain the structure and function of the glomerular basement membrane.Anion exchanger 1 (AE1; SLC4A1), an SLC4 bicarbonate transporter family member, is transcribed as an erythroid isoform (eAE1) and a truncated kidney isoform (kAE1) lacking amino acids 1 through 65 in humans.¹ eAE1 comprises the core of the multiprotein complex of integral and peripheral membrane proteins essential to the structural integrity of the red cell membrane, and its bicarbonate/chloride activity is required for gas transport (see reviews^2,3). In the kidney, kAE1 is localized to the basolateral membrane of collecting duct type A intercalated cells. Normal terminal urinary acidification by these cells requires kAE1-mediated bicarbonate reabsorption into the blood. Specific mutations in AE1 usually cause either autosomal dominant hereditary ovalo-spherocytosis or distal renal tubular acidosis (dRTA).⁴ In rare cases of homozygous recessive or compound heterozygous AE1 mutations, both the erythroid and renal phenotypes can manifest in the same individuals.^5–7 In addition to these established roles, low-level AE1 expression has been detected in the glomerulus,^8,9 but its potential function or interactions in the glomerulus are unknown.AE1 possesses a long cytoplasmic N-terminus, a 12- to 14-span transmembrane transporter domain, and a short C-terminal cytoplasmic tail (Supplemental Figure 1). Both the N- and C-terminal domains of kAE1 contain tyrosine residues critical for basolateral targeting,^10,11 which is likely regulated by phosphorylation.¹¹ The N-terminus of kAE1 interacts with integrin-linked kinase (ILK),¹² a protein that binds the cytoplasmic domains of β-integrins and cytoskeleton-associated proteins.^13,14 The kAE1/ILK interaction enhanced kAE1 trafficking to the plasma membrane in HEK293 cells,¹² but deletion of the majority of the ILK-interacting region in kAE1 did not affect its polarized trafficking in MDCK cells.¹¹ Thus, the physiologic importance of the kAE1–ILK interaction in the kidney remains unclear. We searched for proteins that interact with the C-terminus of kAE1, using a yeast two-hybrid screen of a human kidney cDNA library, and identified a novel interaction between kAE1 and nephrin.Nephrin is a single-spanning transmembrane Ig superfamily protein (Supplemental Figure 1) and an integral component of the podocyte slit diaphragm (SD), a structure critical to the glomerular selectivity filter.¹⁵ Mutations or gene targeting of nephrin results in congenital nephrotic syndrome.^16,17 The nephrin extracellular domain contributes to the structural framework of the SD via homo- and heterodimeric interactions with neighboring nephrin polypeptides and nephrin-like homologs Neph1 and Neph2.^15,18–20 The intracellular domain of nephrin contains multiple tyrosine phosphorylation sites and interacts with podocin,^21,22 CD2-associated protein,^23,24 Nck proteins,^25–27 the ion channel TRPC6,^28,29 and adherens junction proteins.^30,31 These interactions anchor the SD complex to the underlying cytoskeleton and participate in signal transduction. Nephrin also forms a multicomponent ternary complex with ILK.³² The proteinuric phenotype of mice with podocyte-specific deletions of ILK and other components of the basally situated ILK/integrin complex^32–35 suggests that SD and basal domain signaling complexes of podocytes cooperate to maintain integrity of the glomerular filtration barrier.In view of the direct associations of ILK with kAE1¹² and nephrin,³² we investigated the physiologic significance of the nephrin/kAE1 interaction. Our studies demonstrate the importance of nephrin for stable kAE1 expression in podocytes and the in vivo interdependence of levels and subcellular localization among kAE1, nephrin, and ILK in podocytes, suggesting a novel role of kAE1 in glomerular function.