Reduced susceptibility to infectious disease can increase the frequency of otherwise deleterious alleles. In populations of African ancestry, two apolipoprotein-L1 (APOL1) variants with a recessive kidney disease risk, named G1 and G2, occur at high frequency. APOL1 is a trypanolytic protein that confers innate resistance to most African trypanosomes, but not Trypanosoma brucei rhodesiense or T.b. gambiense, which cause human African trypanosomiasis. In this case-control study, we test the prevailing hypothesis that these APOL1 variants reduce trypanosomiasis susceptibility, resulting in their positive selection in sub-Saharan Africa. We demonstrate a five-fold dominant protective association for G2 against T.b. rhodesiense infection. Furthermore, we report unpredicted strong opposing associations with T.b. gambiense disease outcome. G2 associates with faster progression of T.b. gambiense trypanosomiasis, while G1 associates with asymptomatic carriage and undetectable parasitemia. These results implicate both forms of human African trypanosomiasis in the selection and persistence of otherwise detrimental APOL1 kidney disease variants.

Although APOL1 gene variants are associated with nephropathy in African Americans, little is known about APOL1 protein synthesis, uptake, and localization in kidney cells. To address these questions, we examined APOL1 protein and mRNA localization in human kidney and human kidney-derived cell lines. Indirect immunofluorescence microscopy performed on nondiseased nephrectomy cryosections from persons with normal kidney function revealed that APOL1 protein was markedly enriched in podocytes (colocalized with synaptopodin and Wilms' tumor suppressor) and present in lower abundance in renal tubule cells. Fluorescence in situ hybridization detected APOL1 mRNA in glomeruli (podocytes and endothelial cells) and tubules, consistent with endogenous synthesis in these cell types. When these analyses were extended to renal-derived cell lines, quantitative RT-PCR did not detect APOL1 mRNA in human mesangial cells; however, abundant levels of APOL1 mRNA were observed in proximal tubule cells and glomerular endothelial cells, with lower expression in podocytes. Western blot analysis revealed corresponding levels of APOL1 protein in these cell lines. To explain the apparent discrepancy between the marked abundance of APOL1 protein in kidney podocytes observed in cryosections versus the lesser abundance in podocyte cell lines, we explored APOL1 cellular uptake. APOL1 protein was taken up readily by human podocytes in vitro but was not taken up efficiently by mesangial cells, glomerular endothelial cells, or proximal tubule cells. We hypothesize that the higher levels of APOL1 protein in human cryosectioned podocytes may reflect both endogenous protein synthesis and APOL1 uptake from the circulation or glomerular filtrate.

reduced levels of calcifi ed atherosclerotic plaque in coronary and carotid arteries ( 3,4 ).APOL1 nephropathy risk variants have undergone positive selection in sub-Saharan Africa due to protection from Trypanosoma brucei rhodesiense , a cause of African sleeping sickness ( 5 ). The mechanism whereby APOL1 risk variant (G1 and G2) proteins kill trypanosomes is well-understood, and refl ects APOL1 protein uptake by parasites, traffi cking to the lysosome, and an acidic pH-induced conformational change with subsequent APOL1 protein insertion into lysosomal membranes. Chloride transport ensues via the APOL1 channel with osmotic swelling and eventual lysosomal rupture leading to parasite death. In contrast, the mechanism(s) whereby APOL1 renal risk variants produce progressive nondiabetic nephropathy remain poorly understood. Moreover, the basic biology of APOL1 proteins has not yet been elucidated and will be of utmost importance to defi ne its role in human diseases. We and others have shown that APOL1 mRNA and protein are present in podocytes, renal tubule cells, and glomerular endothelial cells, but not in mesangial cells ( 6, 7 ). APOL1 protein is also present in the circulation ( 8 ) and may thus play an important role in its pathology.Although APOL1 is produced by several cell types ( 9, 10 ), few details regarding its production and secretion are known. APOL1 is reported to bind to HDL ( 8 ). Because the liver is a major source of HDL production ( 11 ) and circulating apolipoproteins, and is likely an important contributor to the circulating pool of APOL1, the present study was performed using a hepatoma cell line and primary hepatocytes. These studies have revealed novel traffi cking behavior of APOL1 and identify potential pathways involved in APOL1-induced cell injury and death.Abstract Two APOL1 gene variants, which likely evolved to protect individuals from African sleeping sickness, are strongly associated with nondiabetic kidney disease in individuals with recent African ancestry. Consistent with its role in trypanosome killing, the pro-death APOL1 protein is toxic to most cells, but its mechanism of cell death is poorly understood and little is known regarding its intracellular traffi cking and secretion. Because the liver appears to be the main source of circulating APOL1, we examined its secretory behavior and mechanism of toxicity in hepatoma cells and primary human hepatocytes. APOL1 is poorly secreted in vitro, even in the presence of chemical chaperones; however, it is effi ciently secreted in wild-type transgenic mice, suggesting that APOL1 secretion has specialized requirements that cultured cells fail to support. In hepatoma cells, inducible expression of APOL1 and its risk variants promoted cell death, with the G1 variant displaying the highest degree of toxicity. To explore the basis for APOL1-mediated cell toxicity, endoplasmic reticulum stress, pyroptosis, autophagy, and apoptosis were examined. Our results suggest that autophagy represents the predominant mechanism of APOL1-mediated ce...

This article is available online at http://www.jlr.org G1 and G2 renal-risk variants on chromosome 22q13.1 ( 1-3 ). Although APOL1 mRNA and APOL1 protein are present in human kidney ( 4, 5 ), the major APOL1 reservoir appears to be circulating protein ( 5, 6 ). APOL1 was initially discovered as a minor apolipoprotein of plasma HDLs ( 6 ); however, its distribution among HDL subfractions has not been well-defi ned. APOL1 nephropathy variants associate with HDL subfraction concentrations ( 7 ) and CVD risk, although controversial results have been reported with CVD ( 8-11 ). Trypanosome lytic factors (TLF1 and TLF2) contain APOL1 protein ( 12 ) and are minor HDL subfractions in humans that contribute to innate immunity via protection from infection, including from African trypanosomes ( 13 ).Association was not observed between plasma APOL1 concentrations and APOL1 genotype in African Americans with treated HIV infection; plasma APOL1 levels also did not associate with the risk of HIV-associated nephropathy or chronic kidney disease ( 14 ). Whether serum APOL1 protein levels and their distribution among HDL particles are associated with APOL1 genotypes in healthy individuals is unknown. Because free APOL1 protein may be taken up by podocytes in vitro ( 5 ), it remains critical to determine whether serum APOL1 concentrations or the structure/composition of variant APOL1 proteins and their associated complexes are specifi c to the G1 and G2 renalrisk variants, relative to nonrisk G0.To address these issues, serum APOL1 protein levels and size distribution were examined in age-and gender-matched African Americans without kidney disease based on APOL1 genotype using fast protein LC (FPLC) and immunoblot analysis. Proteomics analysis was performed to compare the composition of APOL1 protein-containing complexes. These Abstract APOL1 gene renal-risk variants are associated with nephropathy and CVD in African Americans; however, little is known about the circulating APOL1 variant proteins which reportedly bind to HDL. We examined whether APOL1 G1 and G2 renal-risk variant serum concentrations or lipoprotein distributions differed from nonrisk G0 APOL1 in African Americans without nephropathy. Serum APOL1 protein concentrations were similar regardless of APOL1 genotype. In addition, serum APOL1 protein was bound to protein complexes in two nonoverlapping peaks, herein referred to as APOL1 complex A (12.2 nm diameter) and complex B (20.0 nm diameter). Neither of these protein complexes associated with HDL or LDL. Proteomic analysis revealed that complex A was composed of APOA1, haptoglobin-related protein (HPR), and complement C3, whereas complex B contained APOA1, HPR, IgM, and fibronectin. Serum HPR was less abundant on complex B in individuals with G1 and G2 renal-risk variant genotypes, relative to G0 ( P = 0.0002-0.037). These circulating complexes may play roles in HDL metabolism and susceptibility to CVD. A major breakthrough in human molecular genetics was identifi cation of the powerful contribution of APOL1 gene ...

Adipocyte Abca1 is a key regulator of adipocyte lipogenesis and lipid accretion, likely because of increased adipose tissue membrane cholesterol, resulting in decreased activation of lipogenic transcription factors PPARγ and SREBP1.

No abstract

To gain a better understanding of the mechanism of chromosomal translocations in cancer, we investigated the spatial proximity between CBFB and MYH11 genes involved in inv(16)(p13q22) found in acute myeloid leukemia patients. Previous studies have demonstrated a role for spatial genome organization in the formation of tumorigenic abnormalities. The non-random localization of chromosomes and, more specifically, of genes appears to play a role in the mechanism of chromosomal translocations. Here, two-color fluorescence in situ hybridization and confocal microscopy were used to measure the interphase distance between CBFB and MYH11 in hematopoietic stem cells, where inv(16)(p13q22) is believed to occur, leading to leukemia development. The measured distances in hematopoietic stem cells were compared to mesenchymal stem cells, peripheral blood lymphocytes and fibroblasts, as spatial genome organization is determined to be cell-type specific. Results indicate that CBFB and MYH11 are significantly closer in hematopoietic stem cells compared to all other cell types examined. Furthermore, the CBFB-MYH11 distance is significantly reduced compared to CBFB and a control locus in hematopoietic stem cells, although separation between CBFB and the control is ~70% of that between CBFB and MYH11 on metaphase chromosomes. Hematopoietic stem cells were also treated with fragile site-inducing chemicals since both genes contain translocation breakpoints within these regions. However, treatment with fragile site-inducing chemicals did not significantly affect the interphase distance. Consistent with previous studies, our results suggest that gene proximity may play a role in the formation of cancer-causing rearrangements, providing insight into the mechanism of chromosomal abnormalities in human tumors.