The functionality of African-specific variants in the TGFB1 regulatory region and their potential role in HIVAN
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Transcription of transforming growth factor beta-1 (TGF-β1) is regulated by a polymorphic promoter region containing African-specific single nucleotide polymorphisms (SNPs). Some of these SNPs have higher frequencies among Southern Africans compared to other African populations and their functionality has only been partially studied. Due to the high prevalence of HIV-associated nephropathy (HIVAN) in Africans we hypothesized that functional African TGFB1-promoter SNPs may contribute to HIVAN pathogenesis.
The functionality of the TGFB1 -1347 C>T variant and African-specific variants (-1287 G>A, -1154 C>T, -387 C>T and -14 G>A) were examined by measuring reporter gene expression in kidney and fibroblast cell lines co-transfected with TGFB1-promoter constructs and an HIV-Tat expression vector. TGF-β1 immunohistochemical staining was performed on kidney biopsies with HIVAN (n = 18) and compared to control biopsies without HIVAN or tubulointerstitial disease (n = 12) using semi-quantitative and digital image analysis. HIVAN cases were genotyped for TGFB1 -1347 and -387 SNP variants.
TGFB1-promoter haplotypes containing the African -387 T-allele resulted in ~ five-fold repression of TGFB1-promoter activity compared to -387 C haplotypes (p ≤ 0.024). HIV-Tat upregulated TGFB1-promoter activity for haplotypes containing -1347 T and -387 T in transfected renal cells (≈ 1.6-fold; p ≤ 0.030) and fibroblasts (≈ 1.3-fold; p ≤ 0.016). The renal interstitium from HIVAN biopsies, compared to HIV-positive and -negative controls, differed in the semi-quantitative TGF-β1 staining and digital optical density analyses. The TGFB1 -1347 and -387 genotypes in HIVAN cases were similar to population controls.
African-specific haplotypes lower TGFB1-promoter activity and expression levels and HIV-Tat upregulates TGFB1 promoter activity irrespective of the haplotype.
KeywordsTransforming growth factor B1 Promoter Polymorphism HIVAN Kidney Africa
The authors wish to thank Professor Mitra (National Center for Cell Sciences, India) who kindly donated the plasmid pcDNA-Tat, Mrs. Padmini Govender (Division of Anatomical Pathology, University of Cape Town) for assistance with the immunohistochemical staining. In addition, a special thanks to Ms Susan Cooper and Prof DM Lang for their technical assistance with the digital image analysis (Confocal & Light Microscope Imaging Facility, University of Cape Town). J-MB and SP received funding from the South African National Research foundation (NRF), MN from the UCT Neurology fund, and JMH and NW from the South African Medical Research Council.
Compliance with ethical standards
Conflict of interest
The authors have declared that no conflict of interest exists.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the University of Cape Town’s Health Sciences Faculty institutional research committee at which the studies were conducted (HREC 491/2008) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.