Apolipoprotein L1
| APOL1 | |||
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| Location (UCSC) | Chr 22: 36.25 – 36.27 Mb | n/a | |||||||
| PubMed search | [2] | n/a | |||||||
| View/Edit Human | |||
Apolipoprotein L1 is a
Species distribution
This gene is found only in humans, African green monkeys, and gorillas.[7][8]
Structure
The gene that encodes the APOL1 protein is 14,522 base pairs long and found on the human chromosome 22, on the long arm at position 13.1 from base pair 36,253,070 to base pair 36,267,530.[4][9]
The protein is a 398 amino acid protein. It consists of 5 functional domains:
- S domain-secretory signal
- MAD (membrane-addressing domain)-ph sensor and regulator of cell death
- BH3 domain - associated with programmed cell death
- PFD (pore forming domain)
- SRA (serum resistance-associated binding domain)- confers resistance to Trypanosoma brucei
Mutations
Two coding variants, G1 and G2, have been recently identified with relevance to human phenotypes. The G1 is a pair of two non-synonymous single nucleotide polymorphisms (SNPs) in almost complete linkage disequilibrium. G2 is an in-frame deletion of the two amino acid residues, N388 and Y389.[citation needed]
Function
Apolipoprotein L1 (apoL1) is a minor apolipoprotein component of HDL cholesterol which is synthesized in the liver and also in many other tissues, including pancreas, kidney, and brain. APOL1 is found in vascular endothelium, liver, heart, lung, placenta,[7] podocytes, proximal tubules, and arterial cells.[10] The protein as a secreted form that allows it to circulate in the blood. It forms a complex, known as a trypanosome lytic factor (TLF),[11] with high-density lipoprotein 3 (HDL3) particles that also contain apolipoprotein A1 (APOA1) and the hemoglobin-binding, haptoglobin-related protein (HPR). The APOL1 protein acts as the main lytic component in this complex.[11] Once uptaken by the trypanosome, the complex is trafficked to acidic endosomes, where the APOL1 protein may insert into the endosomal membrane. If the endosome is then recycled to the plasma membrane, where it encounters neutral pH conditions, APOL1 may form cation-selective channels.[12]
APOL1 is a member of a family of apolipoproteins which also includes six other proteins and it is a member of bcl2 genes which are involved in autophagic cell death. In fact an overabundance of APOL1 within a cell results in autophagy.[13]
APOL1 may play a role in the inflammatory response. Pro-inflammatory cytokines
APOL1 has a role in innate immunity by protecting against Trypanosoma brucei infection, which is a parasite transmitted by the tsetse fly. Trypanosomes endocytose the secreted form of APOL1; APOL1 forms pores on the lysosomal membranes of the trypanosomes which causes in influx of chloride, swelling of the lysosome and lysis of the trypanosome.[5][14]
Clinical significance
African trypanosomiasis (sleeping sickness)
Although its intracellular function has not been elucidated, apoL1 circulating in plasma has the ability to kill the trypanosome
Kidney disease
The distribution of the variants most associated with kidney disease risk was analyzed in African populations and found to be more prevalent in western compared to northeastern African populations and absent in Ethiopia,[17] consistent with the reported protection from forms of kidney disease known to be associated with the APOL1 variants.[18] In the Yoruba people of Nigeria (West Africa), the prevalence of G1 and G2 risk alleles are 40% and 8% respectively.[15][19] African nations with high frequencies of APOL1 risk alleles also have large populations of Trypanosomes suggesting that the risk alleles underwent positive selection as a defense mechanism. The existence of these variants are only found on African chromosomes and exist in people with recent African ancestry (<10,000 years).
Many African Americans are descendants of people of West African nations and consequently, also have a high prevalence of APOL1 risk alleles as well as APOL1 associated kidney diseases. The frequency of the risk alleles in African Americans is more than 30%.
The prevalence of the risk alleles in African Americans with these kidney diseases shown in recent studies are 67% in HIVAN, 66% in FSGS, and 47% in hypertension-attributed ESKD.[20][21] Hispanic populations such as Dominicans and Puerto Ricans demonstrate a mixture of genetic influences that include African ancestry resulting in a prevalence of the APOL1 variants as well.[22] Studies have also determined the prevalence of each individual allele in FSGS cases as well.
Focal segmental glomerulosclerosis (FSGS)
The prevalence of the G1 risk allele in African Americans with FSGS is 52% and 18-23% in those without FSGS. The prevalence of the G2 risk allele in African Americans with FSGS is 23% and 15% in those without FSGS.[15][21] FSGS is a kidney disease that affects younger individuals therefore, its effects are slightly different from the effects of general non-diabetic ESKD. In a recent study, the mean ages of onset of FSGS for African Americans with 2, 1, and 0 APOL1 risk alleles was 32yrs, 36yrs and 39yrs, respectively. APOL1 variants also have a tendency to manifest FSGS at relatively young ages; FSGS begins between the ages of 15 and 39 in 70% of individuals with two APOL1 risk alleles and 42% of individuals with of 0 or 1 risk alleles.[21]
Pathogenesis
Although possession of the APOL1 risk variants increases susceptibility to non-diabetic kidney disease, not all people who possess these variants develop kidney disease, which indicates another factor may initiate progression of kidney disease.[23] Similarly in HIV positive patients, although the majority of African-American patients with HIVAN have two APOL1 risk alleles other as yet unknown factors in the host, including genetic risk variants and environmental or viral factors, may influence the development of this disorder in those with zero or one APOL1 risk allele. Kidney Int. 2012 Aug;82(3):338-43. The African American population has a total lifetime risk of developing FSGS of 0.8%. For those with 0 risk alleles the risk of developing FSGS is 0.2%, 0.3% with 1 risk allele, 4.25% with 2 risk alleles and a 50% chance of developing HIVAN for untreated HIV infected individuals.[21]
People with these allelic variants who develop ESKD begin dialysis at an earlier age than ESKD patients without the risk alleles. On average, those with two risk alleles begin dialysis approximately 10 years earlier than ESKD patients without the risk variants.[22][24] The mean ages of initiation of dialysis of African American ESKD patients with two risk alleles, one risk allele, or no risk alleles are approximately 48yrs, 53yrs, and 58 yrs, respectively.[22][24] Compared to African American ESKD patients, Hispanic ESKD patients with two APOL1 risk variants start dialysis at an earlier age, 41 yrs.
Although, the age of initiation of dialysis is earlier with one risk allele this effect is only seen in those with the G1 variant. In a study, ~96% of patients with two risk alleles started dialysis before the age of 75 compared to 94% for G1 heterozygotes, and 84% for those with no risk alleles.[22]
Kidneys from donors containing two APOL1 variants experience allograft failure more rapidly than donors with 0 or 1 variants.[25] Kidney recipients who have copies of the APOL1 risk variants, but do not receive kidneys from donors with the risk variants do not have decreased survival rates of the donated kidneys.[26] These observations together suggest that the genotype of the donor only affects allograft survival.
References
- ^ a b c GRCh38: Ensembl release 89: ENSG00000100342 – Ensembl, May 2017
- ^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- PMID 9325276.
- ^ PMID 11374903.
- ^ S2CID 33189804.
- ^ a b "Entrez Gene: APOL1 apolipoprotein L, 1".
- ^ PMID 11944986.
- PMID 14747153.
- PMID 11290834.
- PMID 21997392.
- ^ PMID 10085035.
- PMID 25730870.
- ^ PMID 18505729.
- S2CID 4310920.
- ^ PMID 20647424.
- PMID 24808134.
- PMID 20635188.
- PMID 16377389.
- S2CID 23728209.
- PMID 21698141.
- ^ PMID 21997394.
- ^ PMID 22357707.
- PMID 22695330.
- ^ PMID 21997398.
- PMID 21486385.
- PMID 22487534.
External links
- Human APOL1 genome location and APOL1 gene details page in the UCSC Genome Browser.
Further reading
- Duchateau PN, Movsesyan I, Yamashita S, Sakai N, Hirano K, Schoenhaus SA, O'Connor-Kearns PM, Spencer SJ, Jaffe RB, Redberg RF, Ishida BY, Matsuzawa Y, Kane JP, Malloy MJ (August 2000). "Plasma apolipoprotein L concentrations correlate with plasma triglycerides and cholesterol levels in normolipidemic, hyperlipidemic, and diabetic subjects". Journal of Lipid Research. 41 (8): 1231–6. PMID 10946010.
- Duchateau PN, Pullinger CR, Cho MH, Eng C, Kane JP (April 2001). "Apolipoprotein L gene family: tissue-specific expression, splicing, promoter regions; discovery of a new gene". Journal of Lipid Research. 42 (4): 620–30. PMID 11290834.
- Monajemi H, Fontijn RD, Pannekoek H, Horrevoets AJ (April 2002). "The apolipoprotein L gene cluster has emerged recently in evolution and is expressed in human vascular tissue". Genomics. 79 (4): 539–46. PMID 11944986.
- Vanhamme L, Paturiaux-Hanocq F, Poelvoorde P, Nolan DP, Lins L, Van Den Abbeele J, Pays A, Tebabi P, Van Xong H, Jacquet A, Moguilevsky N, Dieu M, Kane JP, De Baetselier P, Brasseur R, Pays E (March 2003). "Apolipoprotein L-I is the trypanosome lytic factor of human serum". Nature. 422 (6927): 83–7. S2CID 4310920.
- Kang MK, Kameta A, Shin KH, Baluda MA, Kim HR, Park NH (July 2003). "Senescence-associated genes in normal human oral keratinocytes". Experimental Cell Research. 287 (2): 272–81. PMID 12837283.
- Anderson NL, Polanski M, Pieper R, Gatlin T, Tirumalai RS, Conrads TP, Veenstra TD, Adkins JN, Pounds JG, Fagan R, Lobley A (April 2004). "The human plasma proteome: a nonredundant list developed by combination of four separate sources". Molecular & Cellular Proteomics. 3 (4): 311–26. PMID 14718574.
- Lugli EB, Pouliot M, del Pilar Molina Portela M, Loomis MR, Raper J (November 2004). "Characterization of primate trypanosome lytic factors". Molecular and Biochemical Parasitology. 138 (1): 9–20. PMID 15500911.
- Albert TS, Duchateau PN, Deeb SS, Pullinger CR, Cho MH, Heilbron DC, Malloy MJ, Kane JP, Brown BG (March 2005). "Apolipoprotein L-I is positively associated with hyperglycemia and plasma triglycerides in CAD patients with low HDL". Journal of Lipid Research. 46 (3): 469–74. PMID 15604524.
- Liu T, Qian WJ, Gritsenko MA, Camp DG, Monroe ME, Moore RJ, Smith RD (2006). "Human plasma N-glycoproteome analysis by immunoaffinity subtraction, hydrazide chemistry, and mass spectrometry". Journal of Proteome Research. 4 (6): 2070–80. PMID 16335952.
- Vanhollebeke B, Nielsen MJ, Watanabe Y, Truc P, Vanhamme L, Nakajima K, Moestrup SK, Pays E (March 2007). "Distinct roles of haptoglobin-related protein and apolipoprotein L-I in trypanolysis by human serum". Proceedings of the National Academy of Sciences of the United States of America. 104 (10): 4118–23. PMID 17360487.