Authors: Luz María MEDRANO; María Ángeles JIMENEZ-SOUSA; Amanda FERNÁNDEZ-RODRÍGUEZ(); Salvador RESINO()
(*) Both authors contributed equally
Current affiliations: Viral Infection and Immunity Unit, National Centre for Microbiology. Instituto de Salud Carlos III, Majadahonda, Madrid, Spain
Corresponding author: Salvador Resino, Centro Nacional de Microbiología, Instituto de Salud Carlos III (Campus Majadahonda); Carretera Majadahonda- Pozuelo, Km 2.2; 28220 Majadahonda (Madrid); Telf.: +34 918 223 266; Fax: +34 918 223 269; e-mail: email@example.com
Alternative corresponding author: Amanda Fernández-Rodríguez, Centro Nacional de Microbiología, Instituto de Salud Carlos III (Campus Majadahonda); Carretera Majadahonda- Pozuelo, Km 2.2; 28220 Majadahonda (Madrid); Telf.: +34 918 223 278; Fax: +34 918 223 269; e-mail: firstname.lastname@example.org
The pathogenic mechanisms of the accelerated progression of liver injury in HIV/HCV coinfection are incompletely understood. The progression of liver disease is variable between individuals under similar risk factors, suspecting that genetic background is an important factor. The aim of this review is to give a summary of all single nucleotide polymorphisms (SNPs) associated with the severity of liver disease in patients coinfected with HIV/HCV that are described in the literature. Therefore, a systematic search for articles published in this aim was made, 17 of which were selected for this review. In summary, a large number of SNPs have been associated with the severity of liver disease in HIV/HCV-coinfected patients. These genes are involved in different biological processes, seven genes correspond to cytokine genes (IFNL3-4, CXCL9-11, IL15 and TNF), two to receptor genes (IL7R and TLR8), and three are genes related to metabolism (PNPLA3, FTO, GSTM1). In addition, two combinations of polymorphisms (cirrhosis risk score (CRS) and mitochondrial haplogroups) have also been related to severity of liver disease in HIV/HCV-coinfected patients. Although other factors such as environmental and viral factors may be implicated in liver disease progression, the information about genetic variation might be useful in clinical practice, allowing prioritization of those patients with a genetic background that predispose to a worse evolution of HCV-related liver disease.
Key words: Genetic polymorphisms; HCV/HIV coinfection; liver fibrosis; cirrhosis; liver-related disease.
Hepatitis C virus (HCV) infection affects nearly 200 million of people worldwide and it is considered a leading cause of chronic liver disease ranging from mild chronic hepatitis to end stage cirrhosis and hepatocellular carcinoma . In these patients, the coinfection with the human immunodeficiency virus (HIV) and HCV is quite common (10-50% worldwide)  Currently, the combination antiretroviral therapy (cART) has made of chronic hepatitis C (CHC) an important comorbidity and a major cause of death in HIV/HCV-coinfected patients [3, 4]. Additionally, HIV infection modifies the natural history of CHC in HIV/HCV-coinfected patients, with higher probability of fibrosis progression, cirrhosis, and end-stage liver disease than HCV mono-infected patients [5, 6]. Besides, approximately 34% of patients increase at least one Metavir fibrosis stage over 2.5 years .
The pathogenic mechanisms of the accelerated progression of liver injury are incompletely understood. Immunity has a crucial role in HCV persistence and tissue damage during CHC . The interferons (IFNs) are the central cytokines involved in this process, which are able to induce an antiviral state by the transcription activation of hundreds of genes denominated IFN-stimulated genes (ISGs). The ISGs show antiviral effect in different stages of the viral life cycle, but they also induce activation of the immune system and increase the degree of liver inflammation. Moreover, enhanced oxidative stress may also increase profibrogenic cytokine expression and secretion. Thus, the elevated expression of proinflammatory cytokines in the liver may promote the fibrosis development .
In the last years, the development of direct acting antivirals (DAAs) for HCV infection has allowed to achieve an increased efficacy, shorter treatment periods, and decreased adverse events in HIV/HCV-coinfected patients . However, the current high cost of DAAs therapy is limiting its availability in all the countries and for all fibrosis stages. Consequently, it is very important to predict the progression of liver disease in order to prioritize the administration of DAAs. A helpful strategy is to pinpoint genetic biomarkers that are able to predict the disease progression, to prematurely administrate the DAAs in those patients that are predicted to have a worse progression.
The progression of liver disease is variable between individuals under similar risk factors, suspecting that genetic background is an important factor . Apart from the well-known single nucleotide polymorphisms (SNPs) around interleukin 28B (IL28B) gene , other SNPs have also demonstrated to have an important role . The aim of this review is to give a summary of all SNPs associated with the severity of liver disease in HIV/HCV-coinfected patients that are described in the literature. Therefore, a systematic search for articles published in this aim was made, 17 of which were selected for this review (Figure 1).
Figure 1. Flow-chart of systematic search of articles included in this review.
MARKERS OF SEVERITY OF LIVER DISEASE IN CHRONIC HEPATITIS C
In CHC, the hepatic biopsy is the current ‘gold standard’ to diagnosis and quantification of necroinflammatory activity grade and the stage of fibrosis and steatosis. Several scoring systems have been proposed for assessing liver injury and there is no general consensus on the best system. One of the most widely used is the METAVIR score , which has a 5-point fibrosis scale from F0 (no fibrosis) to F4 (cirrhosis) and 4-point necroinflammatory activity scale from A0 (no activity) to A3 (severe activity). Moreover, steatosis is common in HIV/HCV coinfected patients , which has been linked to higher liver fibrosis progression rates . Frequently, steatosis is evaluated according to the existence of hepatocytes containing visible macrovesicular fat droplets (>10%). However, liver biopsy is associated with several drawbacks such as invasiveness, sampling error, cost, and inter-/intra-observer variability.
Nowadays, several non-invasive diagnostic methods have been developed for determining liver fibrosis, including the aspartate aminotransferase-to-platelet ratio index (APRI), FIB-4 index, and the transient elastography (FibroScan) . The most widely studied indirect fibrosis marker is the APRI, which provides an accurate assessment of significant fibrosis and cirrhosis in HCV-monoinfected patients , and slightly less accurate in HIV/HCV-coinfected patients . The APRI cutoff for the correct identification at least significant fibrosis (F>=2) is APRI>=1.5 . The FIB-4 score was developed to identify correctly advanced fibrosis (F?3) in HIV/HCV-coinfected patients, and it is calculated with regard to age, platelet count, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) . The FIB-4 cutoff for the correct identification of patients with at least advanced fibrosis (F>=3) is FIB-4>=3.25 . The transient elastography quantify the liver stiffness by an elastic shear wave passing through liver tissue. Liver stiffness is expressed as kilopascals (kPa) and correlates with fibrosis stage in CHC . The transient elastography is the best validated of the non-invasive techniques, with excellent accuracy for detecting advanced fibrosis and cirrhosis in HIV-HCV-coinfected patients . Several cut-offs have been proposed for the different stages of fibrosis, although no general consensus has been reached.
GENETIC POLYMORPHISMS AT GENES OF CYTOKINES AND CHEMOKINES
IFNL3 and IFNL4 polymorphisms
In the last years, a large number of SNPs around IL28B gene (in both the interferon lambda 3 (IFNL3 or IL28B) and the interferon lambda 4 (IFNL4) gene) have been described as predictors of spontaneous HCV clearance and CHC treatment outcome [11, 21]. Thus, IFNL3 and IFNL4 polymorphisms seem to be related to stronger immune response, which could be mediating a certain protective effect against HCV infection, but also, they could promote greater liver damage associated to higher expression of inflammatory cytokines and more rapid fibrosis progression [22, 23].
Only four polymorphisms (rs8109886, rs12979860, rs12980275, and rs8099917) have been associated with severity of liver disease in HIV/HCV-coinfected patients (Table 1), all of them positioned at IFNL3 and IFNL4 genes (Figure 2).
Figure 2. Interferon (IFN)-L3 and IFN-L4 variants on chromosome 19, which have been related to severity of liver disease in HIV/HCV-coinfected patients.
Table 1: Genetic polymorphisms at genes of cytokines and chemokines associated with the severity of liver disease in HIV/HCV-coinfected patients.
|Gene||Chr. location||SNP||Prot./Risk allele||Location||Outcome||Ethnicity||HCV-GT||Reference|
|IFNL4||19q13.2||rs12979860||T/C||intron 1||ALT||Caucasian||1, 3, 4||[25, 26]|
|Cirrhosis (F4)||Caucasian||1, 3, 4|||
|Significant fibrosis (F>=2)||Caucasian||3|||
|Liver-related death||Afro American|||
|Significant fibrosis (F>=2)||Caucasian||3|||
|APRI (>=1.5)||Caucasian||1, 2, 3, 4|||
|IFNL4||19:39252122||rs8109886||A/G||upstream||Liver-related death||Afro American|||
|Significant fibrosis (F>=2)||Caucasian||1|||
|Significant fibrosis (F>=2)||Caucasian||1|||
|Significant fibrosis (F>2)||Caucasian||1|||
|IL15||4q31||rs10833||G/A||3´UTR||Advanced fibrosis (F>3)||Caucasian||1, 2, 3, 4|||
|TNF-alpha||6p21.3||rs361525||A/G||upstream||Advanced fibrosis (F>3)||Caucasian||1,4|||
|Cirrhosis (F4)||Caucasian||1, 4|||
IFNL, interferon lambda; CXCL, chemokine (C-X-C motif) ligand; IL, interleucina; TNF, tumor necrosis factor. APRI, AST/platelet ratio; FIB-4, Fibrosis-4 score.
The rs12979860 polymorphism is located within the first intron of IFNL4 (Figure 2). This gene encodes for a protein of moderate similarity with IFNL3, which also induces ISGs and generates antiviral response in hepatoma cells . The major allele (C) of rs12979860 has been related to increased values of ALT, AST, and APRI. The rs12979860 CC carriers had higher ALT levels in two cohorts of Spanish HIV/HCV-coinfected patients [25, 26]. Regarding to AST, patients with rs12979860 CC genotype had higher AST levels, whereas rs12979860 CT/TT genotype was a protective factor . Furthermore, the rs12979860 CC genotype has been associated with higher odds of having values of APRI>=1.5, while the rs12979860 CT/TT genotype was protective against APRI>=1.5 [OR=0.03 (0.002-0.41)] . Only Lutz et al. did not find significant association of rs12979860 genotypes with ALT and APRI levels in HIV/HCV-coinfected patients, probably due to the reduced number of patients (n=86) and that they only tested the genetic additive model and not the dominant .
The rs12979860 CC genotype has been also related to liver cirrhosis (F4) in HIV/HCV-coinfected patients. Barreiro et al. found that rs12979860 CC genotype was associated with a higher odds of cirrhosis (>14.5 kPa; F=4) [OR=2.32 (1.22-4.41)] . However, in a longitudinal study over 25 months, Lutz et al. found that liver stiffness in HIV/HCV-coinfected patients with the IFNL4 rs12979860 C allele did not show further progression, while liver stiffness slightly increased in T allele carriers infected with HCV-GT1 .
Downstream the IL28B gene is located the rs12980275 polymorphism (Figure 2). Guzmán-Fulgencio et al.  showed that patients with rs12980275 A allele had higher odds of having significant fibrosis (F>=2) [OR=6.3 (1.5-26.4)] and higher fibrosis progression (fibrosis progression rate (FPR) >=0.075 fibrosis units/years) [OR=1.64 (1.03-2.61)]. In addition, considering the HCV genotype, patients infected with HCV-GT3 and with rs12980275 A allele had higher odds of having values of ALT>=80IU/l [OR=4.12 (1.09-15.6)] and reduced odds for liver steatosis [OR=0.22 (0.09-0.50)] in HCV-GT1 patients. This last finding, though it might seem counterintuitive, is in agreement with a previous study in HCV-monoinfected Japanese patients ; and it could have important clinical implications because persistent fatty liver disease may be a problem for HCV-GT1 patients with rs12980275 G allele even with successful HCV clearance [30, 31]. In other study, Sarkar et al. found also a protective effect of rs12980275 G allele in a cohort of HIV/HCV-coinfected women from different ethnicities . The rs12980275 GG genotype was associated with lower risk of liver-related death (included hepatic decompensation or hepatocellular carcinoma) [adjusted hazard ratio (aHR)=0.36 (0.14-0.90)]. Moreover, the rs12980275 G allele showed a higher frequency in African American women, which is in accordance with the slower fibrosis progression of these patients.
Upstream the IFNL4 gene is located the rs8099917 (Figure 2). Guzmán-Fulgencio et al.  have also found that rs8099917 T allele was related to higher odds of attaining values of ALT>=80IU/l [OR=1.78 (1.01-3.17)], significant fibrosis (F>=2) [OR=1.93 (1.11-3.60)] and rapid fibrosis progression (FPR >=0.075 fibrosis units/years) [OR=2.08 (1.12-3.88)]. Besides, considering the HCV genotype, patients infected with HCV-GT1 and with rs8099917 T allele had also reduced odds for liver steatosis [OR=0.39 (0.16-0.99)]. In other article, Moqueet et al. observed that individuals who had developed significant fibrosis (APRI >=1.5) were also more likely to carry rs8099917 TT genotype compared with patients that carry rs8099917 TG/GG genotype [aHR =1.79 (1.24-2.57)] .
The rs8109886 polymorphism is located upstream the IFNL4 gene (Figure 2). The rs8109886 AA genotype was associated to a lower risk of liver-related death [aHR=0.67 (0.45-0.99)] in 794 coinfected women from three different ethnicities (Afro American, Caucasian and Hispanic), but this association was no longer significant after adjusting for ethnicity .
The chemokines such as the IFN-gamma-inducible protein (IP-10/CXCL10), IFN-gamma-induced monokine (MIG/CXCL9), and IFN-inducible T-cell alpha chemo attractants (I-TAC/CXCL11) may promote the lymphocyte migration from the periphery to liver parenchyma, causing the development of liver fibrosis in response to HCV infection . In fact, high serum CXCL9-11 levels have been related to higher degree of hepatic damage and are able to predict fibrosis stage in patients infected with HCV-GT1, in HCV-monoinfected and HIV/HCV-coinfected patients [35-37]. The CXCL9-11 genes are located on human chromosome 4 in a cluster among several CXC chemokine genes . SNPs in this region are in strong linkage disequilibrium and they have been related to severity of viral infections such as Enterovirus-71 , hepatitis B [40, 41], and hepatitis C .
Pineda-Tenor et al. (Table 1) reported that the homozygosity for minor alleles at CXCL9 rs10336 (T), CXCL10 rs3921 (G), and CXCL11 rs4619915 (A) was linked to higher values of APRI and FIB-4, and higher odds of achieving values of APRI>=1.5 and FIB-4>=3.25 in HIV/HCV-coinfected patients , particularly in patients infected with HCV-GT1. They also observed that patients infected with HCV-GT1 and with rs10336 TT, rs3921 GG and rs4619915 AA had higher odds of having significant fibrosis (F>=2) and severe activity grade (A3). Besides, the TGA haplotype (unfavorable alleles) was related to higher odds of having values of APRI>=1.5 and FIB-4>=3.25, and having significant fibrosis (F?2) and severe activity grade (A3) .
Other gene associated with advanced fibrosis is interleukin 15 (IL15), which is essential for the activation and function of cells involved in response against HCV infection . The IL15 has been related to inflammatory response in HIV/HCV-coinfected patients; where its expression has been positively associated with immune activation in peripheral T-cell and hepatic stellate cells .
Jimenez-Sousa et al. (Table 1) reported that patients with IL15 rs10833 AA genotype had increased odds of developing advanced fibrosis [aOR=2.30 (1.15-4.61)], mainly in males [aOR=2.24 (1.04-4.86)], patients with HCV-RNA<500 000 IU/ml [aOR=5.14 (1.32-19.8)] and patients with IL28B rs12980275 AG/GG genotypes [aOR=2.51 (1.02-6.20)] . Furthermore, the rs10833 AA genotype was also associated with higher serum levels of HGF, sICAM-1, and sVCAM-1 than AG/GG carriers. The IL15 rs10833 polymorphism, located at 3´UTR region, could be part of miRNA binding sites. The authors observed by in silico analyses that rs10833 A allele generates putative target sites for several miRNAs whereas the presence of rs10833 G allele disrupts these target sites and generates others. Therefore, the rs10833 polymorphism might play an important role in regulatory mechanisms.
The tumor necrosis factor alpha (TNF-a) seems to affect liver fibrosis by stimulating hepatic stellate cells . Two polymorphisms at TNF-a have been studied (rs361525 and rs1800629) in relation to liver disease in HIV/HCV-coinfected patients, but only rs361525 (G>A) was significantly associated with liver fibrosis and cirrhosis (Table 1) [48, 49]. This SNP consists of a G to A substitution at position -238 in the proximal promoter of the TNF-a gene, which seems to affect TNF-a transcriptional activity . In a first study, Corchado et al. found patients with the rs361525 GG genotype which showed significantly higher values of liver stiffness than those with genotypes GA/AA (p<0.001) . A second study performed in Caucasian patients by the same research group showed patients carrying rs361525 GG allele which had higher frequency of cirrhosis [97% vs. 77%; p=0.025] . However, there are some controversial results about these findings in HCV-monoinfected patients, because rs361525 A allele has been associated with higher risk of cirrhosis  and other authors did not find any association .
GENETIC POLYMORPHISMS LOCATED ON RECEPTOR GENES
Interleukin-7 (IL-7) is required for T cell development, maintaining, and restoring homeostasis of mature T cells; and it is a critical factor in maintaining or inducing an effective antiviral CD4+ and CD8+ T cell responses . The responsiveness of IL-7 is dependent on the expression of the IL-7 receptor (IL7R). Several IL7R polymorphisms seem to affect the expression of IL7R and the immune response , particularly in HIV infection [55-57].
Guzman-Fulgencio et al. have described an association between IL7R SNPs and severity of liver disease (Table 2) . The homozygosis for major rs3194051 A allele has been associated with higher APRI values [OR=2.52(1.10-5.77)] and values of FIB-4 (>=3.25) [OR=4.01 (1.17-13.71)] in HIV/HCV-coinfected patients . Moreover, the IL7R polymorphisms are also among those which are related to severity of liver disease in hepatic biopsy. The T allele at rs987106 and G allele at rs3194051 on IL7R gene were associated with higher odds of having advanced fibrosis (F>=3) [OR=3.09 (1.32-7.22) and OR=2.73 (1.22-5.87); respectively]. Furthermore, the authors found that IL7R rs6897932 CC genotype was associated with higher odds of having severe activity necroinflammatory grade (A3) [OR=4.16 (1.19-14.59)] .
Table 2: Genetic polymorphisms at receptor genes associated with the severity of liver disease in HIV/HCV-coinfected patients.
|Gene||Chr. location||SNP||Prot./Risk allele||Location||Outcome||Ethnicity||HCV-GT||Reference|
|IL7R||5p13||rs3194051||A/T||exon 8, missense||APRI||Caucasian||1, 2, 3, 4|||
|FIB-4||Caucasian||1, 2, 3, 4|||
|Advanced fibrosis (F>=3)||Caucasian||1, 2, 3, 4|||
|5p13||rs987106||A/T||intron 6||Advanced fibrosis (F>=3)||Caucasian||1, 2, 3, 4|||
|5p13||rs6897932||T/C||exon 6||Activity grade||Caucasian||1, 2, 3, 4|||
|TLR8||Xp22||rs3764880||G/A||exon 1, missense||Non-progression (F0)||Caucasian||1|||
|Xp22||rs1013151||T/C||intron 2||Non-progression (F0)||Caucasian||1|||
|Xp22||rs5744069||T/G||intron 2||Non-progression (F0)||Caucasian||1|||
IL7R, interleukin-7 (IL-7) receptor; TLR8, toll-like receptor 8; APRI, AST/platelet ratio; FIB-4, Fibrosis-4 score
The rs987106 TT, rs3194051 GG, rs6897932 CC genotypes have been associated to higher plasma levels of soluble isoform of IL7R (sCD127) [59, 60]. Thus, elevated levels of sCD127 in plasma limit the bioavailability of circulating IL7 levels and therefore, reduce IL7 effects on development, survival, and proliferation of CD4+ T cells. Furthermore, unfavorable alleles of these three IL7R polymorphisms (rs6897932 C, rs987106 T, and rs3194051 A) have been related to low CD4+ T-cells and rapid AIDS progression in Caucasian naïve HIV infected patients . In this regard, low CD4 counts are associated with accelerated liver fibrosis progression in HIV/HCV-coinfected patients . Thus, it is possible that unfavorable IL7R genotypes (rs6897932 CC, rs987106 TT, and rs3194051 AA) could lead to an increased risk of severe liver disease due to regulation of sCD127 levels, by decreasing CD4+ cells count and enhancing AIDS progression in HIV/HCV-coinfected patients .
Toll-like receptors (TLRs) are highly conserved sensors of microbial and endogenous danger signals, which play a key role in HCV recognition and activation of innate immunity . In particular, TLR8 seems to be critical for clarifying RNA viruses. The TLR8 gene is located at chromosome X, and encodes for an intracellular receptor that recognizes double-stranded RNAs from viruses in endosomal compartments. The TLR8 has been related to an altered innate immune response and susceptibility to HCV infection [65, 66], and progression of HIV disease [67, 68].
Three TLR8 polymorphisms (rs3764880, rs1013151 and rs5744069) were related to non-fibrosis (F0), mainly in men coinfected with HIV and HCV-GT1 (Table 2). Fernandez-Rodriguez et al.  found out that the rs3764880 G allele was a protective allele on fibrosis progression in patients coinfected with HIV and HCV-GT1 [OR=5.65 (1.26-25.36)], possibly due to a putative enhanced immune activation and a better control of HCV infection. Other two polymorphisms, rs1013151 and rs5744069, were also associated to non-fibrosis (F0) both in male patients ([OR=4.49 (1.08-18.62)] and [OR=6.17 (1.45-26.20)] respectively) and HCV-GT1 patients ([OR=5.79 (1.44-23.32)] and [OR=8.01 (2.16-35.65)] respectively).
The TLR8 rs3764880 is a missense polymorphism located at exon 1 that modifies the start codon and it results in a different TLR8 isoform with a shorter signal peptide , which seems to be related to increased expression of TLR8 and NF-kappa B activation . The TLR8 rs1013151 located at intron 2, seems to harbor different transcription start sites depending on the present allele . Dissimilar transcription factors related to fibrosis may bind to alternative alleles, which could affect TLR8 expression . The rs5744069, which is located at intron 2, may generate a target site for the myocyte enhancer factor 2 (MEF2) when the risk allele G is present.
GENETIC POLYMORPHISMS AT GENES RELATED TO METABOLISM
Polymorphisms at the patatin-like phospholipase domain-containing 3 (PNPLA3) gene have been related to liver fibrosis in chronic liver disease . The PNPLA3 gene, located on chromosome 22, encodes for a protein with lipase activity which is highly expressed in the liver and adipose tissue. One missense polymorphism (rs738409) located at exon 3, generates an isoleucine to methionine substitution at position 148 of the protein (I148M). This modification results in a loss of PNPLA3 function, which seems to have implications in nonalcoholic steatohepatitis (NASH) and progressive liver fibrosis in HCV-infected patients .
Jimenez-Sousa et al. described an association between PNPLA3 rs738409 polymorphism and liver fibrosis in HIV/HCV-coinfected patients (Table 3). The PNPLA3 rs738409 G allele was associated with higher odds of developing advanced fibrosis [FIB-4>=3.25 (OR=8.77(1.11-69.0) and F>=3(OR=2.15 (1.07-4.35)] in HIV/HCV-coinfected patients , suggesting that this polymorphism might also play a significant role in the progression of hepatic fibrosis in this group of patients. However, they did not find any association for liver steatosis possibly due to the fact that steatosis was defined as a dichotomous variable (fatty hepatocytes >=10%).
Table 3: Genetic polymorphisms at genes related to metabolism that have been associated with the severity of liver disease in HIV/HCV-coinfected patients.
|Gene||Chr. location||SNP||Prot./Risk allele||Location||Outcome||Ethnicity||HCV-GT||Reference|
|PNPLA3||22q13.31||rs738409||C/G||exon 3, missense||FIB-4||Caucasian||1, 2, 3, 4|||
|Advanced fibrosis (F>=3)||Caucasian||1, 2, 3, 4|||
|FTO||16q12.2||rs9939609||T/A||intron 1||Significant fibrosis (F>=2)||Caucasian||1, 2, 3, 4|||
|Steatosis||Caucasian||1, 2, 3, 4|||
|Haplogroup U (#)|
|MT-CO3||9504||T9504C||Non-U/U||Mitochondria||Cirrhosis (F4)||Caucasian||1, 2, 3, 4|||
|MT-ND3||10398||A10398G||Non-U/U||Mitochondria||Cirrhosis (F4)||Caucasian||1, 2, 3, 4|||
|MT-ND4||10873||T10873C||Non-U/U||Mitochondria||Cirrhosis (F4)||Caucasian||1, 2, 3, 4|||
|MT-ND5||12705||T12705C||Non-U/U||Mitochondria||Cirrhosis (F4)||Caucasian||1, 2, 3, 4|||
|tRNA Leu||12308||A12308G||Non-U/U||Mitochondria||Cirrhosis (F4)||Caucasian||1, 2, 3, 4|||
|Haplogroup H (?)|
|MT-CO3||9504||T9504C||H/Non-H||Mitochondria||Advanced fibrosis (F>=3)/FPR||Caucasian||1, 2, 3, 4|||
|MT-ND3||10398||A10398G||H/Non-H||Mitochondria||Advanced fibrosis (F>=3)/FPR||Caucasian||1, 2, 3, 4|||
|MT-ND4||10873||T10873C||H/Non-H||Mitochondria||Advanced fibrosis (F>=3)/FPR||Caucasian||1, 2, 3, 4|||
|MT-ND5||12705||T12705C||H/Non-H||Mitochondria||Advanced fibrosis (F>=3)/FPR||Caucasian||1, 2, 3, 4|||
|MT-Cytb||14766||T14766C||H/Non-H||Mitochondria||Advanced fibrosis (F>=3)/FPR||Caucasian||1, 2, 3, 4|||
|MT-ND2||4580||G4580C||H/Non-H||Mitochondria||Advanced fibrosis (F>=3)/FPR||Caucasian||1, 2, 3, 4|||
|MT-COI||7028||T7028C||H/Non-H||Mitochondria||Advanced fibrosis (F>=3)/FPR||Caucasian||1, 2, 3, 4|||
|GSTM1||1p13.3||null genotype||null genotype||Non mentioned||Oxidative stress||Caucasian African||–|||
#, T9504C, A10398G, T10873C, T12705C, A122308G mitochondrial DNA polymorphisms belong to haplogroup U. ?, T9504C, A10398G, T10873C, T12705C, T14766C, G4580C, T7028C mitochondrial DNA polymorphisms belong to haplogroup H. MT-CO3, mitochondrially encoded cytochrome c oxidase III; MT-ND, mitochondrially encoded NADH dehydrogenase; MT-COI, mitochondrially encoded cytochrome c oxidase I; MT-Cytb, mitochondrially encoded cytochrome b; MT- tRNA, mitochondrially encoded tRNA; PNPLA3, patatin-like phospholipase domain-containing 3; FTO, fat mass and obesity; FPR, fibrosis progression rate.
The fat mass and obesity-associated (FTO) gene, located on chromosome 16q12.2, encodes for a nuclear protein whose exact physiological function is unknown, although it seems to be involved in the management of energy homeostasis and in the regulation of body weight . The rs9939609 polymorphism is located at the first intron of FTO gene and the risk allele A, which displays an increased FTO expression , has been associated with metabolic disturbances (obesity, metabolic syndrome, insulin resistance, type 2 diabetes mellitus).
Pineda-Tenor et al. described an association between FTO rs9939609 polymorphism and liver disease (Table 3). The rs9939609 AA genotype was associated with higher odds of having significant fibrosis (F>=2) [OR=2.34 (1.02-5.36)] and steatosis [OR=3.65 (1.29-10.36)] in a cohort of 261 Spanish HIV-HCV-coinfected patients . Authors suggest that this association could be due to the metabolic disorders related to CHC, since the development of liver fibrosis is strongly associated with obesity/overweight, insulin resistance and steatosis.
Mitochondria are essential organelles that provide energy to eukaryotic cells via oxidative phosphorylation and regulate cellular survival via control of apoptosis while playing a key role in the innate immune response against viral infections . HIV and HCV lead to mitochondrial dysfunction with increased production of reactive oxygen species (ROS) [79, 80].
Mutations in mitochondrial DNA (mtDNA) have been acquired throughout human history, and thus the human population has been subdivided into a number of discrete mitochondrial clades or haplogroups, which are defined on the basis of specific mtDNA polymorphisms . In European Caucasians, 4 major haplogroups or clusters (HV, U, JT, and IWX) and several minor haplogroups have been identified (H, V, pre-V, J, T, Uk, W, X, I, etc.) (Figure 3) . MtDNA haplogroups have been directly associated with susceptibility to disorders such as cancer, sepsis, diabetes, and degenerative diseases . In HIV infection, mtDNA haplogroup H has been associated with a low likelihood of AIDS progression and/or severe immunodeficiency .
Figure 3. List of European mitochondrial DNA (mtDNA) haplogroups with their defining mutation.
García-Álvarez et al. described an association between mitochondrial haplogroups and progression of liver disease (Table 3). They found that haplogroup H, within the major haplotype HV, was strongly associated with reduced odds of advanced fibrosis [OR=0.4 (0.18-0.91)], cirrhosis [OR=0.14 (0.03-0.67)] and fibrosis progression rate [OR=0.47 (0.23-0.95)] in a cohort of Caucasian patients . This haplogroup H is associated with higher ATP and ROS production, but the higher production of ROS could enhance the innate immunity and thus, disease progression will be slower . On the other hand, the major haplogroup U was also strongly associated with an increased odds of cirrhosis [OR=5.25 (1.76-15.64)]. This haplogroup U (lower ATP and ROS production) has been related to disruption of oxidative phosphorylation complexes, antioxidant enzyme deficiency and apoptosis .
In addition, dysregulation of the redox system through mitochondrial transmembrane potential alteration has been observed in coinfected patients, probably due to the viral replication via activation of nuclear factor kB and induction of apoptosis of CD4+ T-cells.  In this respect, Parson et al. explored the role of a well-known detoxification enzyme, the glutathione-S-transferase mu 1 (GSTM1) (Table 3). This gene, located at 1p13.3, encodes a cytosolic GST of the mu subfamily, which plays a role in the detoxification of the ROS. They found that “null genotype” at GSTM1 (no transcription of functional copy) was associated to higher oxidative stress in HIV/HCV-coinfected patients, determined by oxidized glutathione, mitochondrial 8-oxo-dG and apoptosis markers. 
CIRRHOSIS RISK SCORE
The fibrosis progression among HIV/HCV-coinfected patients is highly variable and difficult to predict due to multifactorial interactions between viral and host factors . Host genetic factors may play an important role in fibrosis progression and a cirrhosis risk score (CRS), previously described for HCV monoinfected patients , has been able to predict fibrosis/cirrhosis progression. The CRS signature uses the genetic information of seven SNPs (rs62522600, rs4986791, rs886277, rs2290351, rs17740066, rs2878771 and rs4290029) located in different genomic regions (AZIN, TLR4, TRPM5, AP3S2, STXBP5K, and AQP2, and an intergenic region downstream DGS1, respectively).
Fernández-Rodríguez et al. evaluated this CRS in a cohort of HIV/HCV-coinfected patients (Table 4) . They found that non-progressors (F0) had CRS values significantly lower than progressors (F>=1) (0.61 versus 0.67; p=0.043), but the CRS itself seems not to be a good marker for identifying HIV/HCV coinfected patients who are at high risk of developing liver fibrosis. However, the CRS score coupled with clinical factors (age at HCV infection, IDU, gender, IL28B and HCV genotype) had values of area under the receiver operating characteristic curve (AUROC) of 0.739, and it might help to distinguish between non-progressors and progressors patients.
Table 4: Genetic polymorphisms at genes related to cirrhosis risk score (Huang et al. ), which has been associated with the severity of liver disease in HIV/HCV-coinfected patients.
|Gene||Chr. location||SNP||Prot./Risk allele||Location||Outcome||Ethnicity||HCV-GT||Reference|
|AZIN||8q22.3||rs62522600||A/G||exon 12, synonymous||Mild fibrosis (F>=1)||Caucasian||1, 2, 3, 4|||
|TLR4||9q33.1||rs4986791||T/C||exon 4, missense||Mild fibrosis (F>=1)||Caucasian||1, 2, 3, 4|||
|TRPM5||11p15.5||rs886277||T/C||exon 9, missense||Mild fibrosis (F>=1)||Caucasian||1, 2, 3, 4|||
|AP3S2||15q26.1||rs2290351||G/A||exon 7||Mild fibrosis (F>=1)||Caucasian||1, 2, 3, 4|||
|STXBP5L||3q13.33||rs17740066||G/A||exon 19, missense||Mild fibrosis (F>=1)||Caucasian||1, 2, 3, 4|||
|AQP2||12q13.12||rs2878771||C/G||3´UTR||Mild fibrosis (F>=1)||Caucasian||1, 2, 3, 4|||
|LOC10192714||Chr1||rs4290029||C/G||exon 1||Mild fibrosis (F>=1)||Caucasian||1, 2, 3, 4|||
AZIN, antizyme inhibitor 1; TLR4, toll-like receptor 4; TRPM5, transient receptor potential cation channel subfamily M member 5; AP3S2, adaptor related protein complex 3 sigma 2 subunit; STXBP5L, syntaxin binding protein 5 like; AQP2, aquaporin 2; LOC101927143, uncharacterized LOC101927143.
In summary, today, a large number of SNPs have been associated with the severity of liver disease in HIV/HCV-coinfected patients. These genes are involved in different biological processes, seven genes correspond to cytokine genes (IFNL3-4, CXCL9-11, IL15 and TNF), two to receptor genes (IL7R and TLR8), and three are genes related to metabolism (PNPLA3, FTO, GSTM1). In addition, two combinations of polymorphisms (CRS and mitochondrial haplogroups) have also been related to severity of liver disease in HIV/HCV-coinfected patients. Although other factors such as environmental and viral factors may be implicated in liver-disease progression, the information about genetic variation might be useful in clinical practice. Thus, we could prioritize those patients with a genetic background that predispose to a worse evolution of HCV-liver related disease.
Al authors declare no conflicts of interest.
This work was supported by grants from Fondo de Investigación de Sanidad (FIS) [PI14CIII/00011].
Luz María Medrano is supported by Rio Ortega program, María Ángeles Jimenez-Sousa by Sara Borrell program and Amanda Fernández-Rodríguez is a Miguel Servet I Researcher, (grant numbers CM14CIII/00002, CD13/00013 and CP14/0010); all of them funded by Fondo de Investigación Sanitaria (FIS).
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