Liver transcriptomics highlights interleukin-32 as novel NAFLD-related cytokine and candidate biomarker

Abstract

ObjectiveEfforts to manage non-alcoholic fatty liver disease (NAFLD) are limited by the incomplete understanding of the pathogenic mechanisms and the absence of accurate non-invasive biomarkers. The aim of this study was to identify novel NAFLD therapeutic targets andbiomarkers by conducting liver transcriptomic analysis in patients stratified by the presence of the PNPLA3 I148M genetic risk variant.DesignWe sequenced the hepatic transcriptome of 125 obese individuals. ‘Severe NAFLD’ was defined as the presence of steatohepatitis, NAFLD activity score ≥4 or fibrosis stage ≥2. The circulating levels of the most upregulated transcript, interleukin-32 (IL32), were measured by ELISA.ResultsCarriage of the PNPLA3 I148M variant correlated with the two major components of hepatic transcriptome variability and broadly influenced gene expression. In patients with severe NAFLD, there was an upregulation of inflammatory and lipid metabolism pathways. IL32 was the most robustly upregulated gene in the severe NAFLD group (adjusted p=1×10−6), and its expression correlated with steatosis severity, both in I148M variant carriers and non-carriers. In 77 severely obese, and in a replication cohort of 160 individuals evaluated at the hepatology service, circulating IL32 levels were associated with both NAFLD and severe NAFLD independently of aminotransferases (p<0.01 for both). A linear combination of IL32-ALT-AST showed a better performance than ALT-AST alone in NAFLD diagnosis (area under the curve=0.92 vs 0.81, p=5×10−5).ConclusionHepatic IL32 is overexpressed in NAFLD, correlates with hepatic fat and liver damage, and is detectable in the circulation, where it is independently associated with the presence and severity of NAFLD.

LPIAT1/MBOAT7 depletion increases triglyceride synthesis fueled by high phosphatidylinositol turnover

“…Next, we examined differences in hepatic mRNA levels of genes involved in de novo lipogenesis and fibrosis among the rs641738 genotypes in 123 morbidly obese individuals from Italy. 28 As expected, rs641738 T allele was associated with the reduction of LPIAT1 mRNA ( figure 5B ). Consistently with the results in mice, there was no difference in the liver mRNA levels of genes for de novo lipogenesis and the other pathways involved in hepatic TG handling tested among the LPIAT1 rs641738 genotypes ( figure 5C ).…”

Lack of genetic evidence that fatty liver disease predisposes to COVID-19

“…9 We therefore looked at the impact of genetic risk variants on the hepatic mRNA expression of ACE2, CTSL, TMPRSS2 and PYKFYVE 9 in a cohort of 125 obese individuals. 8 We found no significant impact of MAFLD-GRS and single variants on the expression of known viral receptors. However, we observed a trend towards higher ACE2 expression associated with carriage of the p.I148M PNPLA3 variant that was not statistically significant (p = 0.06).…”

“…However, the current sample size clearly had the power to detect a >6-fold higher risk of severe COVID-19 conferred by MAFLD, as reported by Ji et al 1 We actually detected a trend of protection against COVID-19 conferred by rs738409, encoding for the p.I148M PNPLA3 variant, which is a major genetic determinant of hepatic inflammation. 5,8 Future larger studies are warranted to formally test this hypothesis. A possible reason for differential susceptibility to severe COVID-19 is related to altered expression of SARS-CoV-2 cellular receptors.…”

The role of omics in the pathophysiology, diagnosis and treatment of non-alcoholic fatty liver disease

“…Genetic predisposition determines NAFLD transcriptomic signatures, as shown by recent investigations on the carriage of PNPLA3 I148M on transcriptome variability [ 88 ]. As described above, transcriptomics are also linked to epigenetic modifications in NAFLD [ 56 , 57 ].…”

“…More specifically, the transcriptional snapshot of NASH is defined by upregulation of PDGF , STAT , HNF-3 and SMAD-4 pathway-related genes [ 97 ], as well as downregulation of BNIP1, IGFBP1 [ 97 ] , SLC25A48, C4ORF48 [ 95 ] SDC4 , ATF3 , various inflammatory suppressors [ 94 ] and amino acid-metabolizing and reactive oxygen species (ROS) scavenger genes [ 97 ]. Interleukin-32 (IL-32) was recently ascertained as the most significantly upregulated transcript in advanced NAFLD and NASH (fold-change = 2.3 vs non-NASH), correlating with lipid accumulation and disease severity [ 88 ]. Additionally, several cancer-related genes, such as AKR1B10, KRT23 and GPC3 , are enhanced in NASH compared with NAFL or controls, by up to 155-fold and 460-fold respectively [ 96 ].…”