Expression of genes encoding mitochondrial proteins can distinguish nonalcoholic steatosis from steatohepatitis

In patients without substantial alcohol use, triglyceride accumulation in the liver can lead to nonalcoholic fatty liver disease (NAFLD) that may progress to nonalcoholic steatohepatitis (NASH). The differential diagnosis between NAFLD and NASH can be accomplished only by morphological examination. Although the relationship between mitochondrial dysfunction and the progression of liver pathologic changes has been described, the exact mechanisms initiating primary liver steatosis and its progression to NASH are unknown. We selected 16 genes encoding mitochondrial proteins which expression was compared by quantitative RT-PCR in liver tissue samples taken from patients with NAFLD and NASH. We found that 6 of the 16 examined genes were differentially expressed in NAFLD versus NASH patients. The expression of hepatic HK1, UCP2, ME2, and ME3 appeared to be higher in NASH than in NAFLD patients, whereas HMGCS2 and hnRNPK expression was lower in NASH patients. Although the severity of liver morphological injury in the spectrum of NAFLD-NASH may be defined at the molecular level, expression of these selected 6 genes cannot be used as a molecular marker aiding histological examination. Moreover, it is still unclear whether these differences in hepatic gene expression profiles truly reflect the progression of morphological abnormalities or rather indicate various metabolic and hormonal states in patients with different degrees of fatty liver disease.