1. ¹Inserm 602, Service de Biochimie et Biologie Moléculaire, Hôpital Universitaire Paul Brousse, Université Paris XI, Villejuif Cedex, France
2. ²Pfizer, Centre de Recherche, Amboise, France
3. ³Service de Chirurgie Digestive, Hôpital Tenon, Inserm 444, Université Pierre et Marie Curie, Paris, France
4. ⁴Division of Biostatistics, University of California, Berkeley, CA, USA
5. ⁵Centre Hépato-Biliaire, Hôpital Universitaire Paul Brousse, Villejuif, France
6. ⁶Service d'Anatomie pathologique, Hôpital Universitaire Paul Brousse, Villejuif, France
7. ⁷Service d'Anatomie pathologique, Hôpital Ambroise Paré, Assistance Publique-Hôpitaux de Paris, Boulogne Billamcourt, France

Correspondence: Dr A Lemoine, DPharm, PhD, Service de Biochimie et Biologie Moléculaire—INSERM 602, Hôpital Paul Brousse, 14 avenue Paul Vaillant Couturier, 94804 Villejuif Cedex, France. E-mail: antoinette.lemoine@pbr.ap-hop-paris.fr

Received 2 May 2005; Revised 21 October 2005; Accepted 25 October 2005; Published online 12 December 2005.

Abstract

Understanding the molecular mechanisms underlying fatty liver disease (FLD) in humans is of major importance. We used high-density oligonucleotide microarrays (22.3 K) to assess the mechanisms responsible for the development of human liver steatosis. We compared global gene expression in normal (n=9) and steatotic (n=9) livers without histological signs of inflammation or fibrosis. A total of 34 additional human samples including normal (n=11), steatosis (n=11), HCV-related steatosis (n=4) or steatohepatitis associated with alcohol consumption (n=4) or obesity (n=4) were used for immunohistochemistry or quantitative real-time PCR studies. With unsupervised classification (no gene selection), all steatotic liver samples clustered together. Using step-down maxT multiple testing procedure for controlling the Family-Wise Error-Rate at level 5%, 110 cDNAs (100 over- and 10 underexpressed) were found to be differentially expressed in steatotic and normal livers. Of them were genes involved in mitochondrial phosphorylative and oxidative metabolism. The mean ratio of mitochondrial DNA to nuclear DNA content was higher in liver steatosis compared to normal liver biopsies (1.120.14 vs 0.670.10; P=0.01). An increased expression of genes involved in inflammation (IL-1R family, TGFB) was also observed and confirmed by quantitative RT-PCR or immunochemistry. In steatohepatitis, an increase of the protein expression of mitochondrial antigens, IL-1R1, IGF2 and TGFB1 was also observed, interleukin 1 receptor being always strongly expressed in steatohepatitis linked to alcohol or obesity. In conclusion, mitochondrial alterations play a major role in the development of steatosis per se. Activation of inflammatory pathways is present at a very early stage of steatosis, even if no morphological sign of inflammation is observed.