John D. Phillips1, Maria W. Smith2, Michael Katze2 and James P. Kushner1
Dept. of Medicine, University of Utah School of Medicine, Salt Lake City, UT1 and Dept. of Microbiology, University of Washington, Seattle, WA2
Porphyria cutanea tarda (PCT) is the most common of the porphyric disorders affecting 1 per 5,000 Caucasians. In all cases of PCT the activity of uroporphyrinogen decarboxylase (URO-D) in liver cells is markedly reduced whether mutations in the URO-D gene are present (familial PCT) or not (sporadic PCT). Risk factors predisposing to PCT include alcohol abuse, hepatitis C infection (HCV), the use of medicinal estrogens, and mutant hemochromatosis alleles. In our experience hepatitis C is the most common risk factor as 86% of men with both the familial and sporadic forms of PCT have serologic evidence of HCV. The mechanism by which HCV leads to clinical expression of PCT is not known. We utilized microarray technology to probe the mechanism.
The expression levels of 13,026 unique cDNA clones, purchased from Agilent, were analyzed in liver biopsies samples from 6 HCV positive and 6 HCV negative men with sporadic PCT, and 8 HCV positive patients without PCT. Expression profiles in each group were compared to a pool of 8 normal livers. The microarray format and all protocols are described on the web site http://expression.microslu.washington.edu. A single experiment comparing two samples was done with four replicate arrays using the dye label reverse technique, thus providing mean ratios between the expression levels of each gene in the analyzed sample pair, standard deviations, and P values.
Thirty-seven genes were up-regulated specifically in PCT whether HCV was present or not. These 37 genes had in common an association with macrophage and hepatic stellate cell activation. One-hundred-forty-nine genes were up regulated specifically with HCV whether PCT was present or not. HCV specific genes fell into 5 groups: interferon inducible; proteosome mediated degradation; oxidative stress and lipid metabolism; immune response and chemokines; and genome modifiers. Expression of ALA-S1 was down regulated in all PCT patients and expression of ferrochelatase was up regulated in most. No other genes related to heme biosynthesis, including URO-D, were altered. Expression of heme oxygenase was down regulated in all patients. Expression of iron-related genes was generally unchanged even though all PCT patients had moderate iron loading. All patients with PCT up regulated expression of CYP1A2 whereas HCV alone produced up regulation in some, down regulation in some, and no effect in others. These data indicate a PCT specific response but do not provide a molecular explanation for the role of HCV as a risk factor for the development of PCT. We conclude that alterations in genes other than the synthesis in heme are required to produce the porphyric phenotype.