cDNA microarray analysis of gene expression profiles in human placenta: up-regulation of the transcript encoding muscle subunit of glycogen phosphorylase in preeclampsia.

Objective: Third-trimester human placentas from normal and preeclamptic pregnancies were evaluated for possible changes in gene expression patterns by microarray analysis.

Methods: Placentas from four normal pregnancies and four pregnancies complicated by preeclampsia were studied. In a preliminary effort to identify possible differences between the two groups, complementary DNA (cDNA) probes were prepared from pooled total RNA by reverse transcription in the presence of (33)P-dCTP. After hybridization to human GeneFilter cDNA microarrays (GF211; Research Genetics, Huntsville, AL), 319 positive signals were detected above background out of a possible 4131 human cDNAs spotted on the filters.

Results: Ten most highly expressed mRNA species, ten most up-regulated, and ten most down-regulated genes in placentas from both groups of patients were identified for future studies. Of the 319 positive hybridizations, one transcript was clearly elevated in preeclamptic pregnancy. This cDNA encodes the muscle subtype of glycogen phosphorylase (GP-M) and was increased more than 2.8-fold (P <.05) in the preeclamptic placentas. In contrast, cDNA for glycogen synthase (muscle and liver isoforms) was not significantly increased, being near the limits of detection. The preeclampsia-induced increase of placental GP-M mRNA expression (approximately 3.5-fold) was confirmed by northern blot analysis.

Conclusion: We conclude that microarray analysis can detect trends in mRNA and gene expression in placentas from normal and preeclamptic pregnancies that may be further studied in a more targeted fashion. We found that placental GP-M mRNA level is up-regulated in preeclampsia, which is consistent with previous reports of increased glycogen phosphorylase activity, and we suggest that it may be largely regulated at the level of transcription. Further studies may determine whether such up-regulation might be a response to hypoxia.