LINK: jme.endocrinology-journals.org/c … l/33/2/429
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Effects of dihydrotestosterone on adipose tissue measured by serial analysis of gene expression
Intra-abdominal fat accumulation is related to several diseases, especially diabetes and heart disease. Molecular mechanisms associated with this independent risk factor are not well established. Through the serial analysis of gene expression (SAGE) strategy, we have studied the transcriptomic effects of castration and dihydrotestosterone (DHT) in retroperitoneal adipose tissue of C57BL6 male mice. Approximately 50 000 SAGE tags were isolated in intact and gonadectomized mice, as well as 3 and 24 h after DHT administration. Transcripts involved in energy metabolism, such as glyceraldehyde-3-phosphate dehydrogenase, malic enzyme supernatant, fatty acid synthase, lipoprotein lipase, hormone-sensitive lipase and monoglyceride lipase, were upregulated by DHT. Transcripts involved in adipogenesis, and cell cycle and cell shape organization, such as DDX5, C/EBP, cyclin I, procollagen types I, III, IV, V and VI, SPARC and matrix metalloproteinase 2, were upregulated by DHT. Cell defense, division and signaling, protein expression and many novel transcripts were regulated by castration and DHT. The present results provide global genomic evidence for a stimulation of glycolysis, fatty acids and triacylglycerol production, lipolysis and cell shape reorganization, as well as cell proliferation and differentiation, by DHT. The novel transcripts regulated by DHT may contribute to identify new mechanisms involved in the action of sex hormones and their potential role in obesity.
Genes involved in the glycolysis pathway, such as the aldolase 1 A isoform, enolase 1 alpha non-neuron and glyceraldehyde-3-phosphate dehydrogenase (Table 2), as well as transcripts implicated in de novo fatty acid synthesis, such as ATP citrate lyase and fatty acid synthase, were upregulated by DHT (Table 2). Furthermore, two transcripts of the tri-acylglycerol synthesis pathway, namely, glycerol-3-phosphate dehydrogenase 1 (soluble) (GPD1) and diacylglycerol O-acyltransferase (DGAT) 1, were upregulated (Table 2). Genes involved in lipolysis, such as hormone-sensitive lipase, were also upregulated by DHT. Apolipoprotein E and low-density lipoprotein receptor-related protein 1 gene expression was increased by DHT, whereas a switch of transcript species of lipoprotein lipase (LPL) and monoglyceride lipase was observed (Table 2).
Transcripts implicated in energy metabolism (Table 3) as well as in amino-acid metabolism, nucleotide metabolism, transport metabolism, protein modification and general metabolism (Table 4), displayed numerous patterns of gene expression after androgen modulation. Cell division was also affected, since almost all the differentially expressed genes related to cell cycle, including cyclin I, and the genes associated with apoptosis, such as fat-specific gene 27, were upregulated by DHT (Table 5).
While DHT administration affected the expression of hundreds of genes, 7 days of gonadectomy affected only a few. In fact, only 13 classified transcripts were significantly differentially expressed between the intact and the GDX groups. Several of them, such as NADH dehydrogenase subunit 4, pheromone receptor V3R4 and three novel transcripts, showed an inverse pattern of expression in comparing the effect of castration and DHT injection. The tag CATG ATTTTCAGTTT, classified as a novel transcript, displayed a very sharp regulation by androgen modulation. The expression level of this tag changed from 7 in intact to 136 in GDX, falling back to 7 in DHT3h and rising to 115 in DHT24h. On the other hand, the expression of protamine 2, a transcript associated with chromatin condensation in sperm (Aoki & Carrell 2003), could never be restored after castration. This gene may be a target of testosterone, which may have different effects from DHT on gene expression.
Several HRE possibilities were found in the promoter of the significantly differentially expressed transcripts, many of them being included in the 500 bp upstream region of the transcription initiation start. Since the occurrence of a 6 bp sequence by chance alone is equal to once each 4096 pb, this finding reinforces the idea that these genes are potentially regulated by DHT.
In conclusion, the present data suggest that the administration of DHT to GDX male mice promotes processes involved in glycolysis, fatty acid and triacylglycerol production, lipolysis and cell shape reorganization, as well as cell proliferation and differentiation in retroperitoneal adipose tissue. Moreover, the steroid hormone affected almost all aspects of cell function by modulating hundreds of transcripts. In addition, many of those correspond to novel transcripts.