Endocrine Abstracts

Fibroblasts are important regulators of local inflammatory responses. These responses are further regulated by tissue glucocorticoid levels. Other stromal lineage cells, adipocytes and osteoblasts, express 11beta-hydroxysteroid dehydrogenases (11b-HSDs) which interconvert inactive cortisone and active cortisol. These enzymes are important regulators of local glucocorticoid levels and their expression is regulated by proinflammatory cytokines. We therefore examined expression of 11b-HSDs and their regulation by TNFalpha in primary fibroblasts cultured from a range of human tissues (tonsil, lymph node, spleen, lung, skin, synovium (normal, rheumatoid and osteoarthritic)).
Fibroblasts were generated by outgrowth from donated tissues. Enzyme expression was examined by quantitative RT-PCR with primers for 11b-HSD1 and 2 and GR expression by semi-quantitative RT-PCR. 11b-HSD activity was determined by incubation with 100nM cortisol/cortisone (with tritiated tracer) with conversion quantified by TLC. The effect of 10ng/ml TNFalpha on enzyme expression was determined after 72hr treatments.
11b-HSD1 mRNA was expressed at relatively high levels in fibroblasts from all tissues (n=10). 11b-HSD2 expression was 25 fold less than for 11b-HSD1. Reductase activity (cortisone-cortisol conversion) was present in fibroblasts from all tissues (1.2+/-0.2pmol/mg/hr; mean+/-SE). Dehydrogenase activity was less prominent (0.6+/-0.3pmol/mg/hr).
TNFalpha treatment resulted in a 23 fold (14-37+/-SE; p<0.001) increase in 11b-HSD1 mRNA expression whilst 11b-HSD2 expression was further reduced 4 fold (2-8+/-SE; p<0.05). 11b-HSD1 reductase activity increased substantially (3.8+/-0.8 fold; p<0.05) but dehydrogenase activity was unchanged (1.1+/-0.3 fold) suggesting an independent effect on enzyme directionality. GR expression was unchanged. Interestingly dermal fibroblasts, despite increased 11b-HSD1 mRNA levels with TNFalpha, displayed reduced 11b-HSD1 reductase activity (1.0+/-0.2 vs 0.6+/-0.2pmol/mg/hr; n=4, p<0.05).
Fibroblasts from a range of human tissues express 11b-HSD1 and this activity is predominantly reductase. TNFalpha potently induces this activity in fibroblasts from most, but not all, tissues. Tissue dependent regulation of fibroblastic 11b-HSD1 activity may be a factor in determining tissue specific responses to inflammation.