Glucocorticoids Enhance Insulin Sensitivity in Human Hepatocytes

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SAT 1-25-Glucocorticoid Actions & HPA Axis
Basic
Saturday, June 15, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SAT-11
Maryam Nasiri*1, Iwona Bujalska2, Paul M Stewart1, Laura Louise Gathercole3 and Jeremy W Tomlinson2
1University of Birmingham, Birmingham, United Kingdom, 2University of Birmingham, United Kingdom, 3Univ of Birmingham, Birmingham, United Kingdom
Patients with glucocorticoids (GC) excess develop central obesity, insulin resistance and hepatic steatosis in up to 20% of cases. Current dogma suggests that GCs cause insulin resistance in all tissues. However, we have previously demonstrated that GCs induce insulin sensitisation in adipose tissue in vitro, whilst causing insulin resistance in skeletal muscle. In rodent hepatocytes, GCs enhance insulin stimulated lipogenesis but studies in human hepatocytes have not been performed and the cellular mechanisms underpinning these observations have not been determined.

Cryopreserved human hepatocytes were purchased from Celsis in Vitro Technologies (Baltimore, USA). All donors were healthy, male non-diabetic, on no regular medications. Cells were incubated with variable doses of cortisol (0-1000 nM) for 24h in the presence and absence of insulin (5 nM). Insulin signalling gene expression levels were quantified by real-time PCR and western blotting was performed to determine total and phospho PKB/akt protein expression levels. De novo lipogenesis (DNL) was measured by 1-[14C] acetate incorporation in triglyceride.

GC receptor, IRS1/2, Insulin receptor, AKT1/2, ACC1/2, CPT1, DGAT and FAS were all expressed in primary cultures. Incubation with cortisol alone (0-1000 nM) or in combination with insulin did not alter expression of insulin signalling, steroid hormone regulatory genes or those involved in lipid metabolism. However, whilst cortisol treatment did not alter total PKB/akt protein levels, phosphorylation of PKB/akt at serine 473 after insulin stimulation increased following cortisol pre-treatment in a dose dependant manner (1.23-fold [100nM], 1.68-fold [250nM], 2.44-fold [1000nM] vs. control n=4 p<0.05).

Insulin alone (5nM, 24h) had a modest impact upon acetate incorporation into lipid (129.1±13.0%), however, co-incubation with cortisol significantly enhanced insulin stimulated lipogenesis (43.9±12.7% [250nM], 66.13±9.8% [1000nM] vs. control (23.61±10.7%), p<0.05).

We have demonstrated that in primary human hepatocytes GC treatment enhances insulin signalling through increased serine phosphorylation of PKB/akt and that GCs and insulin can act synergistically to promote lipogenesis. Whilst translation to the clinical setting is crucially important, this mechanism may be fundamental in explaining the interaction between GCs and insulin to drive lipogenesis. Furthermore, this may contribute to the pathogenesis of non-alcoholic fatty liver disease with GC excess.

Nothing to Disclose: MN, IB, PMS, LLG, JWT

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm