Related Experiment Videos
Elevated glucose concentrations inhibit DNA synthesis and expression of c-myc in cultured hepatocytes
O F Dajani1, M Refsnes, T K Guren
1Department of Pharmacology, Faculty of Medicine, University of Oslo, Blindern, Norway.
Abstract:
Glucose depressed DNA synthesis in rat hepatocytes in primary culture. As compared to controls cultured with 5.6 mM glucose, maximal (> or = 75%) inhibition was obtained at 20-30 mM, and half-maximal effect at 10-15 mM. Comparison of D- and L-glucose showed that the effect was specific for the D-form. Maximal inhibition required the presence of glucose during the first 24 hours of culture. The expression of the c-myc gene was reduced when the hepatocytes were cultured in the presence of elevated glucose. The responses to epidermal growth factor, insulin and vasopressin, in terms of percentual stimulation of DNA synthesis, were qualitatively similar at 5.6 and 16.8 mM glucose, while glucagon stimulated more strongly when the glucose concentration was increased; glucagon at concentrations > or = 1 nM reversed the inhibition by glucose. 8-Br-cAMP mimicked the effect of glucagon. These results suggest that an increase in the level of glucose depresses hepatocyte DNA synthesis. The effect is associated with lowered expression of the c-myc gene and is counteracted by cAMP.
Insights
High glucose levels inhibit rat hepatocyte DNA synthesis, specifically the D-form of glucose, by reducing c-myc gene expression. Cyclic AMP (cAMP) can counteract this glucose-induced inhibition.
Area of Science:
- Hepatocyte biology
- Molecular endocrinology
- Cellular metabolism
Background:
- Glucose is a primary energy source for cells.
- Hepatocytes play a crucial role in glucose homeostasis.
- Regulation of hepatocyte DNA synthesis is vital for liver function and regeneration.
Purpose of the Study:
- To investigate the effect of elevated glucose concentrations on DNA synthesis in primary rat hepatocytes.
- To explore the molecular mechanisms underlying glucose-mediated inhibition of hepatocyte proliferation.
- To examine the role of specific signaling pathways, including cyclic AMP (cAMP), in modulating this response.
Main Methods:
- Primary rat hepatocytes were cultured in media with varying glucose concentrations (5.6 mM to 30 mM).
- DNA synthesis was measured using established assays.
- Gene expression, specifically for the c-myc gene, was analyzed.
- Hormonal responses (epidermal growth factor, insulin, vasopressin, glucagon) and the effect of 8-Br-cAMP were assessed.
Main Results:
- Elevated glucose (10-30 mM) significantly inhibited hepatocyte DNA synthesis in a dose-dependent manner, with D-glucose being the active form.
- Maximal inhibition of DNA synthesis occurred when glucose was present during the initial 24 hours of culture.
- Reduced c-myc gene expression was observed under high glucose conditions.
- Glucagon and 8-Br-cAMP counteracted the inhibitory effect of glucose on DNA synthesis.
Conclusions:
- Increased glucose levels suppress hepatocyte DNA synthesis through a mechanism involving decreased c-myc gene expression.
- The inhibitory effect of high glucose is specific to the D-isomer and requires initial exposure.
- The cyclic AMP (cAMP) signaling pathway plays a critical role in reversing glucose-induced suppression of hepatocyte proliferation.