Related Experiment Videos
Okadaic acid decreases the leptin content in isolated mouse fat pads
Hiroko Mitsuishi1, Aya Yoshida, Toshio Motoyashiki
1Faculty of Pharmacy and Pharmaceutical Sciences, Fukuyama University, 1 Gakuen-chou, Fukuyama, Hiroshima 729-0292, Japan.
Abstract:
Okadaic acid (OA) decreased the leptin content in isolated mouse fat pads in a time and dose-dependent manner. MG-132, a membrane-permeable proteasome inhibitor, prevented the decrease by OA, suggesting the involvement of proteasome in the OA action. No significant decrease in the incorporation of [(3)H]leucine into leptin was observed with a 4-h incubation, although the amino acid incorporation was stimulated by insulin and decreased by cycloheximide. These results suggest that the OA action is independent of the decrease in protein synthesis. The proteasome fraction, which had been separated from the fat pads pretreated with OA, enhanced the proteolytic degradation of exogenous [(125)I]leptin in the presence of an ATP-regenerating system together with an ubiquitination system. No enhancement of hydrolytic activity against Suc-Leu-Leu-Val-Tyr-AMC was detected in the OA-treated proteasome fraction, suggesting that the activation of proteasome is not involved in the OA action. The OA-treated proteasome fraction had decreased phosphatase activity against p-nitrophenyl phosphate, suggesting that OA entering the cells may exert its action by preventing dephosphorylation of key molecules. OA may reduce the intracellular leptin content through the increased ubiquitination and proteolytic turnover of leptin by the proteasome, based on the decreased phosphatase activity.
Insights
Okadaic acid (OA) reduces leptin levels by promoting its degradation via the proteasome pathway. This mechanism involves increased ubiquitination and proteolytic turnover, independent of protein synthesis inhibition.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Endocrinology
Background:
- Leptin is a key hormone regulating energy balance and metabolism.
- Okadaic acid (OA) is a potent protein phosphatase inhibitor.
- The precise mechanisms by which OA affects leptin levels are not fully understood.
Purpose of the Study:
- To investigate the effect of Okadaic acid (OA) on leptin content in isolated mouse fat pads.
- To elucidate the role of the proteasome pathway in OA-induced changes in leptin levels.
- To determine if OA affects protein synthesis or degradation pathways related to leptin.
Main Methods:
- Incubation of isolated mouse fat pads with varying concentrations and durations of OA.
- Treatment with MG-132, a proteasome inhibitor, to assess proteasome involvement.
- Measurement of [(3)H]leucine incorporation to evaluate protein synthesis.
- Analysis of proteasome activity and leptin degradation using exogenous [(125)I]leptin.
- Assay of phosphatase activity in OA-treated proteasome fractions.
Main Results:
- Okadaic acid (OA) significantly decreased leptin content in a time- and dose-dependent manner.
- The proteasome inhibitor MG-132 blocked OA-induced leptin reduction, indicating proteasome involvement.
- OA did not affect [(3)H]leucine incorporation into leptin, suggesting protein synthesis was not inhibited.
- OA treatment enhanced the proteolytic degradation of leptin by the proteasome fraction.
- OA-treated proteasome fractions exhibited reduced phosphatase activity.
Conclusions:
- Okadaic acid (OA) reduces intracellular leptin content by increasing its ubiquitination and proteasomal degradation.
- The OA-mediated decrease in leptin is independent of alterations in protein synthesis.
- OA likely exerts its effect by inhibiting key phosphatases, leading to enhanced leptin turnover.