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Mouse 3T3-L1 cells acquire resistance against oxidative stress as the adipocytes differentiate via the transcription
Takayuki Kojima1, Takanari Norose, Keita Tsuchiya
1Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
Abstract:
Repression of excessive increase and enlargement of adipocytes that is closely associated with obesity is effective in the prevention and treatment of metabolic syndrome. Generally, apoptosis is induced in cells via a wide variety of intracellular or extracellular substances, and recently, it has been suggested that the FoxO subfamily is involved in the induction of apoptosis. We aimed to elucidate the mechanism of FoxO-mediated apoptosis-induction in the adipocytes under the reactive oxygen species (ROS) stimulus. The treatment of differentiated and undifferentiated 3T3-L1 cells with glucose oxidase (GOD), an enzyme that generates H(2)O(2), induced apoptosis and led to the accumulation of 8-OHdG. Apoptosis analysis revealed that GOD treatment induced apoptosis in differentiated 3T3-L1 cells less efficiently than in undifferentiated preadipocytes. GOD remarkably increased the levels of Bad, Bax, and Bim-the genes that are actively involved in cell apoptosis. GOD treatment also increased the expression of FoxO3a mRNA and protein. The introduction of FoxO3a-siRNA into 3T3-L1 cells suppressed the oxidative stress-induced expression of Bim mRNA, as well as the GOD-induced apoptosis. Furthermore, the expression of MnSOD, Cu/ZnSOD, and catalase, as well as of FoxO, increased significantly along with the progression of adipocyte differentiation. These results indicated that ROS-induced apoptosis in undifferentiated 3T3-L1 cells via the expression of FoxO3a, whereas FoxO expression suppressed the ROS-induced apoptosis in differentiated 3T3-L1 cells via the expression of ROS-scavenging enzymes.
Insights
Reactive oxygen species (ROS) induce apoptosis in preadipocytes via FoxO3a, but suppress it in differentiated adipocytes. FoxO proteins regulate apoptosis and antioxidant enzymes during adipocyte differentiation, impacting metabolic syndrome.
Area of Science:
- Cell Biology
- Metabolic Syndrome Research
- Oxidative Stress Studies
Background:
- Obesity and metabolic syndrome are linked to adipocyte proliferation.
- Apoptosis (programmed cell death) can be induced by various stimuli.
- The FoxO subfamily of transcription factors is implicated in apoptosis regulation.
Purpose of the Study:
- To investigate the mechanism of FoxO-mediated apoptosis induction in adipocytes under reactive oxygen species (ROS) stimulus.
- To understand the role of FoxO in adipocyte apoptosis and differentiation.
Main Methods:
- 3T3-L1 cells (differentiated and undifferentiated) were treated with glucose oxidase (GOD) to generate hydrogen peroxide (H2O2).
- Apoptosis, gene expression (Bad, Bax, Bim, FoxO3a, MnSOD, Cu/ZnSOD, catalase), and 8-OHdG accumulation were analyzed.
- FoxO3a-siRNA was used to suppress FoxO3a expression.
Main Results:
- GOD treatment induced apoptosis and 8-OHdG accumulation in 3T3-L1 cells.
- Apoptosis was less efficient in differentiated adipocytes compared to undifferentiated preadipocytes.
- GOD increased apoptosis-related genes (Bad, Bax, Bim) and FoxO3a expression.
- FoxO3a-siRNA reduced Bim expression and GOD-induced apoptosis.
- FoxO expression and ROS-scavenging enzymes (MnSOD, Cu/ZnSOD, catalase) increased with adipocyte differentiation.
Conclusions:
- ROS induce apoptosis in undifferentiated adipocytes through FoxO3a-mediated Bim expression.
- In differentiated adipocytes, FoxO expression suppresses ROS-induced apoptosis by upregulating antioxidant enzymes.
- FoxO transcription factors play a dual role in adipocyte apoptosis depending on differentiation status, influencing metabolic syndrome.
