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Updated: Apr 19, 2026
Measurement of Fatty Acid β-Oxidation in a Suspension of Freshly Isolated Mouse Hepatocytes
Published on: September 9, 2021
Effect of NAD on PARP-mediated insulin sensitivity in oleic acid treated hepatocytes
1The Key Laboratory of Geriatrics, Beijing Hospital & Beijing Institute of Geriatrics, Ministry of Health, China.
Abstract:
High serum free fatty acids levels are associated with the development of insulin resistance in type 2 diabetes; however, the precise mechanisms underlying this lipid toxicity are unclear. To investigate whether PARP1 activation and NAD depletion are involved in the impairment of insulin sensitivity associated with lipotoxicity, HepG2 cells were cultured with 500 μM oleic acid for 48 h. Oleic acid-treated cells exhibited increased ROS generation, lipid accumulation and PARP1 activation. Treatment with the PARP1 inhibitor PJ34 and transfection with PARP1 small interfering RNA both prevented the oleic acid-induced impairment of the insulin signaling pathway. Furthermore, treatment with PJ34 reversed the oleic acid-induced decrease in intracellular NAD concentration, while exogenous NAD protected cells against oleic acid-induced insulin insensitivity. Combined NAD and PJ34 administration did not enhance the effects obtained by treatment with either NAD or PJ34 alone. Interestingly, when cells were treated with the SIRT1 inhibitor EX527, the protective effects of PJ34 and NAD treatment were diminished. Taken together, these data suggest that NAD depletion by PARP1 activation is essential for the modulation of insulin sensitivity in oleic acid-induced lipotoxicity.
Insights
High free fatty acids impair insulin sensitivity via PARP1 activation and NAD depletion. Inhibiting PARP1 or supplementing NAD restores insulin signaling in lipotoxicity, highlighting a key mechanism in type 2 diabetes.
Area of Science:
- Biochemistry
- Cell Biology
- Endocrinology
Background:
- High serum free fatty acids are linked to insulin resistance in type 2 diabetes.
- The exact molecular mechanisms of lipotoxicity-induced insulin insensitivity remain unclear.
Purpose of the Study:
- To investigate the role of Poly(ADP-ribose) polymerase 1 (PARP1) activation and NAD depletion in impaired insulin sensitivity due to lipotoxicity.
- To explore the therapeutic potential of targeting PARP1 and NAD levels.
Main Methods:
- HepG2 cells were treated with oleic acid to induce lipotoxicity.
- PARP1 activation, NAD levels, and insulin signaling pathway were assessed.
- Cells were treated with a PARP1 inhibitor (PJ34), PARP1 siRNA, NAD, or a SIRT1 inhibitor (EX527).
Main Results:
- Oleic acid treatment increased reactive oxygen species (ROS), lipid accumulation, and PARP1 activation.
- PARP1 inhibition or knockdown prevented oleic acid-induced insulin signaling impairment.
- PJ34 treatment reversed NAD depletion, and exogenous NAD protected against insulin insensitivity.
- SIRT1 inhibition reduced the protective effects of PJ34 and NAD.
Conclusions:
- PARP1 activation and subsequent NAD depletion are crucial mediators of insulin insensitivity in oleic acid-induced lipotoxicity.
- Targeting PARP1 and restoring NAD levels may offer therapeutic strategies for type 2 diabetes with lipotoxicity.
