Neuronal seipin knockout facilitates Aβ-induced neuroinflammation and neurotoxicity via reduction of PPARγ in hippocampus of mouse.

BACKGROUND: A characteristic phenotype of congenital generalized lipodystrophy 2 (CGL2) that is caused by loss-of-function of seipin gene is mental retardation. Seipin is highly expressed in hippocampal pyramidal cells and astrocytes. Neuronal knockout of seipin in mice (seipin-KO mice) reduces the hippocampal peroxisome proliferator-activated receptor gamma (PPARγ) level without the loss of pyramidal cells. The down-regulation of PPARγ has gained increasing attention in neuroinflammation of Alzheimer's disease (AD). Thus, the present study focused on exploring the influence of seipin depletion on β-amyloid (Aβ)-induced neuroinflammation and Aβ neurotoxicity.

METHODS: Adult male seipin-KO mice were treated with a single intracerebroventricular (i.c.v.) injection of Aβ25-35 (1.2 nmol/mouse) or Aβ1-42 (0.1 nmol/mouse), generally a non-neurotoxic dose in wild-type (WT) mice. Spatial cognitive behaviors were assessed by Morris water maze and Y-maze tests, and hippocampal CA1 pyramidal cells and inflammatory responses were examined.

RESULTS: The Aβ25-35/1-42 injection in the seipin-KO mice caused approximately 30-35 % death of pyramidal cells and production of Hoechst-positive cells with the impairment of spatial memory. In comparison with the WT mice, the number of astrocytes and microglia in the seipin-KO mice had no significant difference, whereas the levels of IL-6 and TNF-α were slightly increased. Similarly, the Aβ25-35/1-42 injection in the seipin-KO mice rather than the WT mice could stimulate the activation of astrocytes or microglia and further elevated the levels of IL-6 and TNF-α. Treatment of the seipin-KO mice with the PPARγ agonist rosiglitazone (rosi) could prevent Aβ25-35/1-42-induced neuroinflammation and neurotoxicity, which was blocked by the PPARγ antagonist GW9962. In the seipin-KO mice, the level of glycogen synthase kinase-3β (GSK3β) phosphorylation at Tyr216 was elevated, while at Ser9, it was reduced compared to the WT mice, which were corrected by the rosi treatment but were unaffected by the Aβ25-35 injection.

CONCLUSIONS: Seipin deficiency in astrocytes increases GSK3β activity and levels of IL-6 and TNF-α through reducing PPARγ, which can facilitate Aβ25-35/1-42-induced neuroinflammation to cause the death of neuronal cells and cognitive deficits.