TGF-ß1 protection against Aß1-42-induced hippocampal neuronal inflammation and apoptosis by TßR-I.

Alzheimer's disease (AD), the most common chronic neurodegenerative disease, is pathologically characterized by the formation of neurofibrillary tangles because of hyperphosphorylation of tau protein and extracellular deposits of amyloid-ß (Aß) protein termed senile plaques. Recent studies indicate that neuronal apoptosis caused by chronic neuroinflammation is one of the important pathogenesis of AD. Transforming growth factor (TGF)-ß1 is a pleiotropic cytokine with immunosuppressive and anti-inflammatory properties. However, it is poorly known whether the anti-inflammatory property of TGF-ß1 is involved in a neuroprotection in AD. Here, an AD cell model of hippocampal neurons induced by Aß1-42 was used to show an anti-inflammatory and neuroprotective effect of TGF-ß1 through its receptor transforming growth factor-ß receptor type I (TßR-I). As expected, Aß1-42-induced an upregulation in neuronal expression of amyloid precursor protein (APP), tumor necrosis factor-α, cyclooxygenase-2, Bax, cleaved caspase-3, and cleaved caspase-9, and a downregulation in the expression of Bcl-2, as well as an increase in the number of NeuN/terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) double-positive cells. TGF-ß1 pretreatment reduced the Aß1-42-induced effects of upregulating APP, tumor necrosis factor-α, Bax, cleaved caspase-3 and cleaved caspase-9, and downregulating Bcl-2, in addition to increasing NeuNTUNEL cell number. TßR-I expression in hippocampal neurons was downregulated by Aß1-42 exposure, but upregulated by TGF-ß1 pretreatment. Silencing of the TßR-I gene in the neurons abolished the anti-inflammatory and antiapoptotic effects of TGF-ß1 in the Aß1-42-induced AD cell model. These findings suggest that TGF-ß1 protects neurons against Aß1-42-induced neuronal inflammation and apoptosis by activation of TßR-I.

[Effects of TGF-ß1 on the expression and secretion of cytokines induced by Aß1-42 in hippocampal neuron and microglia co-cultures].

OBJECTIVE: To investigate the neuroprotective effects of transforming growth factor beta 1(TGF-ß1) on the expression and secretion of cytokines induced by Aß1-42 in hippocampal neurons and microglial co-cultures. METHODS: Hippocampal neurons and microglia obtained from SD rat were co-cultured. TGF-ß1 was applied on day 5 after the neurons and microglia co-cultures were incubated at the concentrations of 5 or 20 ng/ml, Aß1-42 was added 1 h following TGF-ß1 application at a concentration of 5 µmol/L. They were incubated for 72 h and then assessed for further studies. Western blot analyses were employed to examine the expression of inducible nitric oxide synthase (iNOS); Real-time PCR and ELISA were used to detect the mRNA expression and secretion of tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß) and insulin-like growth factor-1 (IGF-1). RESULTS: In the hippocampal neuron-microglia co-cultures, Aß1-42 induced upregulation of iNOS, TNF-α and IL-1ß, downregulation of IGF-1. TGF-ß1 pretreatment ameliorated the pro-inflammatory effects caused by Aß1-42. CONCLUSIONS: TGF-ß1 significantly inhibits the increase in inflammatory cytokines and the decrease in neurotrophic factor which are caused by Aß1-42-induced microglia activation.