TGF-β1 Protects Hippocampal Neurons Against Degeneration Caused by Transient Global Ischemia: Dose-Response Relationship and Potential Neuroprotective Mechanisms

Abstract

Background and Purpose Transforming growth factor-β1 (TGF-β1) has been shown to rescue cultured neurons from excitotoxic and hypoxic cell death and to reduce infarct size after focal cerebral ischemia in mice and rabbits. The present study investigated the effects of TGF-β1 in a different pathophysiological setting and the delayed neuronal death of hippocampal pyramidal cells after transient global ischemia in rats, and evaluated the potential mechanisms of the neuroprotective activity of TGF-β1. Methods Transient forebrain ischemia was induced in male adult Wistar rats with bilateral occlusion of both common carotid arteries combined with systemic hypotension for 10 minutes. Seven days after ischemia, brains were perfusion-fixed and stained for histological evaluation. TGF-β1 or vehicle was injected intracerebroventricularly (ICV; 0.5, 4, and 50 ng) or intrahippocampally (4 ng) 1 hour before ischemia. For in vitro studies, hippocampal neurons were derived from E17 rat embryos and cultured for 10 to 14 days. Cells were exposed to (1) S -nitrosocysteine (SNOC; 30 μmol/L) to induce nitric oxide–induced oxidative injury and (2) staurosporine (0.03 μmol/L) to induce apoptotic cell death. Results Transient forebrain ischemia caused extensive degeneration of CA1 hippocampal pyramidal cells in vehicle-treated control animals. Ischemic injury was not significantly reduced after ICV administration of 0.5 ng TGF-β1 (71±7% damaged neurons versus 84±3% in vehicle-treated controls; n=9 and 11, respectively; P =.07, Mann-Whitney U test). Administration of 4 ng TGF-β1 reduced the percentage of damaged CA1 pyramidal cells from 71±10% in controls to 52±7% in TGF-β1–treated animals (n=11 and 12, respectively; P =.04). TGF-β1 (4 ng) also produced significant protection when injected directly into the hippocampal tissue. In contrast, ICV administration of 50 ng TGF-β1 failed to show a protective effect in two separate sets of experiments. In vitro, a 24-hour pretreatment of the cultured hippocampal neurons with TGF-β1 (0.1 to 10 ng/mL) significantly inhibited both nitric oxide and staurosporine neurotoxicity. Posttreatment with TGF-β1 (10 ng/mL) also inhibited staurosporine neurotoxicity but actually potentiated nitric oxide–induced neuronal injury. Conclusions We demonstrated that TGF-β1 in a surprisingly low dose range has the capacity to reduce injury to CA1 hippocampal neurons caused by transient global ischemia in rats. This protective action could well be associated with the antioxidative and antiapoptotic effects of TGF-β1 demonstrated in vitro.