Insulin but not leptin protects olfactory mucosa from apoptosis

The mammalian olfactory mucosa (OM) is continually renewed throughout life. Owing to their position in the nasal cavity, OM cells are exposed to multiple insults, including high levels of odourants that can induce their death. OM regeneration is therefore essential to maintain olfactory function, and requires the tight control of both cell death and proliferation. Apoptosis has been implicated in OM cell death. Olfaction is one of the senses involved in food intake and depends on individual nutritional status. We have previously reported the influence of hormones related to nutritional status on odour perception and have shown that the OM is a target of insulin and leptin, two hormones known for their anti-apoptotic properties. In the present study, we investigated the potential anti-apoptotic effect of these metabolic hormones on OM cells. Both Odora cells (an olfactive cell line) and OM cells treated with etoposide, a p53 activity inducer, exhibited mitochondrial-dependent apoptosis that was inhibited by the pan-caspase inhibitor zVAD-fmk. Insulin, but not leptin, impaired this apoptotic effect. Insulin addition to the culture medium reduced p53 phosphorylation, caspase-3 and caspase-9 cleavage, and caspase-3 enzymatic activity induced by etoposide. The apoptotic wave observed in the OM after interruption of the neuronal connections between the OM and the olfactory bulb by bulbectomy was impaired by intranasal insulin treatment. These findings suggest that insulin may be involved in OM cellular dynamics, through endocrine and/or paracrine-autocrine effects of circulating or local insulin, respectively.

Fibroblast Growth Factor 1 inhibits p53-dependent apoptosis in PC12 cells

The survival activity of FGF1 and the pro-apoptotic activity of p53 were characterized in vitro and/or in vivo for different types of neurons after different stresses and in different neurodegenerative pathologies. To investigate whether or not FGF1 and p53 pathways interact in neuronal cells, we studied the effect of FGF1 on p53-dependent apoptosis in PC12 cells. We first characterized p53-dependent PC12 cell death induced by etoposide (a DNA damaging agent). We showed that etoposide increased p53 stabilization, phosphorylation (Ser-15), nuclear translocation and transcriptional activity. In particular, p53 promoted mdm2, p21, puma and noxa expression in PC12 cells. The activation of p53 initiated a classical mitochondrial apoptosis process associated with caspases activation and nuclear degradation. We demonstrated that FGF1 protected PC12 cells from p53-dependent apoptosis upstream from mitochondrial and nuclear events. FGF1 inhibited etoposide-induced p53 phosphorylation, stabilization, nuclear translocation and transcriptional activity. This study presents the first evidence that FGF1 and p53 pathways interact in neuronal cells, and that FGF1 protects neuronal cells from p53-dependent apoptosis, suggesting that alterations of FGF1/p53 crosstalk could be involved in a large range of neurons and in neurological disorders.