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Leukemia inhibitory factor (LIF) is a neuroprotective cytokine that is necessary for the normal development of astrocytes. Oxygen-glucose deprivation (OGD) can induce astrocyte proliferation by increasing hypoxia-inducible factor alpha (HIF- 1a) and vascular endothelial growth factor (VEGF). Here, we studied whether LIF affects the proliferation of cultured primary rat astrocytes under OGD conditions by measuring EdU incorporation into astrocyte DNA and the expression of proliferating cell nuclear antigen (PCNA) mRNA and protein. Our findings show that low concentrations of LIF (5 and 10 ng/mL) significantly decreased EdU incorporation and downregulated the expression of PCNA mRNA and PCNA protein in astrocytes subjected to OGD. A low concentration of LIF (10 ng/mL) clearly inhibited astrocyte proliferation induced by OGD, while a higher concentration (50 ng/mL) had no effect. To investigate the mechanism of this inhibition by LIF (10 ng/ mL), the expression of 3 related genes (LIF receptor, HIF-1a, and VEGF) was assessed using real-time PCR; VEGF protein expression was measured by Western blot. Our results indicate that LIFR mRNA was downregulated in astrocytes subjected to OGD. Interestingly, treatment with LIF further reduced LIFR mRNA expression in these cells. LIF treatment also decreased the expression of HIF-1a mRNA, VEGF mRNA, and VEGF protein induced by OGD. Low concentrations of LIF were observed to inhibit astrocyte proliferation induced by OGD.
This study was carried out to optimize a modified droplet-vitrification procedure for the cryopreservation of shoot tips from different carnation genotypes. The best procedure was developed by applying orthogonal tests to the experimental data and by further investigation of the effects on the regrowth percentage. It consisted in preculturing shoot tips in liquid Murashige and Skoog (MS) medium with 0.3 M sucrose for 2 days, pretreating them in liquid MS medium with 5 % Dimethyl sulfoxide +5 % glycerol + 0.3 M sucrose for 10 min, osmoprotecting in Loading solution for 20 min at 25°C, cryoprotecting with Plant vitrification solution No.2 (PVS2) for 60 min at 0°C, transferring in drops of fresh PVS2 over aluminum strips and finally storing them in Liquid nitrogen. With the application of the optimized protocol, four carnation cultivars (‘Master’, ‘Calibra’, ‘Lamour’ and ‘Ofcar’) achieved regrowth percentage after cryopreservation ranging from 41 to 73 %. Ultrastructural observations investigated by using transmission electron microscopy showed that the cells encountered the stress during cryopreservation and the main damages occurred during the dehydration step. For surviving cells, the most of the damaged cells could be repaired after recovery growth. This modified protocol will aid in the long-term conservation of carnation germplasm and the ultrastructural studies will benefit for understanding the damage and recovery of the cells during cryopreservation.
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