Nerve growth factor pretreatment against glutamate-induced hippocampal neuronal injury Action mechanism of phosphatase and tensin homologue deleted on chromosome 10

BACKGROUND： Nerve growth factor （NGF） attenuates glutamate-induced injury to hippocampal neurons, and the human tumor suppressor gene phosphatase and tensin homologue deleted on chromosome 10 （PTEN） promotes neuronal apoptosis. However, effects of PTEN in NGF-mediated neuroprotection against glutamate excitotoxicity remain poorly understood. OBJECTIVE： To investigate the relationship between NGF inhibition of glutamate-induced injury and PTEN. DESIGN, TIME AND SE＇I＇rlNG： The randomized, controlled, in vitro study was performed at the Department of Pathophysiology, Medical School of Nantong University, China from October 2007 to March 2008. MATERIALS： Glutamate, NGF, 4, 6-diamidino-2-phenyl-indolediacetate, 3-[4, 5-dimethylthiazol-2-yl]- 2, 5-diphenyl tetrazoliumbromide （M-I-F）, and lactate dehydrogenase kit （Sigma, USA）, fluorescence microscope and inverted phase contrast microscope （Olympus, Japan） were used in this study. METHODS： Hippocampal neurons were obtained from newborn （〈 24 hours） Sprague Dawley rats and cultured for 7 days. The control group was not treated with any intervention factor, the glutamate group was treated with glutamate （0.2 mmol/L）, and NGF groups were treated with NGF （10, 50, 100, and 200 μg/L, respectively） prior to glutamate treatment. MAIN OUTCOME MEASURES： The MTT and lactate dehydrogenase assays were applied to evaluate viability of hippocampal neurons. Morphological changes in hippocampal neurons were observed using an inverted phase-contrast microscope, and neuronal apoptosis was detected by 4, 6-diamidino-2- phenyl-indolediacetate staining. PTEN mRNA and protein expression were measured by reverse transcription-polymerase chain reaction and Western blot analysis, respectively. RESULTS： Glutamate （0.2 mmol/L） induced significantly decreased neuronal viability and greater lactate dehydrogenase efflux compared with the control group （P 〈 0.01）. However, compared with the glutamate group, cell viability significantly increased and lactate dehydrogenase efflux decreased in the NGF group with increasing NGF concentrations （P 〈 0.05 or P 〈 0.01）. The apoptotic ratio and PTEN mRNA and protein expression decreased in the NGF group compared with the glutamate group （P 〈 0.01）. CONCLUSION： Pretreatment with NGF exerted neuroprotective effects against glutamate-induced injury, partially through inhibition of PTEN expression and neuronal apoptosis.

Increased susceptibility of aging gastric mucosa to injury:The mechanisms and clinical implications

This review updates the current views on aging gastric mucosa and the mechanisms of its increased susceptibility to injury. Experimental and clinical studies indicate that gastric mucosa of aging individuals-“aging gastropathy”-has prominent structural and functional abnormalities vs young gastric mucosa. Some of these abnormalities include a partial atrophy of gastric glands, impaired mucosal defense (reduced bicarbonate and prostaglandin generation, decreased sensory innervation), increased susceptibility to injury by a variety of damaging agents such as ethanol, aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs), impaired healing of injury and reduced therapeutic efficacy of ulcer-healing drugs. Detailed analysis of the above changes indicates that the following events occur in aging gastric mucosa: reduced mucosal blood flow and impaired oxygen delivery cause hypoxia, which leads to activation of the early growth response-1 (egr-1) transcription factor. Activation of egr-1, in turn, upregulates the dual specificity phosphatase, phosphatase and tensin homologue deleted on chromosome ten (PTEN) resulting in activation of pro-apoptotic caspase-3 and caspase-9 and reduced expression of the anti-apoptosis protein, survivin. The imbalance between pro- and anti-apoptosis mediators results in increased apoptosis and increased susceptibility to injury. This paradigm has human relevance since increased expression of PTEN and reduced expression of survivin were demonstrated in gastric mucosa of aging individuals. Other potential mechanisms operating in aging gastric mucosa include reduced telomerase activity, increase in replicative cellular senescence, and reduced expression of vascular endothelial growth factor and importin-α-a nuclear transport protein essential for transport of transcription factors to nucleus. Aging gastropathy is an important and clinically relevant issue because of: (1) an aging world population due to prolonged life span; (2) older patients have much greater risk of gastroduodenal ulcers and gastrointestinal complications (e.g., NSAIDs-induced gastric injury) than younger patients; and (3) increased susceptibility of aging gastric mucosa to injury can be potentially reduced or reversed pharmacologically.

PTEN inhibitor bisperoxovanadium protects against noise-induced hearing loss

Studies have shown that phosphatase and tensin homolog deleted on chromosome ten(PTEN)participates in the regulation of cochlear hair cell survival.Bisperoxovanadium protects against neurodegeneration by inhibiting PTEN expression.However,whether bisperoxovanadium can protect against noise-induced hearing loss and the underlying mechanism remains unclear.In this study,we established a mouse model of noise-induced hearing loss by exposure to 105 dB sound for 2 hours.We found that PTEN expression was increased in the organ of Corti,including outer hair cells,inner hair cells,and lateral wall tissues.Intraperitoneal administration of bisperoxovanadium decreased the auditory threshold and the loss of cochlear hair cells and inner hair cell ribbons.In addition,noise exposure decreased p-PI3K and p-Akt levels.Bisperoxovanadium preconditioning or PTEN knockdown upregulated the activity of PI3K-Akt.Bisperoxovanadium also prevented H_(2)O_(2)-induced hair cell death by reducing mitochondrial reactive oxygen species generation in cochlear explants.These findings suggest that bisperoxovanadium reduces noise-induced hearing injury and reduces cochlear hair cell loss.

Role of phosphatase PTEN in the activation of extracellular signal-regulated kinases induced by estradiol in endometrial carcinoma cells

Objectives To study extracellular signal-regulated kinase (ERK) activation in the endometrial carcinoma cell line Ishikawa with stimulation by 17-β-estradiol, and to elucidate the role of phosphatase and tensin homologue (PTEN) and estrogen receptor (ER) subtype on the activation of ERKs.Methods Western blot was used to examine the expression of PTEN and PTEN (G129E) in Ishikawa cells after stable transfection as well as ERK activation in Ishikawa-EGFP, Ishikawa- PTEN and Ishikawa- PTEN (G129E) stimulated with various doses of 17-β-estradiol for different lengths of time. Western blot was also used for examining the expression of ERα and ERβ in NIH3T3 fibroblasts after transient transfection of pCXN2hERα and pCXN2hERβ. Then, ERK activation was examined after stimulation with 17-β-estradiol. Results 17-β-estradiol activated ERK cascades (mainly ERK2) in Ishikawa cells. The activation of ERK increased gradually as concentration of 17-β-estradiol also increased. The maximal activation of ERK2 took place 5 min after stimulation with 17-β-estradiol. The activation of ERK2 was inhibited markedly by PTEN, but not by PTEN (G129E). 17-β-estradiol activated ERK cascades in NIH3T3 fibroblasts after transient transfection of pCXN2hERα.Conclusions 17-β-estradiol activate ERK cascades in Ishikawa cells by integrating with ERα. Lipid phosphatase PTEN has an inhibitory role on the activation of ERK stimulated by 17-β-estradiol in Ishikawa cells.