| Our previous studies indicated that chronic adequate alcohol intake may enhance the cell turnover of gastric mucosa and lead to an adaptive cytoprotection in rat gastric mucosa, but its mechanism remains unclear. Low concentration of ethanol is the most popular noxious irritant to gastric mucosa. Heat shock proteins (HSPs) are ubiquitous proteins in mammalian cells that are induced by a variety of noxious stimuli, such as heat shock, alcohol, heavy metals, certain metabolic poisons and so on. They are crucial for maintenance of cellular homeostasis during normal cell growth and for survival during and after various cellular stresses. HSP70 is a 70-kDa HSP family known to have cytoprotective effects against various insults, in which it functions as molecular chaperones and reduces stress-induced denaturation and aggregation of intracellular proteins. In addition to the chaperoning activities, HSP70 has been suggested to exert its gastric protective action by protecting key enzymes related to cytoprotection and by promoting ulcer healing. These data support the view that there is a positive correlation between the overproduction of HSP70 and the repeated exposures to low concentration of ethanol in rat gastric mucosa. Increased HSP70 expression in gastric mucosa might play an essential role in cell proliferation andgastric adaptive cytoprotection. To address this issue, the following studies were designed and performed.In the first study we developed a chronic drinking animal model using Sprague-Dawley (SD) rats. Animals received the 6% (v/v) ethanol as their only water intake for 28 days. In the different stages of the 28 days (1st, 3rd, 7th, 14th and 28th days), the expression of HSP70 in gastric mucosa were measured by semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry. Compared to the control animals, the HSP70 mRNA in gastric mucosa of rats exposed to the ethanol was increased dramatically. In immunohistochemical study, specialized cell types in rat gastric mucosa, such as surface mucous cells, mucous neck cells, parietal cells, chief cells and stem cells were identified by morphological observing or immunohistochemical double staining using the specific antibodies of HSP70 and PCNA. In the control rats, the chief cells showed weak positive staining to the HSP70. In rats exposed to the ethanol for 1, 3, 7, 14 and 28 days, the HSP70 positive staining was found both in surface and bottom of the gastric mucosa. The HSP70 positive cells were also localized in the neck portion of the rat fundic gland, in which they exposed to the ethanol in 3rd to 14th days. These cells were recognized as the stem cells by double staining of HSP70 and PCNA. These results suggest that stimulus with the low concentration of ethanol may led to an increased expression of HSP70 in rat gastric mucosa. An overexpressed HSP70 in the stem cells of rat fundic gland may play an important role in adaptive cytoprotection in the rat gastric mucosa.Because inhibitors of HSP70 synthesis could be an important tool to study the function of this protein, we investigated the effect of quercetin, a flavonoid widely distributed in nature, on HSP70 synthesis in the rat stomach. Quercetin was found to affect HSP70 synthesis at more than one level, depending on the conditions used. The rats were treated withquercetin at non-toxic concentrations (50mg/kg or 100mg/kg body wt) by gastric gavage twice a day for 3 days. Treatment with quercetin at the concentration of 100mg/kg was found to inhibit HSP70 synthesis at the post-transcriptional level. Base on this result, a period of three days study was designed to investigate the role of HSP70 in adaptive cytoprotection in the rat gastric mucosa. Rats were divided into four groups as control rats, ethanol treated rats, quercetin treated rats and ethanol+quercetin treated rats. Ethanol group was given 6% ethanol as their only water intake. Quercetin (100 mg/kg body wt) was given by gastric gavage twice a day for quercetin group. In ethanol+q... |
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