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Introduction
Gastroparesis is one of the common chronic complications caused by diabetes mellitus, which primarily manifests as bloating, nausea and vomiting, and results in low gastric motility, delayed gastric emptying and prolonged gastric transit time (1). Although the apoptosis of gastric smooth muscle cells has been shown to be important in the occurrence of diabetic gastroparesis (2,3), the mechanisms upstream of this process remain to be elucidated. The phosphoinositide-3-kinase (PI3K)-protein kinase B (AKT)-mammalian target of rapamycin (mTOR) pathway is an important intracellular signaling cascade capable of affecting a variety of cell behaviors, including cell proliferation, growth, apoptosis and metabolism (4,5). PI3K phosphorylates phosphatidylinositol 4,5-bisphosphate into phosphatidylinositol 3,4,5-triphosphate to recruit and activate AKT, which subsequently activates its downstream target molecule, mTOR. mTOR is also a downstream target of 5′ adenosine monophosphate-activated protein kinase (AMPK), which is widely involved in mediating cell metabolism, and has important biological roles in regulating cell apoptosis, physiological and pathological processes (6). AMPK phosphorylates and activates tuberous sclerosis complex 2 (TSC-2) upstream of mTOR to promote the formation of a TSC-1/TSC-2 complex, which is capable of inhibiting the activity of another upstream guanosine triphosphate-binding protein, Ras homolog enriched in brain, ultimately reducing the activity of mTOR (7,8).
mTOR downstream targets include ribosomal S6 protein kinase (S6K) and eukaryotic translation initiation factor 4-binding protein 1 (4E-BP1) (9,10). The phosphorylation of mTOR has been shown to activate the p70 form of S6K (p70S6K) and inhibit the binding of 4E-BP1 to eukaryotic translation initiation factor 4E (eIF4E), thereby releasing eIF4E and improving the translation of anti-apoptotic proteins (11).
However, the correlation between cell apoptosis, and the PI3K-AKT-mTOR and AMPK-mTOR pathways in diabetic gastroparesis has not been reported. In the present study, a rat model of diabetic gastroparesis was established to examine the apoptosis of gastric smooth muscle cells, and the key proteins involved in PI3K-AKT-mTOR and AMPK-mTOR signaling, including PI3K and phosphorylated forms of AKT (p-AKT), AMPK (p-AMPK), TSC-2 (p-TSC-2), mTOR (p-mTOR), p70S6k (p-p70S6K) and 4E-BP1 (P-4E-BP1). The aim of the present study was to elucidate the pathogenesis of diabetic gastroparesis to provide a scientific theoretical basis and experimental evidence for novel clinical treatments.
Materials and methods
Experimental animals
A total of 40 adult male Sprague-Dawley rats, weighing 200±20 g, were provided by Yanbian University...