Distinct Identity of GLP-1R, GLP-2R, and GIPR Expressing Cells and Signaling Circuits Within the Gastrointestinal Tract

G protein-coupled receptor-mediated autophagy in health and disease

G protein-coupled receptors (GPCRs) constitute the largest and most diverse superfamily of mammalian transmembrane proteins. These receptors are involved in a wide range of physiological functions and are targets for more than a third of available drugs in the market. Autophagy is a cellular process involved in degrading damaged proteins and organelles and in recycling cellular components. Deficiencies in autophagy are involved in a variety of pathological conditions. Both GPCRs and autophagy are essential in preserving homeostasis and cell survival. There is emerging evidence suggesting that GPCRs are direct regulators of autophagy. Additionally, autophagic machinery is involved in the regulation of GPCR signalling. The interplay between GPCR and autophagic signalling mechanisms significantly impacts on health and disease; however, there is still an incomplete understanding of the underlying mechanisms and therapeutic implications in different tissues and disease contexts. This review aims to discuss the interactions between GPCR and autophagy signalling. Studies on muscarinic receptors, beta-adrenoceptors, taste receptors, purinergic receptors and adhesion GPCRs are summarized, in relation to autophagy.

Glucagon-like Peptide-2 Depresses Ileal Contractility in Preparations from Mice through Opposite Modulatory Effects on Nitrergic and Cholinergic Neurotransmission

Glucagon-like peptide-2 (GLP-2) has been reported to influence gastrointestinal motor responses, exerting a modulatory role on enteric neurotransmission. To our knowledge, no data on GLP-2 effects on the motility of the isolated ileum are available; therefore, we investigated whether GLP-2 affects the contractile activity of mouse ileal preparations and the neurotransmitters engaged. Ileal preparations showed tetrodotoxin (TTX)- and atropine-insensitive spontaneous contractile activity, which was unaffected by the nitric oxide synthesis inhibitor, L-NNA. GLP-2 depressed the spontaneous contractility, an effect that was abolished by TTX or L-NNA and not influenced by atropine. Electrical field stimulation induced TTX- and atropine-sensitive contractile responses, which were reduced in amplitude by GLP-2 even in the presence of L-NNA. Immunohistochemical results showed a significant increase in nNOS-positive fibers in the ileal muscle wall and a significant decrease in ChAT-positive myenteric neurons in GLP-2-exposed preparations. The present results offer the first evidence that GLP-2 acts on ileal preparations. The hormone appears to depress ileal contractility through a dual opposite modulatory effect on inhibitory nitrergic and excitatory cholinergic neurotransmission. From a physiological point of view, it could be hypothesized that GLP-2 inhibitory actions on ileal contractility can increase transit time, facilitating nutrient absorption.

The Interaction of Food Allergy and Diabetes: Food Allergy Effects on Diabetic Mice by Intestinal Barrier Destruction and Glucagon-like Peptide 1 Reduction in Jejunum

The increase in food allergies and diabetes leads to the assumption that they are related. This study aimed to (1) verify the interaction between food allergy and diabetes and (2) explore the potential mechanisms by which food allergy promotes diabetes. Female BALB/c mice were grouped into a control group (CK), an ovalbumin-sensitized group (OVA), a diabetes group (STZ), and a diabetic allergic group (STZ + OVA) (Mice were modeled diabetes with STZ first, then were given OVA to model food allergies), and an allergic diabetic group (OVA + STZ) (Mice were modeled food allergies with OVA first, then were given STZ to model diabetes). The results showed that OVA + STZ mice exhibited a more serious Th2 humoral response, and they were more susceptible to diabetes. Furthermore, when the OVA + STZ mice were in the sensitized state, the intestinal barrier function was severely impaired, and mast cell activation was promoted. Moreover, we found that the effect of food allergy on diabetes is related to the inhibition of GLP-1 secretion and the up-regulation of the PI3K/Akt/mTOR/NF-κB P65 signaling pathway in the jejunum. Overall, our results suggest that food allergies have interactions with diabetes, which sheds new light on the importance of food allergies in diabetes.

Neuroprotective effects of glucagon-like peptide-1 (GLP-1) analogues in epilepsy and associated comorbidities

Epilepsy is a common neurological condition induced by losing equilibrium of different pathway as well as neurotransmitters that affects over 50 million people globally. Furthermore, long-term administration of anti-seizure medications has been associated with psychological adverse effects. Also, epilepsy has been related to an increased prevalence of obesity and called type 2 diabetes mellitus. On the other hand, GLP-1 receptors are located throughout the brain, including the hippocampus, which have been associated to majority of neurological conditions, such as epilepsy and psychiatric disorders. Moreover, the impact of different GLP-1 analogues on diverse neurotransmitter systems and associated cellular and molecular pathways as a potential therapeutic target for epilepsy and associated comorbidities has piqued curiosity. In this regard, the anticonvulsant effects of GLP-1 analogues have been investigated in various animal models and promising results such as anticonvulsants as well as cognitive improvements have been observed. For instance, GLP-1 analogues like liraglutide in addition to their possible anticonvulsant benefits, could be utilized to alleviate mental cognitive problems caused by both epilepsy and anti-seizure medication side effects. In this review and growing protective function of GLP-1 in epilepsy induced by disturbed neurotransmitter pathways and the probable mechanisms of action of GLP-1 analogues as well as the GLP-1 receptor in these effects have been discussed.