Shigong Zhu

Effects of ghrelin on the proliferation and secretion of splenic T lymphocytes in mice.

Ghrelin, a novel gut--brain peptide predominantly produced by the stomach, displays strong growth hormone (GH)-releasing activity mediated by the hypothalamus-pituitary GH secretagogue receptor (GHS-R). Recently, the ghrelin receptor has also been detected in peripheral systems including immune tissues, suggesting that ghrelin may play an important role in the regulation of immune function. In this paper, we assessed the presence and function of the ghrelin receptor in murine splenic T cells. The enriched T cells express the mRNA of ghrelin and ghrelin receptor mRNA, and there is a significantly positive correlation between them. Moreover, we showed that ghrelin dose-dependently inhibits proliferation of splenic T cells when they are costimulated by anti-CD3. In addition, ghrelin suppressed Th(1) (IL-2 and IFN-gamma) and Th(2) (IL-4 and IL-10) cytokines mRNA expression. These results demonstrate the presence of the ghrelin receptor in murine spleen T lymphocytes and a functional role of ghrelin as a modulator of lymphocyte function. This function of ghrelin may have some relevance to the pathophysiology of immunologic alterations related to metabolism.

Ghrelin-containing neuron in cerebral cortex and hypothalamus linked with the DVC of brainstem in rat

Ghrelin is a newly discovered brain-gut peptide and an endogenous ligand for growth hormone secretagogues receptor (GHS-R). Ghrelin and GHS-R present extensively in central and peripheral tissues such as stomach, brain and other organs of rodent and human, which suggest it has multiple biological effects. It has been reported that ghrelin has significant role in the regulation of energy homeostasis, food intake and appetite. The organization of central circuitry appears to play an important role in integrating orexigenic effects of ghrelin, but the detail is not fully clear. In this study, we examined the expression of ghrelin, ghrelin mRNA and GHS-R mRNA in cerebrum and brainstem by RT-PCR and immunofluorescence histochemistry, and analyzed the connection among the cerebral cortex, hypothalamus, dorsal vagal complex (DVC). The results showed that the positive staining of ghrelin was found on the pyramidal neuron of layer V in the sensorimotor area of cerebral cortex, cingulate gyrus, as well as in the neuron of lateral hypothalamus (LH), PVN and ARC. The expression of ghrelin mRNA and GHS-R mRNA were also found in the sensorimotor cortex and hypothalamus by method of RT-PCR. The GHS-R mRNA was also found in the DVC of medulla oblongata. Other finding is that the FG/ghrelin dual labeled neurons were found in LH of hypothalamus (not in cortex). The ghrelin-containing neuron in the LH projects its axon to the DVC with the method of retrograde tracing. In conclusion, the ghrelin neurons are located not only in hypothalamus (LH, PVN, ARC), but also in the cortex (sensorimotor area, cingular gyrus), and the fibers of ghrelin neurons in hypothalamus projected directly to the DVC. It suggests that ghrelin plays its role from hypothalamus to brainstem as a neurotransmitter or neuromodulator to regulate function of vagal nuclei in brainstem.

CART attenuates endoplasmic reticulum stress response induced by cerebral ischemia and reperfusion through upregulating BDNF synthesis and secretion

Cocaine and amphetamine regulated transcript (CART), a neuropeptide, has shown strong neuroprotective effects against cerebral ischemia and reperfusion (I/R) injury in vivo and in vitro. Here, we report a new effect of CART on ER stress which is induced by cerebral I/R in a rat model of middle cerebral artery occlusion (MCAO) or by oxygen and glucose deprivation (OGD) in cultured cortical neurons, as well as a new functionality of BDNF in the neuroprotection by CART against the ER stress in cerebral I/R. The results showed that CART was effective in reducing the neuronal apoptosis and expression of ER stress markers (GRP78, CHOP and cleaved caspase12), and increasing the BDNF expression in I/R injury rat cortex both in vivo and in vitro. In addition, the effects of CART on ischemia-induced neuronal apoptosis and ER stress were suppressed by tyrosine receptor kinase B (TrkB) IgG, whereas the effects of CART on BDNF transcription, synthesis and secretion were abolished by CREB siRNA. This work suggests that CART is functional in inhibiting the cerebral I/R-induced ER stress and neuronal apoptosis by facilitating the transcription, synthesis and secretion of BDNF in a CREB-dependent way.

14,15-EET promotes mitochondrial biogenesis and protects cortical neurons against oxygen/glucose deprivation-induced apoptosis.

14,15-Epoxyeicosatrienoic acid (14,15-EET), a metabolite of arachidonic acid, is enriched in the brain cortex and exerts protective effect against neuronal apoptosis induced by ischemia/reperfusion. Although apoptosis has been well recognized to be closely associated with mitochondrial biogenesis and function, it is still unclear whether the neuroprotective effect of 14,15-EET is mediated by promotion of mitochondrial biogenesis and function in cortical neurons under the condition of oxygen-glucose deprivation (OGD). In this study, we found that 14,15-EET improved cell viability and inhibited apoptosis of cortical neurons. 14,15-EET significantly increased the mitochondrial mass and the ratio of mitochondrial DNA to nuclear DNA. Key makers of mitochondrial biogenesis, peroxisome proliferator activator receptor gamma-coactivator 1 alpha (PGC-1α), nuclear respiratory factor 1 (NRF-1) and mitochondrial transcription factor A (TFAM), were elevated at both mRNA and protein levels in the cortical neurons treated with 14,15-EET. Moreover, 14,15-EET markedly attenuated the decline of mitochondrial membrane potential, reduced ROS, while increased ATP synthesis. Knockdown of cAMP-response element binding protein (CREB) by siRNA blunted the up-regulation of PGC-1α and NRF-1 stimulated by 14,15-EET, and consequently abolished the neuroprotective effect of 14,15-EET. Our results indicate that 14,15-EET protects neurons from OGD-induced apoptosis by promoting mitochondrial biogenesis and function through CREB mediated activation of PGC-1α and NRF-1.

14,15‐epoxyeicosatrienoic acid promotes production of brain derived neurotrophic factor from astrocytes and exerts neuroprotective effects during ischaemic injury

14,15‐Epoxyeicosatrienoic acid (14,15‐EET) is abundantly expressed in brain and exerts protective effects against ischaemia. 14,15‐EET is hydrolysed by soluble epoxide hydrolase (sEH). sEH−/− mice show a higher level of 14,15‐EET in the brain. Astrocytes play a pivotal role in neuronal survival under ischaemic conditions. However, it is unclear whether the neuroprotective effect of 14,15‐EET is associated with astrocytes.

Influence of fasting, insulin and glucose on ghrelin in the dorsal vagal complex in rats

The dorsal vagal complex (DVC) is an important site in which ghrelin plays an orexigenic role. However, the relationship between ghrelin expression in DVC and the energy status of the organism is unclear, as well as the role of the vagus nerve in this process. In this study, ghrelin expression in DVC neurons of rats was detected, then levels of ghrelin expression were observed under the conditions of regular diet, fasting, high blood glucose, low blood glucose, and following subdiaphragmatic vagotomy and vagus nerve electrostimulation. The results showed the following: 1) there was positive staining of ghrelin neurons in DVC; 2) ghrelin protein and mRNA levels in DVC increased under fasting condition; 3) Hyperglycemia, induced by glucose production, decreased DVC ghrelin levels and levels did not increase under hypoglycemia induced by insulin injection; 4) the dorsal trunk of the subdiaphragmatic vagus transmits a stimulatory signal to increase DVC ghrelin levels, whereas the ventral trunk transmits inhibitory information; and 5) DVC ghrelin levels decreased with 20 Hz stimulation on the ventral or dorsal trunk of subdiaphragmatic vagus nerves but increased with 1 Hz stimulation on the dorsal trunk. These results indicate that endogenous ghrelin is synthesized in DVC neurons. Conditions such as fasting, hyperglycemia, and hypoglycemia result in changes in DVC ghrelin levels in which the dorsal and ventral trunks of subdiaphragmatic vagus play different modulation roles.

Activation of the Nuclear Receptor Fxr Improves Intestinal Cell Tolerance to Ischemia–reperfusion Injury

ABSTRACT The farnesoid X receptor (FXR) plays an important role in bile acid metabolism, intestinal homeostasis, and intestinal ischemia–reperfusion (I/R) injury. We aimed to clarify the potential effects of FXR on intestinal epithelial cell tolerance to intestinal I/R injury and reveal the underlying mechanisms. An intestinal I/R injury model was established by the occlusion of the superior mesenteric artery for ischemia for 1 h, followed by reperfusion for 4 h in C57BL/6 (wild type [WT]) and FXR−/− mice. The small intestine injury was assessed by histological analysis. Diamine oxidase and TNF-&agr; levels in the serum were measured. Expressions of Bcl-2, Bax, caspase-3, and cystathionine-&ggr;-lyase (CSE) were determined by immunohostochemical staining. Oxygen–glucose deprivation/reperfusion (OGD/R) was used to make injury in cultured Caco-2 cells pretreated with FXR agonist (INT-747) or DL-propargylglycine (PAG) for 24 h. Cell viability and the expressions of NF-&kgr;B, TNF-&agr;, and IL-6 were assessed. Compared with WT I/R mice, FXR knockout mice exacerbated intestinal I/R injury, intestinal epithelial apoptosis, and inflammatory response. The I/R injury in WT mice was alleviated with INT-747 pretreatment. CSE expression increased after intestinal I/R injury in WT but not in FXR−/− mice. INT-747 enhanced Caco-2 cell viability and inhibited inflammatory response by blocking the NF-&kgr;B pathway after OGD/R injury, which was diminished by a CSE-specific inhibitor (PAG). Thus, we demonstrated that FXR activation enhances intestinal epithelial cell tolerance to I/R by suppressing the inflammatory response and NF-&kgr;B pathway via CSE mediation.