Inflammatory bowel disease (IBD) involves functional impairment of intestinal epithelial cells (IECs), concomitant with the infiltration of the lamina propria by inflammatory cells. We explored the reciprocal paracrine and direct interaction between human IECs and macrophages (MΦ) in a co-culture system that mimics some aspects of IBD. We investigated the expression of intercellular junctional proteins in cultured IECs under inflammatory conditions and in tissues from IBD patients. IECs establish functional gap junctions with IECs and MΦ, respectively. Connexin (Cx26) and Cx43 expression in cultured IECs is augmented under inflammatory conditions; while, Cx43-associated junctional complexes partners, E-cadherin, ZO-1, and β-catenin expression is decreased. The expression of Cx26 and Cx43 in IBD tissues is redistributed to the basal membrane of IEC, which is associated with decrease in junctional complex proteins’ expression, collagen type IV expression and infiltration of MΦ. These data support the notion that the combination of paracrine and hetero-cellular communication between IECs and MΦs may regulate epithelial cell function through the establishment of junctional complexes between inflammatory cells and IECs, which ultimately contribute to the dys-regulation of intestinal epithelial barrier.

ABSTRACT

Mechanisms of action of the neuropeptide galanin, a putative neuromodulator in the central and peripheral nervous systems, have been evaluated extensively in insulin-secreting cells isolated from pancreas and cell lines derived from pancreatic tumors. Galanin inhibits insulin secretion from these cells through several mechanisms, including activation of ATP-dependent K+ channels and inhibition of adenylyl cyclase leading to a decrease in cAMP. Here we report that galanin also inhibits a dihydropyridine-sensitive Ca2+ current. Both electrophysiological actions by galanin would result in less Ca2+ entry, as the action to increase K+ current would hyperpolarize the cells and the decrease in voltage-gated Ca2+ current would decrease Ca2+ influx at depolarized potentials where these channels are activated. These galanin actions would directly counter the two opposing electrophysiological responses to carbohydrate stimulation in RINm5f cells, which are to inhibit K+ current and to stimulate Ca2`current. Given that stimulation of presynaptic nerve terminals in pancreas releases galanin, these results suggest that Ca2 -dependent insulin release from native pancreatic ,B cells may also be regulated by similar neuropeptide effects.Galanin-(1-29), a neuroactive peptide originally isolated from porcine intestine (1), is widely distributed throughout the vertebrate central nervous system (2). In the periphery, galanin-containing nerve terminals have been described in association with many tissues, including gut (3, 4) and pancreas (5). Galanin-mediated inhibition of insulin release has been reported in vivo and in vitro (6-10), and the quantity of galanin released by nerve stimulation was shown to be sufficient to affect pancreatic islet function (11).Galanin appears to play an important role in the regulation of neurotransmitter and hormone release. For example, it causes inhibition of electrically or neurochemically stimulated acetylcholine release from myenteric plexus neurons (12). It also causes a decrease in bombesin-stimulated gastric acid secretion, presumably by inhibition of acetylcholine release from myenteric nerve terminals (13). In contrast to these inhibitory actions, galanin increases growth hormone and prolactin release from anterior pituitary in intact brain. However, recent studies of isolated anterior pituitary cells indicate the stimulatory actions ofgalanin did not occur in the absence of the hypothalamic synaptic network (14).Previous electrophysiological studies of the mechanism of galanin regulation of hormone secretion had pointed to its action to increase K+ conductance and hyperpolarize neuronal and secretory cells. However, intracellular recording studies also provided results suggesting that galanin may directly inhibit voltage-gated Ca + currents. In myenteric neurons galanin increased K+ conductance and hyperpolarized the cells, but it also decreased the duration of Ca2l-dependent action potentials recorded using Cs-filled pipettes (15), consistent with a direct effect on Ca2+ currents...

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