Role of perivascular nerve and sensory neurotransmitter dysfunction in inflammatory bowel disease

Abstract

Inflammatory Bowel Disease (IBD) is associated with both impaired intestinal blood flow and increased risk of cardiovascular disease, but the functional role of perivascular nerves that control vasomotor function of mesenteric arteries (MAs) perfusing the intestine during IBD is unknown. Because perivascular sensory nerves and their transmitters calcitonin gene-related peptide (CGRP) and substance P (SP) are important mediators of both vasodilation and inflammatory responses, our objective was to identify IBD-related deficits in perivascular sensory nerve function and vascular neurotransmitter signaling. In MAs from an IL-10-/- mouse model, IBD significantly impairs electrical field stimulation (EFS)-mediated sensory vasodilation and inhibition of sympathetic vasoconstriction, despite decreased sympathetic nerve density and vasoconstriction. The MA content and EFS-mediated release of both CGRP and SP are decreased with IBD, but IBD has unique effects on each transmitter. CGRP nerve density, receptor expression, hyperpolarization and vasodilation are preserved with IBD. In contrast, SP nerve density and receptor expression are increased, and SP hyperpolarization and vasodilation are impaired with IBD. A key finding is that blockade of SP receptors restores EFS-mediated sensory vasodilation and enhanced CGRP-mediated vasodilation in MAs from IBD but not Control mice. Together, these data suggest that an aberrant role for the perivascular sensory neurotransmitter SP and its downstream signaling in MAs underlies vascular dysfunction with IBD. We propose that with IBD, SP signaling impedes CGRP-mediated sensory vasodilation, contributing to impaired blood flow. Thus, substance P and NK1 receptors may represent an important target for treating vascular dysfunction in IBD.

Differential hyperpolarization to substance P and calcitonin gene‐related peptide in smooth muscle versus endothelium of mouse mesenteric artery

“…These findings are consistent with endothelial denudation preventing hyperpolarization of SMCs to SP in unpressurized porcine coronary artery segments 32 . Substance P exerts its actions in the vasculature through neurokinin receptors, 16 and our previous findings confirm that neurokinin 1 receptors are expressed on ECs, but not SMCs, in mouse MAs 23,33 . The present data are also consistent with neurokinin receptor expression on human aortic ECs 16 .…”

“…Finding that the inhibition of NO synthase prevented SMC hyperpolarization to SP in intact MAs (Figure 4) indicates that endothelium‐derived NO mediates SMC hyperpolarization rather than SP acting directly on SMCs to elicit hyperpolarization. Although SP released from sensory nerves does not act directly on SMCs, electrical field stimulation of MAs releases SP that acts upon the endothelium 23 . Furthermore, the neurokinin receptors on ECs can also be activated by circulating SP 34 .…”

“…Each pipette was secured in a custom holder (Warner) held in a three‐axis micromanipulator (DT3‐100; Siskiyou Corp., Grants Pass, OR, USA) secured to the aluminum platform at each end of the tissue chamber. Pipettes were positioned in the chamber; individual MAs were cannulated and secured at each end with a strand of silk suture 22,23 …”

“…During visual observation at 200× magnification, arterial segments were gently triturated to remove SMCs 24 . Once isolated, each end of the endothelial tube was gently pressed against the bottom of the tissue chamber (a 24 × 54 mm coverslip) with a heat‐blunted pipette (tip, diameter ~80 μm) and extended to approximate in situ length 23,25 …”

“…The output of the amplifier was connected to a data acquisition system (Digidata 1322A, Molecular Devices) and an audible baseline monitor (ABM‐3, WPI). Successful impalements were indicated by sharp negative deflection of V m , shift in tone of the ABM, stable V m for >1 min, depolarization (≥20 mV) to 0.1 M KCl (SMCs) or hyperpolarization (≥20 mV) to 10 −5 M ACh (ECs), 23,26 recovery to resting V m after KCl or ACh washout, and prompt return to ~0 mV upon electrode withdrawal. For intact vessels, SMCs are the first cell to be penetrated when approached from the bath; ECs comprise endothelial tubes.…”