Synergistic increase in nerve growth factor secretion by cultured vascular smooth muscle cells treated with injury-related growth factors

TH and NPY in sympathetic neurovascular cultures: role of LIF and NT-3

The sympathetic nervous system is an important determinant of vascular function. The effects of the sympathetic nervous system are mediated via release of neurotransmitters and neuropeptides from postganglionic sympathetic neurons. The present study tests the hypothesis that vascular smooth muscle cells (VSM) maintain adrenergic neurotransmitter/neuropeptide expression in the postganglionic sympathetic neurons that innervate them. The effects of rat aortic and tail artery VSM (AVSM and TAVSM, respectively) on neuropeptide Y (NPY) and tyrosine hydroxylase (TH) were assessed in cultures of dissociated sympathetic neurons. AVSM decreased TH (39 +/- 12% of control) but did not affect NPY. TAVSM decreased TH (76 +/- 10% of control) but increased NPY (153 +/- 20% of control). VSM expressed leukemia inhibitory factor (LIF) and neurotrophin-3 (NT-3), which are known to modulate NPY and TH expression. Sympathetic neurons innervating blood vessels expressed LIF and NT-3 receptors. Inhibition of LIF inhibited the effect of AVSM on TH. Inhibition of neurotrophin-3 (NT-3) decreased TH and NPY in neurons grown in the presence of TAVSM. These data suggest that vascular-derived LIF decreases TH and vascular-derived NT-3 increases or maintains NPY and TH expression in postganglionic sympathetic neurons. NPY and TH in vascular sympathetic nerves are likely to modulate NPY and/or norepinephrine release from these nerves and are thus likely to affect blood flow and blood pressure. The present studies suggest a novel mechanism whereby VSM would modulate sympathetic control of vascular function.

Vascular-derived artemin: a determinant of vascular sympathetic innervation?

Vascular sympathetic innervation is an important determinant of blood pressure and blood flow. The mechanisms that determine vascular sympathetic innervation are not well understood. The present study tests the hypothesis that vascular-derived artemin promotes the development of sympathetic innervation to blood vessels by promoting sympathetic axon growth. RT-PCR and Western analyses indicate that artemin is expressed by cultured vascular smooth muscle and arteries, and artemin coreceptors, glial cell-derived neurotrophic factor family receptor alpha3 and ret, are expressed by postganglionic sympathetic neurons. The effects of artemin on axon growth were assessed on explants of neonatal rat sympathetic ganglia. In the presence, but not in the absence, of nerve growth factor, exogenous artemin stimulated neurite growth. Femoral arteries (FA) from adult rats contain artemin, and these arteries stimulated sympathetic neurite growth. Growth in the presence of FA was 92.2 +/- 11.9 mm, and that in the absence of FA was 26.3 +/- 5.4 mm (P < 0.05). FA stimulation of axon growth was reduced by an antibody that neutralized the activity of artemin (P < 0.05). These data indicate that artemin is expressed in arteries, and its receptors are expressed and functional in the postganglionic sympathetic neurons that innervate them. This suggests that artemin may be a determinant of vascular sympathetic innervation.

Differential responses of intrinsic and extrinsic innervation of smooth muscle cells in rat colitis

Intestinal smooth muscle cells receive neural input from axons that originate within the intestine, as well as from axons of extrinsic origin. In the inflamed intestine, altered motility may arise from damage to the axon/smooth muscle cell relationship, but the extent of change is unknown. Western blotting, histology and immunocytochemistry were used in the TNBS model of colitis in the rat to evaluate intrinsic and extrinsic axon numbers, which were then correlated with circular smooth muscle cell (CSMC) number during the time course from the acute onset of colitis to apparent recovery, at Day 35 post TNBS. Total axon profiles in the circular smooth muscle layer were reduced by nearly 50% on Day 4 of colitis, to 428 +/- 82 axons/section from 757 +/- 125 in control (n = 8-14 animals). The intrinsic innervation density (axon number per CSMC) dropped sharply by Day 2 to less than 30% of control. Although CSMC number nearly tripled during colitis, innervation density was restored to control levels by Day 6 due to a coordinated three-fold increase in axon number. The subpopulation of extrinsic axons expressing tyrosine hydroxylase showed a unique pattern during colitis, with no initial decrease in axon number, followed by axonal proliferation between Days 6 and 16 post-TNBS. We conclude that loss of intrinsic axons is an early event in colitis, and although reversed by axonal proliferation, transient denervation may promote CSMC hyperplasia as seen in earlier work in vitro. Axonal proliferation of both intrinsic and extrinsic axons is identified as a major homeostatic mechanism, with distinct patterns of damage and repair suggesting a structural basis for the altered motility seen in the inflamed colon.

Adrenergic catecholamine trophic activity contributes to flow-mediated arterial remodeling

Stimulation of α1-adrenoceptors (ARs) induces proliferation, hypertrophy, and migration of vascular smooth muscle cells and adventitial fibroblasts in cell and organ culture. In vivo studies have confirmed this direct trophic action and found that endogenous catecholamines contribute to neointimal formation and wall hypertrophy induced by mechanical injury. In murine carotid artery, these effects are mediated by α1B-ARs, whereas α1D-ARs mediate contraction and α1A-ARs are not expressed. Herein, we examined whether catecholamines also contribute to arterial wall growth in a noninjury model, i.e., flow-mediated remodeling. In wild-type mice or mice deficient in norepinephrine and epinephrine synthesis [dopamine β-hydroxylase knockout (DBH-KO)], all distal branches of the left carotid artery (LC) except the thyroid artery were ligated to reduce flow in the LC and increase flow in the right carotid artery (RC). Twenty-one days later, negative hypertrophic remodeling of the LC [i.e., −20% (decrease) in lumen area, −2% in circumference of the external elastic lamina (CEEL), +98% (increase) in thickness of the intima media, and +71% in thickness for adventitia; P < 0.01 vs. sham ligation] and positive eutrophic remodeling of the RC [+23% in lumen area, +11% in CEEL; P < 0.01 vs. sham ligation] were inhibited in DBH-KO mice [LC: +10% intima media and +3% adventitia; RC: +9% lumen area and +3% CEEL]. This inhibition was associated with reduced proliferation in the RC and reduced apoptosis and leukocyte accumulation in the RC and LC when examined 5 days after ligation. Carotid remodeling in α1D-AR-knockout mice evidenced little or no inhibition, which suggests dependence on α1B-ARs. These findings suggest that catecholamine-induced trophic activity contributes to both flow-mediated negative remodeling and adaptive positive arterial remodeling.

Interactions of sympathetic nerves with capsaicin-sensitive sensory nerves: neurogenic mechanisms for phenol-induced hypertension in the rat

BACKGROUND

Previous investigations have shown that norepinephrine is capable of inhibiting neurotransmission in capsaicin-sensitive sensory nerves via a prejunctional mechanism. The alteration in the activity of sympathetic or capsaicin-sensitive sensory nerves in the development of phenol-induced hypertension was observed separately in rats.

METHODS

In the present study, we examined interactions of adrenergic nerves with capsaicin-sensitive sensory nerves in phenol-induced hypertensive rats. Blood pressure, the synthesis and release of calcitonin gene-related peptide (CGRP) and the content of nerve growth factor in (NGF) arteries were determined.

RESULTS

Intrarenal injection of phenol caused a permanent elevation of blood pressure concomitantly with a decrease in the concentration of CGRP in plasma, the content of CGRP in dorsal root ganglia and the density of CGRP-containing nerves in the mesenteric artery, and vascular NGF content. Chronic treatment with prazosin (an alpha1-adrenoreceptor antagonist, 3 mg/kg per day) failed to alter the synthesis and release of CGRP and vascular NGF content, even though it completely normalized blood pressure. However, treatment with yohimbine (an alpha2-adrenoreceptor antagonist, 5 mg/kg per day) significantly increased CGRP level and vascular NGF content. Combined administration of prazosin and yohimbine not only significantly elevated the synthesis and release of CGRP and arterial NGF content, but also completely normalized blood pressure.

CONCLUSION

These results indicate that the decreased production and release of CGRP and reduced vascular NGF content are attributed to the activation of alpha2-adrenoreceptors in phenol-induced hypertensive rats.

Neurotrophin presence in human coronary atherosclerosis and metabolic syndrome: a role for NGF and BDNF in cardiovascular disease?

The development of atherosclerotic cardiovascular disease is a common comorbidity in patients with the metabolic syndrome, a concurrence of cardiovascular risk factors in one individual. While multiple growth factors and adipokines are identified in atherosclerotic lesions, as well as neurotrophins implicated in both cardiac ischemia and lipid and glucose metabolism, the potential role of neurotrophins in human coronary atherosclerosis and in the metabolic syndrome still remains to be elucidated. Here we describe and discuss our results that represent a novel attempt to study the cardiovascular and metabolic biology of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and mast cells (MC). The local amount of NGF, the immunolocalization of p75 neurotrophin receptor (p75NTR) and the number of MC were correlatively examined in coronary vascular wall and in the surrounding subepicardial adipose tissue, obtained from autopsy cases in humans with advanced coronary atherosclerosis. We also analyzed the plasma levels of NGF, BDNF and leptin and the number of MC in biopsies from abdominal subcutaneous adipose tissue in patients with a severe form of the metabolic syndrome. The results demonstrate that NGF levels are decreased in atherosclerotic coronary vascular tissue but increased in the subepicardial adipose tissue, whereas both tissues express a greater number of MC and a stronger p75NTR immunoreactivity, compared to controls. Metabolic syndrome patients display a significant hyponeurotrophinemia and an increased number of adipose MC; the later correlates with elevated plasma leptin levels. In effect, we provide the first evidence for (i) an altered presence of NGF, p75NTR and MC in both coronary vascular and subepicardial adipose tissue in human coronary atherosclerosis, and (ii) a significant decrease in plasma NGF and BDNF levels and an elevated amount of plasma leptin and adipose MC in metabolic syndrome patients. Together our findings suggest that neuroimmune mediators such as NGF, BDNF, leptin and MC may be involved in the development of cardiovascular disease and related disorders.

Nerve growth factor levels and mast cell distribution in human coronary atherosclerosis

Nerve growth factor (NGF), in addition to its neurotrophic function, acts on a variety of non-neuronal cells including immune cells and vascular smooth muscle cells. The aim of the present study was to determine the NGF levels and the distribution of NGF and low-affinity NGF receptor (p75NGFR) and mast cells (MC) in human atherosclerotic coronary arteries. Specimens of human coronary arteries obtained from autopsy cases (n=12, subjects with atherosclerotic lesions; n=9, subjects without atherosclerotic lesions/controls) were used. The present study showed that in the atherosclerosis-lesioned arteries, the amount of NGF decreased, whereas the expression of p75NGFR immunoreactivity and the number, both of MC and vasa vasorum, particularly in the adventitia, significantly increased, compared with the control arteries. Cumulatively, our findings help to set the neurotrophic theory and its currently extended neuroimmune framework into the context of pathobiology of atherosclerosis, suggesting that altered presence of NGF, p75NGFR, and MC may play a role in neuroimmune mechanisms of human coronary atherosclerosis.

Stretch-activated signaling of nerve growth factor secretion in bladder and vascular smooth muscle cells from hypertensive and hyperactive rats

Elevated vascular (VSMC) and bladder smooth muscle (BSMC) NGF are associated with altered visceral innervation in the spontaneously hypertensive rat (SHR: hypertensive, behaviorally hyperactive) compared with control Wistar-Kyotos (WKYs). Stretch stimulates increased NGF production in BSMCs. To elucidate whether stretch induces NGF synthesis in VSMCs, and to determine if disturbances in stretch-mediated NGF production contribute to the elevated tissue levels of NGF in SHRs, we subjected VSMCs and BSMCs cultured from four established inbred rat strains (WKY, WKHA: hyperactive; SHR and WKHT: hypertensive) to several stretch paradigms. For VSMCs, acute and cyclic stretch affected cells derived from hypertensive rats (80-100% increase over control) but not from normotensive strains. For BSMCs, cyclic and static stretch increased NGF secretion in all four strains, but had a two- to threefold greater effect in cells from SHRs and WKHTs (increase up to 600%) at early time points. At later time points of a 24-h experimental period, stretch increased NGF output up to 400% in SHR and WKHA cultures. Thus, defects that influence early induction of stretch-mediated SHR NGF secretion cosegregate with the hypertensive phenotype. Stretch-gated ion channel inhibitors, voltage-gated ion channel inhibitors, and protease inhibitors failed to affect stretch-induced BSMC NGF secretion. In contrast, gene transcription, intracellular calcium, protein kinase C (PKC), and autocrine release of an unknown factor may play a role in the elevated NGF secretion observed in smooth muscle from hypertensive animals. Altered stretch-induced smooth muscle NGF secretion may contribute to the augmented vascular and bladder NGF content associated with high blood pressure and hyperactive voiding in SHRs.

Damage to the enteric nervous system in experimental colitis

Inflammation of the intestine causes pain and altered motility, at least in part through effects on the enteric nervous system. While these changes may be reversed with healing, permanent damage may contribute to inflammatory bowel disease (IBD) and post-enteritis irritable bowel syndrome. Since little information exists, we induced colitis in male Sprague-Dawley rats with dinitrobenzene sulfonic acid and used immunocytochemistry to examine the number and distribution of enteric neurons at times up to 35 days later. Inflammation caused significant neuronal loss in the inflamed region by 24 hours, with only 49% of neurons remaining by days 4 to 6 and thereafter, when inflammation had subsided. Eosinophils were found within the myenteric plexus at only at the earliest time points, despite a general infiltration of neutrophils into the muscle wall. While the number of myenteric ganglia remained constant, there was significant decrease in the number of ganglia in the submucosal plexus. Despite reduced neuronal number and hyperplasia of smooth muscle, the density of axons among the smooth muscle cells remained unchanged during and after inflammation. Intracolonic application of the topical steroid budesonide caused a dose-dependent prevention of neuronal loss, suggesting that evaluation of anti-inflammatory therapy in inflammatory bowel disease should include quantitative assessment of neural components.

Roles of transforming growth factor-alpha and related molecules in the nervous system

The epidermal growth factor (EGF) family of polypeptides is regulators for tissue development and repair, and is characterized by the fact that their mature forms are proteolytically derived from their integral membrane precursors. This article reviews roles of the prominent members of the EGF family (EGF, transforming growth factor-alpha [TGF-alpha] and heparin-binding EGF [HB-EGF]) and the related neuregulin family in the nerve system. These polypeptides, produced by neurons and glial cells, play an important role in the development of the nervous system, stimulating proliferation, migration, and differentiation of neuronal, glial, and Schwann precursor cells. These peptides are also neurotrophic, enhancing survival and inhibiting apoptosis of post-mitotic neurons, probably acting directly through receptors on neurons, or indirectly via stimulating glial proliferation and glial synthesis of other molecules such as neurotrophic factors. TGF-alpha, EGF, and neuregulins are involved in mediating glial-neuronal and axonal-glial interactions, regulating nerve injury responses, and participating in injury-associated astrocytic gliosis, brain tumors, and other disorders of the nerve system. Although the collective roles of the EGF family (as well as those of the neuregulins) are shown to be essential for the nervous system, redundancy may exist among members of the EGF family.

Increased nerve growth factor mRNA stability may underlie elevated nerve growth factor secretion from hypertensive vascular smooth muscle cells

Altered nerve growth factor (NGF) regulation has been linked to the pathophysiology of hypertension. Vascular smooth muscle cells from an inbred hypertensive, but normoactive rat strain (WKHT) secreted NGF at a greater rate than from a hyperactive, normotensive strain (WKHA). Exposure to phorbol ester increased NGF secretion rates from WKHT by 400-800% but not from WKHA vascular muscle. NGF secretion rates from both WKHT and WKHA vascular cells were elevated by co-application of platelet-derived growth factor (PDGF) and transforming growth factor-beta1 (TGF-beta1) by 300-1000%. This response was partially attenuated by actinomycin D, an inhibitor of RNA transcription. These results suggest that regulation of NGF production does not occur solely at the level of transcription and post-transcriptional mechanisms operate. Analysis of NGF mRNA stability in the two strains following PDGF and TGF-beta1 treatment showed that NGF mRNA in WKHT had a half-life of 126.2+/-11.68 min while in WKHA vascular smooth muscle cells, the half-life was 47. 33+/-11.98 min. In addition to increased NGF mRNA stability in WKHT vascular muscle, these cells have an increased translational efficiency of NGF protein; elevated synthesis of NGF protein per unit NGF mRNA. Differences in signaling pathways may result in increased NGF mRNA stability and translational efficiency that may account for the elevated NGF protein in WKHT vascular smooth muscle cells.

Mechanisms of increased NGF production in vascular smooth muscle of the spontaneously hypertensive rat

The spontaneously hypertensive rat (SHR) was developed as a genetic model of essential hypertension. In vivo and in vitro evidence demonstrates that vascular smooth muscle cells (VSMCs) from the SHR produce more nerve growth factor (NGF) than the normotensive Wistar-Kyoto (WKY) control strain. This increased NGF production is accompanied by excessive innervation of target tissues in the SHR. In the present study, a sensitive, competitive, quantitative, reverse-transcriptase polymerase chain reaction (C Q RT-PCR) assay is characterized and used to analyze levels of NGF mRNA in cultured VSMCs derived from the SHR and WKY strains as well as bladder tissue. Differences in NGF secretion rates between SHR and WKY VSMCs were partially due to an increased stability of NGF mRNA in SHR VSMCs. Following treatment with platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta 1) to elevate NGF production, the half-life of the NGF mRNA was 104.5 +/- 18.0 min in SHR VSMCs, compared to only 36.5 +/- 11.6 min in WKY VSMCs. Sequence analysis of the 3' untranslated region (UTR) revealed no strain differences in cis-acting sequences potentially involved in determining mRNA stability. Thus, it seems unlikely to be a 3'UTR mutation that prolongs mRNA lifetime. Rather, differential regulation of an RNA-binding protein may play a role in the abnormal NGF mRNA stability in SHR VSMCs. SHR VSMCs also demonstrate an increased translational efficiency of NGF protein; more NGF protein is synthesized per unit of NGF mRNA. The use of a C Q RT-PCR assay has allowed the determination that abnormal NGF mRNA stabilization as well as altered translational efficiency may contribute to excess NGF synthesis and progressive hypertension in the SHR.