Extracellular matrix molecules influence innervation density in rat cerebral blood vessels

Potential biological targets for bioassay development in drug discovery of Sturge-Weber syndrome

Sturge-Weber Syndrome (SWS) is a neurocutaneous disease with clinical manifestations including ocular (glaucoma), cutaneous (port-wine birthmark), neurologic (seizures), and vascular problems. Molecular mechanisms of SWS pathogenesis are initiated by the somatic mutation in GNAQ. Therefore, no definite treatments exist for SWS and treatment options only mitigate the intensity of its clinical manifestations. Biological assay design for drug discovery against this syndrome demands comprehensive knowledge on mechanisms which are involved in its pathogenesis. By analysis of the interrelated molecular targets of SWS, some in vitro bioassay systems can be allotted for drug screening against its progression. Development of such platforms of bioassay can bring along the implementation of high-throughput screening of natural or synthetic compounds in drug discovery programs. Regarding the fact that study of molecular targets and their integration in biological assay design can facilitate the process of effective drug discovery; some potential biological targets and their respective biological assay for SWS drug discovery are propounded in this review. For this purpose, some biological targets for SWS drug discovery such as acetylcholinesterase, alkaline phosphatase, GABAergic receptors, Hypoxia-Inducible Factor (HIF)-1α and 2α are suggested.

Neuropathology of epilepsy

Epilepsy is one of the most common neurologic disorders, affecting about 50 million people worldwide. The disease is characterized by recurrent seizures, which are due to aberrant neuronal networks resulting in synchronous discharges. The term epilepsy encompasses a large spectrum of syndromes and diseases with different etiopathogenesis. The recent development of imaging and epilepsy surgery techniques is now enabling the identification of structural abnormalities that are part of the epileptic network, and the removal of these lesions may result in control of seizures. Access of this clinically well-characterized neurosurgical material has provided neuropathologists with the opportunity to study a variety of structural brain abnormalities associated with epilepsy, by combining traditional routine histopathologic methods with molecular genetics and functional analysis of the resected tissue. This approach has contributed greatly to a better diagnosis and classification of these structural lesions, and has provided important new insights into their pathogenesis and epileptogenesis. The present chapter provides a detailed description of the large spectrum of histopathologic findings encountered in epilepsy surgery patients, addressing in particular the nonneoplastic pathologies, including hippocampal sclerosis, malformations of cortical development, Sturge-Weber syndrome, and Rasmussen encephalitis, and reviews current knowledge regarding the underlying molecular pathomechanisms and cellular mechanisms mediating hyperexcitability.

Perivascular innervation: a multiplicity of roles in vasomotor control and myoendothelial signaling

The control of vascular resistance and tissue perfusion reflect coordinated changes in the diameter of feed arteries and the arteriolar networks they supply. Against a background of myogenic tone and metabolic demand, vasoactive signals originating from perivascular sympathetic and sensory nerves are integrated with endothelium-derived signals to produce vasodilation or vasoconstriction. PVNs release adrenergic, cholinergic, peptidergic, purinergic, and nitrergic neurotransmitters that lead to SMC contraction or relaxation via their actions on SMCs, ECs, or other PVNs. ECs release autacoids that can have opposing actions on SMCs. Respective cell layers are connected directly to each other through GJs at discrete sites via MEJs projecting through holes in the IEL. Whereas studies of intercellular communication in the vascular wall have centered on endothelium-derived signals that govern SMC relaxation, attention has increasingly focused on signaling from SMCs to ECs. Thus, via MEJs, neurotransmission from PVNs can evoke distinct responses from ECs subsequent to acting on SMCs. To integrate this emerging area of investigation in light of vasomotor control, the present review synthesizes current understanding of signaling events that originate within SMCs in response to perivascular neurotransmission in light of EC feedback. Although often ignored in studies of the resistance vasculature, PVNs are integral to blood flow control and can provide a physiological stimulus for myoendothelial communication. Greater understanding of these underlying signaling events and how they may be affected by aging and disease will provide new approaches for selective therapeutic interventions.

Aging impairs collateral sprouting of nociceptive axons in the rat

Sprouting of uninjured nociceptive axons was examined in young adult, middle aged and aged rats. Axon sprouting from the spared sural nerve, both into adjacent denervated skin and into end-to-side coapted nerve graft, was significantly higher in young rats than in aged rats. Cross-transplantations of the end-to-side coapted nerve grafts between young and aged rats demonstrated that axon sprouting from young recipient nerves into aged donor nerve grafts was significantly deteriorated, whereas the axon sprouting from aged recipient nerves into young donor nerve grafts was not statistically significantly affected. The levels of laminin polypeptides in peripheral nerves were 50-100% higher in young adult than in aged rats. However, the levels of peripherin, NGF isoforms and TrkA in skin, peripheral nerves and DRG, respectively, were not significantly reduced in aged rats. Therefore, impaired sprouting of nociceptive axons in aged rats is due rather to the alterations in peripheral neural pathways, than to the limited sprouting capacity of aged sensory neurons. Decreased levels of extracellular matrix components might be important in this respect.

Fibronectin: characterization of a somatic mutation in Sturge-Weber syndrome (SWS)

Sturge-Weber syndrome (SWS) is a rare, congenital neurocutaneous disorder with a leptomeningeal, facial trigeminal nerve dominative area and choroidal angioma. The cause of this disease remains unclear. Due to the occurrence of localized abnormality of blood vessel formation, somatic mutation has been put forward. Studies have indicated that fibronectin gene expressions in the SWS port-wine-derived fibroblasts are increased. Fibronectin is an important extracellular matrix molecule with key roles in regulating angiogenesis and vasculogenesis, in maintenance of the blood-brain barrier, blood vessel structure and function, as well as brain tissue responses to seizures. This is consistent with the presence of a hypothesized somatic mutation underlying SWS. In this study, we have proposed that fibronectin may be reflection of somatic mutation. Further research should be done to study the role of fibronectin in the pathogenesis of SWS. Understanding the pathophysiology of Sturge-Weber syndrome will help us to establish future neuroprotective strategies and novel treatment modalities.

Chapter 26: Age-related differences in the reinnervation after peripheral nerve injury

Numerous and extensive functional, structural, and biochemical changes characterize intact aged peripheral nervous system. Functional recovery after peripheral nerve injury depends on survival of injured neurons and functional reinnervation of target tissue by regeneration of injured axons and collateral sprouting of uninjured (intact) adjacent axons. The rate of axonal regeneration becomes slower and its extent (density and number of regenerating axons) decreases in aged animals. Aging also impairs terminal sprouting of regenerated axons and collateral sprouting of intact adjacent axons, thus further limiting target reinnervation and its functional recovery. Decreased survival of aged noninjured and injured neurons, limited intrinsic growth potential of neuron, alteration in its responsiveness to stimulatory or inhibitory environmental factors, and changes in the peripheral neural pathways and target tissues are possible reasons for impaired reinnervation after peripheral nerve injury in old age. The review of present data suggests that this impairment is mostly due to the age-related changes in the peripheral neural pathways and target tissues, and not due to the limited intrinsic growth capacity of neurons or their reduced responsiveness to trophic factors. Age-related alterations in the soluble target derived neurotrophic factors, like nerve growth factor, and nonsoluble extracellular matrix components of neural pathways, like laminin, might be important in this respect.

Advances in Sturge-Weber syndrome

PURPOSE OF REVIEW

Recent neuroimaging, clinical and molecular neuropathologic studies have provided new insights into the neurologic aspects of Sturge-Weber syndrome and are summarized here.

RECENT FINDINGS

Molecular studies suggest that abnormal brain blood vessel vasoactive and extracellular matrix molecule expression, as well as aberrant brain vascular innervation, contribute to the vascular malformation and its consequences. New magnetic resonance sequences may be useful for the early diagnosis of Sturge-Weber syndrome and perfusion magnetic resonance imaging, single photon emission computed tomography imaging, and positron emission tomography imaging studies are suggesting that decreased brain blood flow combined with altered hemodynamics during prolonged seizures may contribute to the neurologic declines in Sturge-Weber syndrome.

SUMMARY

Recent advances in our understanding of the neurologic issues offer promise for preventing brain injury in Sturge-Weber syndrome. More research is needed to translate advances in molecular research and neuroimaging advances into new treatment strategies for the disease.

Sturge-Weber syndrome: altered blood vessel fibronectin expression and morphology

Sturge-Weber syndrome presents with vascular malformations of the brain, skin, and eye. Fibronectin has potent effects on angiogenesis, vessel remodeling, and vessel innervation density. To determine fibronectin expression in the blood vessels of Sturge-Weber syndrome brain and skin tissue and to quantify the density and circumference of Sturge-Weber syndrome blood vessels by type compared with controls, we performed in situ hybridization for fibronectin messenger ribonucleic acid (RNA) expression on six Sturge-Weber syndrome cortical brain samples, six epilepsy brain samples, skin from two port-wine stain skin lesions, and two normal skin samples from two subjects with Sturge-Weber syndrome. Fibronectin messenger RNA was expressed in blood vessels and endothelial cells in the parenchyma of both Sturge-Weber syndrome and control brain tissues and in skin samples. Fibronectin expression was significantly reduced by 23% in the Sturge-Weber syndrome meningeal vessels compared with the epilepsy controls (P < .01). Fibronectin expression was significantly increased by 19% in the Sturge-Weber syndrome parenchymal vessels compared with the epilepsy controls (P < .05). No difference was found in the expression of fibronectin in port-wine stain skin blood vessels. The density of leptomeningeal blood vessels in the Sturge-Weber syndrome brain tissue samples was 45% greater than in the epilepsy samples (P < .05). Blood vessel circumference was significantly decreased in the Sturge-Weber syndrome meningeal vessels compared with the controls (27%; P < .05). When blood vessels from different brain regions were compared, fibronectin expression was decreased in Sturge-Weber syndrome meningeal vessels and was increased in the parenchymal vessels. Altered blood vessel fibronectin expression in Sturge-Weber syndrome could contribute to abnormal vascular structure and function in this disorder.

Pathophysiology of Sturge-Weber syndrome

Sturge-Weber syndrome is a neurocutaneous disorder classically presenting with a facial port-wine stain, vascular eye abnormalities, and an ipsilateral occipital leptomeningeal angioma. Children with Sturge-Weber syndrome often develop progressive neurologic problems. Data on the pathophysiology of Sturge-Weber syndrome are briefly reviewed. The embryologic, genetic, and pathologic considerations are discussed, as are theories regarding the mechanisms of the degenerative brain changes. Sturge-Weber syndrome likely results from an early embryologic malformation of vascular development affecting the development of the nearby skin, eye, and brain structures. Studies suggest that complex molecular interactions contribute to the abnormal development and function of blood vessels in Sturge-Weber syndrome. Neurologic deterioration in Sturge-Weber syndrome is likely secondary to impaired blood flow to the brain and is worsened by the presence of seizures. Insights from related areas are discussed, and future research studies are suggested.

Increased fibronectin expression in sturge-weber syndrome fibroblasts and brain tissue

Sturge-Weber syndrome (SWS) is a neurocutaneous disorder that presents with a facial port-wine stain and a leptomeningeal angioma. Fibronectin expression regulates angiogenesis and vasculogenesis and participates in brain tissue responses to ischemia and seizures. We therefore hypothesized that abnormal gene expression of fibronectin and other extracellular matrix genes would be found in SWS brain tissue and SWS port-wine skin fibroblasts. Fibronectin gene and protein expression from port-wine-derived fibroblasts were compared with that from normal skin-derived fibroblasts of four individuals with SWS using microarrays, reverse transcriptase-PCR, Western analysis, and immunocytochemistry. Fibronectin gene and/or protein expression from eight SWS surgical brain samples was compared with that in two surgical epilepsy brain samples and six postmortem brain samples using microarrays, reverse transcriptase-PCR, and Western analysis. The gene expression of fibronectin was significantly increased (p < 0.05) in the SWS port-wine-derived fibroblasts compared with that of fibroblasts from SWS normal skin. A trend for increased protein levels of fibronectin in port-wine fibroblasts was found by Western analysis. No difference in the pattern of fibronectin staining was detected. The gene expression of fibronectin was significantly increased (p < 0.05), and a trend for increased fibronectin protein expression was found in the SWS surgical brain samples compared with the postmortem controls. These results suggest a potential role for fibronectin in the pathogenesis of SWS and in the brain's response to chronic ischemic injury in SWS. The reproducible differences in fibronectin gene expression between the SWS port-wine-derived fibroblasts and the SWS normal skin-derived fibroblasts are consistent with the presence of a hypothesized somatic mutation underlying SWS.

Aging and neuronal plasticity: lessons from a model

In spite of many well-documented examples of age-related reductions in neuronal plasticity, the causes of such changes remain largely unknown. One example of age-reduced plasticity involves an aberrant sprouting response of mature rat sympathetic neurons into the CNS (hippocampal formation). This phenomenon has proven to be useful for exploring the relative contribution of target aging (extrinsic influences) versus neuronal aging (intrinsic influences) to reduced sprouting. Aged sympathetic neurons mount a robust growth response when confronted with young target tissue or when exposed to exogenous trophic factor in vivo. In contrast, the aged target tissue (the hippocampal formation in this example) exhibits reduced receptivity for sympathetic sprouting. This change in the target does not appear to be due to alterations in baseline levels of trophic or substrate support for axonal growth. Rather, aging appears to dampen the consequences of target denervation so that the aged target elicits less sprouting. Age-related reductions in neuronal sprouting are speculated to reflect increasing commitment to information storage at the expense of neuronal plasticity.

Innervation of cerebral blood vessels: morphology, plasticity, age-related, and Alzheimer's disease-related neurodegeneration

The light microscopical and ultrastructural morphology of the innervation of the major cerebral arteries and pial vessels is described, including the origins of the different groups of nerve fibres and their characteristic neurotransmitter phenotype. Species and region specific variations are described and novel data regarding the parasympathetic innervation of cerebral vessels are presented. The dynamic nature, or plasticity, of cerebrovascular innervation is emphasized in describing changes affecting particular subpopulations of neurons during normal ageing and in Alzheimer's disease. The molecular controls on plasticity are discussed with particular reference to target-associated factors such as the neurotrophins and their neuronal receptors, as well as extracellular matrix related factors such as laminin. Hypotheses are presented regarding the principal extrinsic and intrinsic influences on plasticity of the cerebrovascular innervation.

Responsiveness of sympathetic and sensory iridial nerves to NGF treatment in young and aged rats

Altered neuronal responses to trophic factors may play a role in neuronal maintenance in adulthood and may also be involved in neuronal atrophy in old age. We have investigated this issue in the rat iris, studying responsiveness of sympathetic and sensory iridial nerves to a range of NGF concentrations in mature and aged rats. We show here that growth responses of sensory nerves to NGF, as measured by quantitative immunohistochemistry and image analysis, were unchanged in old rats. In contrast, there was a small but significant reduction in responsiveness of aged sympathetic neurons. The shapes of the dose-response curves for sensory and sympathetic neurons were different, with a larger response over a narrower range of concentrations in sensory neurons. Lower levels of p75 immunoreactivity were observed in iridial nerves from old compared to young rats. NGF treatment had no effect on receptor staining in young rats but restored 'young' levels of p75 staining in old rats. Our results do not support the hypothesis of a primary role for NGF in maintenance or atrophy of nerves in ageing.

Cellular terrain surrounding sympathetic nerve pathways in the rat orbit: comparisons of orbital connective tissue and smooth muscle cell phenotypes

Sympathetic axons are abundant within some orbital tissues but are absent from others. This study investigated cellular phenotypes of tissues containing sympathetic nerves en passage and compared these with phenotypes in regions devoid of sympathetic nerves and with smooth muscle targets. Two primary orbital smooth muscle targets, the tarsal muscle and orbital muscle, contained many synaptophysin-immunoreactive nerves. Target cells had ultrastructural features typical of smooth muscle and were immunoreactive for alpha-smooth muscle actin, smooth muscle myosin heavy chain, desmin, vinculin, and laminin, but not non-muscle myosin, vimentin, fibronectin, or type IV collagen; nerve growth factor (NGF) mRNA was detected by reverse transcription-polymerase chain reaction. Periorbital sheath devoid of sympathetic nerves contained elongated fibroblasts that were immunoreactive for vimentin, non-muscle myosin, and fibronectin, but not for alpha-smooth muscle actin, smooth muscle myosin heavy chain, vinculin, desmin, laminin, or type IV collagen, and did not express NGF mRNA. Regions of periorbital sheath containing sympathetic nerves had few synaptophysin-immunoreactive varicosities. Cells in this region contained myofilaments, ribosomes, and rough endoplasmic reticulum and were larger than tarsal muscle cells. They expressed NGF mRNA and showed a unique immunophenotype, reacting for vimentin, alpha-smooth muscle actin and myosin heavy chain, desmin, vinculin, laminin, and type IV collagen. This phenotype reflects both fibroblast and smooth muscle features similar to myofibroblasts or transdifferentiated smooth muscle described in other tissues. The spatial association between these cells and sympathetic nerves suggests that they may be involved in axon guidance or maintenance.

Plasticity in adult and ageing sympathetic neurons

The nature of neural plasticity and the factors that influence it vary throughout life. Adult neurons undergo extensive and continual adaptation in response to demands that are quite different from those of early development. We review the main influences on the survival, growth and neurotransmitter expression in adult and ageing sympathetic neurons, comparing these influences to those at work in early development. This "developmental" approach is proposed because, despite the contrasting needs of different phases of development, each phase has a profound influence on the mechanisms of plasticity available to its successors. Interactions between neurons and their targets, whether effector cells or other neurons, are vital to all of these aspects of neural plasticity. Sympathetic neurons require access to target-derived diffusible neurotrophic factors such as NGF, NT3 and GDNF, as well as to bound elements of the extracellular matrix such as laminin. These factors probably influence plasticity throughout life. In adult life, and even in old age, sympathetic neurons are relatively resistant to cell death. However, they continue to require target-derived diffusible and bound factors for their maintenance, growth and neurotransmitter expression. Failure to maintain appropriate neuronal function in old age, for example in the breakdown of homeostasis, may result partly from a disturbance of the dynamic, trophic relationship between neurons and their targets. However, there is no clear evidence that this is due to a failure of targets to synthesize neurotrophic factors. On the neural side of the equation, altered responsiveness of sympathetic neurons to neurotrophic factors suggests that expression of the trk and p75 neurotrophin receptors contributes to neuronal survival, maintenance and growth in adulthood and old age. Altered receptor expression may therefore underlie the selective vulnerability of some sympathetic neurons in old age. The role of neural connectivity and activity in the regulation of synthesis of target-derived factors, as well as in neurotransmitter dynamics, is reviewed.

Free ureteral replacement in rats: regeneration of ureteral wall components in the acellular matrix graft

OBJECTIVES

To evaluate ureteral replacement by a free homologous graft of acellular matrix in a rat model.

METHODS

In 30 male Sprague-Dawley rats, a 0.3 to 0.8-cm midsegment of the left ureter was resected and replaced with an acellular matrix graft of equal length placed on a polyethylene stent. The animals were killed at varying intervals, and the grafted specimens were prepared for light and electron microscopy.

RESULTS

In all animals, the acellular matrix graft remained in its original position without evidence of incrustation or infection, and histologic examination showed complete epithelialization and progressive infiltration by vessels. At 10 weeks, smooth muscle fibers were observed; at 12 weeks, nerve fibers were first detected; at 4 months, smooth muscle cells had assumed regular configuration.

CONCLUSIONS

The ureteral acellular matrix graft appears to promote the regeneration of all ureteral wall components.

Decreased receptivity of pathway connective tissue to sympathetic nerve ingrowth in the developing rat

Sympathetic axons can form atypical pathways to denervated orbital targets in neonatal rats but not in rats aged 30 or more days. The objective of this study was to determine if connective tissue pathways that carry sympathetic nerves lose their ability to sustain axonal sprouting during the early postnatal period. Regions of periorbital sheath known to contain large numbers of sympathetic axons that travel to distal orbital targets were excised from rats (sympathectomized 3 days previously) on postnatal days 6-7, 14-15, 30-31, and 48-49 and placed in anterior chambers of adult host rats. Tissues were removed 3, 6, or 10 days post-transplant and sympathetic ingrowth was analyzed by catecholamine histofluorescence in whole-mount or cryosectioned specimens. Connective tissue transplants from 6-15-day-old donors showed significant fiber ingrowth by 3 days in oculo, and innervation was maximal by 6 days. In contrast, sprouting into 30-49-day-old tissue was significantly slower, with most transplants lacking fibers at 3 days, and with small numbers of short fibers present at 6 days. We conclude that maturational changes occur in periorbital connective tissue pathways in the early postnatal period which make them less receptive to ingrowth by sympathetic nerves. The findings that connective tissue pathways are better substrates for sympathetic sprouting in the neonatal rat supports the view that developmental changes in these tissues are likely to contribute to the impaired reinnervation of orbital targets by contralateral neurons in juvenile and adult rats.