Expression of angiogenic factors in rabbit spinal cord after transient ischaemia

Unexpected benefits of intermittent hypoxia: enhanced respiratory and nonrespiratory motor function

Intermittent hypoxia (IH) is most often thought of for its role in morbidity associated with sleep-disordered breathing, including central nervous system pathology. However, recent evidence suggests that the nervous system fights back in an attempt to minimize pathology by increasing the expression of growth/trophic factors that confer neuroprotection and neuroplasticity. For example, even modest ("low dose") IH elicits respiratory motor plasticity, increasing the strength of respiratory contractions and breathing. These low IH doses upregulate hypoxia-sensitive growth/trophic factors within respiratory motoneurons but do not elicit detectable pathologies such as hippocampal cell death, neuroinflammation, or systemic hypertension. Recent advances have been made toward understanding cellular mechanisms giving rise to IH-induced respiratory plasticity, and attempts have been made to harness the benefits of low-dose IH to treat respiratory insufficiency after cervical spinal injury. Our recent realization that IH also upregulates growth/trophic factors in nonrespiratory motoneurons and improves limb (or leg) function after incomplete chronic spinal injuries suggests that IH-induced plasticity is a general feature of motor systems. Collectively, available evidence suggests that low-dose IH may represent a safe and effective treatment to restore lost motor function in diverse clinical disorders that impair motor function.

Endothelial nitric oxide synthase in dorsal root ganglia during chronic inflammatory nociception

Nitric oxide (NO) is a gaseous molecule implicated both in vascular tone and nociceptive transmission. The capillary blood supply to the dorsal root ganglia (DRG) is unique because it is highly permeable to several low and high molecular-weight compounds. This anatomical situation leads to a potential role of endothelial nitric oxide synthase (eNOS) in inflammatory nociception, which is not well established. Therefore, we examined the role of eNOS in DRG in a murine chronic inflammatory pain model induced by complete Freund's adjuvant using L-N(5)-(1-iminoethyl)ornithine (L-NIO), a potent inhibitor of eNOS activity. Pain state was examined using a behavioral test. The expression of eNOS, platelet endothelial cell adhesion molecule-1 (CD31) and vascular endothelial growth factor (VEGF) was examined by immunofluorescence. In control animals, CD31 was detected in vessels; VEGF was localized both in vessels and neurons while a weak eNOS immunopositivity was detected in both vessels and in neurons. Under inflammatory pain conditions, eNOS, CD31 and VEGF immunopositivity increased. Administration of L-NIO significantly attenuated thermal hyperalgesia by 24 h and decreased eNOS activity and CD31 immunopositivity by 7 days. VEGF was unaffected. Our results show that eNOS plays a nociceptive role in the early phases of inflammation while in the later phases it may be involved in neurotrophic support.

Modifying effect of arterial hypertension on amyotrophic lateral sclerosis

Given the high oxygen consumption of motor neurons, we sought to assess the frequency and prognostic value of arterial hypertension (affecting brain's oxygen supply) in amyotrophic lateral sclerosis (ALS). We consecutively and prospectively included all ALS patients with regular medical follow-up and documented blood pressure measurements and monitored them until death. Vascular factors diagnosed prior to the onset of motor signs in ALS patients were compared with those in a stratified, age- and gender-matched case-control population. The severity of leukoaraiosis on magnetic resonance imaging (MRI) was blindly assessed. Post mortem examinations were performed when authorized. Compared with controls (n = 408), the 102 ALS patients were significantly more likely to display hypertension (41-57%) and current smoking (15-26%). The number of years of hypertension was associated with survival (HR = 1.04 (1.01-1.07)). In a multivariate analysis, leukoaraiosis severity (HR = 1.214 (1.096-1.344)), current smoking (HR = 1.766 (1.085-2.872)) and low vital capacity (HR = 2.422 (1.266-4.633)) remained independent predictors of survival. Post mortem examinations revealed a greater frequency of leukoaraiosis in ALS patients (p = 0.02). In conclusion, the effect of chronic hypertension on survival might be exerted through abnormal neural perfusion. The higher frequency of recent hypertension in ALS patients may be due to a compensatory increase in blood pressure in response to a lower oxygen supply.

Spinal vascular endothelial growth factor induces phrenic motor facilitation via extracellular signal-regulated kinase and Akt signaling

Although vascular endothelial growth factor (VEGFA-165) is primarily known for its role in angiogenesis, it also plays important neurotrophic and neuroprotective roles for spinal motor neurons. VEGFA-165 signals by activating its receptor tyrosine kinase VEGF receptor-2 (VEGFR-2). Because another growth/trophic factor that signals via a receptor tyrosine kinase (brain derived neurotrophic factor) elicits a long-lasting facilitation of respiratory motor activity in the phrenic nerve, we tested the hypothesis that VEGFA-165 elicits similar phrenic motor facilitation (pMF). Using immunohistochemistry and retrograde labeling techniques, we demonstrate that VEGFA-165 and VEGFR-2 are expressed in identified phrenic motor neurons. Furthermore, intrathecal VEGFA-165 administration at C4 elicits long-lasting pMF; intraspinal VEGFA-165 increased integrated phrenic nerve burst amplitude for at least 90 min after injection (53.1 ± 5.0% at 90 min; p < 0.001). Intrathecal VEGFA-165 increased phosphorylation (and presumed activation) of signaling molecules downstream from VEGFR-2 within the phrenic motor nucleus, including ERK (1.53 ± 0.13 vs 1.0 ± 0.05 arbitrary units in control rats; p < 0.05) and Akt (2.16 ± 0.41 vs 1.0 ± 0.41 arbitrary units in control rats; p < 0.05). VEGF-induced pMF was attenuated by the MEK/ERK inhibitor U0126 [1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto)butadiene] and was abolished by the phosphotidinositol 3 kinase/Akt inhibitor LY294002 [2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride], demonstrating that ERK mitogen-activated protein kinases and Akt are both required for full expression of VEGF-induced pMF. This is the first report that VEGFA-165 elicits plasticity in any motor system. Furthermore, because VEGFA-165 expression is hypoxia sensitive, it may play a role in respiratory plasticity after prolonged exposures to low oxygen.

Deregulation of the hypoxia inducible factor-1α pathway in monocytes from sporadic amyotrophic lateral sclerosis patients

The clinical course of the degenerative motor neuron disorder amyotrophic lateral sclerosis (ALS) is closely related to hypoxia. The normal response to hypoxia involves two pathways in particular: the hypoxia inducible factor 1α (HIF-1α) pathway (which notably controls the synthesis of vascular endothelial growth factor (VEGF)) and the nuclear factor kappa B (NF-κb) pathway (responsible for the production of inflammatory mediators, including prostaglandin E2 (PGE2)). Defects in VEGF gene expression are known to cause motor neuron degeneration in animal models. Circulating monocytes are precursors of the microglia, which are involved in the pathogenesis of ALS. To establish whether the HIF-1 and/or NF-κB pathways are deregulated during hypoxia in early-stage, sporadic ALS, we analyzed the response to acute (1 h) and prolonged (24 h) hypoxia in monocytes from ALS and healthy controls. We measured protein expression and mRNA transcription for VEGF, HIF-1, HIF-2, prolyl hydroxylases 1 and 2 (PHD-1 and -2, part of the HIF proteasome-dependent degradation pathway) and their modulation by PGE2. Our results showed that (i) the HIF-1 (but not HIF-2) and VEGF production induced by acute and prolonged hypoxia was selectively and markedly altered in ALS patients and (ii) this defect was not compensated for by PGE2 addition. Moreover, altered HIF-1α activation was associated with low levels of proteolysis by PHD-2 in cells from sporadic ALS patients (relative to controls). For the first time, we have demonstrated clinical and functional abnormalities in the HIF-1 pathway during hypoxia in monocytes from sporadic ALS patients.

CSF profiles of angiogenic and inflammatory factors depend on the respiratory status of ALS patients

Our objective was to assess the regulation of the hypoxia response of angiogenic and inflammatory factors from 76 cerebrospinal fluids (CSF) of sporadic amyotrophic lateral sclerosis (ALS) patients with different respiratory status. We first analysed the hypoxia response capacity by measuring CSF levels of angiogenin (ANG), VEGF, angiopoietin-2 (ANG-2) and PGE-2 in 40 ALS patients according to their hypoxaemia level and compared it with 40 neurological controls. We then compared the ANG, VEGF, EPO and ANG-2 CSF levels of 36 other ALS patients, divided into three groups with either 1) normoxaemia, 2) intermittent desaturation in the absence of hypoxaemia, or 3) chronic hypoxaemia with or without desaturation. We demonstrated a lack of up-regulation of both ANG and VEGF during hypoxaemia in ALS, compared with hypoxaemic controls. In contrast, PGE-2 and ANG-2 levels were increased in both hypoxaemic ALS patients and controls. ANG and VEGF levels did not increase in patients with long disease durations and with intermittent or chronic hypoxaemia. ANG-2 and EPO levels were up-regulated early in intermittent hypoxaemia and late in chronic hypoxaemia, respectively. Our results suggest alteration of the HIF-1alpha-mediated response to hypoxia during sporadic ALS, whereas the NFK-B pathway seems early activated.

Spinal stenosis: assessment of motor function, VEGF expression and angiogenesis in an experimental model in the rat

Reduction of blood flow in compressed nerve roots is considered as one important mechanism of induction of neurogenic intermittent claudication in lumbar spinal canal stenosis. Vascular endothelial growth factor (VEGF) is a potent stimulator of angiogenesis, and is increased in expression in hypoxic conditions. The objective of this study was to examine if cauda equina compression affects motor function and induces expression of VEGF and angiogenesis. The cauda equina was compressed by placing a piece of silicone rubber into the L5 epidural space. Walking duration was examined by rota-rod testing. The compressed parts of the cauda equina and L5 dorsal root ganglion (DRG) were removed at 3, 7, 14, or 28 days after surgery, and processed for immunohistochemistry for VEGF and Factor VIII (marker for vascular endothelial cells). Numbers of VEGF-immunoreactive (IR) cells and vascular density were examined. Walking duration was decreased after induction of cauda equina compression. The number of VEGF-IR cells in the cauda equina and DRG was significantly increased at 3, 14, and 28 days after cauda equina compression, compared with sham-operated rats (P < 0.05). Vascular density in the cauda equina was not increased at any of the time points examined. Cauda equina compression decreased walking duration, and induced VEGF expression in nerve roots and DRG.

Immunohistochemical demonstration of growth factors at the tendon-bone interface in anterior cruciate ligament reconstruction using a rabbit model

BACKGROUND

The success of anterior cruciate ligament (ACL) reconstruction using tendon grafts depends on biological integration between the tendon and bone. Growth factors play a significant role in this integration process, but few studies have defined the regulating mechanisms of these growth factors during tendon-bone healing. The aim of the present study was to clarify the relationship between the histological changes and the expression of endogenous growth factors at the tendon-bone interface.

METHODS

Using intra-articular tendon transfer in rabbits to stimulate ACL reconstruction, the presence of fibroblast growth factor-2 (FGF-2), vascular endothelial growth factor (VEGF), bone morphogenetic protein-2 (BMP-2), and BMP-7 at the interface between the tendon and bone was evaluated immunohistochemically. Histological and immunohistochemical investigations were performed at 1, 3, 6, and 12 weeks after surgery.

RESULTS

Fibrous integration of the tendon graft to the bone was observed immediately after tendon transfer and followed remodeling of the bone tunnel. Fibroblast and vascular growth factors were found in abundance at the tendon-bone interface in the first 3 weeks of graft incorporation, but were absent in the 12-week specimens. BMPs were found throughout the 12-week study period and were observed at high concentrations near the bone.

CONCLUSIONS

These results indicate that FGF-2 and VEGF contribute to fibrous integration between the tendon and bone during the early postoperative stage, and that BMP-2 and BMP-7 are specifically involved in bone remodeling leading to osseous integration. The early stages of tendon-bone healing might be important in controlling the integration process of the interface in ACL reconstruction surgery as seen in this rabbit model.

Histologic retinacular changes associated with ischemia in painful patellofemoral malalignment

Ischemic changes in 31 samples of lateral retinacula excised at surgical realignment in patients with isolated symptomatic patellofemoral malalignment resistant to conservative treatment were evaluated with conventional histology, electron microscopy, immunohistochemistry, and molecular biology. Morphologic and ultrastructural changes associated with ischemia including hypervascularization and increased vascular endothelial growth factor release were identified in painful patellofemoral malalignment. It is hypothesized that periodic short episodes of ischemia could be implicated in the pathogenesis of anterior knee pain in most cases of isolated symptomatic patellofemoral malalignment in active young patients by triggering neural proliferation.

Vascular endothelial growth factor and the nervous system

Vascular endothelial growth factor (VEGF) is an angiogenic factor essential for the formation of new blood vessels during embryogenesis and in many pathological conditions. A new role for VEGF as a neurotrophic factor has recently emerged. In the developing nervous system, VEGF plays a pivotal role not only in vascularization, but also in neuronal proliferation, and the growth of coordinated vascular and neuronal networks. After injury to the nervous system, activation of VEGF and its receptors may restore blood supply and promote neuronal survival and repair. There is a growing body of evidence that VEGF is essential for motor neurone survival, and that aberrant regulation of VEGF may play a role in the degeneration of neurones in diseases such as amyotrophic lateral sclerosis.

Anterior knee pain in the young patient--what causes the pain? "Neural model"

Anterior knee pain in young patients is the commonest type of knee disorder in clinical practice. However, the pathogenesis of this condition is unknown. On the basis of our recent research, we suggest a "neural model". In our view, hyperinnervation in the lateral retinaculum, mainly nociceptive substance P-positive nerves induced by the release of neural growth factor, is involved in the pathogenesis of anterior knee pain. We hypothesize that periodic short episodes of ischemia may trigger neural proliferation.

VEGF165 therapy exacerbates secondary damage following spinal cord injury

Vascular endothelial growth factor (VEGF) demonstrates potent and well-characterized effects on endothelial cytoprotection and angiogenesis. In an attempt to preserve spinal microvasculature and prolong the endogenous neovascular response observed transiently following experimental spinal cord injury (SCI), exogenous recombinant human VEGF (rhVEGF165) was injected into the injured rat spinal cord. Adult female Fischer 344 rats were subjected to moderate SCI (12.5 g-cm) using the NYU impactor. At 72 h after injury, animals were randomly assigned to three experimental groups receiving no microinjection or injection of saline or saline containing 2 microg of rhVEGF165. Acutely, VEGF injection resulted in significant microvascular permeability and infiltration of leukocytes into spinal cord parenchyma. 6 weeks postinjection, no significant differences were observed in most measures of microvascular architecture following VEGF treatment, but analysis of histopathology in spinal cord tissue revealed profound exacerbation of lesion volume. These results support the idea that intraparenchymal application of the proangiogenic factor VEGF may exacerbate SCI, likely through its effect on vessel permeability.

VEGF: once regarded as a specific angiogenic factor, now implicated in neuroprotection

Both blood vessels and nerves are guided to their target. Vascular endothelial growth factor (VEGF)A is a key signal in the induction of vessel growth (a process termed angiogenesis). Though initial studies, now a decade ago, indicated that VEGF is an endothelial cell-specific factor, more recent findings revealed that VEGF also has direct effects on neural cells. Genetic studies showed that mice with reduced VEGF levels develop adult-onset motor neuron degeneration, reminiscent of the human neurodegenerative disorder amyotrophic lateral sclerosis (ALS). Additional genetic studies confirmed that VEGF is a modifier of motor neuron degeneration in humans and in SOD1(G93A) mice--a model of ALS. Reduced VEGF levels may promote motor neuron degeneration by limiting neural tissue perfusion and VEGF-dependent neuroprotection. VEGF also affects neuron death after acute spinal cord or cerebral ischemia, and has also been implicated in other neurological disorders such as diabetic and ischemic neuropathy, nerve regeneration, Parkinson's disease, Alzheimer's disease and multiple sclerosis. These findings have raised growing interest in assessing the therapeutic potential of VEGF for neurodegenerative disorders.

Vascular and neuronal effects of VEGF in the nervous system: implications for neurological disorders

Vascular endothelial growth factor (VEGF) was originally discovered as an endothelial-specific growth factor. While the predominant role of this growth factor in the formation of new blood vessels (angiogenesis) is unquestioned, recent observations indicate that VEGF also has direct effects on neurons and glial cells, and stimulates their growth, survival and axonal outgrowth. Because of these pleiotropic effects, VEGF has now been implicated in several neurological disorders both in the preterm infant (leukomalacia) and the adult (stroke, neurodegeneration, cerebral and spinal trauma, ischemic and diabetic neuropathy, nerve regeneration). A challenge for the future is to unravel to what extent the effect of VEGF in these disorders relates to its angiogenic activity or direct neurotrophic effect.

Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter causes motor neuron degeneration

Hypoxia stimulates angiogenesis through the binding of hypoxia-inducible factors to the hypoxia-response element in the vascular endothelial growth factor (Vegf) promotor. Here, we report that deletion of the hypoxia-response element in the Vegf promotor reduced hypoxic Vegf expression in the spinal cord and caused adult-onset progressive motor neuron degeneration, reminiscent of amyotrophic lateral sclerosis. The neurodegeneration seemed to be due to reduced neural vascular perfusion. In addition, Vegf165 promoted survival of motor neurons during hypoxia through binding to Vegf receptor 2 and neuropilin 1. Acute ischemia is known to cause nonselective neuronal death. Our results indicate that chronic vascular insufficiency and, possibly, insufficient Vegf-dependent neuroprotection lead to the select degeneration of motor neurons.

Induction of phosphatidylinositol 3-kinase and serine-threonine kinase-like immunoreactivity in rabbit spinal cord after transient ischemia

The mechanism of spinal cord injury has been thought to be related with tissue ischemia, and spinal motor neuron cells are suggested to be vulnerable to ischemia. To evaluate the mechanism of such vulnerability of motor neurons, we attempted to make a reproducible model of rabbit spinal cord ischemia. Using this model, the inductions of phosphatidylinositol 3-kinase (PI3-k) and serine-threonine kinase (Akt) were investigated with immunohistochemical analyses for up to 7 days of the reperfusion following 15 min of ischemia in rabbit spinal cord. It has been demonstrated that both PI3-k and its downstream effector, Akt mediate growth factor-induced neuronal survival. Spinal cord sections from animals sacrificed at 8 h, 1, 2, and 7 days following the 15 min of ischemia were immunohistochemically evaluated using monoclonal antibodies for PI3-k and Akt. Following the 15 min of ischemia, the majority of the motor neurons showed selective cell death at 7 days of reperfusion. Immunoreactivity of PI3-k and Akt were induced at 8 h of reperfusion selectively in motor neuron cells. No glial cells and inter neurons were stained in the spinal cord sections. The activation of PI3-k and Akt protein at the early stage of reperfusion may be one of the factors responsible for the delay in neuronal death after spinal cord ischemia.

Phosphorylation of retinoblastoma protein in rat brain after transient middle cerebral artery occlusion

Although mature neurones do not replicate genomic DNA, some cell cycle-related kinases are aberrantly activated in neurones after ischaemia. As hyper-phosphorylation of retinoblastoma (Rb) protein is the common pathway in mitotic signal cascade, this study investigated the phosphorylation state of the Rb protein as well as its mRNA level in rat brain after transient middle cerebral artery (MCA) occlusion. Immunohisto-chemical analysis revealed that neurones in the sham-operated brain expressed Rb protein without the hyperphosphorylated form. Immunoreactivity for the hyperphosphorylated form of Rb protein progressively increased from 1 h to 3 days after ischaemia in neurones in the MCA territory. Western blot analysis demonstrated a similar change. However, reverse transcription-polymerase chain reaction study revealed that Rb showed no definite change at the mRNA level. These results suggest that Rb protein is progressively hyper-phosphorylated in the brain after ischaemia, which may activate apoptotic mechanisms in neuronal cells of the brain after ischaemia.

PrP immunohistochemistry: different protocols, including a procedure for long formalin fixation, and a proposed schematic classification for deposits in sporadic Creutzfeldt-Jakob disease

The use of immunohistochemistry on formalin-fixed and paraffin-embedded tissue has greatly improved the neuropathological diagnosis of Creutzfeldt-Jakob disease and the other subacute spongiform encephalopathies in human and animals. Two pitfalls of this technique, however, currently exist: low sensitivity after long formalin fixation and difficulties in interpreting some images. Here we review the protocols currently in use for the pretreatment of sections allowing PrP detection by immunohistochemistry. In addition, a technique useful after long formalin fixation is reported: enzymatic digestion with proteinase K (24 degrees C, 1/100 for 8 minutes) was employed in addition to the usual autoclaving (121 degrees C for 10 minutes) followed by formic acid (99% for 5 minutes) and 4M guanidine thiocyanate (4 degrees C for 2 hours). This allowed a substantial increase in the sensitivity of 3F4 immunohistochemistry on paraffin-embedded tissue, especially after prolonged formalin fixation. In addition, we suggest a simple method for classification of PrP immunolabelling in sporadic Creutzfeldt-Jakob disease that would allow easy comparisons.