Immunohistochemical localization of vascular endothelial growth factor receptors-1, -2 and -3 in human spinal cord: altered expression in amyotrophic lateral sclerosis

Mu-opioid receptor and receptor tyrosine kinase crosstalk: Implications in mechanisms of opioid tolerance, reduced analgesia to neuropathic pain, dependence, and reward

Despite the prevalence of opioid misuse, opioids remain the frontline treatment regimen for severe pain. However, opioid safety is hampered by side-effects such as analgesic tolerance, reduced analgesia to neuropathic pain, physical dependence, or reward. These side effects promote development of opioid use disorders and ultimately cause overdose deaths due to opioid-induced respiratory depression. The intertwined nature of signaling via μ-opioid receptors (MOR), the primary target of prescription opioids, with signaling pathways responsible for opioid side-effects presents important challenges. Therefore, a critical objective is to uncouple cellular and molecular mechanisms that selectively modulate analgesia from those that mediate side-effects. One such mechanism could be the transactivation of receptor tyrosine kinases (RTKs) via MOR. Notably, MOR-mediated side-effects can be uncoupled from analgesia signaling via targeting RTK family receptors, highlighting physiological relevance of MOR-RTKs crosstalk. This review focuses on the current state of knowledge surrounding the basic pharmacology of RTKs and bidirectional regulation of MOR signaling, as well as how MOR-RTK signaling may modulate undesirable effects of chronic opioid use, including opioid analgesic tolerance, reduced analgesia to neuropathic pain, physical dependence, and reward. Further research is needed to better understand RTK-MOR transactivation signaling pathways, and to determine if RTKs are a plausible therapeutic target for mitigating opioid side effects.

Elevated Cerebrospinal Fluid Proteins and Albumin Determine a Poor Prognosis for Spinal Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a heterogeneous disease, both in its onset phenotype and in its rate of progression. The aim of this study was to establish whether the dysfunction of the blood–brain barrier (BBB) and blood–spinal cord barrier (BSCB) measured through cerebrospinal fluid (CSF) proteins and the albumin-quotient (QAlb) are related to the speed of disease progression. An amount of 246 patients diagnosed with ALS were included. CSF and serum samples were determined biochemically for different parameters. Survival analysis based on phenotype shows higher probability of death for bulbar phenotype compared to spinal phenotype (p-value: 0.0006). For the effect of CSF proteins, data shows an increased risk of death for spinal ALS patients as the value of CSF proteins increases. The same model replicated for CSF albumin yielded similar results. Statistical models determined that the lowest cut-off value for CSF proteins able to differentiate patients with a good prognosis and worse prognosis corresponds to CSF proteins ≥ 0.5 g/L (p-value: 0.0189). For the CSF albumin, the QAlb ≥0.65 is associated with elevated probability of death (p-value: 0.0073). High levels of QAlb are a bad prognostic indicator for the spinal phenotype, in addition to high CSF proteins levels that also act as a marker of poor prognosis.

TDP-43 Vasculopathy in the Spinal Cord in Sporadic Amyotrophic Lateral Sclerosis (sALS) and Frontal Cortex in sALS/FTLD-TDP

Sporadic amyotrophic lateral sclerosis (sALS) and FTLD-TDP are neurodegenerative diseases within the spectrum of TDP-43 proteinopathies. Since abnormal blood vessels and altered blood-brain barrier have been described in sALS, we wanted to know whether TDP-43 pathology also occurs in blood vessels in sALS/FTLD-TDP. TDP-43 deposits were identified in association with small blood vessels of the spinal cord in 7 of 14 cases of sALS and in small blood vessels of frontal cortex area 8 in 6 of 11 FTLD-TDP and sALS cases, one of them carrying a GRN mutation. This was achieved using single and double-labeling immunohistochemistry, and double-labeling immunofluorescence and confocal microscopy. In the sALS spinal cord, P-TDP43 Ser403-404 deposits were elongated and parallel to the lumen, whereas others were granular, seldom forming clusters. In the frontal cortex, the inclusions were granular, or elongated and parallel to the lumen, or forming small globules within or in the external surface of the blood vessel wall. Other deposits were localized in the perivascular space. The present findings are in line with previous observations of TDP-43 vasculopathy in a subset of FTLD-TDP cases and identify this pathology in the spinal cord and frontal cortex in a subset of cases within the sALS/FTLD-TDP spectrum.

ALS and oxidative stress: the neurovascular scenario

Oxidative stress and angiogenic factors have been placed as the prime focus of scientific investigations after an establishment of link between vascular endothelial growth factor promoter (VEGF), hypoxia, and amyotrophic lateral sclerosis (ALS) pathogenesis. Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter and mutant superoxide dismutase 1 (SOD1) which are characterised by atrophy and muscle weakness resulted in phenotype resembling human ALS in mice. This results in lower motor neurodegeneration thus establishing an important link between motor neuron degeneration, vasculature, and angiogenic molecules. In this review, we have presented human, animal, and in vitro studies which suggest that molecules like VEGF have a therapeutic, diagnostic, and prognostic potential in ALS. Involvement of vascular growth factors and hypoxia response elements also highlights the converging role of oxidative stress and neurovascular network for understanding and treatment of various neurodegenerative disorders like ALS.

Analysis of in situ and ex vivo vascular endothelial growth factor receptor expression during experimental aortic aneurysm progression

OBJECTIVE

Mural inflammation and neovascularization are characteristic pathological features of abdominal aortic aneurysm (AAA) disease. Vascular endothelial growth factor receptor (VEGFR) expression may also mediate AAA growth and rupture. We examined VEGFR expression as a function of AAA disease progression in the Apolipoprotein E-deficient (Apo E(-/-)) murine AAA model.

METHODS AND RESULTS

Apo E(-/-) mice maintained on a high-fat diet underwent continuous infusion with angiotensin II at 1000 ng/kg/min (Ang II) or vehicle (Control) via subcutaneous osmotic pump. Serial transabdominal ultrasound measurements of abdominal aortic diameter were recorded (n=16 mice, 3 to 4 time points per mouse) for up to 28 days. Near-infrared receptor fluorescent (NIRF) imaging was performed on Ang II mice (n=9) and Controls (n=5) with scVEGF/Cy, a single-chain VEGF homo-dimer labeled with Cy 5.5 fluorescent tracer (7 to 18 microg/mouse IV). NIRF with inactivated single chain VEGF/Cy tracer (scVEGF/In, 18 microg/mouse IV) was performed on 2 additional Ang II mice to control for nonreceptor-mediated tracer binding and uptake. After image acquisition and sacrifice, aortae were harvested for analysis. An additional AAA mouse cohort received either an oral angiogenesis inhibitor or suitable negative or positive controls to clarify the significance of angiogenesis in experimental aneurysm progression. Aneurysms developed in the suprarenal aortic segment of all Ang II mice. Significantly greater fluorescent signal was obtained from aneurysmal aorta as compared to remote, uninvolved aortic segments in Ang II scVEGF/Cy mice or AAA in scVEGF/In mice or suprarenal aortic segments in Control mice. Signal intensity increased in a diameter-dependent fashion in aneurysmal segments. Immunostaining confirmed mural VEGFR-2 expression in medial smooth muscle cells. Treatment with an angiogenesis inhibitor attenuated AAA formation while decreasing mural macrophage infiltration and CD-31(+) cell density.

CONCLUSIONS

Mural VEGFR expression, as determined by scVEGF/Cy fluorescent imaging and VEGFR-2 immunostaining, increases in experimental AAAs in a diameter-dependent fashion. Angiogenesis inhibition limits AAA progression. Clinical VEGFR expression imaging strategies, if feasible, may improve real-time monitoring of AAA disease progression and response to suppressive strategies.

VEGF and ALS

In amyotrophic lateral sclerosis (ALS), an adult-onset progressive degeneration of motor neurons occurring as sporadic and familial disease, there is emerging evidence for and against the role of vascular endothelial growth factor (VEGF), an endothelial cell mitogen crucial for angiogenesis, in its etiopathogenesis. Our understanding of the role of VEGF in ALS has come from studies of both experimental models and human cases. In this article, I have examined in detail the in vitro and in vivo evidence for and against VEGF in ALS, concluding that more compelling evidence is required before we can conclusively link VEGF to ALS in humans.

Cellular distribution of vascular endothelial growth factor A (VEGFA) and B (VEGFB) and VEGF receptors 1 and 2 in focal cortical dysplasia type IIB

Members of the vascular endothelial growth factor (VEGF) family are key signaling proteins in the induction and regulation of angiogenesis, both during development and in pathological conditions. However, signaling mediated through VEGF family proteins and their receptors has recently been shown to have direct effects on neurons and glial cells. In the present study, we immunocytochemically investigated the expression and cellular distribution of VEGFA, VEGFB, and their associated receptors (VEGFR-1 and VEGFR-2) in focal cortical dysplasia (FCD) type IIB from patients with medically intractable epilepsy. Histologically normal temporal cortex and perilesional regions displayed neuronal immunoreactivity (IR) for VEGFA, VEGFB, and VEGF receptors (VEGFR-1 and VEGFR-2), mainly in pyramidal neurons. Weak IR was observed in blood vessels and there was no notable glial IR within the grey and white matter. In all FCD specimens, VEGFA, VEGFB, and both VEGF receptors were highly expressed in dysplastic neurons. IR in astroglial and balloon cells was observed for VEGFA and its receptors. VEGFR-1 displayed strong endothelial staining in FCD. Double-labeling also showed expression of VEGFA, VEGFB and VEGFR-1 in cells of the microglia/macrophage lineage. The neuronal expression of both VEGFA and VEGFB, together with their specific receptors in FCD, suggests autocrine/paracrine effects on dysplastic neurons. These autocrine/paracrine effects could play a role in the development of FCD, preventing the death of abnormal neuronal cells. In addition, the expression of VEGFA and its receptors in glial cells within the dysplastic cortex indicates that VEGF-mediated signaling could contribute to astroglial activation and associated inflammatory reactions.

Intrathecal upregulation of granulocyte colony stimulating factor and its neuroprotective actions on motor neurons in amyotrophic lateral sclerosis

To investigate cytokine/chemokine changes in amyotrophic lateral sclerosis (ALS), we simultaneously measured 16 cytokine/chemokines (interleukin [IL]-1beta, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12 [p70], IL-13, IL-17, interferon-gamma, tumor necrosis factor-alpha, granulocyte colony stimulating factor [G-CSF], macrophage chemoattractant protein-1 [MCP-1], and macrophage inflammatory protein-1beta) in cerebrospinal fluid (CSF) and sera from 37 patients with sporadic ALS and 33 controls using a multiplexed fluorescent bead-based immunoassay. We also conducted immunohistochemical analyses from 8 autopsied ALS cases and 6 nonneurologic disease controls as well as cell culture analyses of relevant cytokines and their receptors. We found that concentrations of G-CSF and MCP-1 were significantly increased in ALS CSF compared with controls. In spinal cords, G-CSF was expressed in reactive astrocytes in ALS cases but not controls, whereas G-CSF receptor expression was significantly decreased in motor neurons of spinal cords from ALS cases. Biologically, G-CSF had a protective effect on the NSC34 cell line under conditions of both oxidative and nutritional stress. We suggested that G-CSF has potentially neuroprotective effects on motor neurons in ALS and that downregulation of its receptor might contribute to ALS pathogenesis. On the other hand, MCP-1 correlated with disease severity, which may aggravate motor neuron damage.

Amyotrophic lateral sclerosis: contemporary concepts in etiopathogenesis and pharmacotherapy

Among the neurodegenerative diseases associated with ageing, amyotrophic lateral sclerosis (ALS) remains the most devastating. The disease inexorably progresses, the vast majority of pharmacotherapies have failed to modify the disease course, death ensues on average within 5 years of symptom onset and increasing numbers of individuals are afflicted with the disease. However, significant advances in our understanding of the natural history of ALS and of the fundamental nature of the biological defect underlying motor neuron degeneration have been gained, providing hope for the development of novel pharmacotherapies for ALS. Among these is the recognition that ALS is a biologically heterogeneous disorder in which genetics, environment and ageing all interrelate. The observation of clinical heterogeneity, with initial clinical manifestations serving as predictors of survivorship, is of considerable importance in designing therapeutic trials. The presence of frontotemporal dysfunction in a subset of patients has led to increased interest in the relationship between ALS and the degenerative tauopathies. Ultimately, the degenerating motor neurons do not die alone. The contribution of both microglia and astrocytes to the degenerative process are increasingly recognised. Understanding how these processes interrelate has become critical to understanding the pharmacotherapy of ALS and in the design of clinical trials. This review will highlight recent epidemiological and neurochemical advances in our understanding of ALS, and place them into the context of understanding the development of novel treatment avenues for this devastating disease.

Tumor-induced lymphangiogenesis: a target for cancer therapy?

Recent advances in understanding the biology of lymphangiogenesis, the new growth of lymphatic vessels, have cast new light on the molecular basis of metastasis to regional lymph nodes. The receptor tyrosine kinase VEGFR-3 is virtually exclusively expressed on lymphatic but not blood endothelium in the adult, and activation of VEGFR-3 by its ligands VEGF-C and VEGF-D is sufficient to induce lymphangiogenesis. Correlative studies with human tumors and functional studies using animal tumor models show that increased levels of VEGF-C or VEGF-D in tumors lead to enhanced numbers of lymphatic vessels in the vicinity of tumors, which in turn promotes metastasis to regional lymph nodes by providing a greater number of entry sites into the lymphatic system for invading tumor cells. These findings have prompted studies to investigate whether inhibitors of VEGFR-3 activation might represent novel therapeutic agents for the suppression of metastasis. However, a number of points regarding the therapeutic potential of anti-lymphangiogenic treatments in the context of cancer remain to be addressed. The spectrum and relative importance of molecules that induce lymphangiogenesis and the regulation of their expression during tumor progression, the reversibility of tumor-induced lymphangiogenesis, and possible side-effects of anti-lymphangiogenesis-based therapies all need to be investigated. Most importantly, the extent to which lymph node metastases contribute to the formation of metastases in other organs remains to be elucidated. These aspects are the focus of this review, and their investigation should serve as a roadmap to possible translational application.

Expression of Vascular Endothelial Growth Factor and Its Receptors in the Central Nervous System in Amyotrophic Lateral Sclerosis

Vascular endothelial growth factor (VEGF) prolongs survival in the mutant SOD1 transgenic mouse model of amyotrophic lateral sclerosis (ALS), whereas dysregulation of VEGF through deletion of its hypoxia-regulatory element causes motor neuron degeneration in mice. We investigated the expression of VEGF and its major agonist receptors in the normal central nervous system and in patients with ALS. Immunohistochemistry demonstrated similar expression patterns of VEGF and VEGF receptor 2 (VEGFR2) in the spinal cord with finely punctate staining of the neuropil and strong expression in anterior horn cells (AHCs). Granular staining on the surface of some AHCs, similar to that seen with synaptic markers, suggested synaptic labeling. VEGFR2 staining was reduced in the neuropil of ALS cases (p=0.018) associated with a reduction of synaptophysin but not SNAP25 expression. A greater proportion of AHCs in ALS cases showed low expression of VEGF (p=0.006) and VEGFR2 (p=0.009) compared with controls. Expression of VEGF and VEGFR2 was confirmed by Western blotting and quantitative reverse transcriptase-polymerase chain reaction (QPCR). The similar expression patterns of VEGF and VEGFR2 suggests autocrine/paracrine effects on spinal motor neurons, and the reduction in their expression seen in ALS cases would support the hypothesis that, as in mouse models of the disease, reduced VEGF signaling may play a role in the pathogenesis of ALS.