Pathophysiological Function of Endogenous Calcitonin Gene–Related Peptide in Ocular Vascular Diseases

Calcitonin gene-related peptide and intermedin induce phosphorylation of p44/42 MAPK in primary human lymphatic endothelial cells in vitro

Calcitonin gene-related peptide (CGRP) and adrenomedullin 2/intermedin (AM2/IMD) play important roles in several pathologies, including cardiovascular disease, migraine and cancer. The efficacy of drugs targeting CGRP signalling axis for the treatment of migraine patients is sometimes offset by side effects (e.g. inflammation and microvascular complications, including aberrant neovascularisation in the skin). Recent studies using animal models implicate CGRP in lymphangiogenesis and lymphatic vessel function. However, whether CGRP or AM2/IMD can act directly on lymphatic endothelial cells is unknown. Here, we found that CGRP and AM2/IMD induced p44/42 MAPK phosphorylation in a time- and dose-dependent manner in primary human dermal lymphatic endothelial cells (HDLEC) in vitro, and thus directly affected these cells. These new findings reveal CGRP and AM2/IMD as novel regulators of LEC biology and warrant further investigation of their roles in the context of pathologies associated with lymphatic function in the skin and other organs, and therapies targeting CGRP signalling axis.

The vasoactive effects of bradykinin, vasoactive intestinal peptide, calcitonin gene-related peptide and neuropeptide Y depend on the perivascular tissue in porcine retinal arterioles in vitro

PURPOSE

The retina contains a number of vasoactive neuropeptides and corresponding receptors, but the role of these neuropeptides for tone regulation of retinal arterioles has not been studied in detail.

METHODS

Porcine arterioles with preserved perivascular retinal tissue were mounted in a wire myograph, and the tone was measured after the addition of increasing concentrations of bradykinin, vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), substance P (SP), calcitonin gene-related peptide (CGRP) and brain natriuretic peptide (BNP). The experiments were performed during inhibition of the synthesis of nitric oxide (NO), prostaglandins and dopamine and were repeated after removal of the perivascular retinal tissue.

RESULTS

Bradykinin, VIP and CGRP induced significant concentration-dependent dilatation and NPY significant concentration-dependent contraction of the arterioles in the presence of perivascular retinal tissue (p < 0.03 for all comparisons) but not on isolated arterioles. BNP and SP had no effect on vascular tone. The NOS inhibitor L-NAME reduced bradykinin- and VIP-induced relaxation (p < 0.001 for both comparisons), whereas none of the other inhibitors influenced the vasoactive effects of the studied neuropeptides.

CONCLUSION

The effects of neuropeptides on the tone of retinal arterioles depend on the perivascular retinal tissue and may involve effects other than those mediated by nitric oxide, prostaglandins and adrenergic compounds. Investigation of the mechanisms underlying the vasoactive effect of neuropeptides may be important for understanding and treating retinal diseases where disturbances in retinal flow regulation are involved in the disease pathogenesis.

Reduction in retinal microvascular perfusion during migraine attacks

OBJECTIVE

To determine if there are changes in structure and function of the retinal vasculature during and between migraine attacks using optical coherence tomography angiography (OCTA).

BACKGROUND

Migraine attacks commonly include visual symptoms, but the potential role of the retina in these symptoms is not well understood. OCTA is a rapid, non-invasive imaging technique that is used to visualize the retinal microvasculature with high spatial resolution in a clinical setting. In this study we used OCTA to quantify different features of the retinal vasculature in patients with migraine during and between attacks, as well as in healthy controls (HCs).

METHODS

We performed a prospective cohort study of 37 patients with migraine with aura (MA) (median [interquartile range, IQR] age of 37 [14] years, 86% female) and 30 with migraine without aura (MO) (median [IQR] age of 37 [17] years, 77% female) and 20 HCs (median [IQR] age of 35 [7] years, 50% female). Macular OCTA scans were obtained for all participants for the interictal analysis. In 12 MA and eight MO, scans were captured both during and outside of migraine attacks and five HCs had initial and repeat scans. In addition to analyzing the morphology of the foveal avascular zone, we calculated the vessel flux index (VFI), which is an indicator of retinal perfusion and conventional metrics (such as vessel area density) in the foveal and parafoveal regions.

RESULTS

There was a significant difference in the parafoveal VFI in the ictal state between the groups (p = 0.009). During migraine attacks there was a significant reduction in the parafoveal region VFI in MA (-7%, 95% confidence interval [CI] -10% to -4%; p = 0.006) and MO (-7%, 95% CI -10% to -3%; p = 0.016) from their interictal baseline as compared to the change between repeat scans in HCs (2%, 95% CI -3% to 7%). Interictally, there was a mean (standard deviation [SD]) 13% (10%) (p = 0.003) lower blood perfusion in the MA group as compared to the MO group in the foveal region (mean [SD] 0.093 [0.023] vs. 0.107 [0.021], p = 0.003). Interictal analysis also revealed higher circularity in the superficial foveal avascular zone in the MA group compared with the MO group (mean [SD] 0.686 [0.088] vs. 0.629 [0.120], p = 0.004). In addition, interictal analysis of the patients with MA or MO and unilateral headache showed increased retinal vascular parameters consistent with greater perfusion in the eye ipsilateral to the side of the pain as compared with the contralateral eye.

CONCLUSIONS

These results indicate that perfusion is reduced in MA and MO in the parafoveal retina during the ictal period. Interictally, the foveal retina in MA has reduced perfusion when compared to the foveal retina in MO. Patients with unilateral headache showed interictal asymmetry of retinal perfusion between eyes. These results indicate that changes in retinal perfusion could be a part of migraine pathophysiology, and that distinct retinal vascular signatures identified with OCTA could represent biomarkers for migraine.

Systemic Dendrimer-Peptide Therapies for Wet Age-Related Macular Degeneration

Wet age-related macular degeneration (AMD) is an end-stage event in a complex pathogenesis of macular degeneration, involving the abnormal growth of blood vessels at the retinal pigment epithelium driven by vascular endothelial growth factor (VEGF). Current therapies seek to interrupt VEGF signaling to halt the progress of neovascularization, but a significant patient population is not responsive. New treatment modalities such as integrin-binding peptides (risuteganib/Luminate/ALG-1001) are being explored to address this clinical need but these treatments necessitate the use of intravitreal injections (IVT), which carries risks of complications and restricts its availability in less-developed countries. Successful systemic delivery of peptide-based therapeutics must overcome obstacles such as degradation by proteinases in circulation and off-target binding. In this work, we present a novel dendrimer-integrin-binding peptide (D-ALG) synthesized with a noncleavable, "clickable" linker. In vitro, D-ALG protected the peptide payload from enzymatic degradation for up to 1.5 h (~90% of the compound remained intact) in a high concentration of proteinase (2 mg/mL) whereas ~90% of free ALG-1001 was degraded in the same period. Further, dendrimer conjugation preserved the antiangiogenic activity of ALG-1001 in vitro with significant reductions in endothelial vessel network formation compared to untreated controls. In vivo, direct intravitreal injections of ALG-1001 and D-ALG produced reductions in the CNV lesion area but in systemically dosed animals, only D-ALG produced significant reductions of CNV lesion area at 14 days. Imaging data suggested that the difference in efficacy may be due to more D-ALG remaining in the target area than ALG-1001 after administration. The results presented here offer a clinically relevant route for peptide therapeutics by addressing the major obstacles that these therapies face in delivery.

Role of Adrenomedullin 2/Intermedin in the Pathogenesis of Neovascular Age-Related Macular Degeneration

Adrenomedullin 2 (AM2; also known as intermedin) is a member of the adrenomedullin (AM) peptide family. Similarly to AM, AM2 partakes in a variety of physiological activities. AM2 has been reported to exert protective effects on various organ disorders; however, its significance in the eye is unknown. We investigated the role of AM2 in ocular diseases. The receptor system of AM2 was expressed more abundantly in the choroid than in the retina. In an oxygen-induced retinopathy model, physiological and pathologic retinal angiogenesis did not differ between AM2-knockout (AM2-/-) and wild-type mice. In contrast, in laser-induced choroidal neovascularization, a model of neovascular age-related macular degeneration, AM2-/- mice had enlarged and leakier choroidal neovascularization lesions, with exacerbated subretinal fibrosis and macrophage infiltration. Contrary to this, exogenous administration of AM2 ameliorated the laser-induced choroidal neovascularization-associated pathology and suppressed gene expression associated with inflammation, fibrosis, and oxidative stress, including that of VEGF-A, VEGFR-2, CD68, CTGF, and p22-phox. The stimulation of human adult retinal pigment epithelial (ARPE) cell line 19 cells with TGF-β2 and TNF-α induced epithelial-to-mesenchymal transition (EMT), whereas AM2 expression was also elevated. The induction of EMT was suppressed when the ARPE-19 cells were pretreated with AM2. A transcriptome analysis identified 15 genes, including mesenchyme homeobox 2 (Meox2), whose expression was significantly altered in the AM2-treated group compared with that in the control group. The expression of Meox2, a transcription factor that inhibits inflammation and fibrosis, was enhanced by AM2 treatment and attenuated by endogenous AM2 knockout in the early phase after laser irradiation. The AM2 treatment of endothelial cells inhibited endothelial to mesenchymal transition and NF-κB activation; however, this effect tended to be canceled following Meox2 gene knockdown. These results indicate that AM2 suppresses the neovascular age-related macular degeneration-related pathologies partially via the upregulation of Meox2. Thus, AM2 may be a promising therapeutic target for ocular vascular diseases.

Promotion of corneal angiogenesis by sensory neuron-derived calcitonin gene-related peptide

The normal cornea has no blood vessels but has abundant innervation. There is emerging evidence that sensory nerves, originated from the trigeminal ganglion (TG) neurons, play a key role in corneal angiogenesis. In the current study, we examined the role of TG sensory neuron-derived calcitonin gene-related peptide (CGRP) in promoting corneal neovascularization (CNV). We found that CGRP was expressed in the TG and cultured TG neurons. In the cornea, minimal CGRP mRNA was detected and CGRP immunohistochemical staining was exclusively co-localized with corneal nerves, suggesting corneal nerves are likely the source of CGRP in the cornea. In response to intrastromal suture placement and neovascularization in the cornea, CGRP expression was increased in the TG. In addition, we showed that CGRP was potently pro-angiogenic, leading to vascular endothelial cell (VEC) proliferation, migration, and tube formation in vitro and corneal hemangiogenesis and lymphangiogenesis in vivo. In a co-culture system of TG neurons and VEC, blocking CGRP signaling in the conditioned media of TG neurons led to decreased VEC migration and tube formation. More importantly, subconjunctival injection of a CGRP antagonist CGRP8-37 reduced suture-induced corneal hemangiogenesis and lymphangiogenesis in vivo. Taken together, our data suggest that TG sensory neuron and corneal nerve-derived CGRP promotes corneal angiogenesis.

Immunity and pain in the eye: focus on the ocular surface

Most ocular diseases are associated with pain. While pain has been generally considered a mere (deleterious) additional symptom, it is now emerging that it is a key modulator of innate/adaptive immunity. Because the cornea receives the highest nerve density of the entire body, it is an ideal site to demonstrate interactions between pain and the immune response. Indeed, most neuropeptides involved in pain generation are also potent regulators of innate and adaptive leukocyte physiology. On the other hand, most inflammatory cells can modulate the generation of ocular pain through release of specific mediators (cytokines, chemokines, growth factors, and lipid mediators). This review will discuss the reciprocal role(s) of ocular surface (and specifically: corneal) pain on the immune response of the eye. Finally, we will discuss the clinical implications of such reciprocal interactions in the context of highly prevalent corneal diseases.

Markers of the sympathetic, parasympathetic and sensory nervous system are altered in the human diabetic choroid

BACKGROUND

We sought to evaluate alterations in markers of the autonomic nervous system in human diabetic choroid.

METHODS

Eighteen eyeballs from subjects with diabetes and 22 eyeballs from subjects without diabetes were evaluated in this study. Synaptophysin, tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DβH), neuronal nitric oxide synthase (nNOS), choline acetyltransferase (ChAT), vesicular monoamine transporter II (VMAT-2), vesicular acetylcholine transporter (VAChT), vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP) levels were detected by western blot analysis and immunofluorescence was performed in some cases. Furthermore, differences in adrenergic (α1- and β2-subtypes) and cholinergic (M1 and M3) receptor levels between diabetic subjects and controls were noted.

RESULTS

Decreased synaptophysin levels were found in diabetic choroids by western blot analysis and a reduction of synaptophysin-immunoreactive nerves was also found by immunofluorescence. Furthermore, a decrease of the levels of the key enzyme (TH) and transporter (VMAT2) of norepinephrine was evident both by western blot analysis and immunofluorescence. Additionally, increased NPY, VAChT, nNOS, and CGRP levels were observed in diabetic choroids. The levels of adrenergic (β2 subtype) and acetylcholine (M1 subtype) receptors decreased in diabetic choroids, as shown by western blotting and although the differences in α1 and M3 were not significant, there was a downward trend.

CONCLUSIONS

In the diabetic choroid, the levels of neurotransmitters, enzymes, and receptors associated with choroidal blood flow regulation are altered. These changes may affect the regulation of choroidal blood flow and may be associated with impaired retinal function and retinal pathology.

Corneal Allografts: Factors for and against Acceptance

Cornea is one of the most commonly transplanted tissues worldwide. However, it is usually omitted in the field of transplantology. Transplantation of the cornea is performed to treat many ocular diseases. It restores eyesight significantly improving the quality of life. Advancements in banking of explanted corneas and progressive surgical techniques increased availability and outcomes of transplantation. Despite the vast growth in the field of transplantation laboratory testing, standards for corneal transplantation still do not include HLA typing or alloantibody detection. This standard practice is based on immune privilege dogma that accounts for high success rates of corneal transplantation. However, the increasing need for retransplantation in high-risk patients with markedly higher risk of rejection causes ophthalmology transplantation centers to reevaluate their standard algorithms. In this review we discuss immune privilege mechanisms influencing the allograft acceptance and factors disrupting the natural immunosuppressive environment of the eye. Current developments in testing and immunosuppressive treatments (including cell therapies), when applied in corneal transplantation, may give very good results, decrease the possibility of rejection, and reduce the need for retransplantation, which is fairly frequent nowadays.

Exploring the choroidal vascular labyrinth and its molecular and structural roles in health and disease

The choroid is a key player in maintaining ocular homeostasis and plays a role in a variety of chorioretinal diseases, many of which are poorly understood. Recent advances in the field of single-cell RNA sequencing have yielded valuable insights into the properties of choroidal endothelial cells (CECs). Here, we review the role of the choroid in various physiological and pathophysiological mechanisms, focusing on the role of CECs. We also discuss new insights regarding the phenotypic properties of CECs, CEC subpopulations, and the value of measuring transcriptomics in primary CEC cultures derived from post-mortem eyes. In addition, we discuss key phenotypic, structural, and functional differences that distinguish CECs from other endothelial cells such as retinal vascular endothelial cells. Understanding the specific clinical and molecular properties of the choroid will shed new light on the pathogenesis of the broad clinical range of chorioretinal diseases such as age-related macular degeneration, central serous chorioretinopathy and other diseases within the pachychoroid spectrum, uveitis, and diabetic choroidopathy. Although our knowledge is still relatively limited with respect to the clinical features and molecular pathways that underlie these chorioretinal diseases, we summarise new approaches and discuss future directions for gaining new insights into these sight-threatening diseases and highlight new therapeutic strategies such as pluripotent stem cell‒based technologies and gene therapy.

[Novel migraine treatment with CGRP-related monoclonal antibodies]

Migraine is a common and debilitating neurological disorder characterized by recurrent attacks of moderate to severe throbbing headache accompanied by nausea, vomiting and photophobia/phonophobia. Because of its high prevalence, migraine causes a considerable financial burden on the society as well as impaired quality of life in individual patients. Scientific evidence shows that migraine is a quite complex neurological disorder that involves not only the trigeminovascular and autonomic systems but also the hypothalamus and cerebral cortex. Calcitonin gene-related peptide (CGRP) was originally discovered as a 37-amino acid neuropeptide derived from a calcitonin gene splicing variant. CGRP is found to be expressed in trigeminal ganglion neurons. Much attention has been attracted to this molecule since CGRP was found to be released from trigeminal terminals in animal migraine models. Subsequent studies demonstrated that CGRP administration induced migraine-like headache attacks specifically in migraineurs, thus highlighting a pivotal role of CGRP in the development of migraine attacks. Several CGRP receptor antagonists were shown to be efficacious for the treatment of acute migraine. Among them, telcagepant, was shown to exert a significant migraine prophylactic action as well. Nevertheless, the development of most of these agents were discontinued due to hepatotoxicity. Currently, newer CGRP receptor antagonists are being developed. On the other hand, monoclonal antibodies targeting CGRP and its receptor showed consistent efficacy for migraine prophylaxis with excellent safety profiles in Phase III clinical trials. Furthermore, emerging data support the long-term safety and efficacy of these antibodies. In this review article, the development and perspective of anti-migraine therapeutic strategies using CGRP-related antibodies are discussed.

Calcitonin Gene-Related Peptide in Blind, Painful Eyes

PURPOSE

To determine if calcitonin gene-related peptide (CGRP) is overexpressed in blind, painful eyes.

METHODS

This was a retrospective cross-sectional randomized control study conducted at a tertiary level hospital. Eight specimens of eyes enucleated by a single surgeon were included in the study. The control group patients underwent exenteration for cutaneous malignancy without intraocular involvement, while the case group was enucleated for management of blind, painful eye. Each eye was stained using immunohistochemistry for the expression of CGRP. Expression of CGRP was examined by counting the number of cells staining positive for CGRP in 5 consecutive ×40 fields in the choroid, iris, and cornea of each specimen.

RESULTS

The mean number of cells staining positively for CGRP in the choroid of blind, painful eye group was 45.5 (26.3) versus 5.5 (7.7) in nonpainful enucleated eyes. This difference was found to be statistically significant (p = 0.016). Comparison of iris and cornea did not reach statistical significance. Expression of CGRP was compared using a paired t test.

CONCLUSIONS

This study demonstrates that CGRP is overexpressed in the choroid of enucleated blind, painful eyes. Modulation of this protein may represent a meaningful, nonsurgical therapeutic strategy to addressing the blind, painful eye.

Neuropeptides in sensory signal processing

Peptides released from trigeminal fibers fulfill well-understood functions in neuroinflammatory processes and in the modulation of nociceptive signal processing. In particular, calcitonin gene-related peptide (CGRP) and substance P (SP), released from afferent nerve terminals, exert paracrine effects on the surrounding tissue and this has been recently highlighted by the prominent parcrine role of CGRP in the development of headache and migraine. Some recent communications suggest that these sensory neuropeptides may also modulate the workings of sensory organs and influence afferent signals from nose, tongue, eyes and ears. Here, we briefly review the evidence for modulatory effects of CGRP and SP in the sensory periphery.

Evidence That ADAM17 Mediates the Protective Action of CGRP against Angiotensin II-Induced Inflammation in Vascular Smooth Muscle Cells

Calcitonin gene-related peptide (CGRP) has a potent protective action on the cardiovascular system; however, little is known about the role of CGRP in angiotensin II- (Ang II-) induced inflammation of vascular smooth muscle cells (VSMCs). This study is aimed at determining the anti-inflammatory effect of CGRP in Ang II-treated VSMCs and whether a disintegrin and metalloproteinase 17 (ADAM17) modulates this protective action. Small interference RNA (siRNA) and inhibitors of CGRP, epidermal growth factor receptor (EGFR), and extracellular signal-regulated kinase 1/2 (ERK1/2) were adopted to investigate their effect on Ang II-induced inflammation in VSMCs. Here, we found that CGRP could inhibit inflammation and decrease ADAM17 expression and activation of EGFR and ERK1/2 in VSMCs stimulated with Ang II. Results of siRNA demonstrated that ADAM17 siRNA attenuated Ang II-induced inflammation and up-regulation of activities of EGFR and ERK1/2 in VSMCs. Furthermore, the EGFR-ERK1/2 pathway promoted Ang II-induced VSMC inflammation. In summary, these findings identify the anti-inflammatory effect of CGRP in VSMCs stimulated by Ang II and suggest that ADAM17 is involved in the protective effect of CGRP against Ang II-induced inflammation via the EGFR-ERK1/2 pathway in VSMCs.