The Protective Effects and Mechanisms of Apelin/APJ System on Ischemic Stroke: A Promising Therapeutic Target

Now we just need whomever is running the stroke strategy to see what followup research needs to be done. Oops, that will never occur. WE HAVE NO STROKE LEADERSHIP AND NO STROKE STRATEGY. 

Until we get stroke survivors in charge nothing useful is going to happen to get to 100% recovery. No one in stroke is even thinking about that goal. 

The Protective Effects and Mechanisms of Apelin/APJ System on Ischemic Stroke: A Promising Therapeutic Target

Yanjun Tian^1†, Ruijiao Chen^1†, Yunlu Jiang^2,3, Bo Bai³, Tongju Yang^4* and Haiqing Liu^5*

• ¹Collaborative Innovation Center for Birth Defect Research and Transformation of Shandong Province, Jining Medical University, Jining, China
• ²School of Mental Health, Jining Medical University, Jining, China
• ³Institute of Neurobiology, Jining Medical University, Jining, China
• ⁴Department of Pharmacy, People's Hospital of Zoucheng City, Jining, China
• ⁵Department of Physiology, Shandong First Medical University (Shandong Academy of Medical Sciences), Taian, China

The orphan receptor APJ and its endogenous ligand apelin, which are expressed in the brain, are the major components of the apelin/APJ system. Growing evidence shows that the apelin/APJ system plays a vital role in the pathophysiology of cerebral ischemic injury. Targeting the apelin/APJ system may have protective effects on cerebral ischemic injury. In this review, we sum up the latest research progress relating to the actions and therapeutic potential of the apelin/APJ system in ischemic stroke. An in-depth knowledge of the pathophysiological effects of the apelin/APJ system and the underlying mechanisms will help to develop novel therapeutic interventions for ischemic stroke.

Introduction

In 1993, O'Dowd discovered the orphan G protein–coupled receptor (GPCR) APJ while searching for vasopressin receptor subtypes (1). APJ is encoded by a gene located on chromosome 11q12. Although APJ shares 54% homology with angiotensin II receptor type-1 (AT1R) in the hydrophobic transmembrane region, there's no binding site for angiotensin II (1). Tatemoto et al. isolated apelin, the cognate ligand for APJ receptor, from bovine stomach tissue extracts in 1998 (2). The apelin gene, which is located on chromosome Xq25-26.1, encodes the preproapelin of 77 amino acids (apelin-77). Various bioactive isoforms of apelin are derived from apelin-77, including apelin-55, apelin-36, apelin-17, apelin-13, and apelin-12 (3, 4). Recently Chng et al. discovered apela, another endogenous ligand for APJ, which is encoded by a gene located on chromosome 11 and is critical in embryonic development (5, 6). However, in humans, the apela is only expressed in pluripotent cells and kidney (7). The apelin/APJ system mainly refers to APJ and its endogenous ligand, apelin.

Stroke, which is mainly caused by cerebral vascular occlusion and cerebral blood supply disorder, is one of the leading causes of death and disability worldwide, and 87% of cases are ischemic stroke (8). The cerebral infarction area is composed of the ischemic core and penumbra; apoptosis is the main cause of neuronal damage in the penumbra region, which also provides an opportunity for the treatment of ischemic stroke and makes it possible to use drugs to alleviate neuronal injury since the apoptosis is delayed and reversible (9, 10). Neuronal apoptosis in ischemic penumbra is triggered by diffusion of toxic substances released by the dead neurons of the ischemic core in the acute stage of ischemia, while ischemia injury is aggravated after reperfusion, namely ischemia/reperfusion (I/R) injury, which contributes to the neuron apoptosis in the penumbra via numerous biological mechanisms, including excitotoxicity, oxidative and nitrative stress, inflammatory responses, endoplasmic reticulum stress (ERS), and so on (11–14).

The apelin/APJ system is widely expressed in the central nervous system, especially in neurons and oligodendrocytes (15, 16). Growing evidence indicates that the apelin/APJ system is involved in the pathophysiology of ischemic stroke (17, 18). Targeting the apelin/APJ system may have protective effects on cerebral ischemic injury. In this review, we mainly focus on the latest research progress related to the biological functions and therapeutic potential of the apelin/APJ system in ischemic stroke.

Intranasal Delivery of Apelin-13 Is Neuroprotective and Promotes Angiogenesis After Ischemic Stroke in Mice

We need both the neuroprotection and angiogenesis post-stroke. This should trigger an immediate human clinical trial if we had anyone in stroke with two functional neurons and some leadership skills. But we don't so your children and grandchildren will still be screwed by having a stroke. 

Intranasal Delivery of Apelin-13 Is Neuroprotective and Promotes Angiogenesis After Ischemic Stroke in Mice 

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Dongdong Chen¹²

Dongdong Chen

1Deptartment of Anesthesiology, Emory University School of Medicine, Atlanta, GA, USA2Center for Visual and Neurocognitive Rehabilitation, Atlanta Veterans Affair Medical Center, Decatur, GA, USA
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, Jinhwan Lee¹²

Jinhwan Lee

1Deptartment of Anesthesiology, Emory University School of Medicine, Atlanta, GA, USA2Center for Visual and Neurocognitive Rehabilitation, Atlanta Veterans Affair Medical Center, Decatur, GA, USA
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, Xiaohuan Gu¹²

Xiaohuan Gu

1Deptartment of Anesthesiology, Emory University School of Medicine, Atlanta, GA, USA2Center for Visual and Neurocognitive Rehabilitation, Atlanta Veterans Affair Medical Center, Decatur, GA, USA
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Ling Wei¹²³

Ling Wei

1Deptartment of Anesthesiology, Emory University School of Medicine, Atlanta, GA, USA2Center for Visual and Neurocognitive Rehabilitation, Atlanta Veterans Affair Medical Center, Decatur, GA, USA3Department of Neurology, Emory University School of Medicine, Atlanta, GA, USA
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, Shan Ping Yu¹²

Shan Ping Yu

1Deptartment of Anesthesiology, Emory University School of Medicine, Atlanta, GA, USA2Center for Visual and Neurocognitive Rehabilitation, Atlanta Veterans Affair Medical Center, Decatur, GA, USA
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First Published September 21, 2015 Research Article

https://doi.org/10.1177/1759091415605114

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Article Information

Volume: 7 issue: 5,

Article first published online: September 21, 2015; Issue published: October 15, 2015

https://doi.org/10.1177/1759091415605114

Dongdong Chen¹, ², Jinhwan Lee¹, ², Xiaohuan Gu¹, ², Ling Wei¹, ², ³, Shan Ping Yu¹²

¹Deptartment of Anesthesiology, Emory University School of Medicine, Atlanta, GA, USA

²Center for Visual and Neurocognitive Rehabilitation, Atlanta Veterans Affair Medical Center, Decatur, GA, USA

³Department of Neurology, Emory University School of Medicine, Atlanta, GA, USA

Corresponding Author: Shan Ping Yu, Emory University, 101 Woodruff Circle, Woodruff Memorial Research Building, Suite 620, Atlanta, GA 30322, USA. Email: spyu@emory.edu

This article is distributed under the terms of the Creative Commons Attribution 3.0 License (http://www.creativecommons.org/licenses/by/3.0/) which permits any use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access page (https://us.sagepub.com/en-us/nam/open-access-at-sage).

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Abstract

Apelin is a peptide originally isolated from bovine stomach tissue extracts and identified as an endogenous ligand of the APJ receptor; recent work showed that apelin ameliorates the ischemic injury in the heart and the brain. Being an analogue to the angiotensin II receptor, the apelin/APJ signaling may mediate angiogenesis process. We explored the noninvasive intranasal brain delivery method and investigated therapeutic effects of apelin-13 in a focal ischemic stroke model of mice. Intranasal administration of apelin-13 (4 mg/kg) was given 30 min after the onset of stroke and repeated once daily. Three days after stroke, mice received apelin-13 had significantly reduced infarct volume and less neuronal death in the penumbra. Western blot analyses showed upregulated levels of apelin, apelin receptor APLNR, and Bcl-2 and decreased caspase-3 activation in the apelin-13-treated brain. The proinflammatory cytokines tumor necrosis factor-alpha, interleukin-1β, and chemokine monocyte chemoattractant protein-1 mRNA increased in the ischemic brain, which were significantly attenuated by apelin-13. Apelin-13 remarkably reduced microglia recruitment and activation in the penumbra according to morphological features of Iba-1-positive cells 3 days after ischemia. Apelin-13 significantly increased the expression of angiogenic factor vascular endothelial growth factor and matrix metalloproteinase-9 14 days after stroke. Angiogenesis illustrated by collagen IV + /5-bromo-2′-deoxyuridin + colabeled cells was significantly increased by the apelin-13 treatment 21 days after stroke. Finally, apelin-13 promoted the local cerebral blood flow restoration and long-term functional recovery. This study demonstrates a noninvasive intranasal delivery of apelin-13 after stroke, suggesting that the reduced inflammatory activities, decreased cell death, and increased angiogenesis contribute to the therapeutic benefits of apelin-13.

Keywords apelin-13, neuroprotection, angiogenesis, inflammation, functional recovery, ischemic stroke

Introduction

Stroke is a leading cause of human death and disability in the adult population in the United States and around the world. Among all stroke patients, 87% suffer from ischemic stroke (Roger et al., 2012). So far effective stroke treatments are still limited to thrombolytic therapy using tissue plasminogen activator with a narrow time window of 4.5 hr after the onset of an ischemic attack (Shobha et al., 2011; Jauch et al., 2013). Thus, stroke represents a clinical entity that requires more innovative treatments both for acute neuroprotection and for regenerative tissue repair.
Apelin was originally isolated from bovine stomach tissue extracts. It has been identified as an endogenous ligand of the APJ receptor, a G protein-coupled receptor related to angiotensin receptor AT1 (Lee et al., 2000a). Apelin is derived from a 77-amino acid length precursor peptide that can be cleaved by angiotensin-converting enzyme 2 into active apelins, including apelin-36 (42–77), apelin-17 (61–77), and apelin-13 (65–77; Lee et al., 2000b). Apelin-13 has completely conserved 13 C-terminal amino acids that are cross all species and exhibits the highest biological potency, including cardiomyocytes protection (Hosoya et al., 2000; Kleinz and Davenport, 2005; Simpkin et al., 2007). The active apelins are widely distributed in various organs and tissues, including the brain, lungs, testis, and uterus, and are highly expressed in the cardiovascular system. In the brain, apelins are widely expressed in neuronal cell bodies and fibers throughout the entire neuroaxis (Cheng et al., 2012). In neurological diseases, apelin level is significantly altered in the central nervous system. For example, apelin is significantly elevated in the epileptogenic temporal neocortex and absent in glial cells of temporal lobe epilepsy patients (Zhang et al., 2011).
Apelin receptor AGTRL1 was shown to associate with the development of ischemic stroke in the most recent genome-wide association study for ischemic stroke (Hata et al., 2011). As a neuropeptide, apelin exhibits neuroprotective function in both in vitro and in vivo studies. Pretreatment with apelin-13 or apelin-36 peptides, alone or in combination, increased hippocampal neuronal survival from 25% to 50% to 75% after HIV-induced excitotoxic injury (O’Donnell et al., 2007). Our previous in vitro study also showed that apelin-13 reduced serum deprivation-induced reactive oxygen species generation, mitochondria depolarization, cytochrome c release, and activation of caspase-3. We showed that apelin-13 could regulate cell survival kinases the protein kinase B (PKB, also known as AKT) and extracellular signal-regulated kinase (ERK)1/2 in cultured cortical neurons (Zeng et al., 2010). Most recently, apelin-13 was also demonstrated to protect brain from ischemia/reperfusion (IR) injury through activation of AKT and ERK1/2 signaling pathways in a mouse focal transient cerebral ischemia model (Yang et al., 2014). In a cerebral middle artery occlusion filament stroke model, apelin-36 reduced cell death and cerebral edema (Khaksari et al., 2012; Gu et al., 2013).
APJ has high-sequence homology with the angiotensin II type I receptor, but it binds to apelin instead of angiotensin II (O’Dowd et al., 1993; Lee et al., 2000a). Due to its similarity to the angiotensin II receptor, the functions of APJ have been widely studied on the cardiovascular system. Increasing evidence shows that the apelin/APJ signaling mediates the angiogenesis process. Overexpression of apelin increased Sirt3, vascular endothelial growth factor (VEGF)/VEGFR2, and angiopoietin-1 (Ang-1)/Tie-2 expression and the density of capillary and arteriole in the heart of diabetic mice (Zeng et al., 2014). Inhibition of apelin expression switched endothelial cells from proliferative to mature state in pathological retinal angiogenesis (Kasai et al., 2013). The proangiogenic role of apelin was also demonstrated in myocardial IR injury and murine hindlimb ischemia model. The loss of apelin impaired the angiogenesis and functional recovery, and exacerbated myocardial IR injury, while the elevation of apelin expression induced by adeno-associated virus transduction benefited the postischemic hindlimb perfusion (Qin et al., 2013; Wang et al., 2013). All the above evidence indicates the potential regenerative effects of apelin and a therapeutic application after ischemia. However, in all these in vivo studies, apelin was administered through lateral cerebral ventricle injection, which is highly invasive and less feasible in clinical conditions. As a potential protective drug for ischemic stroke treatment, it is important to seek for a noninvasive method to deliver apelin.
Intranasal administration is a noninvasive method to direct protein and peptide drugs into the brain by utilizing the olfactory neuronal distribution pathways in the cribriform plate, which leads to direct nose-to-brain drug distribution, bypasses the blood–brain barrier (BBB), and directly guides therapeutics to the brain (Hanson and Frey, 2008; Dhuria et al., 2010). Intranasal administration can directly transfer protein and peptides to the brain in similar or higher concentrations than that can be obtained by systemic administration (Scafidi et al., 2014). In this investigation, we tested the hypothesis that the neuroprotective effects of apelin-13 can be achieved by noninvasive intranasal delivery via reducing the infarct formation and inflammatory activities after ischemic stroke, leading to a long-term angiogenesis and functional recovery after stroke.