Protective effect of [Pyr1]-apelin-13 on oxidative stress-induced apoptosis in hair cell-like cells derived from bone marrow mesenchymal stem cells

Innovative treatment of age-related hearing loss using MSCs and EVs with Apelin

Utilizing single-cell transcriptome sequencing (scRNA-seq) technology, this study explores the viability of employing mesenchymal stem cells (MSCs) as a therapeutic approach for age-related hearing loss (ARHL). The research demonstrates MSCs' ability to differentiate into inner ear cell subpopulations, particularly hair cells, delivering Apelin via extracellular vesicles (EVs) to promote M2 macrophage polarization. In vitro experiments show reduced inflammation and preservation of hair cell health. In elderly mice, MSCs transplantation leads to hair cell regeneration, restoring auditory function. These findings highlight the regenerative capabilities of MSCs and EV-mediated therapeutic approaches for ARHL.

Protective effect of apelin-13 in lens epithelial cells via inhibiting oxidative stress-induced apoptosis

BACKGROUND

It is widely accepted that glaucoma-induced oxidative stress expedites cataracts' process. Therefore, we examined the effects of apelin-13 against oxidative stress-induced damage in human lens epithelial cells (HLECs) and investigated the potential pathogenic mechanism of acute primary angle-closure glaucoma.

METHODS

This experiment included five groups: control, H2O2, apelin-13 + H2O2, ML221 + H2O2, and apelin-13 + ML221 + H2O2. ML221 was employed in rescue experiments as an APJ antagonist. HLECs were pretreated with or without apelin-13 and subsequently exposed to H2O2. HLECs' viability was assessed by CCK8. Cell apoptosis was determined using Annexin V-FITC/PI staining. The mitochondrial membrane potential was assessed by fluorescent probe JC-1. Intracellular G6PD activity, NADPH/NADP+, and GSH/GSSG ratios were detected to assess the cells' oxidative damage.

RESULT

Apelin-13 reversed the H2O2-induced decrease in cell viability. The increased expression of G6PD and GLTU1, the G6PD, GSH/GSSG and NADPH/NADP + levels showed that apelin-13 can mitigate the H2O2-induced inhibition of the pentose phosphate pathway and dysregulation of cell redox status in the apelin-13 + H2O2 group compared with the H2O2 group. In H2O2-treated HLECs, apelin-13 can mitigate cell apoptosis, promote Bcl-2 expression, and suppress the Bax and Caspase-3 expression. In addition, H2O2 substantially reduced the mitochondrial membrane potential in HLECs, which was reversed by apelin-13. Notably, the inhibition of APJ intensified oxidative damage in H2O2-induced HLECs, demonstrating that the effects of apelin-13 were hindered by ML221.

CONCLUTIONS

Apelin-13 reduced oxidative damage and apoptosis in HLECs through APJ. These results demonstrate that apelin-13 can be employed as a potential drug for glaucoma with cataracts to delay the progression of cataracts.

Exploring the therapeutic potential: Apelin-13's neuroprotective effects foster sustained functional motor recovery in a rat model of Huntington's disease

Huntington's disease (HD) is a hereditary condition considered by the progressive degeneration of nerve cells in the brain, resultant in motor dysfunction and cognitive impairment. Despite current treatment modalities including pharmaceuticals and various therapies, a definitive cure remains elusive. Therefore, this study investigates the therapeutic potential effect of Apelin-13 in HD management. Thirty male Wistar rats were allocated into three groups: a control group, a group with HD, and a group with both HD and administered Apelin-13. Apelin-13 was administered continuously over a 28-day period at a dosage of around 30 mg/kg to mitigate inflammation in rats subjected to 3-NP injection within an experimental HD model. Behavioral tests, such as rotarod, electromyography (EMG), elevated plus maze, and open field assessments, demonstrated that Apelin-13 improved motor function and coordination in rats injected with 3-NP. Apelin-13 treatment significantly increased neuronal density and decreased glial cell counts compared to the control group. Immunohistochemistry analysis revealed reduced gliosis and expression of inflammatory factors in the treatment group. Moreover, Apelin-13 administration led to elevated levels of glutathione and reduced reactive oxygen species (ROS) level in the treated group. Apelin-13 demonstrates neuroprotective effects, leading to improved movement and reduced inflammatory and fibrotic factors in the HD model.

Neuroprotective effect of human cord blood-derived extracellular vesicles by improved neuromuscular function and reduced gliosis in a rat model of Huntington's disease

Huntington's disease (HD) is a hereditary condition characterized by the gradual deterioration of nerve cells in the striatum. Recent scientific investigations have revealed the promising potential of Extracellular vesicles (EVs) as a therapy to mitigate inflammation and enhance motor function. This study aimed to examine the impact of administering EVs derived from human umbilical cord blood (HUCB) on the motor abilities and inflammation levels in a rat model of HD. After ultracentrifugation to prepare EVs from HUCB to determine the nature of the obtained contents, the expression of CD markers 81 and 9, the average size and also the morphology of its particles were investigated by DLS and Transmission electron microscopy (TEM). Then, in order to induce the HD model, 3-nitropropionic acid (3-NP) neurotoxin was injected intraperitoneal into the rats, after treatment by HUCB-EVs, rotarod, electromyogram (EMG) and the open field tests were performed on the rats. Finally, after rat sacrifice and the striatum was removed, Hematoxylin and eosin staining (H&E), stereology, immunohistochemistry, antioxidant tests, and western blot were performed. Our results showed that the contents of the HUCB-EVs express the CD9 and CD81 markers and have spherical shapes. In addition, the injection of HUCB-EVs improved motor and neuromuscular function, reduced gliosis, increased antioxidant activity and inflammatory factor, and partially prevented the decrease of neurons. The findings generally show that HUCB-EVs have neuroprotective effects and reduce neuroinflammation from the toxic effects of 3-NP, which can be beneficial for the recovery of HD.

Atoh1 overexpression promotes Guinea pig bone marrow mesenchymal stem cells to differentiate into neural stem cell

Sensorineural hearing loss (SNHL) is a prevalent condition in otolaryngology. A key obstacle is finding effective strategies for regenerating damaged cochlear hair cells in adult animals. A practical and reliable approach has been developed to create a superior cell source for stem cell transplantation in the inner ear to treat SNHL. Atoh1 is involved in the differentiation of neurons, intestinal secretory cells, and mechanoreceptors including auditory hair cells, and thus plays an important role in neurogenesis. Lentivirus-mediated transfection of bone marrow mesenchymal stem cells (BMSCs) was utilized to achieve stable expression of the essential transcription factor Atoh1, which is crucial for developing auditory hair cells without compromising cell survival. By manipulating the induction conditions through altering the cell growth environment using anti-adherent culture, the synergistic impact of basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) was effectively applied to significantly improve the differentiation efficiency of bone marrow-derived mesenchymal stem cells (BMSC) into neural stem cells (NSCs) following Atoh1 transfection, thereby reducing the induction time. The study indicated that the newly proposed transdifferentiation method effectively transformed BMSCs into NSCs in a controlled environment, presenting a potential approach for stem cell transplantation to promote hair cell regeneration.

Apelin‑13 reduces high glucose‑induced mitochondrial dysfunction in cochlear hair cells by inhibiting endoplasmic reticulum stress

The complex manifestation of diabetic hearing loss and the relative inaccessibility of the inner ear contribute to the lack of research. The present study aimed to reveal the role of Apelin-13, a critical regulator of lipid metabolism, in diabetes-induced hearing loss. Cochlear hair cells treated with high glucose (HG) were adopted as an in vitro research model, and the impacts of Apelin-13 on cellular oxidative stress, apoptosis, mitochondrial dysfunction and endoplasmic reticulum (ER) stress were determined. In addition, cells were treated with the ER stress agonist tunicamycin to further explore its potential role in the regulatory effects of Apelin-13. Apelin-13 inhibited oxidative stress and apoptosis in the HG-induced cells. Additionally, Apelin-13 elevated mitochondrial membrane potential and ATP production, whereas it reduced mitochondrial reactive oxygen species levels. The levels of ER stress-related proteins exhibited a downward trend in response to Apelin-13. By contrast, tunicamycin reversed the effects of Apelin-13 on the aforementioned aspects, suggesting the role of ER stress in the regulatory effects of Apelin-13. In conclusion, the present study elucidated the protective role of Apelin-13 in ameliorating HG-induced mitochondrial functional impairment in cochlear hair cells by inhibiting ER stress.

Exosome Therapy and Photobiomodulation Therapy Regulate mi-RNA 21, 155 Expressions, Nucleus Acetylation and Glutathione in a Polycystic Ovary Oocyte: An In Vitro Study

Introduction: Polycystic ovary syndrome (PCOS) is a complex condition that can have various symptoms and complications, one of which is infertility. Dysregulation of miRNA has been associated with the pathogenesis of numerous illnesses such as PCOS. In this study, we evaluated the effect of photobiomodulation therapy (PBMT) and exosome therapy (EXO) on the regulation of miRNA and nucleus acetylation in a PCOS oocyte. Methods: In this research, 36 oocytes divided into three groups: control, EXO, and PBM (Wavelength of 640 nm). Subsequently, in-vitro maturation (IVM) was evaluated. Real-time PCR was used to evaluate miRNA-21,16,19,24,30,106,155 and GAPDH. Afterward, oocyte glutathione (GSH) and nucleus acetylation were measured by H4K12. Results: The expression of the miR-16, miRNA-19, miRNA-24, miRNA-106 and miRNA-155 genes in the EXO and PBMT groups was significantly down-regulated in comparison to the control group, but the expression of miRNA-21 and miR-30 significantly increased in the EXO and PBMT groups in comparison to the control group. The EXO and PBMT significantly increased GSH and nucleus acetylation (P<0.0001). Conclusion: The results of this study showed that the use of EXO and PBMT can improve GSH and nucleus acetylation in the PCOS oocyte and also change the expression of miRNAs.

Beneficial effects of Apelin-13 on metabolic diseases and exercise

Apelin, a novel endogenous ligand of the G-protein-coupled receptor APJ, is encoded by the APLN gene and can be hydrolyzed into multiple subtypes, with Apelin-13 being one of the most active subtypes of the Apelin family. Recent studies have revealed that Apelin-13 functions as an adipokine that participates in the regulation of different biological processes, such as oxidative stress, inflammation, apoptosis, and energy metabolism, thereby playing an important role in the prevention and treatment of various metabolic diseases. However, the results of recent studies on the association between Apelin-13 and various metabolic states remain controversial. Furthermore, Apelin-13 is regulated or influenced by various forms of exercise and could therefore be categorized as a new type of exercise-sensitive factor that attenuates metabolic diseases. Thus, in this review, our purpose was to focus on the relationship between Apelin-13 and related metabolic diseases and the regulation of response movements, with particular reference to the establishment of a theoretical basis for improving and treating metabolic diseases.

Apelin-13 protects against cisplatin-induced ototoxicity by inhibiting apoptosis and regulating STAT1 and STAT3

The ototoxic side effect of cisplatin is a main cause of sensorineural hearing loss. This side effect limits the clinical application of cisplatin and affects patients' quality of life. This study was designed to investigate the effect of apelin-13 on cisplatin-induced C57BL/6 mice hearing loss model and explore the potential underlying molecular mechanisms. Mice were intraperitoneally injected with 100 μg/kg apelin-13 2 h before 3 mg/kg cisplatin injection for 7 consecutive days. Cochlear explants cultured in vitro were pretreated with 10 nM apelin-13 2 h prior to 30 μM cisplatin treatment for another 24 h. Hearing test and morphology results showed that apelin-13 attenuated cisplatin-induced mice hearing loss and protected cochlear hair cells and spiral ganglion neurons from damage. In vivo and in vitro experimental results showed that apelin-3 reduced cisplatin-induced apoptosis of hair cells and spiral ganglion neurons. In addition, apelin-3 preserved mitochondrial membrane potential and inhibited ROS production in cultured cochlear explants. Mechanistic studies showed that apelin-3 decreased cisplatin-induced cleaved caspase 3 expression but increased Bcl-2; inhibited the expression of pro-inflammatory factors TNF-a and IL-6; and increased STAT1 phosphorylation but decreased STAT3 phosphorylation. In conclusion, our results indicate that apelin-13 could be a potential otoprotective agent to prevent cisplatin-induced ototoxicity by inhibiting apoptosis, ROS production, TNF-α and IL-6 expression, and regulating phosphorylation of STAT1 and STAT3 transcription factors.

The effects of apelin on IGF1/FSH-induced steroidogenesis, proliferation, Bax expression, and total antioxidant capacity in granulosa cells of buffalo ovarian follicles

Apelin (APLN) was believed to be an adipokine secreted from adipose tissue. However, studies demonstrate that it is a pleiotropic peptide and has several effects on the female reproductive system. In this study, We examined the effects of different doses of IGF1 and FSH in the presence of APLN-13 on the production of progesterone in buffalo ovary granulosa cells. Furthermore, different doses of APLN isoforms (APLN-13 and APLN-17) were tested on proliferation, Bax protein expression, and antioxidant capacity in the same cells. Granulosa cells of buffalo ovaries were cultured in the presence of different doses of IGF1 and FSH with or without APLN-13 (10-9 M) to evaluate its effect on the secretion of progesterone tested by ELISA assay. The WST-1 method was used to survey the effect of APLN on granulosa cell proliferation and cytotoxicity. In addition, the antioxidant capacity of the cells in the presence of APLN was assessed using the FRAP method. mRNA and Bax protein levels were measured in granulosa cells treated with APLN using real-time PCR and western blot techniques. APLN-13 (10-9) stimulated the effect of IGF1 on the production of progesterone, and its levels were affected by APLN-13 dose-dependently. However, it did not significantly stimulate the effect of FSH on the secretion of progesterone. APLN-13 (all doses) and APLN-17 (10-8 and 10-9 M) improved the proliferation of granulosa cells. Moreover, preincubation of the cells for an hour by APLN receptor antagonist (ML221, 10 µM) did not significantly affect the proliferation of cells induced by APLN. Neither APLN-13 nor APLN-17 were not cytotoxic for the cells compared to the control treatment. APLN-13 at the doses of 10-6 and 10-8 M substantially up and down-regulated Bax protein expression; however, such effects were not observed when the cells were preincubated with ML221. In addition, APLN-17 did not influence the expression amount of Bax. Furthermore, both APLN-13 and -17 improved the total antioxidant capacity of the ovarian granulosa cells, but such effects were not seen when the cells were preincubated with ML221. According to these results, APLN enhanced the steroidogenesis induced by IGF1 but did not affect the steroidogenesis induced by FSH. APLN also enhanced the cell proliferation and antioxidant capacity of buffalo ovaries follicular granulosa cells; however, its effect on Bax expression was different.

Effect of Noise and Music on Neurotransmitters in the Amygdala: The Role Auditory Stimuli Play in Emotion Regulation

Stress caused by noise is becoming widespread globally. Noise may lead to deafness, endocrine disorders, neurological diseases, and a decline in mental health. The mechanism behind noise-induced neurodevelopmental abnormalities is unclear, but apoptosis and pro-inflammatory signals may play an important role. In this study, weaned piglets were used as a model to explore noise-induced neurodevelopmental abnormalities. We hypothesized that long-term noise exposure would induce anxiety and cause acute stress, exhibited by alterations in neurotransmission in the amygdala. A total of 72 hybrid piglets (Large White × Duroc × Min Pig) were randomly divided into three groups, including noise (exposed to mechanical noise, 80-85 dB), control (blank, exposed to natural background sound, <40 dB), and music (positive control, exposed to Mozart K.448, 60-70 dB) groups. The piglets were exposed to 6 h of auditory noise daily (10:00-16:00) for 28 days. Compared with the control group, piglets exposed to noise showed more aggressive behavior. The expression of Caspase3, Caspase9, Bax, NF-κB (p56), TLR4, MYD88, I κ B α, IL-1 β, TNF-α, and IL-12RB2 was significantly upregulated in the amygdala, while the expression of Nrf2, HO-1, CAT, and SOD was downregulated in piglets in the noise group. Cell death occurred, and numerous inflammatory cells accumulated in the amygdala of piglets in the noise group. Targeted metabolomics showed that the content of inhibitory neurotransmitter GABA was higher in the amygdala of piglets in the noise group. Compared with the noise group, piglets in the music group displayed more positive emotion-related behaviors. Compared with the noise group, the expression of genes related to apoptosis, inflammation, and oxidative damage was lower in the music group. Cells of the amygdala in the music group were also of normal morphology. Our results show that noise-induced stress causes apoptosis and neuroinflammation in the amygdala and induces anxiety during the early neonatal neural development of piglets. In contrast, to some extent, music alleviates noise-induced anxiety.

Apelin-13, a regulator of autophagy, apoptosis and inflammation in multifaceted bone protection

Apelin/APJ is widely distributed in various tissues in the body and participates in the regulation of physiological and pathological mechanisms such as autophagy, apoptosis, inflammation, and oxidative stress. Apelin-13 is an adipokine family member with multiple biological roles and has been shown to be involved in the development and progression of bone diseases. In the process of osteoporosis and fracture healing, Apelin-13 plays an osteoprotective role by regulating the autophagy and apoptosis of BMSCs, and promotes the osteogenic differentiation of BMSCs. In addition, Apelin-13 also attenuates the progression of arthritis by regulating the inflammatory response of macrophages. In conclusion, Apelin-13 has an important connection with bone protection, which provides a new strategy for the clinical treatment of bone-related diseases.

Apelin-13 Improves Cognitive Impairment and Repairs Hippocampal Neuronal Damage by Activating PGC-1α/PPARγ Signaling

Alzheimer's disease (AD) is a complex neurodegenerative disease that is prevalent around the world. Both Apelin-13 and proliferator-activated receptor-γ (PPARγ)/PPARγ co-activator 1α (PGC-1α) are regarded as candidate targets for treating AD. The investigation examined whether Apelin-13 exerts neuroprotective effects via PGC-1α/PPARγ signaling. In this study, Apelin-13 improved cognitive deficits in AD mice, while SR-18,292 (a PGC-1α inhibitor) interfered with the therapeutic effects of Apelin-13. Mechanistically, Apelin-13, PGC-1α and PPARγ were decreased in AD mice and oxygen-glucose deprivation (OGD)-induced neuronal cells. Apelin-13 bound to PGC-1α and negatively regulated the expression of PGC-1α and PPARγ. In turn, PGC-1α accelerated the accumulation of Apelin-13 and PPARγ. Additionally, neuronal apoptosis was inhibited, and the abundance of apoptosis-related proteins (Bax, Bcl-2, and cleaved caspase 3) was induced. The content of reactive oxygen species (ROS), malondialdehyde (MDA) and superoxide dismutase (SOD) fluctuated. The level of inflammatory factors (interleukin-6, IL-6, IL-10, tumor necrosis factor-α, TNF-α) was regulated. In short, Apelin-13 exerted anti-apoptosis, anti-oxidant stress and anti-inflammatory effects. Interestingly, PGC-1α silencing promoted neuronal apoptosis, oxidant stress and inflammation, and overexpression of PGC-1α exhibited the opposite. More importantly, inhibition of PGC-1α attenuated Apelin-13-enhanced cognitive impairment and neuronal damage. Therefore, our findings suggested that Apelin-13 exerted neuroprotective effects in part via the PGC-1α/PPARγ pathway.

G protein-coupled receptors in cochlea: Potential therapeutic targets for hearing loss

The prevalence of hearing loss-related diseases caused by different factors is increasing worldwide year by year. Currently, however, the patient’s hearing loss has not been effectively improved. Therefore, there is an urgent need to adopt new treatment measures and treatment techniques to help improve the therapeutic effect of hearing loss. G protein-coupled receptors (GPCRs), as crucial cell surface receptors, can widely participate in different physiological and pathological processes, particularly play an essential role in many disease occurrences and be served as promising therapeutic targets. However, no specific drugs on the market have been found to target the GPCRs of the cochlea. Interestingly, many recent studies have demonstrated that GPCRs can participate in various pathogenic process related to hearing loss in the cochlea including heredity, noise, ototoxic drugs, cochlear structure, and so on. In this review, we comprehensively summarize the functions of 53 GPCRs known in the cochlea and their relationships with hearing loss, and highlight the recent advances of new techniques used in cochlear study including cryo-EM, AI, GPCR drug screening, gene therapy vectors, and CRISPR editing technology, as well as discuss in depth the future direction of novel GPCR-based drug development and gene therapy for cochlear hearing loss. Collectively, this review is to facilitate basic and (pre-) clinical research in this area, and provide beneficial help for emerging GPCR-based cochlear therapies.

Endogenous Vasoactive Peptides and Vascular Aging-Related Diseases

Vascular aging is a specific type of organic aging that plays a central role in the morbidity and mortality of cardiovascular and cerebrovascular diseases among the elderly. It is essential to develop novel interventions to prevent/delay age-related vascular pathologies by targeting fundamental cellular and molecular aging processes. Endogenous vasoactive peptides are compounds formed by a group of amino acids connected by peptide chains that exert regulatory roles in intercellular interactions involved in a variety of biological and pathological processes. Emerging evidence suggests that a variety of vasoactive peptides play important roles in the occurrence and development of vascular aging and related diseases such as atherosclerosis, hypertension, vascular calcification, abdominal aortic aneurysms, and stroke. This review will summarize the cumulative roles and mechanisms of several important endogenous vasoactive peptides in vascular aging and vascular aging-related diseases. In addition, we also aim to explore the promising diagnostic function as biomarkers and the potential therapeutic application of endogenous vasoactive peptides in vascular aging-related diseases.

Cryopreservation of porcine skin-derived stem cells using melatonin or trehalose maintains their ability to self-renew and differentiate

Porcine skin-derived stem cells (pSDSCs) are a type of adult stem cells (ASCs) that retain the ability to self-renew and differentiate. Currently, pSDSCs research has entered an intense period of development; however there has been no research regarding methods of cryopreservation. In this paper, we explored an efficient cryopreservation method for pSDSCs. Our results demonstrated that cryopreserving 50 μm diameter pSDSCs aggregates resulted in a lower apoptosis rate and a greater ability to proliferate to form larger spherical cell aggregates than during single-cell cryopreservation. To further optimize the cryopreservation method, we added different concentrations of melatonin (N-acetyl-5-methoxytryptamine, MLT) and trehalose (d-trehalose anhydrous, TRE) to act as cryoprotectants (CPAs) for the pSDSCs. After comparative experiments, we found that the cryopreservation efficiency of 50 mM TRE was superior. Further experiments demonstrated that the reason why 50 mM TRE improved cryopreservation efficiency was that it reduced the intracellular oxidative stress and mitochondrial damage caused by cryopreservation. Taken together, our results suggest that cryopreserving 50 μm diameter pSDSCs aggregates in F12 medium with 10% dimethyl sulfoxide (DMSO) and 50 mM TRE promotes the long-term storage of pSDSCs.

Combined treatment of retinoic acid with olfactory ensheathing cells protect gentamicin-induced SGNs damage in the rat cochlea in vitro

Hearing is mainly dependent on the function of hair cells (HCs) and spiral ganglion neurons (SGNs) which damage or loss of them leads to irreversible hearing loss. Olfactory ensheathing cells (OECs) are specialized glia that forms the fascicles of the olfactory nerve by surrounding the olfactory sensory axons. The OECs, as a regenerating part of the nervous system, play a supporting function in axonal regeneration and express a wide range of growth factors. In addition, retinoic acid (RA) enhances the proliferation and differentiation of these cells into the nerve. In the present study, we co-cultured human OECs (hOECs) with cochlear SGNs in order to determine whether hOECs and RA co-treatment can protect the repair process in gentamycin-induced SGNs damage in vitro. For this purpose, cochlear cultures were prepared from P4 Wistar rats, which were randomly appointed to four groups: normal cultivated SGNs (Control), gentamicin-lesioned SGNs culture (Gent), gentamicin-lesioned SGNs culture treated with OECs (Gent + OECs) and gentamicin-lesioned SGNs culture co-treated with OECs and RA (Gent + OEC& RA). The expression of a specific protein in SGNs was examined using immunohistochemical and Western blotting technique. TUNEl staining was used to detect cell apoptosis. Here, we revealed that combined treatment of OECs and RA protect synapsin and Tuj-1 expression in the lesioned SGNs and attenuate cell apoptosis. These findings suggest that RA co-treatment can enhance efficiency of OECs in repair of SGNs damage induced by ototoxic drug.

Research Progress on Mechanism of Neuroprotective Roles of Apelin-13 in Prevention and Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is the most common type of dementia. Currently, more than 50 million people live with dementia worldwide, and this number is expected to increase. Some of the typical pathological changes of AD include amyloid plaque, hyperphosphorylation of tau protein, secretion of inflammatory mediators, and neuronal apoptosis. Apelin is a neuroprotective peptide that is widely expressed in the body. Among members of apelin family, apelin-13 is the most abundant with a high neuroprotective function. Apelin-13/angiotensin domain type 1 receptor-associated proteins (APJ) system regulates several physiological and pathophysiological cell activities, such as apoptosis, autophagy, synaptic plasticity, and neuroinflammation. It has also been shown to prevent AD development. This article reviews the research progress on the relationship between apelin-13 and AD to provide new ideas for prevention and treatment of AD.

Apelin-13 prevents apoptosis in the cochlear tissue of noise-exposed rat via Sirt-1 regulation

Noise-induced hearing loss (NIHL) is the second most common cause of acquired hearing loss. Acoustic trauma can cause oxidative damage in the cochlear hair cells (HCs) through apoptotic pathways. Apelin is a newly discovered neuropeptide with neuroprotective effects against the oxidative stress in neurodegenerative disorder. We investigated the preventive effects of apelin-13 on the cochlear HCs and spiral ganglion neurons (SGNs) against acoustic trauma via Sirtuin-1 (Sirt-1) regulation in rats. Animals were assigned to control, control + apelin-13 (50 or 100 μg/kg, ip), and noise exposure groups without any treatment or were administered apelin-13 (50 or 100 μg/kg, ip) and EX-527 (an inhibitor of Sirt-1) prior to each noise session. In the noise groups, 110 dB white noise was applied for 6 h per 5 days. Pre- and post-exposure distortion product otoacoustic emissions (DPOAE) and cochlear superoxide dismutase (SOD) activity were assessed. Western blot evaluated the cochlear protein expressions of Sirt-1, cleaved-caspase-3, Bax, and Bcl-2. Cell apoptosis was detected through TUNEL staining. Immunofluorescence was used to examine expression of HCs and SGNs specific protein. DPOAE level were significantly improved in the noise exposure group receiving 100 μg/kg apelin-13. At high doses, apelin augmented SOD levels in the rat cochlea subjected to noise. Apelin 100 markedly increased Sirt-1, and decreased cleaved- caspase-3 expression as well as Bax/Bcl-2 ratio in the cochlea tissue of noise-exposed rats. These findings suggest the promising therapeutic potential of apelin-13 for the prevention of noise-induced injury to cochlea and hearing loss.

Anti-Apoptotic Effect of Apelin in Human Placenta: Studies on BeWo Cells and Villous Explants from Third-Trimester Human Pregnancy

Previously, we demonstrated the expression of apelin and G-protein-coupled receptor APJ in human placenta cell lines as well as its direct action on placenta cell proliferation and endocrinology. The objective of this study was to examine the effect of apelin on placenta apoptosis in BeWo cells and villous explants from the human third trimester of pregnancy. The BeWo cells and villous explants were incubated with apelin (2 and 20 ng/mL) alone or with staurosporine for 24 to 72 h. First, we analysed the dose- and time-dependent effect of apelin on the expression of apoptotic factors on the mRNA level by real-time PCR and on the protein level using Western blot. Next, we checked caspase 3 and 7 activity by Caspase-Glo 3/7, DNA fragmentation by the Cell Death Detection ELISA kit and oxygen consumption by the MitoXpress-Xtra Oxygen Consumption assay. We found that apelin increased the expression of pro-survival and decreased proapoptotic factors on mRNA and protein levels in both BeWo cells and villous explants. Additionally, apelin inhibited caspase 3 and 7 activity and DNA fragmentation in staurosporine-induced apoptosis as also attenuated oxidative stress by increasing extracellular oxygen consumption. The antiapoptotic effect of apelin in BeWo cells was mediated by the APJ receptor and mitogen-activated protein kinase (ERK1/2/MAP3/1) and protein kinase B (AKT). The obtained results showed the antiapoptotic effect of apelin on trophoblast cells, suggesting its participation in the development of the placenta.

Relationship between Apelin/APJ Signaling, Oxidative Stress, and Diseases

Apelin, a peptide hormone, is an endogenous ligand for G protein-coupled receptor and has been shown to be widely expressed in human and animal tissues, such as the central nervous system and adipose tissue. Recent studies indicate that the apelin/APJ system is involved in the regulation of multiple physiological and pathological processes, and it is associated with cardiovascular diseases, metabolic disorders, neurological diseases, ischemia-reperfusion injury, aging, eclampsia, deafness, and tumors. The occurrence and development of these diseases are closely related to the local inflammatory response. Oxidative stress is that the balance between oxidation and antioxidant is broken, and reactive oxygen species are produced in large quantities, causing cell or molecular damage, which leads to vascular damage and a series of inflammatory reactions. Hence, this article reviewed recent advances in the relationship between apelin/APJ and oxidative stress, and inflammation-related diseases, and highlights them as potential therapeutic targets for oxidative stress-related inflammatory diseases.

Resveratrol ameliorates renal damage by inhibiting oxidative stress-mediated apoptosis of podocytes in diabetic nephropathy

Diabetic nephropathy (DN) is the major cause of end-stage renal disease. Resveratrol (RSV) has been shown to exert a renoprotective effect against DN, but despite research progress, the protective mechanisms of RSV have not been fully elucidated. Here, we demonstrated that RSV relieved a series of pathological characteristics of DN and attenuated oxidative stress and apoptosis in the renal tissues of diabetic (db/db) mice. In addition, RSV inhibited oxidative stress production and apoptosis in human podocytes exposed to high glucose. Furthermore, inhibition of reactive oxygen species generation by reactive oxygen species scavengers N-acetylcysteine and 2,2,6,6-tetramethyl-1-piperidinyloxy had the same anti-apoptosis effects on podocytes as did RSV. Finally, we found that 5' adenosine monophosphate-activated protein kinase (AMPK) was activated by RSV in db/db mice and podocytes exposed to high glucose. The protective effects of RSV on podocytes were suppressed by Compound C, a pharmacological inhibitor of AMPK. Together, our results indicate that RSV effectively attenuated renal damage by suppressing oxidative stress-mediated apoptosis of podocytes, which was dependent on AMPK activation. This study revealed a possible mechanism to protect podocytes against apoptosis in DN.

Insight into adipokines to optimize therapeutic effects of stem cell for tissue regeneration

Stem cell therapy is considered as a promising regenerative medicine for repairing and treating damaged tissues and/or preventing various diseases. But there are still some obstacles such as low cell migration, poor stem cell engraftment and decreased cell survival that need to be overcome before transplantation. Therefore, a large body of studies has focused on improving the efficiency of stem cell therapy. For instance, preconditioning of stem cells has emerged as an effective strategy to reinforce therapeutic efficacy. Adipokines are signaling molecules, secreted by adipose tissue, which regulate a variety of biological processes in adipose tissue and other organs including the brain, liver, and muscle. In this review article, we shed light on the biological effects of some adipokines including apelin, oncostatin M, omentin-1 and vaspin on stem cell therapy and the most recent preclinical advances in our understanding of how these functions ameliorate stem cell therapy outcome.