Humanin rescues cultured rat cortical neurons from NMDA-induced toxicity through the alleviation of mitochondrial dysfunction

Neuroprotective Action of Humanin and Humanin Analogues: Research Findings and Perspectives

Humanin is a 24-mer peptide first reported in the early 2000s as a new neuroprotective/cytoprotective factor rescuing neuronal cells from death induced by various Alzheimer's disease-associated insults. Nowadays it is known that humanin belongs to the novel class of the so-called mitochondrial-derived peptides (which are encoded by mitochondrial DNA) and has been shown to exert beneficial cytoprotective effects in a series of in vitro and/or in vivo experimental models of human diseases, including not only neurodegenerative disorders but other human diseases as well (e.g., age-related macular degeneration, cardiovascular diseases, or diabetes mellitus). This review article is focused on the presentation of recent in vitro and in vivo research results associated with the neuroprotective action of humanin as well as of various, mainly synthetic, analogues of the peptide; moreover, the main mode(s)/mechanism(s) through which humanin and humanin analogues may exert in vitro and in vivo regarding neuroprotection have been reported. The prospects of humanin and humanin analogues to be further investigated in the frame of future research endeavors against neurodegenerative/neural diseases have also been briefly discussed.

Protective effects of chronic humanin treatment in mice with diabetic encephalopathy: A focus on oxidative stress, inflammation, and apoptosis

Diabetes is known to cause cognitive impairments through various mechanisms, including oxidative stress, inflammation, and apoptosis. Humanin (HN) has been shown to have protective effects on cognitive impairments induced by factors such as Aβ, muscarinic receptor antagonists, and aging in rodents. However, the mechanisms underlying the protective effects of HN in the prefrontal cortex and hippocampus in the context of diabetes are not well understood. In this study, we aimed to investigate the potential protective role of HN on oxidative stress, inflammation, and apoptosis in mice with diabetes. We divided the mice into four groups, including a control group (treated with saline), a humanin group (treated with 4 mg/kg of HN), a streptozotocin (STZ) group (diabetic control), and an STZ+Humanin group. The mice were administered HN daily for 15 days. Our results showed that in the prefrontal cortex and hippocampus of the diabetes group, oxidative stress parameters, pro-inflammatory cytokines, apoptosis and, blood glucose levels were increased, while antioxidant and anti-inflammatory cytokines were diminished compared to the control group. However, HN treatment was able to modulate these markers, including blood glucose and the markers of oxidative stress, inflammation, and apoptosis. In conclusion, our findings suggest that hyperglycemia, oxidative stress, inflammation, and apoptosis may contribute to the development of diabetes-induced cognitive impairments. By regulating these changes with HN treatment, we may be able to positively contribute to the treatment of cognitive impairments induced by diabetes.

A novel beneficial role of humanin on intestinal apoptosis and dysmotility in a rat model of ischemia reperfusion injury

A prevalent clinical problem including sepsis, shock, necrotizing enterocolitis, and mesenteric thrombosis is intestinal ischemia/reperfusion (I/R) injury. Humanin (HN), a recently identified mitochondrial polypeptide, exhibits antioxidative and antiapoptotic properties. This work aimed to study the role of HN in a model of experimental intestinal I/R injury and its effect on associated dysmotility. A total of 36 male adult albino rats were allocated into 3 equal groups. Sham group: merely a laparotomy was done. I/R group: for 1 h, clamping of the superior mesenteric artery was done, and then reperfusion was allowed for 2 h later. HN-I/R group: rats underwent ischemia and reperfusion, and 30 min before the reperfusion, they received an intraperitoneal injection of 252 μg/kg of HN. Small intestinal motility was evaluated, and jejunal samples were got for biochemical and histological analysis. I/R group showed elevation of intestinal NO, MDA, TNF- α, and IL-6 and decline of GPx and SOD levels. Furthermore, histologically, there were destructed jejunal villi especially their tips and increased tissue expression of caspase-3 and i-NOS, in addition to reduced small intestinal motility. Compared to I/R group, HN-I/R group exhibited decrease intestinal levels of NO, MDA, TNF- α, and IL-6 and increase GPx and SOD. Moreover, there was noticeable improvement of the histopathologic features and decreased caspase-3 and iNOS immunoreactivity, beside enhanced small intestinal motility. HN alleviates inflammation, apoptosis, and intestinal dysmotility encouraged by I/R. Additionally, I/R-induced apoptosis and motility alterations depend partly on the production of nitric oxide.

The Molecular Structure and Role of Humanin in Neural and Skeletal Diseases, and in Tissue Regeneration

Humanin (HN) belongs to a member of mitochondrial-derived peptides (MDPs) which are encoded by mitochondrial genes. HN shares sequence homology with thirteen HN-like proteins, named MTRNR2L1 to MTRNR2L13, which encompass 24–28 amino acid residues in length. HN mediates mitochondrial status and cell survival by acting via an intracellular mechanism, or as a secreted factor via extracellular signals. Intracellularly, it binds Bcl2-associated X protein (BAX), Bim and tBid, and IGFBP3 to inhibit caspase activity and cell apoptosis. When released from cells as a secreted peptide, HN interacts with G protein-coupled formyl peptide receptor-like 1 (FPRL1/2) to mediate apoptosis signal-regulating kinase (ASK) and c-Jun N-terminal kinase (JNK) signalling pathways. Additionally, it interacts with CNTFR-α/gp130/WSX-1 trimeric receptors to induce JAK2/STA3 signalling cascades. HN also binds soluble extracellular proteins such as VSTM2L and IGFBP3 to modulate cytoprotection. It is reported that HN plays a role in neuronal disorders such as Alzheimer’s disease, as well as in diabetes mellitus, infertility, and cardiac diseases. Its roles in the skeletal system are emerging, where it appears to be involved with the regulation of osteoclasts, osteoblasts, and chondrocytes. Understanding the molecular structure and role of HN in neural and skeletal diseases is vital to the application of HN in tissue regeneration.

Humanin ameliorates late-onset hypogonadism in aged male rats

BACKGROUND

The reproductive potential declines with age. Late-onset hypogonadism is characterized by reduced serum testosterone. Humanin is a mitochondrial-derived signaling peptide encoded by short open reading frames within the mitochondrial genome. It may protect against some age-related diseases such as atherosclerosis by its cytoprotective effects.

OBJECTIVE

it aimed to investigate the potential anti-aging effects of humanin on the testicular architecture, oxidative stress, some apoptotic and inflammatory markers in the hypogonadal aged male rats.

METHODS

Forty male albino rats were divided into 4 groups: normal adult controls, aged vehicle-treated group, aged testosterone-treated group, and aged humanin-treated group. Twenty-month-old male rats with declined serum testosterone were selected to be the animal models of late-onset hypogonadism. Testicular weights, serum testosterone, and some sperm parameters were measured. Testicular tissue IL-6 and TNF-α, superoxide dismutase activity, glutathione peroxidase, and malondialdehyde were assessed. The activity of caspase-3, BCL2, PCNA, and the nuclear factor erythroid 2-related factor 2-antioxidant response element pathway were evaluated. Testes were subjected to histopathological and immunohistochemical examination. Statistical analysis was executed using One Way Analysis of variance (ANOVA) followed by Post hoc (LSD) test to compare means among all studied groups.

RESULTS

humanin treatment significantly improved serum testosterone, some sperm characteristics, and antioxidant defenses. It decreased active caspase-3, pro-apoptotic BAX expression, and increased antiapoptotic BCL2 and proliferating cell nuclear antigen (PCNA) possibly via activating the (Nrf2-ARE) pathway.

CONCLUSION

humanin might be a promising therapeutic modality in late-onset hypogonadism as it ameliorated some age-related testicular and hormonal adverse effects.

NMDA mediates disruption of blood-brain barrier permeability via Rho/ROCK signaling pathway

Glutamate can activate the N-methyl-D-aspartatic acid (NMDA) receptor (NMDAR), damage brain microvascular endothelial cells, and disturb the intercellular tight junctions (TJs). These result in changes in the permeability of the blood brain barrier (BBB). In neurons, the activation of Rho/ROCK signaling pathway is related to the activation of NMDAR，however, whether human brain vascular endothelial cells NMDAR mediates the Rho/ROCK pathway is not fully understood. The present study evaluates the effects of excessive NMDAR activation induced by NMDA (a glutamate analog) on the Rho/ROCK signaling pathway and the permeability of BBB by using a primary human brain microvascular endothelial cell (HBMEC) model. NMDAR subunit GluN1 was expressed in HBMECs and promoted by NMDA detected by Western blot and qRT-PCR. Furthermore, NMDA exposure decreased HBMEC viability, promoted HBMEC apoptosis, increased intracellular reactive oxygen species (ROS) levels, and destroyed the endothelial cytoskeleton. Additionally, NMDA exposure suppressed transendothelial electrical resistance (TEER) values and the expression of TJ proteins occludin and claudin5; it also promoted ROCK activated substrate myosin phosphatase target subunit-1 (MYPT)-1 phosphorylation and the transmittance of sodium fluorescein. In contrast, these effects were attenuated by ROCK inhibitor hydroxyfasudil (HF) and NMDAR antagonist MK801, respectively. Therefore, these results indicate that excessive endothelial NMDAR activation induced by NMDA may induce TJs and cytoskeleton damage, while HF attenuated NMDA-induced cytotoxicity in HBMECs by inhibiting the Rho/ROCK signaling pathway.

Novel Insights Into the Role of Mitochondria-Derived Peptides in Myocardial Infarction

Mitochondria-derived peptides (MDPs) are a new class of bioactive peptides encoded by small open reading frames (sORFs) within known mitochondrial DNA (mtDNA) genes. MDPs may affect the expression of nuclear genes and play cytoprotective roles against chronic and age-related diseases by maintaining mitochondrial function and cell viability in the face of metabolic stress and cytotoxic insults. In this review, we summarize clinical and experimental findings indicating that MDPs act as local and systemic regulators of glucose homeostasis, immune and inflammatory responses, mitochondrial function, and adaptive stress responses, and focus on evidence supporting the protective effects of MDPs against myocardial infarction. These insights into MDPs actions suggest their potential in the treatment of cardiovascular diseases and should encourage further research in this field.

The Muscle-Brain Axis and Neurodegenerative Diseases: The Key Role of Mitochondria in Exercise-Induced Neuroprotection

Regular exercise is associated with pronounced health benefits. The molecular processes involved in physiological adaptations to exercise are best understood in skeletal muscle. Enhanced mitochondrial functions in muscle are central to exercise-induced adaptations. However, regular exercise also benefits the brain and is a major protective factor against neurodegenerative diseases, such as the most common age-related form of dementia, Alzheimer's disease, or the most common neurodegenerative motor disorder, Parkinson's disease. While there is evidence that exercise induces signalling from skeletal muscle to the brain, the mechanistic understanding of the crosstalk along the muscle-brain axis is incompletely understood. Mitochondria in both organs, however, seem to be central players. Here, we provide an overview on the central role of mitochondria in exercise-induced communication routes from muscle to the brain. These routes include circulating factors, such as myokines, the release of which often depends on mitochondria, and possibly direct mitochondrial transfer. On this basis, we examine the reported effects of different modes of exercise on mitochondrial features and highlight their expected benefits with regard to neurodegeneration prevention or mitigation. In addition, knowledge gaps in our current understanding related to the muscle-brain axis in neurodegenerative diseases are outlined.

Brain Insulin Resistance: Focus on Insulin Receptor-Mitochondria Interactions

Current hypotheses implicate insulin resistance of the brain as a pathogenic factor in the development of Alzheimer’s disease and other dementias, Parkinson’s disease, type 2 diabetes, obesity, major depression, and traumatic brain injury. A variety of genetic, developmental, and metabolic abnormalities that lead to disturbances in the insulin receptor signal transduction may underlie insulin resistance. Insulin receptor substrate proteins are generally considered to be the node in the insulin signaling system that is critically involved in the development of insulin insensitivity during metabolic stress, hyperinsulinemia, and inflammation. Emerging evidence suggests that lower activation of the insulin receptor (IR) is another common, while less discussed, mechanism of insulin resistance in the brain. This review aims to discuss causes behind the diminished activation of IR in neurons, with a focus on the functional relationship between mitochondria and IR during early insulin signaling and the related roles of oxidative stress, mitochondrial hypometabolism, and glutamate excitotoxicity in the development of IR insensitivity to insulin.

Mechanisms of protection of retinal pigment epithelial cells from oxidant injury by humanin and other mitochondrial-derived peptides: Implications for age-related macular degeneration

The mitochondrial-derived peptides (MDPs) are a new class of small open reading frame encoded polypeptides with pleiotropic properties. The prominent members are Humanin (HN) and small HN-like peptide (SHLP) 2, which encode 16S rRNA, while mitochondrial open reading frame of the twelve S c (MOTS-c) encodes 12S rRNA of the mitochondrial genome. While the multifunctional properties of HN and its analog 14-HNG have been well documented, their protective role in the retinal pigment epithelium (RPE)/retina has been investigated only recently. In this review, we have summarized the multiple effects of HN and its analogs, SHLP2 and MOTS-c in oxidatively stressed human RPE and the regulatory pathways of signaling, mitochondrial function, senescence, and inter-organelle crosstalk. Emphasis is given to the mitochondrial functions such as biogenesis, bioenergetics, and autophagy in RPE undergoing oxidative stress. Further, the potential use of HN and its analogs in the prevention of age-related macular degeneration (AMD) are also presented. In addition, the role of novel, long-acting HN elastin-like polypeptides in nanotherapy of AMD and other ocular diseases stemming from oxidative damage is discussed. It is expected MDPs will become a promising group of mitochondrial peptides with valuable therapeutic applications in the treatment of retinal diseases.

Humanin protects cortical neurons from calyculin A-induced neurotoxicities by increasing PP2A activity and SOD

BACKGROUND

Humanin (HN) is an extensive neuroprotective peptide. This study aims to investigate the neuroprotective effects of HN on Calyculin A (CA)-induced neurotoxicities in cortical neurons and the underlying mechanism.

METHODS

CA was added into the cultured cortical neurons to induce neurotoxicity. Cortical neurons were preincubated with HN which plays a protective role. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), lactate dehydrogenase (LDH), and Calcein-AM were applied to evaluate the neural insults. Caspase 3 signal and Tunnel were performed to test neural apoptosis. Western blot analysis was used to detect the expressions of phosphorylated tau. The corresponding kits were used to measure the contents of malondialdehyde (MDA) and superoxide dismutase (SOD), and the activity of PP2A, respectively.

RESULTS

HN preincubation preserved cell viability, protected the neurons, alleviated oxidative stress, and reserved PP2A activity. It also blocked tau overphosphorylation at Ser199/202, Ser396, and Thr231 sites and protected neurons against CA-induced insults.

CONCLUSION

These results suggest that HN may serve as a potential therapeutic agent to prevent the pathological changes induced by CA via modulating the activity of PP2A and oxidative stress in neurodegenerative diseases.

The Mitochondria-Derived Peptide Humanin Improves Recovery from Intracerebral Hemorrhage: Implication of Mitochondria Transfer and Microglia Phenotype Change

Astrocytes are an integral component of the neurovascular unit where they act as homeostatic regulators, especially after brain injuries, such as stroke. One process by which astrocytes modulate homeostasis is the release of functional mitochondria (Mt) that are taken up by other cells to improve their function. However, the mechanisms underlying the beneficial effect of Mt transfer are unclear and likely multifactorial. Using a cell culture system, we established that astrocytes release both intact Mt and humanin (HN), a small bioactive peptide normally transcribed from the Mt genome. Further experiments revealed that astrocyte-secreted Mt enter microglia, where they induce HN expression. Similar to the effect of HN alone, incorporation of Mt by microglia (1) upregulated expression of the transcription factor peroxisome proliferator-activated receptor gamma and its target genes (including mitochondrial superoxide dismutase), (2) enhanced phagocytic activity toward red blood cells (an in vitro model of hematoma clearance after intracerebral hemorrhage [ICH]), and (3) reduced proinflammatory responses. ICH induction in male mice caused profound HN loss in the affected hemisphere. Intravenously administered HN penetrated perihematoma brain tissue, reduced neurological deficits, and improved hematoma clearance, a function that normally requires microglia/macrophages. This study suggests that astrocytic Mt-derived HN could act as a beneficial secretory factor, including when transported within Mt to microglia, where it promotes a phagocytic/reparative phenotype. These findings also indicate that restoring HN levels in the injured brain could represent a translational target for ICH. These favorable biological responses to HN warrant studies on HN as therapeutic target for ICH.SIGNIFICANCE STATEMENT Astrocytes are critical for maintaining brain homeostasis. Here, we demonstrate that astrocytes secrete mitochondria (Mt) and the Mt-genome-encoded, small bioactive peptide humanin (HN). Mt incorporate into microglia, and both Mt and HN promote a "reparative" microglia phenotype characterized by enhanced phagocytosis and reduced proinflammatory responses. Treatment with HN improved outcomes in an animal model of intracerebral hemorrhage, suggesting that this process could have biological relevance to stroke pathogenesis.

Murine maternal dietary restriction affects neural Humanin expression and cellular profile

To understand the cellular basis for the neurodevelopmental effects of intrauterine growth restriction (IUGR), we examined the global and regional expression of various cell types within murine (Mus musculus) fetal brain. Our model employed maternal calorie restriction to 50% daily food intake from gestation day 10-19, producing IUGR offspring. Offspring had smaller head sizes with larger head:body ratios indicating a head sparing IUGR effect. IUGR fetuses at embryonic day 19 (E19) had reduced nestin (progenitors), β-III tubulin (immature neurons), Glial fibrillary acidic protein (astrocytes), and O4 (oligodendrocytes) cell lineages via immunofluorescence quantification and a 30% reduction in cortical thickness. No difference was found in Bcl-2 or Bax (apoptosis) between controls and IUGR, though qualitatively, immunoreactivity of doublecortin (migration) and Ki67 (proliferation) was decreased. In the interest of examining a potential therapeutic peptide, we next investigated a novel pro-survival peptide, mouse Humanin (mHN). Ontogeny examination revealed highest mHN expression at E19, diminishing by postnatal day 15 (P15), and nearly absent in adult (3 months). Subanalysis by sex at E19 yielded higher mHN expression among males during fetal life, without significant difference between sexes postnatally. Furthermore, female IUGR mice at E19 had a greater increase in cortical mHN versus the male fetus over their respective controls. We conclude that maternal dietary restriction-associated IUGR interferes with neural progenitors differentiating into the various cellular components populating the cerebral cortex, and reduces cerebral cortical size. mHN expression is developmental stage and sex specific, with IUGR, particularly in the females, adaptively increasing its expression toward mediating a pro-survival approach against nutritional adversity.

Mitochondrial Peptide Humanin Protects Silver Nanoparticles-Induced Neurotoxicity in Human Neuroblastoma Cancer Cells (SH-SY5Y)

The extensive usage of silver nanoparticles (AgNPs) as medical products such as antimicrobial and anticancer agents has raised concerns about their harmful effects on human beings. AgNPs can potentially induce oxidative stress and apoptosis in cells. However, humanin (HN) is a small secreted peptide that has cytoprotective and neuroprotective cellular effects. The aim of this study was to assess the harmful effects of AgNPs on human neuroblastoma SH-SY5Y cells and also to investigate the protective effect of HN from AgNPs-induced cell death, mitochondrial dysfunctions, DNA damage, and apoptosis. AgNPs were prepared with an average size of 18 nm diameter to study their interaction with SH-SY5Y cells. AgNPs caused a dose-dependent decrease of cell viability and proliferation, induced loss of plasma-membrane integrity, oxidative stress, loss of mitochondrial membrane potential (MMP), and loss of ATP content, amongst other effects. Pretreatment or co-treatment of HN with AgNPs protected cells from several of these AgNPs induced adverse effects. Thus, this study demonstrated for the first time that HN protected neuroblastoma cells against AgNPs-induced neurotoxicity. The mechanisms of the HN-mediated protective effect on neuroblastoma cells may provide further insights for the development of novel therapeutic agents against neurodegenerative diseases.

Protective Effect of Hyperbaric Oxygen Therapy on Cognitive Function in Patients with Vascular Dementia

Recent studies have shown that hyperbaric oxygen (HBO) has a therapeutic effect on vascular dementia (VD); however, the exact mechanism remains unclear. This article aims to reveal the protective effects and underlying mechanisms of HBO on VD. A total of 158 patients with VD were prospectively included in the study and were randomly divided into control group and HBO group. The control group was given conventional treatment and the HBO group was treated with HBO in addition to conventional treatment. The following HBO protocol was practiced: 5 days per week, 60 min each, 100% oxygen at 2 standard atmospheric pressures for 12 weeks. The Mini-Mental State Examination (MMSE) scores and serum Humanin levels were detected before and after treatments in both groups. The baseline characteristics were not different dramatically between groups (p > 0.05). There was no significant difference in MMSE scores and serum Humanin levels between the two groups before treatment (p > 0.05). After treatment, compared with the control group, the MMSE scores and serum Humanin levels in the HBO group were significantly increased (p < 0.05). Spearman correlation analysis showed that the serum Humanin levels were positively correlated with MMSE scores (r = 0.409, p < 0.05) and this correlation was independent of baseline characteristics (β = 0.312, p < 0.05). HBO therapy can improve cognitive function in patients with VD, and its mechanism may be related to elevated serum Humanin levels.

Humanin, a Mitochondrial-Derived Peptide Released by Astrocytes, Prevents Synapse Loss in Hippocampal Neurons

Astroglial cells are crucial for central nervous system (CNS) homeostasis. They undergo complex morpho-functional changes during aging and in response to hormonal milieu. Ovarian hormones positively affect different astroglia parameters, including regulation of cell morphology and release of neurotrophic and neuroprotective factors. Thus, ovarian hormone loss during menopause has profound impact in astroglial pathophysilogy and has been widely associated to the process of brain aging. Humanin (HN) is a secreted mitochondrial-encoded peptide with neuroprotective effects. It is localized in several tissues with high metabolic rate and its expression decreases with age. In the brain, humanin has been found in glial cells in physiological conditions. We previously reported that surgical menopause induces hippocampal mitochondrial dysfunction that mimics an aging phenotype. However, the effect of ovarian hormone deprivation on humanin expression in this area has not been studied. Also, whether astrocytes express and release humanin and the regulation of such processes by ovarian hormones remain elusive. Although humanin has also proven to be beneficial in ameliorating cognitive impairment induced by different insults, its putative actions on structural synaptic plasticity have not been fully addressed. In a model of surgical menopause in rats, we studied hippocampal humanin expression and localization by real-time quantitative polymerase chain reaction (RT-qPCR) and double immunohistochemistry, respectively. Humanin production and release and ovarian hormone regulation of such processes were studied in cultured astrocytes by flow cytometry and ELISA, respectively. Humanin effects on glutamate-induced structural synaptic alterations were determined in primary cultures of hippocampal neurons by immunocytochemistry. Humanin expression was lower in the hippocampus of ovariectomized rats and its immunoreactivity colocalized with astroglial markers. Chronic ovariectomy also promoted the presence of less complex astrocytes in this area. Ovarian hormones increased humanin intracellular content and release by cultured astrocytes. Humanin prevented glutamate-induced dendritic atrophy and reduction in puncta number and total puncta area for pre-synaptic marker synaptophysin in cultured hippocampal neurons. In conclusion, astroglial functional and morphological alterations induced by chronic ovariectomy resemble an aging phenotype and could affect astroglial support to neuronal function by altering synaptic connectivity and functionality. Reduced astroglial-derived humanin may represent an underlying mechanism for synaptic dysfunction and cognitive decline after menopause.

Humanin levels in human seminal plasma and spermatozoa are related to sperm quality

BACKGROUND

Humanin has reportedly been expressed in testis and spermatozoa, but no study has yet reported its presence in human seminal plasma (SP).

OBJECTIVE

The aim of this study was to investigate the presence of humanin in human SP and to determine the correlation between humanin levels in SP/spermatozoa and sperm quality.

MATERIALS AND METHODS

Semen samples for SP/sperm humanin level measurement were collected from 164 patients who attended our andrology clinic for fertility evaluation. The localization of humanin in spermatozoa was evaluated using an immunofluorescence method, and SP/sperm humanin levels were measured with ELISA. Correlations between SP/sperm humanin levels and sperm parameters were analyzed.

RESULTS

Humanin was expressed in the midpiece of the spermatozoa. Humanin concentrations in the SP ranged from 24.4 to 285.1 pg/mL, with a median of 89.7 pg/mL. The SP humanin concentrations in patients with normospermia were significantly higher than those in patients with oligospermia (p < 0.001), asthenospermia (p = 0.002), and oligoasthenospermia (p < 0.001). Spearman analysis showed a positive and significant correlation between SP humanin concentration and sperm concentration (r = 0.75, p < 0.001), and progressive sperm motility (r = 0.29, p < 0.001). Sperm humanin level was significantly and positively associated with progressive sperm motility (r = 0.70, p < 0.001). In addition, a significantly higher level of humanin was found in swim-up spermatozoa than in non-swim-up spermatozoa (p = 0.03).

CONCLUSIONS

Seminal plasma and sperm humanin levels were significantly and positively correlated with sperm quality, especially sperm motility. Further studies of the origin of SP humanin and its role in spermatogenesis should be conducted.

Humanin Attenuates NMDA-Induced Excitotoxicity by Inhibiting ROS-dependent JNK/p38 MAPK Pathway

Humanin (HN) is a novel 24-amino acid peptide that protects neurons against N-methyl-d-aspartate (NMDA)-induced toxicity. However, the contribution of the different mitogen-activated protein kinases (MAPKs) signals to HN neuroprotection against NMDA neurotoxicity remains unclear. The present study was therefore aimed to investigate neuroprotective mechanisms of HN. We analyzed intracellular Ca2+ levels, reactive oxygen species (ROS) production, and the MAPKs signal transduction cascade using an in vitro NMDA-mediated excitotoxicity of cortical neurons model. Results showed that: (1) HN attenuated NMDA-induced neuronal insults by increasing cell viability, decreasing lactate dehydrogenase (LDH) release, and increasing cell survival; (2) HN reversed NMDA-induced increase in intracellular calcium; (3) pretreatment by HN or 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM), an intracellular calcium chelator, decreased ROS generation after NMDA exposure; (4) administration of HN or N-Acetyl-l-cysteine (NAC), a ROS scavenger, inhibited NMDA-induced JNK and p38 MAPK activation. These results indicated that HN reduced intracellular elevation of Ca2+ levels, which, in turn, inhibited ROS generation and subsequent JNK and p38 MAPK activation that are involved in promoting cell survival in NMDA-induced excitotoxicity. Therefore, the present study suggests that inhibition of ROS-dependent JNK/p38 MAPK signaling pathway serves an effective strategy for HN neuroprotection against certain neurological diseases.

Role of Signaling Molecules in Mitochondrial Stress Response

Mitochondria are established essential regulators of cellular function and metabolism. Mitochondria regulate redox homeostasis, maintain energy (ATP) production through oxidative phosphorylation, buffer calcium levels, and control cell death through apoptosis. In addition to these critical cell functions, recent evidence supports a signaling role for mitochondria. For example, studies over the past few years have established that peptides released from the mitochondria mediate stress responses such as the mitochondrial unfolded protein response (UPR^MT) through signaling to the nucleus. Mitochondrial damage or danger associated molecular patterns (DAMPs) provide a link between mitochondria, inflammation and inflammatory disease processes. Additionally, a new class of peptides generated by the mitochondria affords protection against age-related diseases in mammals. In this short review, we highlight the role of mitochondrial signaling and regulation of cellular activities through the mitochondrial UPR^MT that signals to the nucleus to affect homeostatic responses, DAMPs, and mitochondrial derived peptides.