Identification of essential amino acids in Humanin, a neuroprotective factor against Alzheimer's disease-relevant insults

Mitochondria‑derived peptides: Promising microproteins in cardiovascular diseases (Review)

Mitochondria‑derived peptides (MDPs) are a unique class of peptides encoded by short open reading frames in mitochondrial DNA, including the mitochondrial open reading frame of the 12S ribosomal RNA type‑c (MOTS‑c). Recent studies suggest that MDPs offer therapeutic benefits in various diseases, including neurodegenerative disorders and types of cancer, due to their ability to increase cellular resilience. Mitochondrial dysfunction is a key factor in the onset and progression of cardiovascular diseases (CVDs), such as atherosclerosis and heart failure, as it disrupts energy metabolism, increases oxidative stress and promotes inflammation. MDPs such as humanin and MOTS‑c have emerged as important regulators of mitochondrial health, as they show protective effects against these processes. Recent studies have shown that MDPs can restore mitochondrial function, reduce oxidative damage and alleviate inflammation, thus counteracting the pathological mechanisms that drive CVDs. Therefore, MDPs hold promise as therapeutic agents that are capable of slowing, stopping, or even reversing CVD progression and their use presents a promising strategy for future treatments. However, the clinical application of MDPs remains challenging due to their low bioavailability, poor stability and high synthesis costs. Thus, it is necessary to improve drug delivery systems to enhance the bioavailability of MDPs. Moreover, integrating basic research with clinical trials is essential to bridge the gap between experimental findings and clinical applications.

The Role of Mitokines in Diabetic Nephropathy

Diabetic nephropathy (DN) has gradually become one of the main causes of end-stage renal disease (ESRD). However, there is still a lack of effective preventive measures to delay its progression. As the energy factory in the cell, mitochondria play an irreplaceable role in maintaining cell homeostasis. Interestingly, recent studies have shown that in addition to maintaining homeostasis in cells in which mitochondria reside, when mitochondrial perturbations occur in one tissue, distal tissues can also sense and act through mitochondrial stress response pathways through a group of proteins or peptides called "mitokines". Here, we reviewed the mitokines that have been found thus far and summarized their research progress in DN. Finally, we explored the possibility of mitokines as potential therapeutic targets for DN.

Mitochondrial-derived peptides in cardiovascular disease: Novel insights and therapeutic opportunities

BACKGROUND

Mitochondria-derived peptides (MDPs) represent a recently discovered family of peptides encoded by short open reading frames (ORFs) found within mitochondrial genes. This group includes notable members including humanin (HN), mitochondrial ORF of the 12S rDNA type-c (MOTS-c), and small humanin-like peptides 1-6 (SHLP1-6). MDPs assume pivotal roles in the regulation of diverse cellular processes, encompassing apoptosis, inflammation, and oxidative stress, which are all essential for sustaining cellular viability and normal physiological functions. Their emerging significance extends beyond this, prompting a deeper exploration into their multifaceted roles and potential applications.

AIM OF REVIEW

This review aims to comprehensively explore the biogenesis, various types, and diverse functions of MDPs. It seeks to elucidate the central roles and underlying mechanisms by which MDPs participate in the onset and development of cardiovascular diseases (CVDs), bridging the connections between cell apoptosis, inflammation, and oxidative stress. Furthermore, the review highlights recent advancements in clinical research related to the utilization of MDPs in CVD diagnosis and treatment.

KEY SCIENTIFIC CONCEPTS OF REVIEW

MDPs levels are diminished with aging and in the presence of CVDs, rendering them potential new indicators for the diagnosis of CVDs. Also, MDPs may represent a novel and promising strategy for CVD therapy. In this review, we delve into the biogenesis, various types, and diverse functions of MDPs. We aim to shed light on the pivotal roles and the underlying mechanisms through which MDPs contribute to the onset and advancement of CVDs connecting cell apoptosis, inflammation, and oxidative stress. We also provide insights into the current advancements in clinical research related to the utilization of MDPs in the treatment of CVDs. This review may provide valuable information with MDPs for CVD diagnosis and treatment.

Humanin inhibits lymphatic endothelial cells dysfunction to alleviate myocardial infarction-reperfusion injury via BNIP3-mediated mitophagy

OBJECTIVE

Acute myocardial infarction (AMI) ranks among the top contributors to sudden death and disability worldwide. It should be noted that current therapies always cause increased reperfusion damage. Evidence suggests that humanin (HN) reduces mitochondrial dysfunction to have cardio-protective effects against MI-reperfusion injury. In this context, we hypothesized that HN may attenuate MI-reperfusion injury by alleviating lymphatic endothelial cells dysfunction through the regulation of mitophagy.

MATERIALS AND METHODS

In this study, primary lymphatic endothelial cells were selected as the experimental model. Cells were maintained under 1% O2 to induce a hypoxic phenotype. For in vivo experiments, the left coronary arteries of C57/BL6 mice were clamped for 45 min followed by 24 h reperfusion to develop MI-reperfusion injury. The volume of infarcted myocardium in MI-reperfusion injury mouse models were TTC staining. PCR and western blot were used to quantify the expression of autophagy-, mitophagy- and mitochondria-related markers. The fibrosis and apoptosis in the ischemic area were evaluated for Masson staining and TUNEL respectively. We also used western blot to analyze the expression of VE-Cadherin in lymphatic endothelial cells.

RESULTS

We firstly exhibited a specific mechanism by which HN mitigates MI-reperfusion injury. We demonstrated that HN effectively reduces such injury in vivo and also inhibits dysfunction in lymphatic endothelial cells in vitro. Importantly, this inhibitory effect is mediated through BNIP3-associated mitophagy.

CONCLUSIONS

In conclusion, HN alleviates myocardial infarction-reperfusion injury by inhibiting lymphatic endothelial cells dysfunction, primarily through BNIP3-mediated mitophagy.

Mitochondrial-derived peptides: Antidiabetic functions and evolutionary perspectives

Mitochondrial-derived peptides (MDPs) are a novel class of bioactive microproteins encoded by short open-reading frames (sORF) in mitochondrial DNA (mtDNA). Currently, three types of MDPs have been identified: Humanin (HN), MOTS-c (Mitochondrial ORF within Twelve S rRNA type-c), and SHLP1-6 (small Humanin-like peptide, 1 to 6). The 12 S ribosomal RNA (MT-RNR1) gene harbors the sequence for MOTS-c, whereas HN and SHLP1-6 are encoded by the 16 S ribosomal RNA (MT-RNR2) gene. Special genetic codes are used in mtDNA as compared to nuclear DNA: (i) ATA and ATT are used as start codons in addition to the standard start codon ATG; (ii) AGA and AGG are used as stop codons instead of coding for arginine; (iii) the standard stop codon UGA is used to code for tryptophan. While HN, SHLP6, and MOTS-c are encoded by the H (heavy owing to high guanine + thymine base composition)-strand of the mtDNA, SHLP1-5 are encoded by the L (light owing to less guanine + thymine base composition)-strand. MDPs attenuate disease pathology including Type 1 diabetes (T1D), Type 2 diabetes (T2D), gestational diabetes, Alzheimer's disease (AD), cardiovascular diseases, prostate cancer, and macular degeneration. The current review will focus on the MDP regulation of T2D, T1D, and gestational diabetes along with an emphasis on the evolutionary pressures for conservation of the amino acid sequences of MDPs.

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.

Evidence of natural selection in the mitochondrial-derived peptides humanin and SHLP6

Mitochondrial-derived peptides are encoded by mitochondrial DNA but have biological activity outside mitochondria. Eight of these are encoded by sequences within the mitochondrial 12S and 16S ribosomal genes: humanin, MOTS-c, and the six SHLP peptides, SHLP1-SHLP6. These peptides have various effects in cell culture and animal models, affecting neuroprotection, insulin sensitivity, and apoptosis, and some are secreted, potentially having extracellular signaling roles. However, except for humanin, their importance in normal cell function is unknown. To gauge their importance, their coding sequences in vertebrates have been analyzed for synonymous codon bias. Because they lie in RNA genes, such bias should only occur if their amino acids have been conserved to maintain biological function. Humanin and SHLP6 show strong synonymous codon bias and sequence conservation. In contrast, SHLP1, SHLP2, SHLP3, and SHLP5 show no significant bias and are poorly conserved. MOTS-c and SHLP4 also lack significant bias, but contain highly conserved N-terminal regions, and their biological importance cannot be ruled out. An additional potential mitochondrial-derived peptide sequence was discovered preceding SHLP2, named SHLP2b, which also contains a highly conserved N-terminal region with synonymous codon bias.

Stability Determination of Intact Humanin-G with Characterizations of Oxidation and Dimerization Patterns

Humanin is the first identified mitochondrial-derived peptide. Humanin-G (HNG) is a variant of Humanin that has significantly higher cytoprotective properties. Here, we describe the stability features of HNG in different conditions and characterize HNG degradation, oxidation, and dimerization patterns over short-term and long-term periods. HNG solutions were prepared in high-performance liquid chromatography (HPLC) water or MO formulation and stored at either 4 °C or 37 °C. Stored HNG samples were analyzed using HPLC and high-resolution mass spectrometry (HRMS). Using HPLC, full-length HNG peptides in HPLC water decreased significantly with time and higher temperature, while HNG in MO formulation remained stable up to 95% at 4 °C on day 28. HNG peptides in HPLC water, phosphate-buffered saline (PBS) and MO formulation were incubated at 37 °C and analyzed at day 1, day 7 and day 14 using HRMS. Concentrations of full-length HNG peptide in HPLC water and PBS declined over time with a corresponding appearance of new peaks that increased over time. These new peaks were identified to be singly oxidized HNG, doubly oxidized HNG, homodimerized HNG, singly oxidized homodimerized HNG, and doubly oxidized homodimerized HNG. Our results may help researchers improve the experimental design to further understand the critical role of HNG in human diseases.

Humanin derivative, HNG, enhances neurotransmitter release

BACKGROUND

Humanin (HN) is an endogenous 24-residue peptide that was first identified as a protective factor against neuronal death in Alzheimer's disease (AD). We previously demonstrated that the highly potent HN derivative HNG (HN with substitution of Gly for Ser14) ameliorated cognitive impairment in AD mouse models. Despite the accumulating evidence on the antagonizing effects of HN against cognitive deficits, the mechanisms behind these effects remain to be elucidated.

METHODS

The extracellular fluid in the hippocampus of wild-type young mice was collected by microdialysis and the amounts of neurotransmitters were measured. The kinetic analysis of exocytosis was performed by amperometry using neuroendocrine cells.

RESULTS

The hippocampal acetylcholine (ACh) levels were increased by intraperitoneal injection of HNG. HNG did not affect the physical activities of the mice but modestly improved their object memory. In a neuronal cell model, rat pheochromocytoma PC12 cells, HNG enhanced ACh-induced dopamine release. HNG increased ACh-induced secretory events and vesicular quantal size in primary neuroendocrine cells.

CONCLUSIONS

These findings suggest that HN directly enhances regulated exocytosis in neurons, which can contribute to the improvement of cognitive functions.

GENERAL SIGNIFICANCE

The regulator of exocytosis is a novel physiological role of HN, which provides a molecular clue for HN's effects on brain functions under health and disease.

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.

Mitochondrial-derived peptides: New markers for cardiometabolic dysfunction

Great attention is being paid to the evaluation of new markers in blood circulation for the estimation of tissue metabolism disturbance. This endogenous disturbance may contribute to the onset and progression of cardiometabolic disease. In addition to their role in energy production and metabolism, mitochondria play a main function in cellular mechanisms, including apoptosis, oxidative stress and calcium homeostasis. Mitochondria produce mitochondrial-derived peptides that mediate the transcriptional stress response by translocating into the nucleus and interacting with deoxyribonucleic acid. This class of peptides includes humanin, mitochondrial open reading frame of the 12S ribosomal ribonucleic acid type c (MOTS-c) and small humanin-like peptides. Mitochondrial-derived peptides are regulators of metabolism, exerting cytoprotective effects through antioxidative stress, anti-inflammatory responses and antiapoptosis; they are emerging biomarkers reflecting mitochondrial function, and the circulating concentration of these proteins can be used to diagnose cardiometabolic dysfunction. The aims of this review are: (1) to describe the emerging role for mitochondrial-derived peptides as biomarkers; and (2) to discuss the therapeutic application of these peptides.

Computers and preventative diagnosis. A survey with bioinformatics examples of mitochondrial small open reading frame peptides as portents of a new generation of powerful biomarkers

The present brief survey is to alert developers in datamining, machine learning, inference methods, and other approaches in relation to diagnostic, predictive, and risk assessment medicine about a relatively new class of bioactive messaging peptides in which there is escalating interest. They provide patterns of communication and cross-chatter about states of health and disease within and, importantly, between cells (they also appear extracellularly in biological fluids). This chatter needs to be analyzed somewhat in the manner of the decryption of the Enigma code in the Second World War. It could lead not only to improved diagnosis but to predictive diagnosis, prediction of organ failure, and preventative medicine. This involves peptide products of short reading frames that have been previously somewhat neglected as unlikely gene products, with probably many examples in nuclear DNA, but certainly several known in the mitochondrial DNA. There is a great deal of knowledge now becoming available about the latter and itis believed thatthat the mRNA can be translated both by standard cytosolic and mitochondrial genetic codes, resulting in different peptides, adding a further level of complexity to the applications of bioinformatics and computational biology but a higher level of detail and sophistication to preventative diagnosis. The code to crack could be sophisticated and combinatorically complex to analyze by computers. Mitochondria may have combined with proto-eucaryotic cells some 2 billion years ago, only about a 7th of the age of the universe. Cells appeared some 2 billion years before that, also with possible signaling based on similar ideas. This makes life small in space but huge in time, refinement of which centrally involves these signaling processes.

The protective effects of S14G-humanin (HNG) against mono-sodium urate (MSU) crystals- induced gouty arthritis

Gout is a common and complex form of arthritis that has brought great inconveniences to the normal lives of patients. It is reported that oxidative stress and nod-like receptor family protein 3 (NLRP3) inflammasome-mediated inflammatory reactions are involved in the pathogenesis of gout arthritis. S14G-humanin (S14G-HNG) is a modified peptide of HNG with higher inhibitory activity on the accumulation and deposition of Aβ. Recently, S14G-HNG has been reported to exert great anti-inflammatory effects. The present study proposed to explore the possible therapeutic property of S14G-HNG against gout arthritis. An animal model was established by stimulation with mono-sodium urate (MSU) crystals, followed by treatment with colchicine and S14G-HNG, respectively. The elevated Gait score promoted synovitis score and activated myeloperoxidase (MPO) observed in MSU crystals-treated mice were significantly reversed by colchicine and S14G-HNG. Bone marrow-derived macrophages (BMDMs) were isolated from mice and stimulated with MSU crystals, followed by being treated with 25 and 50 μM S14G-HNG. The increased mitochondrial reactive oxygen species (ROS) and Malondialdehyde (MDA) levels, upregulated NADPH oxidase-4 (NOX-4), activated NLRP3 inflammasome, and elevated production of inflammatory factors in MSU crystals-treated BMDMs were dramatically reversed by S14G-HNG, accompanied by the upregulation of sirtuin type-1 (SIRT1). Lastly, the protective effects of S14G-HNG against MSU crystals-induced NLRP3 inflammasome activation were significantly abolished by the knockdown of SIRT1. In conclusion, our data reveal that S14G-HNG could possess potential benefits against MSU crystals-induced gout arthritis, with colchicine displaying a better effect.

The emerging role of mitochondrial derived peptide humanin in the testis

The discovery of mitochondrial derive peptides (MDPs) has spotlighted mitochondria as central hubs in control and regulation of cell viability and metabolism in the testis in response to intracellular and extracellular stresses. MDPs (Humanin, MOTS-c and SHLP-2) are present in testes. Humanin, the first MDP, is predominantly expressed in Leydig cells, and moderately in germ cells and seminal plasma. The administration of synthetic humanin peptide agonist HNG protects male germ cells against apoptosis induced by intratesticular hormonal deprivation, testicular hyperthermia, and chemotherapeutic agents in rodent testes. Humanin interacting with IGFBP-3 and/or Bax (pro-apoptotic proteins) prevents the activation of germ cell apoptosis. Humanin participates in the network of IL-12/IL-27 family of cytokines to exert the immune-modulation of the testicular environment. Humanin and other MDPs may be important in the amelioration of testicular stress and prevention of cell injury with possible implications for male infertility, fertility preservation and contraceptive development.

Humanin and Alzheimer's disease: The beginning of a new field

BACKGROUND

Humanin (HN) is an endogenous peptide factor and known as a member of mitochondrial-derived peptides. We first found the gene encoding this novel 24-residue peptide in a brain of an Alzheimer's disease (AD) patient as an antagonizing factor against neuronal cell death induced by AD-associated insults.

SCOPE OF REVIEW

This review presents an overview of HN actions in AD-related conditions among its wide range of action spectrum as well as a brief history of the discovery.

MAJOR CONCLUSIONS

HN exhibits multiple intracellular and extracellular anti-cell death actions and antagonizes various AD-associated pathomechanisms including amyloid plaque accumulation.

GENERAL SIGNIFICANCE

This review concisely reflects accumulated knowledge on HN since the discovery focusing on its functions related to AD pathogenesis and provides a perspective to its potential contribution in AD treatments.

The largely unexplored biology of small proteins in pro- and eukaryotes

The large abundance of small open reading frames (smORFs) in prokaryotic and eukaryotic genomes and the plethora of smORF-encoded small proteins became only apparent with the constant advancements in bioinformatic, genomic, proteomic, and biochemical tools. Small proteins are typically defined as proteins of < 50 amino acids in prokaryotes and of less than 100 amino acids in eukaryotes, and their importance for cell physiology and cellular adaptation is only beginning to emerge. In contrast to antimicrobial peptides, which are secreted by prokaryotic and eukaryotic cells for combatting pathogens and competitors, small proteins act within the producing cell mainly by stabilizing protein assemblies and by modifying the activity of larger proteins. Production of small proteins is frequently linked to stress conditions or environmental changes, and therefore, cells seem to use small proteins as intracellular modifiers for adjusting cell metabolism to different intra- and extracellular cues. However, the size of small proteins imposes a major challenge for the cellular machinery required for protein folding and intracellular trafficking and recent data indicate that small proteins can engage distinct trafficking pathways. In the current review, we describe the diversity of small proteins in prokaryotes and eukaryotes, highlight distinct and common features, and illustrate how they are handled by the protein trafficking machineries in prokaryotic and eukaryotic cells. Finally, we also discuss future topics of research on this fascinating but largely unexplored group of proteins.

Protective Mechanism of Humanin Against Oxidative Stress in Aging-Related Cardiovascular Diseases

Physiological reactive oxygen species (ROS) are important regulators of intercellular signal transduction. Oxidative and antioxidation systems maintain a dynamic balance under physiological conditions. Increases in ROS levels destroy the dynamic balance, leading to oxidative stress damage. Oxidative stress is involved in the pathogenesis of aging-related cardiovascular diseases (ACVD), such as atherosclerosis, myocardial infarction, and heart failure, by contributing to apoptosis, hypertrophy, and fibrosis. Oxidative phosphorylation in mitochondria is the main source of ROS. Increasing evidence demonstrates the relationship between ACVD and humanin (HN), an endogenous peptide encoded by mitochondrial DNA. HN protects cardiomyocytes, endothelial cells, and fibroblasts from oxidative stress, highlighting its protective role in atherosclerosis, ischemia-reperfusion injury, and heart failure. Herein, we reviewed the signaling pathways associated with the HN effects on redox signals, including Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2), chaperone-mediated autophagy (CMA), c-jun NH2 terminal kinase (JNK)/p38 mitogen-activated protein kinase (p38 MAPK), adenosine monophosphate-activated protein kinase (AMPK), and phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)-Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3). Furthermore, we discussed the relationship among HN, redox signaling pathways, and ACVD. Finally, we propose that HN may be a candidate drug for ACVD.

Novel humanin analogs confer neuroprotection and myoprotection to neuronal and myoblast cell cultures exposed to ischemia-like and doxorubicin-induced cell death insults

Humanin (HN) is a 24-amino acid mitochondrial-derived peptide, best known for its ability to protect neurons from damage caused by ischemic stroke and neurodegenerative insults and cardiomyocytes from myocardial infarction or doxorubicin (Dox)-induced cardiotoxicity. This study examines the neuroprotective and myoprotective effects of HN novel synthetic analogs HUJInin and c(D-Ser14-HN), prepared by solid-phase peptide synthesis. The cellular models employed were oxygen-glucose-deprivation (OGD) followed by reoxygenation (R)-induced neurotoxicity in PC12 and SH-SY5Y neuronal cell cultures and Dox-induced cardiotoxicity in H9c2 and C2C12 myoblast cell cultures, respectively. Necrotic and apoptotic cell death was measured by LDH release and caspase-3 activity. Erk 1/2 and AKT phosphorylations were examined by western blotting. Mitochondrial calcium and mitochondrial membrane potential were measured using the fluorescent dye tetramethylrhodamine-methyl ester. It was found that HUJInin and c(D-Ser14-HN) conferred significant dose-dependent neuroprotection, a phenomenon related to attenuation of OGD insult-induced Erk 1/2 phosphorylation, stimulation of AKT phosphorylation and improvement of mitochondrial functions. These peptides also conferred myoprotective effect towards Dox-induced apo-necrotic cell death insults. HUJInin and c(D-Ser14-HN) synthetic analogs may provide new lead compounds for the development of a potential candidate drug for stroke treatment and/or Dox-induced cardiotoxicity therapy in cancer patients.

Interaction of amyloid beta with humanin and acetylcholinesterase is modulated by ATP

Humanin (HN) is known to bind amyloid beta (Aβ)‐inducing cytoprotective effects, while binding of acetylcholinesterase (AChE) to Aβ increases its aggregation and cytotoxicity. Previously, we showed that binding of HN to Aβ blocks aggregation induced by AChE and that HN decreases but does not abolish Aβ‐AChE interactions in A549 cell media. Here, we set out to shed light on factors that modulate the interactions of Aβ with HN and AChE. We found that binding of either HN or AChE to Aβ is not affected by heparan sulfate, while ATP, thought to reduce misfolding of Aβ, weakened interactions between AChE and Aβ but strengthened those between Aβ and HN. Using media from either A549 or H1299 lung cancer cells, we observed that more HN was bound to Aβ upon addition of ATP, while levels of AChE in a complex with Aβ were decreased by ATP addition to A549 cell media. Exogenous addition of ATP to either A549 or H1299 cell media increased interactions of endogenous HN with Aβ to a comparable extent despite differences in AChE expression in the two cell lines, and this was correlated with decreased binding of exogenously added HN to Aβ. Treatment with exogenous ATP had no effect on cell viability under all conditions examined. Exogenously added ATP did not affect viability of cells treated with AChE‐immunodepleted media, and there was no apparent protection against the cytotoxicity resulting from immunodepletion of HN. Moreover, exogenously added ATP had no effect on the relative abundance of oligomer versus total Aβ in either cell line.

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.

Role of humanin, a mitochondrial-derived peptide, in cardiovascular disorders

The mitochondria produce specific peptides-mitochondrial-derived peptides-that mediate the transcriptional stress response by their translocation into the nucleus and interaction with deoxyribonucleic acid. Mitochondrial-derived peptides are regulators of metabolism. This class of peptides comprises humanin, mitochondrial open reading frame of the 12S ribosomal ribonucleic acid type c (MOTS-c) and small humanin-like peptides (SHLPs). Humanin inhibits mitochondrial complex 1 activity and limits the level of oxidative stress in the cell. Data show that mitochondrial-derived peptides have a role in improving metabolic diseases, such as type 2 diabetes. Perhaps humanin can be used as a marker for mitochondrial function in cardiovascular disease or as a pharmacological strategy in patients with endothelial dysfunction. The goal of this review is to discuss the newly emerging functions of humanin, and its biological role in cardiovascular disorders.

Humanin Blocks the Aggregation of Amyloid-β Induced by Acetylcholinesterase, an Effect Abolished in the Presence of IGFBP-3

It is known that the humanin (HN) peptide binding to amyloid-β (Aβ) protects against its cytotoxic effects, while acetylcholinesterase (AChE) binding to Aβ increases its aggregation and cytotoxicity. HN is also known to bind the insulin-like growth factor binding protein-3 (IGFBP-3). Here, we examined the regulation of Aβ conformations by HN, AChE, and IGFBP-3 both in vitro and in the conditioned media from A549 and H1299 lung cancer cells. Our in vitro results showed the following: IGFBP-3 binds HN and blocks it from binding Aβ in the absence or presence of AChE; HN and AChE can simultaneously bind Aβ but not when in the presence of IGFBP-3; HN is unable to reduce the aggregation of Aβ in the presence of IGFBP-3; and HN abolishes the aggregation of Aβ induced by the addition of AChE in the absence of IGFBP-3. In the media, AChE and HN can simultaneously bind Aβ. While both AChE and HN are detected when using 6E10 Aβ antibodies, only AChE is detected when using the Aβ 17-24 antibody 4G8, the anti-oligomer A11, and the anti-amyloid fibril LOC antibodies. No signal was observed for IGFBP-3 with any of the anti-amyloid antibodies used. Exogenously added IGFBP-3 reduced the amount of HN found in a complex when using 6E10 antibodies and correlated with a concomitant increase in the amyloid oligomers. Immunodepletion of HN from the media of the A549 and H1299 cells increased the relative abundance of the oligomer vs the total amount of Aβ, the A11-positive prefibrillar oligomers, and to a lesser extent the LOC-positive fibrillar oligomers, and was also correlated with diminished cell viability and increased apoptosis.

Humanin Promotes Tumor Progression in Experimental Triple Negative Breast Cancer

Humanin (HN) is a mitochondrial-derived peptide with cytoprotective effect in many tissues. Administration of HN analogs has been proposed as therapeutic approach for degenerative diseases. Although HN has been shown to protect normal tissues from chemotherapy, its role in tumor pathogenesis is poorly understood. Here, we evaluated the effect of HN on the progression of experimental triple negative breast cancer (TNBC). The meta-analysis of transcriptomic data from The Cancer Genome Atlas indicated that HN and its receptors are expressed in breast cancer specimens. By immunohistochemistry we observed up-regulation of HN in TNBC biopsies when compared to mammary gland sections from healthy donors. Addition of exogenous HN protected TNBC cells from apoptotic stimuli whereas shRNA-mediated HN silencing reduced their viability and enhanced their chemo-sensitivity. Systemic administration of HN in TNBC-bearing mice reduced tumor apoptotic rate, impaired the antitumor and anti-metastatic effect of chemotherapy and stimulated tumor progression, accelerating tumor growth and development of spontaneous lung metastases. These findings suggest that HN may exert pro-tumoral effects and thus, caution should be taken when using exogenous HN to treat degenerative diseases. In addition, our study suggests that HN blockade could constitute a therapeutic strategy to improve the efficacy of chemotherapy in breast cancer.

Effects of Mitochondrial-Derived Peptides (MDPs) on Mitochondrial and Cellular Health in AMD

Substantive evidence demonstrates the contribution of mitochondrial dysfunction in the etiology and pathogenesis of Age-related Macular Degeneration (AMD). Recently, extensive characterization of Mitochondrial-Derived Peptides (MDPs) has revealed their cytoprotective role in several diseases, including AMD. Here we summarize the varied effects of MDPs on cellular and mitochondrial health, which establish the merit of MDPs as therapeutic targets for AMD. We argue that further research to delve into the mechanisms of action and delivery of MDPs may advance the field of AMD therapy.

Using Small Peptide Segments of Amyloid-β and Humanin to Examine their Physical Interactions

BACKGROUND

Amyloid fibrils in Alzheimer's disease are composed of amyloid-β (Aβ) peptides of variant lengths. Humanin (HN), a 24 amino acid residue neuroprotective peptide, is known to interact with the predominant Aβ isoform in the brain, Aβ (1-40).

METHODS

Here, we constructed smaller segments of Aβ and HN and identified residues in HN important for both HN-HN and HN-Aβ interactions. Peptides corresponding to amino acid residues 5- 15 of HN, HN (5-15), HN (5-15, L11S), where Leu11 was replaced with Ser, and residues 17-28 of Aβ, Aβ (17-28), were synthesized and tested for their ability to block formation of the complex between HN and Aβ (1-40).

RESULTS

Co-immunoprecipitation and binding kinetics showed that HN (5-15) was more efficient at blocking the complex between HN and Aβ (1-40) than either HN (5-15, L11S) or Aβ (17-28). Binding kinetics of these smaller peptides with either full-length HN or Aβ (1-40) showed that HN (5- 15) was able to bind either Aβ (1-40) or HN more efficiently than HN (5-15, L11S) or Aβ (17-28). Compared to full-length HN, however, HN (5-15) bound Aβ (1-40) with a weaker affinity suggesting that while HN (5-15) binds Aβ, other residues in the full length HN peptide are necessary for maximum interactions.

CONCLUSION

L11 was more important for interactions with Aβ (1-40) than with HN. Aβ (17-28) was relatively ineffective at binding to either Aβ (1-40) or HN. Moreover, HN, and the smaller HN (5-15), HN (5-15 L11S), and Aβ (17-28) peptides, had different effects on regulating Aβ (1-40) aggregation kinetics.

Identification of a prosurvival neuroprotective mitochondrial peptide in a mammalian hibernator

Hibernation requires the intricate regulation of physiological and biochemical adaptations to facilitate the decrease in metabolic rate and activation of prosurvival factors needed for winter survival. Mitochondria play important roles in eliciting these responses and in coordinating the required energy shifts. Herein, we report the presence of a novel mitochondrial peptide, s-humanin, in the hibernating 13-lined ground squirrel, Ictidomys tridecemlineatus. S-humanin was shown to have strong structural and sequence similarities to its human analogue, humanin-a powerful neuroprotective mitochondrial peptide. An assessment of the protein and gene expression levels of this peptide in ground squirrels revealed stark tissue-specific regulatory responses whereby transcript levels increased in brain cortex, skeletal muscle, and adipose tissues during hibernation, suggesting a protective torpor-induced activation. Accompanying peptide measurements found that s-humanin levels were suppressed in liver of torpid squirrels but enhanced in brain cortex. The enhanced transcript and protein levels of s-humanin in brain cortex suggest that it is actively involved in protecting delicate brain tissues and neuronal connections from hibernation-associated stresses. We propose that this squirrel-specific peptide is involved in modulating tissue-specific cytoprotective functions, expanding its role from human-specific neuroprotection to environmental stress protection. SIGNIFICANCE OF THE STUDY: Understanding the molecular mechanisms, which protect against oxidative stress in a model hibernator such as the ground squirrel, could be pivotal to the regulation of cytoprotection. This study expands on our knowledge of metabolic rate depression and could suggest a potential role for humanin therapy in neurodegenerative diseases.

Humanin is a novel regulator of Hedgehog signaling and prevents glucocorticoid-induced bone growth impairment

Glucocorticoids (GCs) are frequently used to treat chronic disorders in children, including inflammation and cancer. Prolonged treatment with GCs is well known to impair bone growth, an effect linked to increased apoptosis and suppressed proliferation in growth plate chondrocytes. We hypothesized that the endogenous antiapoptotic protein humanin (HN) may prevent these effects. Interestingly, GC-induced bone growth impairment and chondrocyte apoptosis was prevented in HN overexpressing mice, HN-treated wild-type mice, and in HN-treated cultured rat metatarsal bones. GC-induced suppression of chondrocyte proliferation was also prevented by HN. Furthermore, GC treatment reduced Indian Hedgehog expression in growth plates of wild-type mice but not in HN overexpressing mice or HN-treated wild-type animals. A Hedgehog (Hh) antagonist, vismodegib, was found to suppress the growth of cultured rat metatarsal bones, and this effect was also prevented by HN. Importantly, HN did not interfere with the desired anti-inflammatory effects of GCs. We conclude that HN is a novel regulator of Hh signaling preventing GC-induced bone growth impairment without interfering with desired effects of GCs. Our data may open for clinical studies exploring a new possible strategy to prevent GC-induced bone growth impairment by cotreating with HN.-Zaman, F., Zhao, Y., Celvin, B., Mehta, H. H., Wan, J., Chrysis, D., Ohlsson, C., Fadeel, B., Cohen, P., Sävendahl, L. Humanin is a novel regulator of Hedgehog signaling and prevents glucocorticoid-induced bone growth impairment.

Follicular fluid humanin concentration is related to ovarian reserve markers and clinical pregnancy after IVF-ICSI: a pilot study

RESEARCH QUESTION

Is humanin present in the human ovary and follicular fluid? What relationship exists between humanin concentration in the follicular fluid and ovarian reserve and clinical outcomes after IVF and intracytoplasmic sperm injection (ICSI)?

DESIGN

Follicular fluid samples were collected from 179 patients undergoing their first IVF or ICSI cycle during oocyte retrieval. Ovarian tissues were collected from two patients undergoing surgery for ovarian cysts. Ovarian humanin localization was analysed using immunofluorescence staining. Expression of humanin in granulosa cells was confirmed by reverse transcription polymerase chain reaction (RT-PCR) analysis. Follicular fluid humanin levels were evaluated with enzyme-linked immunosorbent assay. Relationships between follicular fluid humanin levels and ovarian reserve markers and clinical outcomes were analysed.

RESULTS

Strong humanin expression was found in the granulosa cells, oocytes and stromal cells of the ovary. Agarose gel electrophoresis of RT-PCR products showed rich humanin mRNA expression in human granulosa cells (119 bp). Follicular fluid humanin concentrations ranged from 86.40 to 417.60 pg/ml. They significantly correlated with FSH (r = -0.21; P < 0.01), LH (r = -0.18; P = 0.02), antral follicle count (r = 0.27; P < 0.01), anti-Müllerian hormone (r = 0.24; P = 0.03) and inhibin B (r = 0.46; P < 0.01) levels. Patients were subdivided into four groups according to follicular fluid humanin concentration quartiles (Q1-Q4). Patients in Q4 were more likely to achieve a pregnancy than Q1 (OR = 3.60; 95% CI 1.09 to 11.84).

CONCLUSIONS

Humanin concentration in the follicular fluid was positively associated with ovarian reserve and clinical pregnancy rate.

Humanin decreases mitochondrial membrane permeability by inhibiting the membrane association and oligomerization of Bax and Bid proteins

Humanin (HN) is a 24-residue peptide identified from the brain of a patient with Alzheimer's disease (AD). HN has been found to protect against neuronal insult caused by Aβ peptides or transfection of familial AD mutant genes. In order to elucidate the molecular mechanisms of HN neuroprotection, we explored the effects of HN on the association of Bax or Bid with lipid bilayers and their oligomerization in the membrane. By using single-molecule fluorescence and Förster resonance energy transfer techniques, we showed that Bax was mainly present as monomers, dimers and tetramers in lipid bilayers, while truncated Bid (tBid) enhanced the membrane association and tetramerization of Bax. HN (100 nmol/L) inhibited the self-association and tBid-activated association of Bax with the bilayers, and significantly decreased the proportion of Bax in tetramers. Furthermore, HN inhibited Bid translocation to lipid bilayers. HN could bind with Bax and Bid either in solution or in the membrane. However, HN could not pull the proteins out of the membrane. Based on these results, we propose that HN binds to Bax and cBid in solution and inhibits their translocation to the membrane. Meanwhile, HN interacts with the membrane-bound Bax and tBid, preventing the recruitment of cytosolic Bax and its oligomerization in the membrane. In this way, HN inhibits Bax pore formation in mitochondrial outer membrane and suppresses cytochrome c release and mitochondria-dependent apoptosis.

The mitochondrial-derived peptide humanin activates the ERK1/2, AKT, and STAT3 signaling pathways and has age-dependent signaling differences in the hippocampus

Humanin is a small secreted peptide that is encoded in the mitochondrial genome. Humanin and its analogues have a protective role in multiple age-related diseases including type 2 diabetes and Alzheimer's disease, through cytoprotective and neuroprotective effects both in vitro and in vivo. However, the humanin-mediated signaling pathways are not well understood. In this paper, we demonstrate that humanin acts through the GP130/IL6ST receptor complex to activate AKT, ERK1/2, and STAT3 signaling pathways. Humanin treatment increases phosphorylation in AKT, ERK 1/2, and STAT3 where PI3K, MEK, and JAK are involved in the activation of those three signaling pathways, respectively. Furthermore, old mice, but not young mice, injected with humanin showed an increase in phosphorylation in AKT and ERK1/2 in the hippocampus. These findings uncover a key signaling pathway of humanin that is important for humanin's function and also demonstrates an age-specific in vivo effect in a region of the brain that is critical for memory formation in an age-dependent manner.

The Mitochondrial-Derived Peptides, HumaninS14G and Small Humanin-like Peptide 2, Exhibit Chaperone-like Activity

Mitochondrial-derived peptides (MDPs) and their analogs have emerged as wide-spectrum, stress response factors protective in amyloid disease models. MDP cytoprotective functions are generally attributed to anti-apoptotic activity, however, little is known about their capacity to facilitate the cell’s unfolded protein response via direct interactions with amyloidogenic proteins. Here, we explored the effects of the MDP-analog, humaninS14G (HNG), and the MDP, small humanin-like peptide 2 (SHLP2), on the misfolding of islet amyloid polypeptide (IAPP), a critical pathogenic step in type 2 diabetes mellitus (T2DM). Our thioflavin T fluorescence studies show that HNG inhibits IAPP misfolding at highly substoichiometric concentrations. Seeded fluorescence and co-sedimentation studies demonstrate MDPs block amyloid seeding and directly bind misfolded, seeding-capable IAPP species. Furthermore, our electron paramagnetic resonance spectroscopy and circular dichroism data indicate MDPs do not act by binding IAPP monomers. Taken together our results reveal a novel chaperone-like activity wherein these MDPs specifically target misfolded amyloid seeds to inhibit IAPP misfolding which, along with direct anti-apoptotic activity and beneficial metabolic effects, make HNG and SHLP2 exciting prospects as T2DM therapeutics. These data also suggest that other mitochondrial stress response factors within the MDP family may be amenable to development into therapeutics for protein-misfolding diseases.

Protective Mechanisms of the Mitochondrial-Derived Peptide Humanin in Oxidative and Endoplasmic Reticulum Stress in RPE Cells

Age-related macular degeneration (AMD) is the leading cause of severe and irreversible vision loss and is characterized by progressive degeneration of the retina resulting in loss of central vision. The retinal pigment epithelium (RPE) is a critical site of pathology of AMD. Mitochondria and the endoplasmic reticulum which lie in close anatomic proximity to each other are targets of oxidative stress and endoplasmic reticulum (ER) stress, respectively, and contribute to the progression of AMD. The two organelles exhibit close interactive function via various signaling mechanisms. Evidence for ER-mitochondrial crosstalk in RPE under ER stress and signaling pathways of apoptotic cell death is presented. The role of humanin (HN), a prominent member of a newly discovered family of mitochondrial-derived peptides (MDPs) expressed from an open reading frame of mitochondrial 16S rRNA, in modulation of ER and oxidative stress in RPE is discussed. HN protected RPE cells from oxidative and ER stress-induced cell death by upregulation of mitochondrial GSH, inhibition of ROS generation, and caspase 3 and 4 activation. The underlying mechanisms of ER-mitochondrial crosstalk and modulation by exogenous HN are discussed. The therapeutic use of HN and related MDPs could potentially prove to be a valuable approach for treatment of AMD.

Humanin G (HNG) protects age-related macular degeneration (AMD) transmitochondrial ARPE-19 cybrids from mitochondrial and cellular damage

Age-related macular degeneration (AMD) ranks third among the leading causes of visual impairment with a blindness prevalence rate of 8.7%. Despite several treatment regimens, such as anti-angiogenic drugs, laser therapy, and vitamin supplementation, being available for wet AMD, to date there are no FDA-approved therapies for dry AMD. Substantial evidence implicates mitochondrial damage and retinal pigment epithelium (RPE) cell death in the pathogenesis of AMD. However, the effects of AMD mitochondria and Humanin G (HNG), a more potent variant of the mitochondrial-derived peptide (MDP) Humanin, on retinal cell survival have not been elucidated. In this study, we characterized mitochondrial and cellular damage in transmitochondrial cybrid cell lines that contain identical nuclei but possess mitochondria from either AMD or age-matched normal (Older-normal (NL)) subjects. AMD cybrids showed (1) reduced levels of cell viability, lower mtDNA copy numbers, and downregulation of mitochondrial replication/transcription genes and antioxidant enzyme genes; and (2) elevated levels of genes related to apoptosis, autophagy and ER-stress along with increased mtDNA fragmentation and higher susceptibility to amyloid-β-induced toxicity compared to NL cybrids. In AMD cybrids, HNG protected the AMD mitochondria, reduced pro-apoptosis gene and protein levels, upregulated gp130 (a component of the HN receptor complex), and increased the protection against amyloid-β-induced damage. In summary, in cybrids, damaged AMD mitochondria mediate cell death that can be reversed by HNG treatment. Our results also provide evidence of Humanin playing a pivotal role in protecting cells with AMD mitochondria. In the future, it may be possible that AMD patient's blood samples containing damaged mitochondria may be useful as biomarkers for this condition. In conclusion, HNG may be a potential therapeutic target for treatment of dry AMD, a debilitating eye disease that currently has no available treatment. Further studies are needed to establish HNG as a viable mitochondria-targeting therapy for dry AMD.

Mitochondrially derived peptides as novel regulators of metabolism

Mitochondrially derived peptides represent a new class of circulating signalling molecules. Humanin, the first member of this class, has been shown to have several metabolic effects such as reducing weight gain and visceral fat and increasing glucose-stimulated insulin release. The discovery of several other new members, such as MOTS-c and SHLP1-6, has further added to this group. These new peptides have also been found to affect metabolism with MOTS-c potently decreasing weight gain in mice on a high-fat diet. This review covers the basic biology of this class of peptides and discusses the relevance to organismal metabolism.

Breaking the ritual metabolic cycle in order to save acetyl CoA: A potential role for mitochondrial humanin in T2 bladder cancer aggressiveness

INTRODUCTION

Cancer cells may exhibit outsourcing of their high energy need in order to avoid the intrinsic mitochondrial apoptosis. Reduced mitochondrial respiration and accumulation of mitochondrial genome mutations are among metabolic transformations in this regard. Mitochondrial humanin (MT-RNR2) is a small peptide with anti-apoptotic activities attributed to binding some pro-apoptotic proteins.

AIM OF THE WORK

The current study aims at investigating the expression of mitochondrial humanin in bladder tumor cells and the possible casting of humanin anti-apoptotic action through orchestrating some of the mitochondrial metabolic enzymes.

MATERIAL AND METHODS

Here messenger RNA of humanin, succinate dehydrogenase, glutaminase, isocitrate dehydrogenase were compared in tissues from patients with T2 bladder carcinoma in comparison to tumor associated normal tissues from the same patients. Levels of lactate and mitochondrial pyruvate carrier (MPC1) mRNA were determined to scrutinize the prevalence of aerobic glycolysis.

RESULTS

The present study found that tumor cells had suppressed aerobic glycolysis, augmented mitochondrial respiration and interrupted tricarboxylic acid cycle, all of which were suggested to serve tumor aggressiveness. MT-RNR2 was found closely related to the alterations in mitochondrial activity.

CONCLUSION

MT-RNR2 plays its anti-apoptotic role partly by avoiding deploying energy from complete oxidation of organic compounds to inorganic wastes. Thus MT-RNR2 can potentially serve as a new biomarker in the diagnosis of bladder carcinoma especially that it is present in blood circulation.

Humanin: Functional Interfaces with IGF-I

Humanin is the first newly discovered peptide encoded in the mitochondrial genome in over three decades. It is the first member of a novel class of mitochondrial derived peptides. This small, 24 amino acid peptide was initially discovered to have neuroprotective effects and subsequent experiments have shown that it is beneficial in a diverse number of disease models including stroke, cardiovascular disease, and cancer. Over a decade ago, our lab found that humanin bound IGFBP-3 and more recent studies have found it to decrease circulating IGF-I levels. In turn, IGF-I also seems to regulate humanin levels and in this review, we cover the known interaction between humanin and IGF-I. Although the exact mechanism for how humanin and IGF-I regulate each other still needs to be elucidated, it is clear that humanin is a new player in IGF-I signaling.

The effects of humanin and its analogues on male germ cell apoptosis induced by chemotherapeutic drugs

Human (HN) prevents stress-induced apoptosis in many cells/tissues. In this study we showed that HN ameliorated chemotherapy [cyclophosphamide (CP) and Doxorubicin (DOX)]-induced male germ cell apoptosis both ex vivo in seminiferous tubule cultures and in vivo in the testis. HN acts by several putative mechanisms via binding to: an IL-12 like trimeric membrane receptor; BAX; or insulin-like growth factor binding protein-3 (IGFBP-3, a proapoptotic factor). To understand the mechanisms of HN on male germ cell apoptosis, we studied five HN analogues including: HNG (HN-S14G, a potent agonist), HNG-F6A (no binding to IGFBP-3), HN-S7A (no self-dimerization), HN-C8P (no binding to BAX), and HN-L12A (a HN antagonist) on CP-induced male germ cell apoptosis in mice. CP-induced germ cell apoptosis was inhibited by HN, HNG, HNG-F6A, HN-S7A, and HN-C8P (less effective); but not by HN-L12A. HN-L12A, but not HN-S7A or HN-C8P, blocked the protective effect of HN against CP-induced male germ cell apoptosis. HN, HN-S7A, and HN-C8P restored CP-suppressed STAT3 phosphorylation. These results suggest that HN: (1) decreases DOX (ex vivo) and CP (in vivo) induced male germ cell apoptosis; (2) action is mediated by the membrane receptor/STAT3 with minor contribution by BAX-binding pathway; (3) self-dimerization or binding to IGFBP-3 may not be involved in HN's effect in testis. HN is an important molecule in the regulation of germ cell homeostasis after injury and agonistic analogues may be developed for treating male infertility or protection against chemotherapy side effects.

Protection effect of [Gly14]-Humanin from apoptosis induced by high glucose in human umbilical vein endothelial cells

AIMS

Humanin (HN) is known for its anti-apoptotic functions in neuronal cells. In this study, we sought to investigate the protective effect of [Gly14]-Humanin (HNG) in high glucose (HG)-induced apoptosis of human umbilical vein endothelial cells (HUVECs).

METHODS

3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to examine cell viability, DNA chromatin morphology was assessed using Hoechst 33342 staining, and the generation of intracellular reactive oxygen species (ROS) was assessed using the fluorescent probe dichlorofluorescein diacetate (DCFH-DA). The expression of poly ADP-ribose polymerase (PARP), the pro-apoptotic protein bax and the anti-apoptotic protein bcl-2 were examined using western blot analysis. The mRNA level of bax and bcl-2 were detected by quantitative Real-Time PCR.

RESULTS

Compared with treatment with HG 72h, pretreatment with HNG for 3h significantly increased cell viability (P<0.001), reduced nuclear fluorescence of HUVECs (P<0.05), the levels of cleaved PARP (P<0.05), ROS formation (P<0.05) and the ratio of bax/bcl-2 (P<0.05) compared with treatment with HG for 72h. Quantitative Real-Time PCR showed that mRNA level of bax reduced (P<0.05) and mRNA level of bcl-2 increased (P<0.05) after pretreatment with HNG.

CONCLUSIONS

Our results imply that HNG can protect HUVECs from apoptosis induced by HG through the bax/bcl-2 pathway.

Humanin and age-related diseases: a new link?

Humanin (HN) is 24-amino acid mitochondria-associated peptide. Since its initial discovery over a decade ago, a role for HN has been reported in many biological processes such as apoptosis, cell survival, substrate metabolism, inflammatory response, and response to stressors such as oxidative stress, ischemia, and starvation. HN and its potent analogs have been shown to have beneficial effects in many age-related diseases including Alzheimer's disease, stroke, diabetes, myocardial ischemia and reperfusion, atherosclerosis, amyotrophic lateral sclerosis, and certain types of cancer both in vitro and in vivo. More recently, an association between HN levels, growth hormone/insulin-like growth factor-1 (GH/IGF axis), and life span was demonstrated using various mouse models with mutations in the GH/IGF axis. The goal of this review is to summarize the current understanding of the role of HN in aging and age-related diseases.

Inactive C8A‑humanin analog is as stable as a potent S14G‑humanin analog

We have previously shown that the structural stability of humanin (HN), a neuroprotective peptide ligand, is one of the attributes to the observed activity differences between HN analogs. It has been observed that the activity increased consecutively in the S7A‑HN analog, the parent HN and the S14G‑HN analog, consistent with the increased stability observed in that order. In the present study, the structure and stability of another inactive analog, C8A‑HN, was measured, which has been revealed to have no neuroprotective activity similar to that of the S7A‑HN analog and hence may have compromised stability. While all these analogs of HN demonstrated a similar disordered secondary structure in phosphate-buffered saline at 5˚C, as determined by circular dichroism spectroscopy, they revealed different structures at 37˚C. At 37˚C, less active HN and inactive S7A‑HN revealed a structure with a valley at ~217 nm, indicating a conversion from the disordered structure to a β‑sheet. Such a conversion was largely irreversible. By contrast, C8A‑HN and S14G‑HN demonstrated a similar structure at 37˚C and at 5˚C and remained largely disordered. The observed small structural changes of the C8A‑HN analog at 37˚C and its reversibility upon cooling do not support a hypothesis that the instability at 37˚C may have caused the reduced activity of this analog. Therefore an alternative explanation for its activity loss is required.