Humanin expression in skeletal muscles of patients with chronic progressive external ophthalmoplegia

Humanin's impact on pain markers and neuronal viability in diabetic neuropathy model

OBJECTIVE

This study investigates the impact of chronic humanin (HN) treatment on pain-related markers (NMDA, substance P, TRPV1, and IL-1β) in diabetic mice's dorsal root ganglia (DRG). Additionally, we assess the effects of HN on cellular viability in DRG neurons.

METHODS

In vivo experiments involved 15 days of HN administration (4 mg/kg) to diabetic mice (n = 10). Protein levels of NMDA, IL-1β, TRPV1, and substance P were measured in diabetic DRG. In vitro experiments explored HN's impact on apoptosis and cellular viability, focusing on the JAK2/STAT3 pathway.

RESULTS

Humanin significantly reduced the elevated expression of NMDA, IL-1β, TRPV1, and substance P induced by diabetes (p < .05). Furthermore, HN treatment increased cellular viability in DRG neurons through JAK2/STAT3 pathway activation (p < .05).

CONCLUSION

These findings highlight the significance of understanding mitochondrial function and pain markers, as well as apoptosis in diabetes. The study provides insights for managing the condition and its complications.

A New Antioxidant Marker in Cord Blood of Fetuses with Late Fetal Growth Restriction: Humanin

Purpose: This study investigated the Humanin levels in the umbilical cord blood of fetuses with late fetal growth restriction (FGR) and -evaluated their association with perinatal outcomes. Materials and Methods: A total of 95 single pregnancies between 32-41 wk (45 with late FGR and 50 controls) were included. Doppler parameters, birth weight and the need for neonatal intensive care unit admission (NICU) were assessed. Correlations between Humanin levels and these parameters were analyzed. Results: Higher Humanin levels were found in fetuses with late FGR compared to the control group (p < 0.05). No significant correlation was observed between Humanin levels and Doppler parameters. Elevated Humanin levels were associated with an increased need for NICU (p < 0.05). Conclusions: The statistically higher levels of Humanin in fetuses with late FGR may suggest the potential of Humanin as an indicator of late FGR. Further research is needed to explore the clinical utility of Humanin.

Primary oxidative phosphorylation defects lead to perturbations in the human B cell repertoire

Introduction

The majority of studies on oxidative phosphorylation in immune cells have been performed in mouse models, necessitating human translation. To understand the impact of oxidative phosphorylation (OXPHOS) deficiency on human immunity, we studied children with primary mitochondrial disease (MtD).

Methods

scRNAseq analysis of peripheral blood mononuclear cells was performed on matched children with MtD (N = 4) and controls (N = 4). To define B cell function we performed phage display immunoprecipitation sequencing on a cohort of children with MtD (N = 19) and controls (N = 16).

Results

Via scRNAseq, we found marked reductions in select populations involved in the humoral immune response, especially antigen presenting cells, B cell and plasma populations, with sparing of T cell populations. MTRNR2L8, a marker of bioenergetic stress, was significantly elevated in populations that were most depleted. mir4485, a miRNA contained in the intron of MTRNR2L8, was co-expressed. Knockdown studies of mir4485 demonstrated its role in promoting survival by modulating apoptosis. To determine the functional consequences of our findings on humoral immunity, we studied the antiviral antibody repertoire in children with MtD and controls using phage display and immunoprecipitation sequencing. Despite similar viral exposomes, MtD displayed antiviral antibodies with less robust fold changes and limited polyclonality.

Discussion

Overall, we show that children with MtD display perturbations in the B cell repertoire which may impact humoral immunity and the ability to clear viral infections.

An evidence of Humanin-like peptide and Humanin mediated cryosurvival of spermatozoa in buffalo bulls

Buffalo spermatozoa are vulnerable to cryo-injuries due to inherent deficiency of endogenous antioxidants, high polyunsaturated fatty acids (PUFA) content in plasma membrane and low cholesterol/phospholipid (C/P) ratio. Humanin is a potent cytoprotective agent that protects the cells against oxidative stress and apoptosis. The present study was designed to establish the presence of Humanin in buffalo and effect of Humanin supplementation on freezability of buffalo spermatozoa. Indirect immunofluorescence test revealed presence of Humanin in ejaculated and epididymal spermatozoa, and, elongated spermatids and interstitial space in the testicular tissue section. Humanin levels in seminal plasma were significantly and positively correlated with sperm concentration and individual progressive motility (IPM) in good (n = 22; IPM >70%) and poor (n = 10; IPM <50%) quality ejaculates. For supplementation studies, a total of 24 ejaculates (IPM ≥70%) were collected and each ejaculate was then divided into four aliquots. First aliquot was diluted with egg yolk-tris-glycerol (EYTG) extender without Humanin and served as control group (Group I). Rest three aliquots were diluted with extender containing 2 (Group II), 5 (Group III) and 10 μM Humanin (Group IV), respectively. Semen was cryopreserved using standard protocol and evaluated at pre-freeze for lipid peroxidation (LPO) and post-thaw stages for spermatozoa kinematics, LPO, mitochondrial membrane potential (MMP), capacitation, apoptotic status and DNA integrity. The treatment group that showed best results (5 μM) was compared with control group for in vitro fertility assessment by homologous zona binding assay. The LPO levels were lower (p < 0.05) in 5 and 10 μM Humanin supplemented group. The MMP and DNA integrity were higher (p < 0.05) in 5 μM group than other groups. F-pattern was higher (p < 0.05) and B-pattern was lower (p < 0.05) in 5 and 10 μM Humanin supplemented groups. Lower apoptotic and higher viable spermatozoa (p < 0.05) were observed in 5 μM Humanin group. The mean number of spermatozoa bound to zona pellucida was higher (p < 0.05) in 5 μM Humanin treated group than the control group. The study established the presence of Humanin in buffalo spermatozoa and seminal plasma for very first time and concluded that Humanin supplementation at 5 μM concentration improves the freezability and in vitro fertility of buffalo spermatozoa.

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 and diabetes mellitus: A review of in vitro and in vivo studies

Humanin (HN) is a 24-amino acid mitochondrial-derived polypeptide with cyto-protective and anti-apoptotic effects that regulates the mitochondrial functions under stress conditions. Accumulating evidence suggests the role of HN against age-related diseases, such as Alzheimer’s disease. The decline in insulin action is a metabolic feature of aging and thus, type 2 diabetes mellitus is considered an age-related disease, as well. It has been suggested that HN increases insulin sensitivity, improves the survival of pancreatic beta cells, and delays the onset of diabetes, actions that could be deployed in the treatment of diabetes. The aim of this review is to present the in vitro and in vivo studies that examined the role of HN in insulin resistance and diabetes and to discuss its newly emerging role as a therapeutic option against those conditions.

Oxidative Damage? Not a Problem! The Characterization of Humanin-like Mitochondrial Peptide in Anoxia Tolerant Freshwater Turtles

Mitochondria was long thought to be an "end function" organelle that regulated the metabolic flux and apoptosis in the cell. However, with the discovery of the mitochondrial peptide (MDP) humanin (HN/MTRNR2), the cytoprotective and pro-survival applications of MDPs have taken the forefront of therapeutic and diagnostic research. However, the regulation of humanin-like MDPs in natural model systems that can tolerate lethal environmental and cytotoxic insults remains to be investigated. Red-eared sliders are champion anaerobes that can withstand three continuous months of anoxia followed by rapid bouts of oxygen reperfusion without incurring cellular damage. Freshwater turtles employ extensive physiological and biochemical strategies to combat anoxia, with metabolic rate depression and a global enhancement of antioxidant and cytoprotective pathways being the two most important contributors. The main aim of this study was to uncover and characterize the humanin-homologue in freshwater turtles as well as investigate the differential regulation of humanin in response to short and long-term oxygen deprivation. In this study we have used de novo and homology-based protein modelling to elucidate the putative structure of humanin in red-eared sliders as well as an ELISA and western immunoblotting to confirm the protein abundance in the turtle brain and six peripheral tissues during control, 5 h, and 20 h anoxia (n = 4/group). We found that a humanin-homologue (TSE-humanin) is present in red-eared sliders and it may play a cytoprotective role against oxidative damage.

Mitochondrial-derived peptides in energy metabolism

Mitochondrial-derived peptides (MDPs) are small bioactive peptides encoded by short open-reading frames (sORF) in mitochondrial DNA that do not necessarily have traditional hallmarks of protein-coding genes. To date, eight MDPs have been identified, all of which have been shown to have various cyto- or metaboloprotective properties. The 12S ribosomal RNA (MT-RNR1) gene harbors the sequence for MOTS-c, whereas the other seven MDPs [humanin and small humanin-like peptides (SHLP) 1-6] are encoded by the 16S ribosomal RNA gene. Here, we review the evidence that endogenous MDPs are sensitive to changes in metabolism, showing that metabolic conditions like obesity, diabetes, and aging are associated with lower circulating MDPs, whereas in humans muscle MDP expression is upregulated in response to stress that perturbs the mitochondria like exercise, some mtDNA mutation-associated diseases, and healthy aging, which potentially suggests a tissue-specific response aimed at restoring cellular or mitochondrial homeostasis. Consistent with this, treatment of rodents with humanin, MOTS-c, and SHLP2 can enhance insulin sensitivity and offer protection against a range of age-associated metabolic disorders. Furthermore, assessing how mtDNA variants alter the functions of MDPs is beginning to provide evidence that MDPs are metabolic signal transducers in humans. Taken together, MDPs appear to form an important aspect of a retrograde signaling network that communicates mitochondrial status with the wider cell and to distal tissues to modulate adaptative responses to metabolic stress. It remains to be fully determined whether the metaboloprotective properties of MDPs can be harnessed into therapies for metabolic disease.

Cytoprotective role of humanin in lens epithelial cell oxidative stress‑induced injury

Oxidative stress-induced injury and apoptosis of human lens epithelial cells (HLECs) are early events in the development of age-related cataracts (ARCs). Humanin (HN) is a mitochondrial-related peptide that serves a cytoprotective role in various cell types and animal models. Following HN knockdown or overexpression, the level of reactive oxygen species (ROS), mitochondrial membrane potential and mitochondrial DNA copy number, cell viability, LDH activity and apoptosis of HLECs under oxidative stress were detected, and apoptosis and autophagy were detected via transmission electron microscopy. The results suggested that HN may be involved in the response of HLECs to oxidative stress, and that HN expression was significantly upregulated under oxidative stress conditions. Furthermore, exogenous HN reduced intracellular ROS content and mitochondrial damage, and enhanced mitochondrial biosynthesis; however, this protection was lost in an endogenous HN knockdown cell model. In addition, to the best of our knowledge, the present study was the first to identify that HN increased mitochondrial autophagy, which was involved in reducing ROS production under oxidative stress. The present study indicated a potential mechanism underlying the anti-oxidative damage and apoptotic effects of HN under oxidative stress. In conclusion, HN may be a potential therapeutic target for ARCs as it has a significant cellular protective effect on HLECs under oxidative stress; therefore, further study is required to investigate its role in the occurrence and development of ARCs.

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.

Comparison of serum concentrations of humanin in women with and without gestational diabetes mellitus

Humanin (MT-RNR2) is an endogenous polypeptide that is involved in many diseases, including T2DM. Gestational diabetes mellitus (GDM) is defined as hyperglycemia during pregnancy. The aim of this study was to evaluate serum humanin levels in women with or without GDM and to elucidate possible correlations with anthropometric parameters, metabolic parameters and the incidence of GDM. Eighty-four women with GDM and 73 control women were enrolled in this study. The clinical and biochemical parameters of all subjects were determined. Serum humanin levels were measured by an ELISA. Serum humanin levels were significantly lower in women with GDM than in control women. Moreover, humanin levels were significantly negatively correlated with the presence of GDM, body weight, BMI at 24 weeks of gestation, TG, FPG, 1 hPG, 2 hPG, FINS, and HOMA-IR. In contrast, humanin levels were significantly positively correlated with FT3 and FT4. A binary logistic analysis showed that humanin levels were associated with the incidence of GDM. Additional follow-up studies are needed to highlight whether and how decreased humanin levels play an important role in GDM.

Humanin (HN) and glucose transporter 8 (GLUT8) in pregnancies complicated by intrauterine growth restriction

Background

Intrauterine growth restriction (IUGR) results from a lack of nutrients transferred to the developing fetus, particularly oxygen and glucose. Increased expression of the cytoprotective mitochondrial peptide, humanin (HN), and the glucose transporter 8, GLUT8, has been reported under conditions of hypoxic stress. However, the presence and cellular localization of HN and GLUT8 in IUGR-related placental pathology remain unexplored. Thus, we undertook this study to investigate placental expression of HN and GLUT8 in IUGR-affected versus normal pregnancies.

Results

We found 1) increased HN expression in human IUGR-affected pregnancies on the maternal aspect of the placenta (extravillous trophoblastic (EVT) cytoplasm) compared to control (i.e. appropriate for gestational age) pregnancies, and a concomitant increase in GLUT8 expression in the same compartment, 2) HN and GLUT8 showed a protein-protein interaction by co-immunoprecipitation, 3) elevated HN and GLUT8 levels in vitro under simulated hypoxia in human EVT cells, HTR8/SVneo, and 4) increased HN expression but attenuated GLUT8 expression in vitro under serum deprivation in HTR8/SVneo cells.

Conclusions

There was elevated HN expression with cytoplasmic localization to EVTs on the maternal aspect of the human placenta affected by IUGR, also associated with increased GLUT8 expression. We found that while hypoxia increased both HN and GLUT8, serum deprivation increased HN expression alone. Also, a protein-protein interaction between HN and GLUT8 suggests that their interaction may fulfill a biologic role that requires interdependency. Future investigations delineating molecular interactions between these proteins are required to fully uncover their role in IUGR-affected pregnancies.

Sex differences in the late first trimester human placenta transcriptome

Background

Development of the placenta during the late first trimester is critical to ensure normal growth and development of the fetus. Developmental differences in this window such as sex-specific variation are implicated in later placental disease states, yet gene expression at this time is poorly understood.

Methods

RNA-sequencing was performed to characterize the transcriptome of 39 first trimester human placentas using chorionic villi following genetic testing (17 females, 22 males). Gene enrichment analysis was performed to find enriched canonical pathways and gene ontologies in the first trimester. DESeq2 was used to find sexually dimorphic gene expression. Patient demographics were analyzed for sex differences in fetal weight at time of chorionic villus sampling and birth.

Results

RNA-sequencing analyses detected 14,250 expressed genes, with chromosome 19 contributing the greatest proportion (973/2852, 34.1% of chromosome 19 genes) and Y chromosome contributing the least (16/568, 2.8%). Several placenta-enriched genes as well as histone-coding genes were identified to be unique to the first trimester and common to both sexes. Further, we identified 58 genes with significantly different expression between males and females: 25 X-linked, 15 Y-linked, and 18 autosomal genes. Genes that escape X inactivation were highly represented (59.1%) among X-linked genes upregulated in females. Many genes differentially expressed by sex consisted of X/Y gene pairs, suggesting that dosage compensation plays a role in sex differences. These X/Y pairs had roles in parallel, ancient canonical pathways important for eukaryotic cell growth and survival: chromatin modification, transcription, splicing, and translation.

Conclusions

This study is the first characterization of the late first trimester placenta transcriptome, highlighting similarities and differences among the sexes in ongoing human pregnancies resulting in live births. Sexual dimorphism may contribute to pregnancy outcomes, including fetal growth and birth weight, which was seen in our cohort, with males significantly heavier than females at birth. This transcriptome provides a basis for development of early diagnostic tests of placental function that can indicate overall pregnancy heath, fetal-maternal health, and long-term adult health.

Electronic supplementary material

The online version of this article (10.1186/s13293-018-0165-y) contains supplementary material, which is available to authorized users.

Defining the momiome: Promiscuous information transfer by mobile mitochondria and the mitochondrial genome

Mitochondria are complex intracellular organelles that have long been identified as the powerhouses of eukaryotic cells because of the central role they play in oxidative metabolism. A resurgence of interest in the study of mitochondria during the past decade has revealed that mitochondria also play key roles in cell signaling, proliferation, cell metabolism and cell death, and that genetic and/or metabolic alterations in mitochondria contribute to a number of diseases, including cancer. Mitochondria have been identified as signaling organelles, capable of mediating bidirectional intracellular information transfer: anterograde (from nucleus to mitochondria) and retrograde (from mitochondria to nucleus). More recently, evidence is now building that the role of mitochondria extends to intercellular communication as well, and that the mitochondrial genome (mtDNA) and even whole mitochondria are indeed mobile and can mediate information transfer between cells. We define this promiscuous information transfer function of mitochondria and mtDNA as "momiome" to include all mobile functions of mitochondria and the mitochondrial genome. Herein, we review the "momiome" and explore its role in cancer development, progression, and treatment.

Humanin directly protects cardiac mitochondria against dysfunction initiated by oxidative stress by decreasing complex I activity

Humanin (HN) is an endogenous peptide that exerts cytoprotection against oxidative stress and apoptosis. We recently reported that Humanin analogue (HNG) pretreatment can reduce reactive oxygen species production in the heart subjected to ischemia/reperfusion (I/R) injury via attenuating mitochondrial dysfunction. However, it is unclear if HNG has direct effects on mitochondrial function against oxidative stress. Thus, we sought to determine the effects of HNG on mitochondrial function under hydrogen peroxide (H₂O₂) induced oxidative stress in isolated cardiac mitochondria. We found that HNG has direct protective effects on cardiac mitochondrial function against H₂O₂ induced oxidative stress through decreasing complex I activity.

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.

Serum humanin concentrations in women with pre-eclampsia compared to women with uncomplicated pregnancies

PURPOSE

To compare serum humanin concentrations in pregnant women with and without pre-eclampsia (PE).

MATERIALS AND METHODS

A case-control study where pregnant women (PE group, n = 37; control group, n = 34) studied through history parameters (gynecological, obstetrical, personal, and family), physical and sonographic examination parameters [body mass index (BMI), blood pressure obstetrical ultrasound], and biochemical/hormonal assays [creatinine, urea, serum glutamic oxaloacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT), uric acid, platelets, urinary protein, and humanin].

RESULTS

There was no difference in basic characteristics between women with PE and control, except in parity and gravidity. Humanin concentrations were higher in women with PE compared to controls (422.2 ± 33.5 vs. 319.1 ± 28.1 pg/ml, p = 0.023). In a binary logistic analysis, humanin was associated with the presence of PE [odds ratio 1.003, 95% confidence interval (CI); 1.000-1.006]. The ability of humanin to discriminate between women with PE and controls was evaluated by receiver operation characteristics (ROC) analysis [area under the curve (AUC) 0.639, 95% CI; 0.510-0.768, p = 0.045].

CONCLUSIONS

Serum humanin concentrations are increased in women with PE, compared to women with uncomplicated pregnancies, suggesting a potential protective role of humanin against the oxidative stress and endothelial dysfunction occurring in PE.

Functional Mitochondria in Health and Disease

The ability to rapidly adapt cellular bioenergetic capabilities to meet rapidly changing environmental conditions is mandatory for normal cellular function and for cancer progression. Any loss of this adaptive response has the potential to compromise cellular function and render the cell more susceptible to external stressors such as oxidative stress, radiation, chemotherapeutic drugs, and hypoxia. Mitochondria play a vital role in bioenergetic and biosynthetic pathways and can rapidly adjust to meet the metabolic needs of the cell. Increased demand is met by mitochondrial biogenesis and fusion of individual mitochondria into dynamic networks, whereas a decrease in demand results in the removal of superfluous mitochondria through fission and mitophagy. Effective communication between nucleus and mitochondria (mito-nuclear cross talk), involving the generation of different mitochondrial stress signals as well as the nuclear stress response pathways to deal with these stressors, maintains bioenergetic homeostasis under most conditions. However, when mitochondrial DNA (mtDNA) mutations accumulate and mito-nuclear cross talk falters, mitochondria fail to deliver critical functional outputs. Mutations in mtDNA have been implicated in neuromuscular and neurodegenerative mitochondriopathies and complex diseases such as diabetes, cardiovascular diseases, gastrointestinal disorders, skin disorders, aging, and cancer. In some cases, drastic measures such as acquisition of new mitochondria from donor cells occurs to ensure cell survival. This review starts with a brief discussion of the evolutionary origin of mitochondria and summarizes how mutations in mtDNA lead to mitochondriopathies and other degenerative diseases. Mito-nuclear cross talk, including various stress signals generated by mitochondria and corresponding stress response pathways activated by the nucleus are summarized. We also introduce and discuss a small family of recently discovered hormone-like mitopeptides that modulate body metabolism. Under conditions of severe mitochondrial stress, mitochondria have been shown to traffic between cells, replacing mitochondria in cells with damaged and malfunctional mtDNA. Understanding the processes involved in cellular bioenergetics and metabolic adaptation has the potential to generate new knowledge that will lead to improved treatment of many of the metabolic, degenerative, and age-related inflammatory diseases that characterize modern societies.

The Role of Mitochondria in AMD: Current Knowledge and Future Applications

Mitochondria are organelles which comprise the main respiratory machinery in the eukaryotic cells. In addition to their crucial role in energy production, they have profound effects on apoptosis and retrograde signaling to nucleus. Mitochondria have their own DNA, which codes for different proteins mostly involved in oxidative phosphorylation. Significant changes in the mitochondria of retinal pigment epithelium have been reported in age-related macular degeneration (AMD), which is correlated with the severity of the disease. Cybrid cell lines that have identical nuclei but mitochondria from different individuals can provide a unique means for studying the relationship between mitochondria and AMD. Different approaches for protection of mitochondria have been introduced which can be considered as potential future treatments for AMD and other age- related disorders.

Humanin: a mitochondrial signaling peptide as a biomarker for impaired fasting glucose-related oxidative stress

Mitochondrial RNR-2 (mt-RNR2, humanin) has been shown to play a role in protecting several types of cells and tissues from the effects of oxidative stress. Humanin (HN) functions through extracellular and intracellular pathways adjusting mitochondrial oxidative phosphorylation and ATP production. Addition of HN improved insulin sensitivity in animal models of diabetes mellitus but no clinical studies have been carried out to measure HN levels in humans associated with hyperglycemia. The plasma levels of HN in participants attending a diabetes complications screening clinic were measured. Clinical history and anthropometric data were obtained from all participants. Plasma levels of HN were measured by a commercial ELISA kit. All data were analyzed applying nonparametric statistics and general linear modeling to correct for age and gender. A significant decrease (P = 0.0001) in HN was observed in the impaired fasting glucose (IFG) group (n = 23; 204.84 ± 92.87 pg mL(-1)) compared to control (n = 58; 124.3 ± 83.91 pg mL(-1)) consistent with an adaptive cellular response by HN to a slight increase in BGL.

The Mitochondrial-Derived Peptide Humanin Protects RPE Cells From Oxidative Stress, Senescence, and Mitochondrial Dysfunction

PURPOSE

To investigate the expression of humanin (HN) in human retinal pigment epithelial (hRPE) cells and its effect on oxidative stress-induced cell death, mitochondrial bioenergetics, and senescence.

METHODS

Humanin localization in RPE cells and polarized RPE monolayers was assessed by confocal microscopy. Human RPE cells were treated with 150 μM tert-Butyl hydroperoxide (tBH) in the absence/presence of HN (0.5-10 μg/mL) for 24 hours. Mitochondrial respiration was measured by XF96 analyzer. Retinal pigment epithelial cell death and caspase-3 activation, mitochondrial biogenesis and senescence were analyzed by TUNEL, immunoblot analysis, mitochondrial DNA copy number, SA-β-Gal staining, and p16INK4a expression and HN levels by ELISA. Oxidative stress-induced changes in transepithelial resistance were studied in RPE monolayers with and without HN cotreatment.

RESULTS

A prominent localization of HN was found in the cytoplasmic and mitochondrial compartments of hRPE. Humanin cotreatment inhibited tBH-induced reactive oxygen species formation and significantly restored mitochondrial bioenergetics in hRPE cells. Exogenous HN was taken up by RPE and colocalized with mitochondria. The oxidative stress-induced decrease in mitochondrial bioenergetics was prevented by HN cotreatment. Humanin treatment increased mitochondrial DNA copy number and upregulated mitochondrial transcription factor A, a key biogenesis regulator protein. Humanin protected RPE cells from oxidative stress-induced cell death by STAT3 phosphorylation and inhibiting caspase-3 activation. Humanin treatment inhibited oxidant-induced senescence. Polarized RPE demonstrated elevated cellular HN and increased resistance to cell death.

CONCLUSIONS

Humanin protected RPE cells against oxidative stress-induced cell death and restored mitochondrial function. Our data suggest a potential role for HN therapy in the prevention of retinal degeneration, including AMD.

Protective effects of Humanin and calmodulin-like skin protein in Alzheimer's disease and broad range of abnormalities

Humanin is a 24-amino acid, secreted bioactive peptide that prevents various types of cell death and improves some types of cell dysfunction. Humanin inhibits neuronal cell death that is caused by a familial Alzheimer's disease (AD)-linked gene via binding to the heterotrimeric Humanin receptor (htHNR). This suggests that Humanin may play a protective role in AD-related pathogenesis. Calmodulin-like skin protein (CLSP) has recently been identified as a physiological agonist of htHNR with 10(5)-fold more potent anti-cell death activity than Humanin. Humanin has also shown to have protective effects against some metabolic disorders. In this review, the broad range of functions of Humanin and the functions of CLSP that have been characterized thus far are summarized.

Humanin rescues cultured rat cortical neurons from NMDA-induced toxicity not by NMDA receptor

Excitatory neurotoxicity has been implicated in many pathological situations and there is no effective treatment available. Humanin is a 24-aa peptide cloned from the brain of patients with Alzheimer's disease (AD). In the present study, excitatory toxicity was induced by N-methyl-D-aspartate (NMDA) in primarily cultured rat cortical neurons. MTT assessment, lactate dehydrogenase (LDH) release, and calcein staining were employed to evaluate the protective activity of humanin on NMDA induced toxicity. The results suggested that NMDA (100 μmol/L, 2.5 hr) triggered neuronal morphological changes, lactate dehydrogenase (LDH) release (166% of the control), reduction of cell viability (about 50% of the control), and the decrease of living cell density (about 50% of the control). When pretreated with humanin, the toxicity was suppressed. The living cells' density of humanin treated group was similar to that of control. The cell viability was attenuated dose-dependently (IC50 = 0.132 nmol/L). The LDH release was also neutralized in a dose-dependent manner. In addition, the intracellular Ca(2+) overloading triggered by NMDA reverted quickly and humanin could not inhibit it. These findings indicate that humanin can rescue cortical neurons from NMDA-induced toxicity in rat but not through interfering with NMDA receptor directly.

Humanin: a harbinger of mitochondrial-derived peptides?

Mitochondria have been largely considered as 'end-function' organelles, servicing the cell by producing energy and regulating cell death in response to complex signals. Being cellular entities with vital roles, mitochondria communicate back to the cell and actively engage in determining major cellular policies. These signals, collectively referred to as retrograde signals, are encoded in the nuclear genome or are secondary products of mitochondrial metabolism. Here, we discuss humanin, the first small peptide of a putative set of mitochondrial-derived peptides (MDPs), which exhibits strong cytoprotective actions against various stress and disease models. The study of humanin and other mitochondrial-derived retrograde signal peptides will aid in the identification of genes and peptides with therapeutic and diagnostic potential in treating human diseases.

Secreted calmodulin-like skin protein inhibits neuronal death in cell-based Alzheimer's disease models via the heterotrimeric Humanin receptor

Humanin is a secreted bioactive peptide that is protective in a variety of death models, including cell-based neuronal death models related to Alzheimer's disease (AD). To mediate the protective effect in AD-related death models, Humanin signals via a cell-surface receptor that is generally composed of three subunits: ciliary neurotrophic factor receptor α, WSX-1 and gp130 (heterotrimeric Humanin receptor; htHNR). However, the protective effect of Humanin via the htHNR is weak (EC₅₀=1–10 μℳ); therefore, it is possible that another physiological agonist for this receptor exists in vivo. In the current study, calmodulin-like skin protein (CLSP), a calmodulin relative with an undefined function, was shown to be secreted and inhibit neuronal death via the htHNR with an EC₅₀ of 10–100 pℳ. CLSP was highly expressed in the skin, and the concentration in circulating normal human blood was ∼5 nℳ. When administered intraperitoneally in mice, recombinant CLSP was transported across the blood-cerebrospinal fluid (CSF)-barrier and its concentration in the CSF reaches 1/100 of its serum concentration at 1 h after injection. These findings suggest that CLSP is a physiological htHNR agonist.

Humanin, a cytoprotective peptide, is expressed in carotid atherosclerotic [corrected] plaques in humans

OBJECTIVE

The mechanism of atherosclerotic plaque progression leading to instability, rupture, and ischemic manifestation involves oxidative stress and apoptosis. Humanin (HN) is a newly emerging endogenously expressed cytoprotective peptide. Our goal was to determine the presence and localization of HN in carotid atherosclerotic plaques.

METHODS AND RESULTS

Plaque specimens from 34 patients undergoing carotid endarterectomy were classified according to symptomatic history. Immunostaining combined with digital microscopy revealed greater expression of HN in the unstable plaques of symptomatic compared to asymptomatic patients (29.42±2.05 vs. 14.14±2.13% of plaque area, p<0.0001). These data were further confirmed by immunoblot (density of HN/β-actin standard symptomatic vs. asymptomatic 1.32±0.14 vs. 0.79±0.11, p<0.01). TUNEL staining revealed a higher proportion of apoptotic nuclei in the plaques of symptomatic patients compared to asymptomatic (68.25±3.61 vs. 33.46±4.46% of nuclei, p<0.01). Double immunofluorescence labeling revealed co-localization of HN with macrophages (both M1 and M2 polarization), smooth muscle cells, fibroblasts, and dendritic cells as well as with inflammatory markers MMP2 and MMP9.

CONCLUSIONS

The study demonstrates a higher expression of HN in unstable carotid plaques that is localized to multiple cell types within the plaque. These data support the involvement of HN in atherosclerosis, possibly as an endogenous response to the inflammatory and apoptotic processes within the atheromatous plaque.

Advances in molecular diagnostics for mitochondrial diseases

BACKGROUND

Mitochondrial disorders (MD) are diseases caused by impairment of the mitochondrial respiratory chain. Phenotypes are polymorphous and may range from pure myopathy to multisystemic disorders. The genetic defect can be located on mitochondrial or nuclear DNA. At present, diagnosis of MD requires a complex approach: measurement of serum lactate, electromyography, muscle histology and enzymology, and genetic analysis. Magnetic resonance spectroscopy allows the assessment of tissue metabolic alterations, thus providing useful information for the diagnosis and monitoring of MD. Molecular soluble markers of mitochondrial dysfunction, at rest and during exercise, can identify the impairment of the aerobic system in MD, but a reliable biomarker for the screening or diagnosis of MD is still needed.

OBJECTIVE

Molecular and genetic characterization of MD, together with other experimental approaches, contribute to add new insights to these diseases. Here, the role and advances of diagnostic techniques for MD are reviewed.

CONCLUSION

Possible applications of the results obtained by new molecular investigative approaches could in future guide therapeutic strategies.

Evidence for potential functionality of nuclearly-encoded humanin isoforms

Humanin (HN) is a recently identified neuroprotective and antiapoptotic peptide derived from a portion of the mitochondrial MT-RNR2 gene. We provide bioinformatic and expression data suggesting the existence of 13 MT-RNR2-like nuclear loci predicted to maintain the open reading frames of 15 distinct full-length HN-like peptides. At least ten of these nuclear genes are expressed in human tissues, and respond to staurosporine (STS) and beta-carotene. Sequence comparisons of the nuclear HN isoforms and their homologues in other species reveal two consensus motifs, encompassing residues 5-11 (GFS/NCLLL), and 14-19 (SEIDLP/S). Proline vs serine in position 19 may determine whether the peptide is secreted or not, while threonine in position 13 may be important for cell surface receptor binding. Cytoprotection against the STS-induced apoptosis conferred by the polymorphic HN5 variant, in which threonine in position 13 is replaced with isoleucine, is reduced compared to the wild type HN5 peptide.