New role for the mitochondrial peptide humanin: protective agent against chemotherapy-induced side effects

The Relative Efficacy of Available Proteasome Inhibitors in Preventing Muscle Contractures Following Neonatal Brachial Plexus Injury

BACKGROUND

Contractures following neonatal brachial plexus injury (NBPI) are associated with growth deficits in denervated muscles. This impairment is mediated by an increase in muscle protein degradation, as contractures can be prevented in an NBPI mouse model with bortezomib (BTZ), a proteasome inhibitor (PI). However, BTZ treatment causes substantial toxicity (0% to 80% mortality). The current study tested the hypothesis that newer-generation PIs can prevent contractures with less severe toxicity than BTZ.

METHODS

Unilateral brachial plexus injuries were surgically created in postnatal (5-day-old) mice. Following NBPI, mice were treated with either saline solution or various doses of 1 of 3 different PIs: ixazomib (IXZ), carfilzomib (CFZ), or marizomib (MRZ). Four weeks post-NBPI, mice were assessed for bilateral passive range of motion at the shoulder and elbow joints, with blinding to the treatment group, through an established digital photography technique to determine contracture severity. Drug toxicity was assessed with survival curves.

RESULTS

All PIs prevented contractures at both the elbow and shoulder (p < 0.05 versus saline solution controls), with the exception of IXZ, which did not prevent shoulder contractures. However, their efficacies and toxicity profiles differed. At lower doses, CFZ was limited by toxicity (30% to 40% mortality), whereas MRZ was limited by efficacy. At higher doses, CFZ was limited by loss of efficacy, MRZ was limited by toxicity (50% to 60% mortality), and IXZ was limited by toxicity (80% to 100% mortality) and loss of efficacy. Comparisons of the data on these drugs as well as data on BTZ generated in prior studies revealed BTZ to be optimal for preventing contractures, although it, too, was limited by toxicity.

CONCLUSIONS

All of the tested second-generation PIs were able to reduce NBPI-induced contractures, offering further proof of concept for a regulatory role of the proteasome in contracture formation. However, the narrow dose ranges of efficacy for all PIs highlight the necessity of precise proteasome regulation for preventing contractures. Finally, the substantial toxicity stemming from proteasome inhibition underscores the importance of identifying muscle-targeted strategies to suppress protein degradation and prevent contractures safely.

CLINICAL RELEVANCE

Although PIs offer unique opportunities to establish critical mechanistic insights into contracture pathophysiology, their clinical use is contraindicated in patients with NPBI at this time.

Mitochondrially mediated RNA interference, a retrograde signaling system affecting nuclear gene expression

Several functional classes of short noncoding RNAs are involved in manifold regulatory processes in eukaryotes, including, among the best characterized, miRNAs. One of the most intriguing regulatory networks in the eukaryotic cell is the mito-nuclear crosstalk: recently, miRNA-like elements of mitochondrial origin, called smithRNAs, were detected in a bivalve species, Ruditapes philippinarum. These RNA molecules originate in the organelle but were shown in vivo to regulate nuclear genes. Since miRNA genes evolve easily de novo with respect to protein-coding genes, in the present work we estimate the probability with which a newly arisen smithRNA finds a suitable target in the nuclear transcriptome. Simulations with transcriptomes of 12 bivalve species suggest that this probability is high and not species specific: one in a hundred million (1 × 10-8) if five mismatches between the smithRNA and the 3' mRNA are allowed, yet many more are allowed in animals. We propose that novel smithRNAs may easily evolve as exaptation of the pre-existing mitochondrial RNAs. In turn, the ability of evolving novel smithRNAs may have played a pivotal role in mito-nuclear interactions during animal evolution, including the intriguing possibility of acting as speciation trigger.

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.

Exploring the potential of humanin as a biomarker for early breast cancer detection: a study of serum levels and diagnostic performance

INTRODUCTION

Breast cancer is a leading cause of cancer death in women worldwide, and early detection is crucial for effective treatment. Mitochondrial dysfunction has been linked to cancer development and progression. Humanin, a mitochondrial-derived peptide, has been shown to have cytoprotective effects and may be involved in breast cancer development. In this study, we aimed to investigate the potential of humanin as a biomarker for breast cancer.

METHODS

We recruited 45 female patients diagnosed with primary invasive ductal breast cancer and 45 healthy volunteers. Serum humanin levels were measured using ELISA, and other cancer markers were measured using an Advia Centaur Immunology Analyser.

RESULTS

Our results showed that serum humanin levels were significantly higher in breast cancer patients than in healthy controls (p = 0.008). ROC curve analysis indicated that humanin could effectively discriminate between patients and healthy individuals, with a sensitivity of 62.5% and a specificity of 77.5%.

CONCLUSION

This suggests that humanin may be a potential new biomarker for breast cancer screening and early detection. Further research is needed to fully understand the relationship between humanin and breast cancer and to develop new diagnostic and therapeutic strategies.

A comparative analysis of mitochondrial ORFs provides new insights on expansion of mitochondrial genome size in Arcidae

BACKGROUND

Arcidae, comprising about 260 species of ark shells, is an ecologically and economically important lineage of bivalve mollusks. Interestingly, mitochondrial genomes of several Arcidae species are 2-3 times larger than those of most bilaterians, and are among the largest bilaterian mitochondrial genomes reported to date. The large mitochondrial genome size is mainly due to expansion of unassigned regions (regions that are functionally unassigned). Previous work on unassigned regions of Arcidae mtDNA genomes has focused on nucleotide-level analyses to observe sequence characteristics, however the origin of expansion remains unclear.

RESULTS

We assembled six new mitogenomes and sequenced six transcriptomes of Scapharca broughtonii to identify conserved functional ORFs that are transcribed in unassigned regions. Sixteen lineage-specific ORFs with different copy numbers were identified from seven Arcidae species, and 11 of 16 ORFs were expressed and likely biologically active. Unassigned regions of 32 Arcidae mitogenomes were compared to verify the presence of these novel mitochondrial ORFs and their distribution. Strikingly, multiple structural analyses and functional prediction suggested that these additional mtDNA-encoded proteins have potential functional significance. In addition, our results also revealed that the ORFs have a strong connection to the expansion of Arcidae mitochondrial genomes and their large-scale duplication play an important role in multiple expansion events. We discussed the possible origin of ORFs and hypothesized that these ORFs may originate from duplication of mitochondrial genes.

CONCLUSIONS

The presence of lineage-specific mitochondrial ORFs with transcriptional activity and potential functional significance supports novel features for Arcidae mitochondrial genomes. Given our observation and analyses, these ORFs may be products of mitochondrial gene duplication. These findings shed light on the origin and function of novel mitochondrial genes in bivalves and provide new insights into evolution of mitochondrial genome size in metazoans.

Mitochondria-derived peptides in aging and healthspan

The mechanisms that explain mitochondrial dysfunction in aging and healthspan continue to be studied, but one element has been unexplored: microproteins. Small open reading frames in circular mitochondria DNA can encode multiple microproteins, called mitochondria-derived peptides (MDPs). Currently, eight MDPs have been published: humanin, MOTS-c, and SHLPs 1–6. This Review describes recent advances in microprotein discovery with a focus on MDPs. It discusses what is currently known about MDPs in aging and how this new understanding could add to the way we understand age-related diseases including type 2 diabetes, cancer, and neurodegenerative diseases at the genomic, proteomic, and drug-development levels.

MicroRNA Cues from Nature: A Roadmap to Decipher and Combat Challenges in Human Health and Disease?

MicroRNAs are small non-coding RNA (18–24 nt long) that fine-tune gene expression at the post-transcriptional level. With the advent of “multi-omics” analysis and sequencing approaches, they have now been implicated in every facet of basic molecular networks, including metabolism, homeostasis, and cell survival to aid cellular machinery in adapting to changing environmental cues. Many animals must endure harsh environmental conditions in nature, including cold/freezing temperatures, oxygen limitation (anoxia/hypoxia), and food or water scarcity, often requiring them to revamp their metabolic organization, frequently on a seasonal or life stage basis. MicroRNAs are important regulatory molecules in such processes, just as they are now well-known to be involved in many human responses to stress or disease. The present review outlines the role of miRNAs in natural animal models of environmental stress and adaptation including torpor/hibernation, anoxia/hypoxia tolerance, and freeze tolerance. We also discuss putative medical applications of advances in miRNA biology including organ preservation for transplant, inflammation, ageing, metabolic disorders (e.g., obesity), mitochondrial dysfunction (mitoMirs) as well as specialized miRNA subgroups respective to low temperature (CryomiRs) and low oxygen (OxymiRs). The review also covers differential regulation of conserved and novel miRNAs involved at cell, tissue, and stress specific levels across multiple species and their roles in survival. Ultimately, the species-specific comparison and conserved miRNA responses seen in evolutionarily disparate animal species can help us to understand the complex miRNA network involved in regulating and reorganizing metabolism to achieve diverse outcomes, not just in nature, but in human health and disease.

Mitochondrial Genomic Landscape: A Portrait of the Mitochondrial Genome 40 Years after the First Complete Sequence

Notwithstanding the initial claims of general conservation, mitochondrial genomes are a largely heterogeneous set of organellar chromosomes which displays a bewildering diversity in terms of structure, architecture, gene content, and functionality. The mitochondrial genome is typically described as a single chromosome, yet many examples of multipartite genomes have been found (for example, among sponges and diplonemeans); the mitochondrial genome is typically depicted as circular, yet many linear genomes are known (for example, among jellyfish, alveolates, and apicomplexans); the chromosome is normally said to be “small”, yet there is a huge variation between the smallest and the largest known genomes (found, for example, in ctenophores and vascular plants, respectively); even the gene content is highly unconserved, ranging from the 13 oxidative phosphorylation-related enzymatic subunits encoded by animal mitochondria to the wider set of mitochondrial genes found in jakobids. In the present paper, we compile and describe a large database of 27,873 mitochondrial genomes currently available in GenBank, encompassing the whole eukaryotic domain. We discuss the major features of mitochondrial molecular diversity, with special reference to nucleotide composition and compositional biases; moreover, the database is made publicly available for future analyses on the MoZoo Lab GitHub page.

Humanin: A mitochondrial-derived peptide in the treatment of apoptosis-related diseases

Humanin (HN) is a small mitochondrial-derived cytoprotective polypeptide encoded by mtDNA. HN exhibits protective effects in several cell types, including leukocytes, germ cells, neurons, tissues against cellular stress conditions and apoptosis through regulating various signaling mechanisms, such as JAK/STAT pathway and interaction of BCL-2 family of protein. HN is an essential cytoprotective peptide in the human body that regulates mitochondrial functions under stress conditions. The present review aims to evaluate HN peptide's antiapoptotic activities as a potential therapeutic target in the treatment of cancer, diabetes mellitus, male infertility, bone-related diseases, cardiac diseases, and brain diseases. Based on in vitro and in vivo studies, HN significantly suppressed the apoptosis during the treatment of bone osteoporosis, cardiovascular diseases, diabetes mellitus, and neurodegenerative diseases. According to accumulated data, it is concluded that HN exerts the proapoptotic activity of TNF-α in cancer, which makes HN as a novel therapeutic agent in the treatment of cancer and suggested that along with HN, the development of another mitochondrial-derived peptide could be a viable therapeutic option against different oxidative stress and apoptosis-related diseases.

Timing of proteasome inhibition as a pharmacologic strategy for prevention of muscle contractures in neonatal brachial plexus injury

Neonatal brachial plexus injury (NBPI) causes disabling and incurable contractures, or limb stiffness, which result from proteasome‐mediated protein degradation impairing the longitudinal growth of neonatally denervated muscles. We recently showed in a mouse model that the 20S proteasome inhibitor, bortezomib, prevents contractures after NBPI. Given that contractures uniquely follow neonatal denervation, the current study tests the hypothesis that proteasome inhibition during a finite window of neonatal development can prevent long‐term contracture development. Following neonatal forelimb denervation in P5 mice, we first outlined the minimum period for proteasome inhibition to prevent contractures 4 weeks post‐NBPI by treating mice with saline or bortezomib for varying durations between P8 and P32. We then compared the ability of varying durations of longer‐term proteasome inhibition to prevent contractures at 8 and 12 weeks post‐NBPI. Our findings revealed that proteasome inhibition can be delayed 3‐4 days after denervation but is required throughout skeletal growth to prevent contractures long term. Furthermore, proteasome inhibition becomes less effective in preventing contractures beyond the neonatal period. These therapeutic effects are primarily associated with bortezomib‐induced attenuation of 20S proteasome β1 subunit activity. Our collective results, therefore, demonstrate that temporary neonatal proteasome inhibition is not a viable strategy for preventing contractures long term. Instead, neonatal denervation causes a permanent longitudinal growth deficiency that must be continuously ameliorated during skeletal growth. Additional mechanisms must be explored to minimize the necessary period of proteasome inhibition and reduce the risk of toxicity from long‐term treatment.

Proteasome inhibition preserves longitudinal growth of denervated muscle and prevents neonatal neuromuscular contractures

Muscle contractures are a prominent and disabling feature of many neuromuscular disorders, including the 2 most common forms of childhood neurologic dysfunction: neonatal brachial plexus injury (NBPI) and cerebral palsy. There are currently no treatment strategies to directly alter the contracture pathology, as the pathogenesis of these contractures is unknown. We previously showed in a mouse model of NBPI that contractures result from impaired longitudinal muscle growth. Current presumed explanations for growth impairment in contractures focus on the dysregulation of muscle stem cells, which differentiate and fuse to existing myofibers during growth, as this process has classically been thought to control muscle growth during the neonatal period. Here, we demonstrate in a mouse model of NBPI that denervation does not prevent myonuclear accretion and that reduction in myonuclear number has no effect on functional muscle length or contracture development, providing definitive evidence that altered myonuclear accretion is not a driver of neuromuscular contractures. In contrast, we observed elevated levels of protein degradation in NBPI muscle, and we demonstrate that contractures can be pharmacologically prevented with the proteasome inhibitor bortezomib. These studies provide what we believe is the first strategy to prevent neuromuscular contractures by correcting the underlying deficit in longitudinal muscle growth.

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.

Mitochondrial biology and prostate cancer ethnic disparity

Prostate cancer remains the second most prevalent cancer in men. Its incidence, progression and mortality profiles vary significantly by race and ethnicity, with African-American men having the highest incidence rate and mortality rate in the world. Although these disparities can be partially explained by socioeconomic factors, the underlying molecular causes are complex and require careful research. A considerable amount of literature exists, supporting the association between mitochondrial health and the incidence, aggression and risk of prostate cancer. Genetic alterations in mitochondrial DNA are frequent in prostate cancer; therefore, the resulting mitochondrial dysfunction and metabolic dysregulation may contribute to or indicate oncogenesis. Many of the prominent features of cancer cells are also closely related to mitochondrial functions, such as resistance to apoptosis, excess reactive oxygen species production and altered oxidative phosphorylation. In addition, prostate cancer ethnic disparity is influenced by environmental and lifestyle factors, which involves differences in mitochondrial metabolism and retrograde signaling events.

The humanin analogue (HNG) prevents temozolomide-induced male germ cell apoptosis and other adverse effects in severe combined immuno-deficiency (SCID) mice bearing human medulloblastoma

Subfertility is a major concern of long-term cancer survivors at the reproductive age. We have previously demonstrated that a potent humanin analogue, HNG, protected chemotherapy-induced apoptosis in germ cells but not cancer cells in a metastatic melanoma allograft model. In this study, we utilized severe combined immuno-deficiency (SCID) mice bearing human medulloblastoma to study the effect of HNG in Temozolomide (TMZ) induced male germ cell apoptosis and white blood cell (WBC) suppression. Human medulloblastoma DAOY cells were injected subcutaneously into the right flank of male SCID mice. Three weeks later, groups of tumor-bearing mice received one of the following treatments: vehicle, HNG, TMZ, or TMZ + HNG. 24 h after last injection, the tumors weights, complete blood counts, liver and spleen weights, male germ cell apoptosis was assessed. HNG did not affect TMZ's significant anti-tumor action. HNG significantly prevented TMZ-induced germ cell apoptosis and attenuated the suppressed total WBC and granulocyte counts in SCID mice with or without TMZ treatment. HNG also attenuated TMZ-induced body weight loss and decrease of spleen and liver weights. In conclusion, HNG ameliorated TMZ-induced germ cell apoptosis; WBC and granulocytes loss; and decreased body/organ weights without compromising the TMZ's anti-cancer action on medulloblastoma xenografts in SCID mice.

Circular RNA circNOL10 Inhibits Lung Cancer Development by Promoting SCLM1-Mediated Transcriptional Regulation of the Humanin Polypeptide Family

circNOL10 is a circular RNA expressed at low levels in lung cancer, though its functions in lung cancer remain unknown. Here, the function and molecular mechanism of circNOL10 in lung cancer development are investigated using in vitro and in vivo studies, and it is shown that circNOL10 significantly inhibits the development of lung cancer and that circNOL10 expression is co-regulated by methylation of its parental gene Pre-NOL10 and by splicing factor epithelial splicing regulatory protein 1 (ESRP1). circNOL10 promotes the expression of transcription factor sex comb on midleg-like 1 (SCML1) by inhibiting transcription factor ubiquitination and thus also affects regulation of the humanin (HN) polypeptide family by SCML1. circNOL10 also affects mitochondrial function through regulating the humanin polypeptide family and affecting multiple signaling pathways, ultimately inhibiting cell proliferation and cell cycle progression, and promoting the apoptosis of lung cancer cells, thereby inhibiting lung cancer development. This study investigates the functions and molecular mechanisms of circNOL10 in the development of lung cancer and reveals its involvement in the transcriptional regulation of the HN polypeptide family by SCML1. The results also demonstrate the inhibitory effect of HN on lung cancer cells growth. These findings may identify novel targets for the molecular therapy of lung cancer.

Characterizing the protective effects of SHLP2, a mitochondrial-derived peptide, in macular degeneration

Mitochondrial-derived peptides (MDPs) are rapidly emerging therapeutic targets to combat development of neurodegenerative diseases. SHLP2 (small humanin-like peptide 2) is a newly discovered MDP that is coded from the MT-RNR2 (Mitochondrially encoded 16S rRNA) gene in mitochondrial DNA (mtDNA). In the current study, we examined the biological consequences of treatment with exogenously-added SHLP2 in an in vitro human transmitochondrial age-related macular degeneration (AMD) ARPE-19 cell model. In AMD cells, we observed significant down-regulation of the MDP-coding MT-RNR2 gene, and remarkably reduced levels of all five oxidative phosphorylation (OXPHOS) complex I-V protein subunits that are involved in the electron transport chain; these results suggested mitochondrial toxicity and abnormal OXPHOS complex protein subunits' levels in AMD cells. However, treatment of AMD cells with SHLP2: (1) restored the normal levels of OXPHOS complex protein subunits, (2) prevented loss of viable cells and mitochondria, (3) increased the number of mtDNA copies, (4) induced anti-apoptotic effects, and (5) attenuated amyloid-β-induced cellular and mitochondrial toxicity. Cumulatively, our findings established the protective role of SHLP2 in AMD cells in vitro. In conclusion, this novel study supports the merit of SHLP2 in the treatment of AMD, a primary retinal disease that is a leading cause of blindness among the elderly population in the United States as well as worldwide.

Interaction of Insulin-Like Growth Factor-Binding Protein 3 With Hyaluronan and Its Regulation by Humanin and CD44

Insulin-like growth factor-binding protein-3 (IGFBP-3) belongs to a family of IGF-binding proteins. Humanin is a peptide known to bind residues 215-232 of mature IGFBP-3 in the C-terminal region of the protein. This region of IGFBP-3 was shown earlier to bind certain glycosaminoglycans including hyaluronan (HA). Here, we characterized the binding affinities of the IGFBP-3 protein and peptide (²¹⁵-KKGFYKKKQCRPSKGRKR-²³²) to HA and to humanin and found that HA binds with a weaker affinity to this region than does humanin. Either HA or humanin could bind to this IGFBP-3 segment, but not simultaneously. The HA receptor, CD44, blocked HA binding to IGFBP-3 but had no effect on binding of humanin to either IGFBP-3 or its peptide. Upon incubation of HA with CD44 and either IGFBP-3 protein or peptide, humanin was effective at binding and sequestering IGFBP-3 or peptide, thereby enabling access of CD44 to HA. We show that IGFBP-3 and humanin in the medium of A549 lung cancer cells can immunoprecipitate in a complex. However, the fraction of IGFBP-3 in the medium that is able to bind HA was not complexed with humanin suggesting that HA binding to the 215-232 segment renders it inaccessible for binding to humanin. Moreover, while the cytotoxic effects of IGFBP-3 on cell viability were reversed by humanin, blocking HA-CD44 interaction with an anti-CD44 antibody in combination with IGFBP-3 did not have an additive negative effect on cell viability suggesting that IGFBP-3 exerts its cytotoxic effects on cell survival through a mechanism that depends on HA-CD44 interactions.

Humanin inhibits apoptosis in pituitary tumor cells through several signaling pathways including NF-κB activation

Humanin (HN) and Rattin (HNr), its homologous in the rat, are peptides with cytoprotective action in several cell types such as neurons, lymphocytes and testicular germ cells. Previously, we have shown that HNr is expressed in pituitary cells and that HN inhibited the apoptotic effect of TNF-α in both normal and tumor pituitary cells. The aim of the present study was to identify signaling pathways that mediate the antiapoptotic effect of HN in anterior pituitary cells from ovariectomized rats and in GH3 cells, a somatolactotrope cell line. We assessed the role of STAT3, JNK, Akt and MAPKs as well as proteins of the Bcl-2 family, previously implicated in the antiapoptotic effect of HN. We also evaluated the participation of NF-κB in the antiapoptotic action of HN. STAT3 inhibition reversed the inhibitory effect of HN on TNF-α-induced apoptosis in normal and pituitary tumor cells, indicating that STAT3 signaling pathway mediates the antiapoptotic effect of HN on pituitary cells. Inhibition of NF-κB pathway did not affect action of HN on normal anterior pituitary cells but blocked the cytoprotective effect of HN on TNF-α-induced apoptosis of GH3 cells, suggesting that the NF-κB pathway is involved in HN action in tumor pituitary cells. HN also induced NF-κB-p65 nuclear translocation in these cells. In pituitary tumor cells, JNK and MEK inhibitors also impaired HN cytoprotective action. In addition, HN increased Bcl-2 expression and decreased Bax mitochondrial translocation. Since HN expression in GH3 cells is higher than in normal pituitary cells, we may suggest that through multiple pathways HN could be involved in pituitary tumorigenesis.

Gly[14]-humanin inhibits ox-LDL uptake and stimulates cholesterol efflux in macrophage-derived foam cells

Foam cell formation, which is caused by imbalanced cholesterol influx and efflux by macrophages, plays a vital role in the occurrence and development of atherosclerosis. Humanin (HN), a mitochondria-derived peptide, can prevent the production of reactive oxygen species and death of human aortic endothelial cells exposed to oxidized low-density lipoprotein (ox-LDL) and has a protective effect on patients with in early atherosclerosis. However, the effects of HN on the regulation of cholesterol metabolism in RAW 264.7 macrophages are still unknown. This study was designed to investigate the role of [Gly14]-humanin (HNG) in lipid uptake and cholesterol efflux in RAW 264.7 macrophages. Flow cytometry and live cell imaging results showed that HNG reduced Dil-ox-LDL accumulation in the RAW 264.7 macrophages. A similar result was obtained for lipid accumulation by measuring cellular cholesterol content. Western blot analysis showed that ox-LDL treatment upregulated not only the protein expression of CD36 and LOX-1, which mediate ox-LDL endocytosis, but also ATP-binding cassette (ABC) transporter A1 and ABCG1, which mediate ox-LDL exflux. HNG pretreatment inhibited the upregulation of CD36 and LOX-1 levels, prompting the upregulation of ABCA1 and ABCG1 levels induced by ox-LDL. Therefore we concluded that HNG could inhibit ox-LDL-induced macrophage-derived foam cell formation, which occurs because of a decrease in lipid uptake and an increase in cholesterol efflux from macrophage cells.

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.

The Potent Humanin Analogue (HNG) Protects Germ Cells and Leucocytes While Enhancing Chemotherapy-Induced Suppression of Cancer Metastases in Male Mice

Humanin is a peptide that is cytoprotective against stresses in many cell types. We investigated whether a potent humanin analogue S14G-humanin (HNG) would protect against chemotherapy-induced damage to normal cells without interfering with the chemotherapy-induced suppression of cancer cells. Young adult male mice were inoculated iv with murine melanoma cells. After 1 week, cancer-bearing mice were randomized to receive either: no treatment, daily ip injection of HNG, a single ip injection of cyclophosphamide (CP), or CP+HNG and killed at the end of 3 weeks. HNG rescued the CP-induced suppression of leucocytes and protected germ cell from CP-induced apoptosis. Lung metastases were suppressed by HNG or CP alone, and further suppressed by CP+HNG treatment. Plasma IGF-1 levels were suppressed by HNG with or without CP treatment. To investigate whether HNG maintains its protective effects on spermatogonial stem cells, sperm output, and peripheral leucocytes after repeated doses of CP, normal adult male mice received: no treatment, daily sc injection of HNG, 6 ip injections of CP at 5-day intervals, and the same regimens of CP+HNG and killed at the end of 4 weeks of treatment. Cauda epididymal sperm counts were elevated by HNG and suppressed by CP. HNG rescued the CP-induced suppression of spermatogonial stem cells, sperm count and peripheral leucocytes. We conclude that HNG 1) protects CP-induced loss of male germ cells and leucocytes, 2) enhances CP-induced suppression of cancer metastases, and 3) acts as a caloric-restriction mimetic by suppressing IGF-1 levels. Our findings suggest that humanin analogues may be promising adjuvants to chemotherapy.

To Know How a Gene Works, We Need to Redefine It First but then, More Importantly, to Let the Cell Itself Decide How to Transcribe and Process Its RNAs

Recent genomic and ribonomic research reveals that our genome produces a stupendous amount of non-coding RNAs (ncRNAs), including antisense RNAs, and that many genes contain other gene(s) in their introns. Since ncRNAs either regulate the transcription, translation or stability of mRNAs or directly exert cellular functions, they should be regarded as the fourth category of RNAs, after ribosomal, messenger and transfer RNAs. These and other research advances challenge the current concept of gene and raise a question as to how we should redefine gene. We can either consider each tiny part of the classically-defined gene, such as each mRNA variant, as a “gene”, or, alternatively and oppositely, regard a whole genomic locus as a “gene” that may contain intron-embedded genes and produce different types of RNAs and proteins. Each of the two ways to redefine gene not only has its strengths and weaknesses but also has its particular concern on the methodology for the determination of the gene's function: Ectopic expression of complementary DNA (cDNA) in cells has in the past decades provided us with great deal of detail about the functions of individual mRNA variants, and will make the data less conflicting with each other if just a small part of a classically-defined gene is considered as a “gene”. On the other hand, genomic DNA (gDNA) will better help us in understanding the collective function of a genomic locus. In our opinion, we need to be more cautious in the use of cDNA and in the explanation of data resulting from cDNA, and, instead, should make delivery of gDNA into cells routine in determination of genes' functions, although this demands some technology renovation.

The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis and reduces obesity and insulin resistance

Mitochondria are known to be functional organelles, but their role as a signaling unit is increasingly being appreciated. The identification of a short open reading frame (sORF) in the mitochondrial DNA (mtDNA) that encodes a signaling peptide, humanin, suggests the possible existence of additional sORFs in the mtDNA. Here we report a sORF within the mitochondrial 12S rRNA encoding a 16-amino-acid peptide named MOTS-c (mitochondrial open reading frame of the 12S rRNA-c) that regulates insulin sensitivity and metabolic homeostasis. Its primary target organ appears to be the skeletal muscle, and its cellular actions inhibit the folate cycle and its tethered de novo purine biosynthesis, leading to AMPK activation. MOTS-c treatment in mice prevented age-dependent and high-fat-diet-induced insulin resistance, as well as diet-induced obesity. These results suggest that mitochondria may actively regulate metabolic homeostasis at the cellular and organismal level via peptides encoded within their genome.

IGF-I regulates the age-dependent signaling peptide humanin

Aging is influenced by endocrine pathways including the growth hormone/insulin-like growth factor-1 (GH/IGF) axis. Mitochondrial function has also been linked to the aging process, but the relevant mitochondrial signals mediating the effects of mitochondria are poorly understood. Humanin is a novel signaling peptide that acts as a potent regulator of cellular stress responses and protects from a variety of in vitro and in vivo toxic and metabolic insults. The circulating levels of humanin decline with age in mice and humans. Here, we demonstrate a negative correlation between the activity of the GH-IGF axis and the levels of humanin, as well as a positive correlation between humanin and lifespan in mouse models with altered GH/IGF-I axis. Long-lived, GH-deficient Ames mice displayed elevated humanin levels, while short-lived GH-transgenic mice have reduced humanin levels. Furthermore, treatment with GH or IGF-I reduced circulating humanin levels in both mice and human subjects. Our results indicate that GH and IGF are potent regulators of humanin levels and that humanin levels correlate with lifespan in mice. This suggests that humanin represents a circulating mitochondrial signal that participates in modulating the aging process, adding a coordinated mitochondrial element to the endocrine regulation of aging.

A resourceful genome: updating the functional repertoire and evolutionary role of animal mitochondrial DNAs

Recent data from mitochondrial genomics and proteomics research demonstrate the existence of several atypical mitochondrial protein-coding genes (other than the standard set of 13) and the involvement of mtDNA-encoded proteins in functions other than energy production in several animal species including humans. These results are of considerable importance for evolutionary and cellular biology because they indicate that animal mtDNAs have a larger functional repertoire than previously believed. This review summarizes recent studies on animal species with a non-standard mitochondrial functional repertoire and discusses how these genetic novelties represent promising candidates for studying the role of the mitochondrial genome in speciation.