Mitochondrial-derived peptides: New markers for cardiometabolic dysfunction

Mitochondrial DNA Missense Mutations ChrMT: 8981A > G and ChrMT: 6268C > T Identified in a Caucasian Female with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) Triggered by the Epstein-Barr Virus

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a multisystem disabling disease with unclear etiology and pathophysiology, whose typical symptoms include prolonged debilitating recovery from fatigue or postexertional malaise (PEM). Disrupted production of adenosine triphosphate (ATP), the intracellular energy that fuels cellular activity, is a cause for fatigue. Here, we present a long-term case of ME/CFS: a 75-year-old Caucasian female patient, whose symptoms of ME/CFS were clearly triggered by an acute infection of the Epstein-Barr virus 24 years ago (mononucleosis). Before then, the patient was a healthy professional woman. A recent DNA sequence analysis identified missense variants of mitochondrial respiratory chain enzymes, including ATP6 (ChrMT: 8981A > G; Q152R) and Cox1 (ChrMT: 6268C > T; A122V). Protein subunits ATP6 and Cox1 are encoded by mitochondrial DNA outside of the nucleus: the Cox1 gene encodes subunit 1 of complex IV (CIV: cytochrome c oxidase) and the ATP6 gene encodes subunit A of complex V (CV: ATP synthase). CIV and CV are the last two of five essential enzymes that perform the mitochondrial electron transport respiratory chain reaction to generate ATP. Further analysis of the blood sample using transmission electron microscopy demonstrated abnormal, circulating, extracellular mitochondria. These results indicate that the patient had dysfunctional mitochondria, which may contribute directly to her major symptoms, including PEM and neurological and cognitive changes. Furthermore, the identified variants of ATP6 (ChrMT: 8981A > G; Q152R) and Cox1 (ChrMT: 6268C > T; A122V), functioning at a later stage of mitochondrial ATP production, may play a role in the abnormality of the patient's mitochondria and the development of her ME/CFS symptoms.

Impact of Radiation Therapy on Serum Humanin and MOTS-c Levels in Patients with Lung or Breast Cancer

BACKGROUND

Lung and breast cancer are the most frequent causes of death from cancer globally. The objectives of this research were to evaluate the serum mitochondrial open reading frame of the 12S rRNA-c (MOTS-c) and humanin levels in lung or breast cancer patients, and investigate the impacts of radiation therapy on the circulating levels of these peptides.

METHODS

35 lung cancer patients, 34 breast cancer patients, and healthy volunteers as a control group were recruited in this prospective observatory research. Lung cancer patients with stage IIIA/IIIB were treated with paclitaxel-based chemotherapy plus radiotherapy (2 Gy per day, 30 times, 60 Gy total dose). Breast cancer stage IIA/IIB patients were treated with postoperative locoregional radiation therapy (2 Gy per day, 25 times, 50 Gy total dose). The ELISA method was used to detect serum humanin and MOTS-c levels during, before, and after radiotherapy.

RESULTS

We observed marked elevations in circulating MOTS-c, but not humanin levels in patients with lung cancer (P < 0.001). Radiation therapy led to a marked augmentation in MOTS-c levels in these patients (P < 0.001). On the other hand, there was a marked decline in humanin, but not MOTS-c, levels in breast cancer patients (P < 0.001).

CONCLUSION

Our research has shown, for the first time, that increased MOTS-c and decreased humanin levels play a role in lung cancer and breast cancer, respectively. Additionally, radiotherapy modifies MOTS-c levels in patients with lung, but not breast cancer.

Interplay between efferocytosis and atherosclerosis

In an adult human, billions of cells die and turn over daily. During this process, many apoptotic cells are produced and subsequently cleared by phagocytes - a process termed efferocytosis, which plays a critical role in tissue homeostasis. Efferocytosis is an important mechanism in the control of inflammatory processes. Efficient efferocytosis inhibits accumulation of apoptotic cells/debris and maintains homeostasis before the onset of necrosis (secondary necrosis), which promotes inflammation or injury. During efferocytosis, mitochondrial fission and the oxidative stress process are linked through reactive oxygen species production and oxidative stress control. Autophagy plays an important role in inhibiting inflammation and apoptosis, and in promoting efferocytosis by activated inflammatory cells, particularly neutrophils and macrophages. Autophagy in neutrophils is activated by phagocytosis of pathogens or activation of pattern recognition receptors. Autophagy is essential for major neutrophil functions, including degranulation, reactive oxygen species production, oxidative stress and release of neutrophil extracellular cytokines. Failed efferocytosis is a key mechanism driving the development and progression of chronic inflammatory diseases, including atherosclerosis, cardiometabolic pathology, neurodegenerative disease and cancer. Impairment of efferocytosis in apoptotic macrophages is a determinant of atherosclerosis severity and the vulnerability of plaques to rupture. Recent results suggest that inhibition of efferocytosis in the protection of the myocardium results in reduced infiltration of reparatory macrophages into the tissue, in association with oxidative stress reduction. Activated macrophages play a central role in the development and resolution of inflammation. The resolution of inflammation through efferocytosis is an endogenous process that protects host tissues from prolonged or excessive inflammation. Accordingly, therapeutic strategies that ameliorate efferocytosis control would be predicted to dampen inflammation and improve resolution. Thus, therapies targeting efferocytosis will provide a new means of treating and preventing cardiovascular and metabolic diseases involving the chronic inflammatory state.

Lipid Peroxidation and Iron Metabolism: Two Corner Stones in the Homeostasis Control of Ferroptosis

Regulated cell death (RCD) has a significant impact on development, tissue homeostasis, and the occurrence of various diseases. Among different forms of RCD, ferroptosis is considered as a type of reactive oxygen species (ROS)-dependent regulated necrosis. ROS can react with polyunsaturated fatty acids (PUFAs) of the lipid (L) membrane via the formation of a lipid radical L• and induce lipid peroxidation to form L-ROS. Ferroptosis is triggered by an imbalance between lipid hydroperoxide (LOOH) detoxification and iron-dependent L-ROS accumulation. Intracellular iron accumulation and lipid peroxidation are two central biochemical events leading to ferroptosis. Organelles, including mitochondria and lysosomes are involved in the regulation of iron metabolism and redox imbalance in ferroptosis. In this review, we will provide an overview of lipid peroxidation, as well as key components involved in the ferroptotic cascade. The main mechanism that reduces ROS is the redox ability of glutathione (GSH). GSH, a tripeptide that includes glutamic acid, cysteine, and glycine, acts as an antioxidant and is the substrate of glutathione peroxidase 4 (GPX4), which is then converted into oxidized glutathione (GSSG). Increasing the expression of GSH can inhibit ferroptosis. We highlight the role of the x_c^- GSH-GPX4 pathway as the main pathway to regulate ferroptosis. The system x_c^-, composed of subunit solute carrier family members (SLC7A11 and SLC3A2), mediates the exchange of cystine and glutamate across the plasma membrane to synthesize GSH. Accumulating evidence indicates that ferroptosis requires the autophagy machinery for its execution. Ferritinophagy is used to describe the removal of the major iron storage protein ferritin by the autophagy machinery. Nuclear receptor coactivator 4 (NCOA4) is a cytosolic autophagy receptor used to bind ferritin for subsequent degradation by ferritinophagy. During ferritinophagy, stored iron released becomes available for biosynthetic pathways. The dysfunctional ferroptotic response is implicated in a variety of pathological conditions. Ferroptosis inducers or inhibitors targeting redox- or iron metabolism-related proteins and signal transduction have been developed. The simultaneous detection of intracellular and extracellular markers may help diagnose and treat diseases related to ferroptotic damage.

MOTS-c, the Most Recent Mitochondrial Derived Peptide in Human Aging and Age-Related Diseases

MOTS-c, a 16 amino acid mitochondrial derived peptide, is encoded from the 12S rRNA region of the mitochondrial genome. Under stress conditions, MOTS-c translocates to the nucleus where it regulates a wide range of genes in response to metabolic dysfunction. It is colocalized to mitochondria in various tissues and is found in plasma, but the levels decline with age. Since MOTS-c has important cellular functions as well as a possible hormonal role, it has been shown to have beneficial effects on age-related diseases including Diabetes, Cardiovascular diseases, Osteoporosis, postmenopausal obesity and Alzheimer. Aging is characterized by gradual loss of (mitochondrial) metabolic balance, decreased muscle homeostasis and eventual diminished physical capability, which potentially can be reversed with MOTS-c treatment. This review examines the latest findings on biological effects of MOTS-c as a nuclear regulatory peptide and focuses on the role of MOTS-c in aging and age-related disorders, including mechanisms of action and therapeutic potential.