Neuroglobin, clues to function and mechanism

Harlequin mice exhibit cognitive impairment, severe loss of Purkinje cells and a compromised bioenergetic status due to the absence of Apoptosis Inducing Factor

The functional integrity of the central nervous system relies on complex mechanisms in which the mitochondria are crucial actors because of their involvement in a multitude of bioenergetics and biosynthetic pathways. Mitochondrial diseases are among the most prevalent groups of inherited neurological disorders, affecting up to 1 in 5000 adults and despite considerable efforts around the world there is still limited curative treatments. Harlequin mice correspond to a relevant model of recessive X-linked mitochondrial disease due to a proviral insertion in the first intron of the Apoptosis-inducing factor gene, resulting in an almost complete depletion of the corresponding protein. These mice exhibit progressive degeneration of the retina, optic nerve, cerebellum, and cortical regions leading to irremediable blindness and ataxia, reminiscent of what is observed in patients suffering from mitochondrial diseases. We evaluated the progression of cerebellar degeneration in Harlequin mice, especially for Purkinje cells and its relationship with bioenergetics failure and behavioral damage. For the first time to our knowledge, we demonstrated that Harlequin mice display cognitive and emotional impairments at early stage of the disease with further deteriorations as ataxia aggravates. These functions, corresponding to higher-order cognitive processing, have been assigned to a complex network of reciprocal connections between the cerebellum and many cortical areas which could be dysfunctional in these mice. Consequently, Harlequin mice become a suitable experimental model to test innovative therapeutics, via the targeting of mitochondria which can become available to a large spectrum of neurological diseases.

Charged Amino Acid Substitutions Affect Conformation of Neuroglobin and Cytochrome c Heme Groups

Neuroglobin (Ngb) is a cytosolic heme protein that plays an important role in protecting cells from apoptosis through interaction with oxidized cytochrome c (Cyt c) released from mitochondria. The interaction of reduced Ngb and oxidized Cyt c is accompanied by electron transfer between them and the reduction in Cyt c. Despite the growing number of studies on Ngb, the mechanism of interaction between Ngb and Cyt c is still unclear. Using Raman spectroscopy, we studied the effect of charged amino acid substitutions in Ngb and Cyt c on the conformation of their hemes. It has been shown that Ngb mutants E60K, K67E, K95E and E60K/E87K demonstrate changed heme conformations with the lower probability of the heme planar conformation compared to wild-type Ngb. Moreover, oxidized Cyt c mutants K25E, K72E and K25E/K72E demonstrate the decrease in the probability of methyl-radicals vibrations, indicating the higher rigidity of the protein microenvironment. It is possible that these changes can affect electron transfer between Ngb and Cyt c.

Molecular Interactions between Neuroglobin and Cytochrome c: Possible Mechanisms of Antiapoptotic Defense in Neuronal Cells

Neuroglobin, which is a heme protein from the globin family that is predominantly expressed in nervous tissue, can promote a neuronal survivor. However, the molecular mechanisms underlying the neuroprotective function of Ngb remain poorly understood to this day. The interactions between neuroglobin and mitochondrial cytochrome c may serve as at least one of the mechanisms of neuroglobin-mediated neuroprotection. Interestingly, neuroglobin and cytochrome c possibly can interact with or without electron transfer both in the cytoplasm and within the mitochondria. This review provides a general picture of molecular interactions between neuroglobin and cytochrome c based on the recent experimental and computational work on neuroglobin and cytochrome c interactions.

Effects of naturally occurring S47F/A mutations on the structure and function of human cytochrome c

The sequence and structure of human cytochrome c (hCyt c) exhibit evolutionary conservations, with only a limited number of naturally occurring mutations in humans. Herein, we investigated the effects of the naturally occurring S47F/A mutations on the structure and function of hCyt c in the oxidized form. Although the naturally occurring S47F/A mutations did not largely alter the protein structure, the S47F and S47A variants exhibited a small fraction of high-spin species. Kinetic studies showed that the peroxidase activity of the variants was enhanced by ∼2.5-fold under neutral pH conditions, as well as for the rate in reaction with H₂O₂, when compared to those of wild-type hCyt c. In addition, we evaluated the interaction between hCyt c and human neuroglobin (hNgb) by isothermal titration calorimetry (ITC) studies, which revealed that the binding constant was reduced by ∼8-fold as result of the mutation of the hydrophilic Ser to the hydrophobic Phe/Ala. These findings provide valuable insights into the role of Ser47 in Ω-loop C in sustaining the structure and function of hCyt c.

Neuroglobin inhibits pancreatic cancer proliferation and metastasis by targeting the GNAI1/EGFR/AKT/ERK signaling axis

Pancreatic cancer is an extremely aggressive malignancy with a very disappointing prognosis. Neuroglobin (NGB), a member of the globin family, has been demonstrated to have a significant role in a variety of tumor forms. The possible role of NGB as a tumor suppressor gene in pancreatic cancer was investigated in this work. Information from the public dataset TCGA combined with GTEx was used to analyze the finding that NGB was commonly downregulated in pancreatic cancer cell lines and tissues, correlating with patient age and prognosis. The expression of NGB in pancreatic cancer was investigated via RT-PCR, qRT-PCR, and Western blot experiments. In-vitro and in-vivo assays, NGB elicited cell cycle arrest in the S phase and apoptosis, hindered migration and invasion, reversed the EMT process, and suppressed cell proliferation and development. The mechanism of action of NGB was predicted via bioinformatics analysis and validated using Western blot and co-IP experiments revealed that NGB inhibited the EGFR/AKT/ERK pathway by binding to and reducing expression of GNAI1 and p-EGFR. In addition, pancreatic cancer cells overexpressing NGB showed increased drug sensitivity to gefitinib (EGFR-TKI). In conclusion, NGB inhibits pancreatic cancer progression by specifically targeting the GNAI1/EGFR/AKT/ERK signaling axis.

Ligand-Based Regulation of Dynamics and Reactivity of Hemoproteins

Hemoproteins include several heme-binding proteins with distinct structure and function. The presence of the heme group confers specific reactivity and spectroscopic properties to hemoproteins. In this review, we provide an overview of five families of hemoproteins in terms of dynamics and reactivity. First, we describe how ligands modulate cooperativity and reactivity in globins, such as myoglobin and hemoglobin. Second, we move on to another family of hemoproteins devoted to electron transport, such as cytochromes. Later, we consider heme-based reactivity in hemopexin, the main heme-scavenging protein. Then, we focus on heme-albumin, a chronosteric hemoprotein with peculiar spectroscopic and enzymatic properties. Eventually, we analyze the reactivity and dynamics of the most recently discovered family of hemoproteins, i.e., nitrobindins.

NO and Heme Proteins: Cross-Talk between Heme and Cysteine Residues

Heme proteins are a diverse group that includes several unrelated families. Their biological function is mainly associated with the reactivity of the heme group, which-among several other reactions-can bind to and react with nitric oxide (NO) and other nitrogen compounds for their production, scavenging, and transport. The S-nitrosylation of cysteine residues, which also results from the reaction with NO and other nitrogen compounds, is a post-translational modification regulating protein activity, with direct effects on a variety of signaling pathways. Heme proteins are unique in exhibiting this dual reactivity toward NO, with reported examples of cross-reactivity between the heme and cysteine residues within the same protein. In this work, we review the literature on this interplay, with particular emphasis on heme proteins in which heme-dependent nitrosylation has been reported and those for which both heme nitrosylation and S-nitrosylation have been associated with biological functions.

Interactions of reactive sulfur species with metalloproteins

Reactive sulfur species (RSS) entail a diverse family of sulfur derivatives that have emerged as important effector molecules in H₂S-mediated biological events. RSS (including H₂S) can exert their biological roles via widespread interactions with metalloproteins. Metalloproteins are essential components along the metabolic route of oxygen in the body, from the transport and storage of O₂, through cellular respiration, to the maintenance of redox homeostasis by elimination of reactive oxygen species (ROS). Moreover, heme peroxidases contribute to immune defense by killing pathogens using oxygen-derived H₂O₂ as a precursor for stronger oxidants. Coordination and redox reactions with metal centers are primary means of RSS to alter fundamental cellular functions. In addition to RSS-mediated metalloprotein functions, the reduction of high-valent metal centers by RSS results in radical formation and opens the way for subsequent per- and polysulfide formation, which may have implications in cellular protection against oxidative stress and in redox signaling. Furthermore, recent findings pointed out the potential role of RSS as substrates for mitochondrial energy production and their cytoprotective capacity, with the involvement of metalloproteins. The current review summarizes the interactions of RSS with protein metal centers and their biological implications with special emphasis on mechanistic aspects, sulfide-mediated signaling, and pathophysiological consequences. A deeper understanding of the biological actions of reactive sulfur species on a molecular level is primordial in H₂S-related drug development and the advancement of redox medicine.

Prognostic Values Serum Cav-1 and NGB Levels in Early Neurological Deterioration After Intravenous Thrombolysis in Patients with Acute Ischemic Stroke

Early neurological deterioration after intravenous thrombolysis (IAT) leads to increased mortality and morbidity in patients with acute ischemic stroke (AIS). This study investigated the correlation between serum Cav-1 and NGB levels and END after IAT and explored their predictive values for poor prognosis of AIS. Totally 210 patients with AIS who underwent IAT within 4.5 h of onset were included and assigned into END group (n = 90) and Non-END group (n = 120). ELISA was used to detect serum Cav-1 and NGB levels before IAT in AIS patients. The prognosis of END patients after 3 months of treatment was evaluated using the modified Rankin Scale. Logistic multifactorial regression was used to analyze independent risk factors for END and poor prognosis after IAT. ROC curve was used to analyze the predictive effect of Cav-1 and NGB on END and poor prognosis after IAT. The area under the ROC curve was analyzed by MedCalc comparison. Compared with the Non-END group, serum Cav-1 was lower and NGB was higher in the END group. Cav-1 and NGB were independent risk factors for END after IAT. Cav-1 + NGB better predicted END after IAT than Cav-1 or NGB alone. Cav-1 and NGB were independent risk factors for END poor prognosis after IAT. Cav-1 combined with NGB better predicted poor prognosis of END after IAT than Cav-1 or NGB alone. Serum Cav-1 combined with NGB may assist in predicting the risk of END occurrence and poor prognosis after IAT in patients with AIS.

New Strategies for Stroke Therapy: Nanoencapsulated Neuroglobin

Stroke is a global health and socio-economic problem. However, no efficient preventive and/or palliative treatments have yet been found. Neuroglobin (Ngb) is an endogen neuroprotective protein, but it only exerts its beneficial action against stroke after increasing its basal levels. Therefore, its systemic administration appears to be an efficient therapy applicable to stroke and other neurodegenerative pathologies. Unfortunately, Ngb cannot cross the blood-brain barrier (BBB), making its direct pharmacological use unfeasible. Thus, the association of Ngb with a drug delivery system (DDS), such as nanoparticles (NPs), appears to be a good strategy for overcoming this handicap. NPs are a type of DDS which efficiently transport Ngb and increase its bioavailability in the infarcted area. Hence, we previously built hyaluronate NPS linked to Ngb (Ngb-NPs) as a therapeutic tool against stroke. This nanoformulation induced an improvement of the cerebral infarct prognosis. However, this innovative therapy is still in development, and a more in-depth study focusing on its long-lasting neuroprotectant and neuroregenerative capabilities is needed. In short, this review aims to update the state-of-the-art of stroke therapies based on Ngb, paying special attention to the use of nanotechnological drug-delivering tools.

Treatment and prevention of pathological mitochondrial dysfunction in retinal degeneration and in photoreceptor injury

Pathological deterioration of mitochondrial function is increasingly linked with multiple degenerative illnesses as a mediator of a wide range of neurologic and age-related chronic diseases, including those of genetic origin. Several of these diseases are rare, typically defined in the United States as an illness affecting fewer than 200,000 people in the U.S. population, or about one in 1600 individuals. Vision impairment due to mitochondrial dysfunction in the eye is a prominent feature evident in numerous primary mitochondrial diseases and is common to the pathophysiology of many of the familiar ophthalmic disorders, including age-related macular degeneration, diabetic retinopathy, glaucoma and retinopathy of prematurity - a collection of syndromes, diseases and disorders with significant unmet medical needs. Focusing on metabolic mitochondrial pathway mechanisms, including the possible roles of cuproptosis and ferroptosis in retinal mitochondrial dysfunction, we shed light on the potential of α-lipoyl-L-carnitine in treating eye diseases. α-Lipoyl-L-carnitine is a bioavailable mitochondria-targeting lipoic acid prodrug that has shown potential in protecting against retinal degeneration and photoreceptor cell loss in ophthalmic indications.

Estradiol and Estrogen-like Alternative Therapies in Use: The Importance of the Selective and Non-Classical Actions

Estrogen is one of the most important female sex hormones, and is indispensable for reproduction. However, its role is much wider. Among others, due to its neuroprotective effects, estrogen protects the brain against dementia and complications of traumatic injury. Previously, it was used mainly as a therapeutic option for influencing the menstrual cycle and treating menopausal symptoms. Unfortunately, hormone replacement therapy might be associated with detrimental side effects, such as increased risk of stroke and breast cancer, raising concerns about its safety. Thus, tissue-selective and non-classical estrogen analogues have become the focus of interest. Here, we review the current knowledge about estrogen effects in a broader sense, and the possibility of using selective estrogen-receptor modulators (SERMs), selective estrogen-receptor downregulators (SERDs), phytoestrogens, and activators of non-genomic estrogen-like signaling (ANGELS) molecules as treatment.

Ordered Motions in the Nitric-Oxide Dioxygenase Mechanism of Flavohemoglobin and Assorted Globins with Tightly Coupled Reductases

Nitric-oxide dioxygenases (NODs) activate and combine O₂ with NO to form nitrate. A variety of oxygen-binding hemoglobins with associated partner reductases or electron donors function as enzymatic NODs. Kinetic and structural investigations of the archetypal two-domain microbial flavohemoglobin-NOD have illuminated an allosteric mechanism that employs selective tunnels for O₂ and NO, gates for NO and nitrate, transient O₂ association with ferric heme, and an O₂ and NO-triggered, ferric heme spin crossover-driven, motion-controlled, and dipole-regulated electron-transfer switch. The proposed mechanism facilitates radical-radical coupling of ferric-superoxide with NO to form nitrate while preventing suicidal ferrous-NO formation. Diverse globins display the structural and functional motifs necessary for a similar allosteric NOD mechanism. In silico docking simulations reveal monomeric erythrocyte hemoglobin alpha-chain and beta-chain intrinsically matched and tightly coupled with NADH-cytochrome b₅ oxidoreductase and NADPH-cytochrome P450 oxidoreductase, respectively, forming membrane-bound flavohemoglobin-like mammalian NODs. The neuroprotective neuroglobin manifests a potential NOD role in a close-fitting ternary complex with membrane-bound NADH-cytochrome b₅ oxidoreductase and cytochrome b₅. Cytoglobin interfaces weakly with cytochrome b₅ for O₂ and NO-regulated electron-transfer and coupled NOD activity. The mechanistic model also provides insight into the evolution of O₂ binding cooperativity in hemoglobin and a basis for the discovery of allosteric NOD inhibitors.