Neuronal expression of the mitochondrial protein prohibitin confers profound neuroprotection in a mouse model of focal cerebral ischemia

Comparative Brain Proteomic Analysis between Sham and Cerebral Ischemia Experimental Groups

Sham control groups are essential in experimental animal studies to reduce the influence of surgical intervention. The intraluminal filament procedure is one of the most common models of middle cerebral artery occlusion (MCAO) used in the study of brain ischemia. However, a sham group is usually not included in the experimental design of these studies. In this study, we aimed to evaluate the relevance of the sham group by analyzing and comparing the brain protein profiles of the sham and MCAO groups. In the sham group, 98 dysregulated proteins were detected, compared to 171 in the ischemic group. Moreover, a comparative study of protein profiles revealed the existence of a pool of 57 proteins that appeared to be dysregulated in both sham and ischemic animals. These results indicated that the surgical procedure required for the intraluminal occlusion of the middle cerebral artery (MCA) induces changes in brain protein expression that are not associated with ischemic lesions. This study highlights the importance of including sham control groups in the experimental design, to ensure that surgical intervention does not affect the therapeutic target under study.

The many "Neurofaces" of Prohibitins 1 and 2: Crucial for the healthy brain, dysregulated in numerous brain disorders

Prohibitin 1 (PHB1) and prohibitin 2 (PHB2) are proteins that are nearly ubiquitously expressed. They are localized in mitochondria, cytosol and cell nuclei. In the healthy CNS, they occur in neurons and non-neuronal cells (oligodendrocytes, astrocytes, microglia, and endothelial cells) and fulfill pivotal functions in brain development and aging, the regulation of brain metabolism, maintenance of structural integrity, synapse formation, aminoacidergic neurotransmission and, probably, regulation of brain action of certain hypothalamic-pituitary hormones.With regard to the diseased brain there is increasing evidence that prohibitins are prominently involved in numerous major diseases of the CNS, which are summarized and discussed in the present review (brain tumors, neurotropic viruses, Alzheimer disease, Down syndrome, Fronto-temporal and vascular dementia, dementia with Lewy bodies, Parkinson disease, Huntington disease, Multiple sclerosis, Amyotrophic lateral sclerosis, stroke, alcohol use disorder, schizophrenia and autism). Unfortunately, there is no PHB-targeted therapy available for any of these diseases.

Neuron-targeted Knockout of APE1 Forces Premature Cognitive Impairment and Synaptic Dysfunction in Adult Mice

Adaptable and consistent neural function relies at least in part on the ongoing repair of oxidative damage that can accumulate in the brain over a lifespan. To determine whether forebrain neuron-targeted knockout of AP endonuclease 1 (APE1), a critical enzyme in the base excision DNA repair pathway, contributes to neuronal impairments, we generated APE1 conditional knockout mice under the control of the CamKIIα promotor (APE1 cKO). Spatial learning and memory were tested using the Morris water maze. Synaptic markers, including synapsin, vGLUT, GABA1, and GAD were immunostained and quantified. Dendritic morphology and number were characterized using Golgi staining. Long-term potentiation (LTP) was measured in slices from the 6-month-old brain. APE1 cKO mice did not significantly differ from WT mice in the learning phase of the Morris water maze, but performed significantly worse during the memory phase of the Morris water maze. vGLUT, GABA1, and GAD immunostaining was significantly decreased in APE1 cKO mice without concomitant changes in the number of synapsin-positive structures, suggesting that neural networks may be impaired but not at the level of total presynaptic structures. Dendrites were reduced both in number and length of spines in APE1 cKO mice. APE1 cKO brain slices exhibited decreased LTP induction compared to WT brain slices. Together, these data indicate that the conditional loss of APE1 in forebrain neurons leads to a phenotype consistent with expedited brain aging.

Identification of HMGCR, PPGARG and prohibitin as potential druggable targets of dihydrotestosterone for treatment against traumatic brain injury using system pharmacology

BACKGROUND

Traumatic Brain Injury (TBI) has long-term devastating effects for which there is no accurate and effective treatment for inflammation and chronic oxidative stress. As a disease that affects multiple signalling pathways, the search for a drug with a broader spectrum of pharmacological action is of clinical interest. The fact that endocrine disruption (e.g hypogonadism) has been observed in TBI patients suggests that endogenous therapy with testosterone, or its more androgenic derivative, dihydrotestosterone (DHT), may attenuate, at least in part, the TBI-induced inflammation, but the underlying molecular mechanisms by which this occurs are still not completely clear.

AIMS AND METHODS

In this study, the main aim was to investigate proteins that may be related to the pathophysiological mechanism of TBI and also be pharmacological targets of DHT in order to explore a possible therapy with this androgen using network pharmacology.

RESULTS AND CONCLUSIONS

We identified 2.700 proteins related to TBI and 1.567 that are potentially molecular targets of DHT. Functional enrichment analysis showed that steroid (p-value: 2.1-22), lipid metabolism (p-value: 2.8-21) and apoptotic processes (p-value: 5.2-21) are mainly altered in TBI. Furthermore, being mitochondrion an organelle involved on these molecular processes we next identified that out of 32 mitochondrial-related proteins 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR), peroxisome proliferator activated receptor gamma (PPGARG) and prohibitin are those found highly regulated in the network and potential targets of DHT in TBI. In conclusion, the identification of these cellular nodes may prove to be essential as targets of DHT for therapy against post-TBI inflammation.

Role of Nitric Oxide and Protein S-Nitrosylation in Ischemia-Reperfusion Injury

Ischemia-reperfusion injury (IRI) is a process in which damage is induced in hypoxic tissue when oxygen supply is resumed after ischemia. During IRI, restoration of reduced nitric oxide (NO) levels may alleviate reperfusion injury in ischemic organs. The protective mechanism of NO is due to anti-inflammatory effects, antioxidant effects, and the regulation of cell signaling pathways. On the other hand, it is generally known that S-nitrosylation (SNO) mediates the detrimental or protective effect of NO depending on the action of the nitrosylated target protein, and this is also applied in the IRI process. In this review, the effect of each change of NO and SNO during the IRI process was investigated.

Role of Prohibitins in Aging and Therapeutic Potential Against Age-Related Diseases

A decline in mitochondrial function has long been associated with age-related health decline. Several lines of evidence suggest that interventions that stimulate mitochondrial autophagy (mitophagy) can slow aging and prolong healthy lifespan. Prohibitins (PHB1 and PHB2) assemble at the mitochondrial inner membrane and are critical for mitochondrial homeostasis. In addition, prohibitins (PHBs) have diverse roles in cell and organismal biology. Here, we will discuss the role of PHBs in mitophagy, oxidative phosphorylation, cellular senescence, and apoptosis. We will also discuss the role of PHBs in modulating lifespan. In addition, we will review the links between PHBs and diseases of aging. Finally, we will discuss the emerging concept that PHBs may represent an attractive therapeutic target to counteract aging and age-onset disease.

PHB blocks endoplasmic reticulum stress and apoptosis induced by MPTP/MPP+ in PD models

Ample empirical evidence suggests that mitochondrial dysfunction and endoplasmic reticulum (ER) stress play a crucial role in the pathogenesis of Parkinson's disease (PD). Prohibitin (PHB), a mitochondrial inner-membrane protein involved in mitochondrial homeostasis and function, may be involved in the pathogenesis of PD. We investigated the functional role of PHB in mitochondrial biogenesis and ER stress in methyl-4-phenylpyridinium (MPP +)-induced in vivo and in vitro models of PD. The overexpression of PHB in SH-SY5Y cells block ed cell death and the apoptosis induced by MPP + incubation. PHB also block ed the activation of ER stress markers, including glucose-regulated protein 78, while increasing the expression of Xbox- binding protein 1 and caspase-12. Moreover, the intracerebroventricular administration of the PHB overexpression vector greatly block ed motor dysfunction and the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-mediated neurodegeneration in the mouse model of PD. The production of reactive oxygen species, ER stress, and autophagic stress induced by MPTP were also significantly block ed in PD mice overexpressing PHB. Our results suggest that PHB blocks the dopaminergic-neuron depletion by preserving mitochondrial function and inhibiting ER stress. The genetic manipulation of PHB may feature potential as a treatment for PD.

Prohibitin S-Nitrosylation Is Required for the Neuroprotective Effect of Nitric Oxide in Neuronal Cultures

Prohibitin (PHB) is a critical protein involved in many cellular activities. In brain, PHB resides in mitochondria, where it forms a large protein complex with PHB2 in the inner TFmembrane, which serves as a scaffolding platform for proteins involved in mitochondrial structural and functional integrity. PHB overexpression at moderate levels provides neuroprotection in experimental brain injury models. In addition, PHB expression is involved in ischemic preconditioning, as its expression is enhanced in preconditioning paradigms. However, the mechanisms of PHB functional regulation are still unknown. Observations that nitric oxide (NO) plays a key role in ischemia preconditioning compelled us to postulate that the neuroprotective effect of PHB could be regulated by NO. Here, we test this hypothesis in a neuronal model of ischemia-reperfusion injury and show that NO and PHB are mutually required for neuronal resilience against oxygen and glucose deprivation stress. Further, we demonstrate that NO post-translationally modifies PHB through protein S-nitrosylation and regulates PHB neuroprotective function, in a nitric oxide synthase-dependent manner. These results uncover the mechanisms of a previously unrecognized form of molecular regulation of PHB that underlies its neuroprotective function.SIGNIFICANCE STATEMENT Prohibitin (PHB) is a critical mitochondrial protein that exerts a potent neuroprotective effect when mildly upregulated in mice. However, how the neuroprotective function of PHB is regulated is still unknown. Here, we demonstrate a novel regulatory mechanism for PHB that involves nitric oxide (NO) and shows that PHB and NO interact directly, resulting in protein S-nitrosylation on residue Cys69 of PHB. We further show that nitrosylation of PHB may be essential for its ability to preserve neuronal viability under hypoxic stress. Thus, our study reveals a previously unknown mechanism of functional regulation of PHB that has potential therapeutic implications for neurologic disorders.

Prohibitin levels regulate OMA1 activity and turnover in neurons

The GTPase OPA1 and the AAA-protease OMA1 serve well-established roles in mitochondrial stress responses and mitochondria-initiated cell death. In addition to its role in mitochondrial membrane fusion, cristae structure, and bioenergetic function, OPA1 controls apoptosis by sequestering cytochrome c (cyt c) in mitochondrial cristae. Cleavage of functional long OPA1 (L-OPA1) isoforms by OMA1 inactivates mitochondrial fusion and primes apoptosis. OPA1 cleavage is regulated by the prohibitin (PHB) complex, a heteromeric, ring-shaped mitochondrial inner membrane scaffolding complex composed of PHB1 and PHB2. In neurons, PHB plays a protective role against various stresses, and PHB deletion destabilizes OPA1 causing neurodegeneration. While deletion of OMA1 prevents OPA1 destabilization and attenuates neurodegeneration in PHB2 KO mice, how PHB levels regulate OMA1 is still unknown. Here, we investigate the effects of modulating neuronal PHB levels on OMA1 stability and OPA1 cleavage. We demonstrate that PHB promotes OMA1 turnover, effectively decreasing the pool of OMA1. Further, we show that OMA1 binds to cardiolipin (CL), a major mitochondrial phospholipid. CL binding promotes OMA1 turnover, as we show that deleting the CL-binding domain of OMA1 decreases its turnover rate. Since PHB is known to stabilize CL, these data suggest that PHB modulates OMA1 through CL. Furthermore, we show that PHB decreases cyt c release induced by tBID and attenuates caspase 9 activation in response to hypoxic stress in neurons. Taken together, our results suggest that PHB-mediated CL stabilization regulates stress responses and cell death through OMA1 turnover and cyt c release.

Curcumin: Novel Treatment in Neonatal Hypoxic-Ischemic Brain Injury

Hypoxic-ischemic encephalopathy (HIE) is a major cause of mortality and morbidity in neonates, with an estimated global incidence of 3/1,000 live births. HIE brain damage is associated with an inflammatory response and oxidative stress, resulting in the activation of cell death pathways. At present, therapeutic hypothermia is the only clinically approved treatment available for HIE. This approach, however, is only partially effective. Therefore, there is an unmet clinical need for the development of novel therapeutic interventions for the treatment of HIE. Curcumin is an antioxidant reactive oxygen species scavenger, with reported anti-tumor and anti-inflammatory activity. Curcumin has been shown to attenuate mitochondrial dysfunction, stabilize the cell membrane, stimulate proliferation, and reduce injury severity in adult models of spinal cord injury, cancer, and cardiovascular disease. The role of curcumin in neonatal HIE has not been widely studied due to its low bioavailability and limited aqueous solubility. The aim of this study was to investigate the effect of curcumin treatment in neonatal HIE, including time of administration and dose-dependent effects. Our results indicate that curcumin administration prior to HIE in neonatal mice elevated cell and tissue loss, as well as glial activation compared to HI alone. However, immediate post-treatment with curcumin was significantly neuroprotective, reducing grey and white matter tissue loss, TUNEL+ cell death, microglia activation, reactive astrogliosis, and iNOS oxidative stress when compared to vehicle-treated littermates. This effect was dose-dependent, with 200 μg/g body weight as the optimal dose-regimen, and was maintained when curcumin treatment was delayed by 60 or 120 min post-HI. Cell proliferation measurements showed no changes between curcumin and HI alone, suggesting that the protective effects of curcumin on the neonatal brain following HI are most likely due to curcumin’s anti-inflammatory and antioxidant properties, as seen in the reduced glial and iNOS activity. In conclusion, this study suggests curcumin as a potent neuroprotective agent with potential for the treatment of HIE. The delayed application of curcumin further increases its clinical relevance.

Prohibitin is a positive modulator of mitochondrial function in PC12 cells under oxidative stress

Prohibitin (PHB) is a ubiquitously expressed and evolutionarily conserved mitochondrial protein with multiple functions. We have recently shown that PHB up-regulation offers robust protection against neuronal injury in models of cerebral ischemia in vitro and in vivo, but the mechanism by which PHB affords neuroprotection remains to be elucidated. Here, we manipulated PHB expression in PC12 neural cells to investigate its impact on mitochondrial function and the mechanisms whereby it protects cells exposed to oxidative stress. PHB over-expression promoted cell survival, whereas PHB down-regulation diminished cell viability. Functionally, manipulation of PHB levels did not affect basal mitochondrial respiration, but it increased spare respiratory capacity. Moreover, PHB over-expression preserved mitochondrial respiratory function of cells exposed to oxidative stress. Preserved respiratory capacity in differentiated PHB over-expressing cells exposed to oxidative stress was associated with an elongated mitochondrial morphology, whereas PHB down-regulation enhanced fragmentation. Mitochondrial complex I oxidative degradation was attenuated by PHB over-expression and increased in PHB knockdown cells. Changes in complex I degradation were associated with alterations of respiratory chain supercomplexes. Furthermore, we showed that PHB directly interacts with cardiolipin and that down-regulation of PHB results in loss of cardiolipin in mitochondria, which may contribute to destabilizing respiratory chain supercomplexes. Taken together, these data demonstrate that PHB modulates mitochondrial integrity and bioenergetics under oxidative stress, and suggest that the protective effect of PHB is mediated by stabilization of the mitochondrial respiratory machinery and its functional capacity, by the regulation of cardiolipin content. Open Data: Materials are available on https://cos.io/our-services/open-science-badges/ https://osf.io/93n6m/.

Significance of prohibitin domain family in tumorigenesis and its implication in cancer diagnosis and treatment

Prohibitin (PHB) was originally isolated and characterized as an anti-proliferative gene in rat liver. The evolutionarily conserved PHB gene encodes two human protein isoforms with molecular weights of ~33 kDa, PHB1 and PHB2. PHB1 and PHB2 belong to the prohibitin domain family, and both are widely distributed in different cellular compartments such as the mitochondria, nucleus, and cell membrane. Most studies have confirmed differential expression of PHB1 and PHB2 in cancers compared to corresponding normal tissues. Furthermore, studies verified that PHB1 and PHB2 are involved in the biological processes of tumorigenesis, including cancer cell proliferation, apoptosis, and metastasis. Two small molecule inhibitors, Rocaglamide (RocA) and fluorizoline, derived from medicinal plants, were demonstrated to interact directly with PHB1 and thus inhibit the interaction of PHB with Raf-1, impeding Raf-1/ERK signaling cascades and significantly suppressing cancer cell metastasis. In addition, a short peptide ERAP and a natural product xanthohumol were shown to target PHB2 directly and prohibit cancer progression in estrogen-dependent cancers. As more efficient biomarkers and targets are urgently needed for cancer diagnosis and treatment, here we summarize the functional role of prohibitin domain family proteins, focusing on PHB1 and PHB2 in tumorigenesis and cancer development, with the expectation that targeting the prohibitin domain family will offer more clues for cancer therapy.