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.

The many facets of CD26/dipeptidyl peptidase 4 and its inhibitors in disorders of the CNS - a critical overview.

Dipeptidyl peptidase 4 is a serine protease that cleaves X-proline or X-alanine in the penultimate position. Natural substrates of the enzyme are glucagon-like peptide-1, glucagon inhibiting peptide, glucagon, neuropeptide Y, secretin, substance P, pituitary adenylate cyclase-activating polypeptide, endorphins, endomorphins, brain natriuretic peptide, beta-melanocyte stimulating hormone and amyloid peptides as well as some cytokines and chemokines. The enzyme is involved in the maintenance of blood glucose homeostasis and regulation of the immune system. It is expressed in many organs including the brain. DPP4 activity may be effectively depressed by DPP4 inhibitors. Apart from enzyme activity, DPP4 acts as a cell surface (co)receptor, associates with adeosine deaminase, interacts with extracellular matrix, and controls cell migration and differentiation. This review aims at revealing the impact of DPP4 and DPP4 inhibitors for several brain diseases (virus infections affecting the brain, tumours of the CNS, neurological and psychiatric disorders). Special emphasis is given to a possible involvement of DPP4 expressed in the brain.While prominent contributions of extracerebral DPP4 are evident for a majority of diseases discussed herein; a possible role of "brain" DPP4 is restricted to brain cancers and Alzheimer disease. For a number of diseases (Covid-19 infection, type 2 diabetes, Alzheimer disease, vascular dementia, Parkinson disease, Huntington disease, multiple sclerosis, stroke, and epilepsy), use of DPP4 inhibitors has been shown to have a disease-mitigating effect. However, these beneficial effects should mostly be attributed to the depression of "peripheral" DPP4, since currently used DPP4 inhibitors are not able to pass through the intact blood-brain barrier.

The Ryanodine receptor stabilizer S107 fails to support motor neuronal neuritogenesis in vitro.

Calcium homeostasis is essential for neuronal cell survival/differentiation. Imbalance of the Ca2+ homeostasis due to excessive Ca2+ overload is essential for spinal cord injury (SCI). The overload resulted from Ca2+ flux across the plasma membrane and from internal Ca2+ store release (mitochondria, endoplasmic reticulum, ER). Inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) are involved in releasing Ca2+ from ER contributing to axonal degeneration following SCI. In turn, block of both receptors is axoprotective. The calstabin RyR subunit, stabilizing the channel in a state of reduced activity, prevents pathological Ca2+ release too. We investigated whether S107, a RyR-stabilizing compound (Rycal), is beneficial for survival and neuritogenesis of spinal cord motor neurons in vitro. We used a spinal cord slice model and the motor neuron-like NSC-34 cell line. Effects of S107 were tested by propidium iodide/fluorescein diacetate vital staining, mitotic index determination via BrdU-incorporation, and neurite sprouting parameters. Results showed that S107 (i) had no effect on gliosis resulting from slices preparation; (ii) had no effect on motor neuronal survival and proliferation; and (iii) impaired neurite sprouting, no matter whether it was a differentiation (NSC-34 cells) or regeneration (spinal cord slices) process. The results underline the need for a flexible Ca2+homeostasis provided by the ER for re-initiation of neuritogenesis.

Effects of Gynostemma pentaphyllum on spinal cord motor neurons and microglial cells in vitro.

The regenerative capability of spinal cord neurons is limited to impossible. Thus, experimental approaches supporting reconstruction/regeneration are in process. This study focused on the evaluation of the protective potency of an extract from Gynostemma pentaphyllum (GP), a plant used in traditional medicine with anti-oxidative and neuroprotective activities, in vitro on organotypic spinal cord cultures, the motor-neuron-like NSC-34 cell line and the microglial cell line BV-2. Organotypic cultures were mechanically stressed by the slicing procedure and the effect of GP on motor neuron survival and neurite sprouting was tested by immunohistochemistry. NSC-34 cells were neuronal differentiated by using special medium. Afterwards, cell survival (propidium iodide/fluorescein diacetate labeling), proliferation (BrdU-incorporation), and neurite sprouting were evaluated. BV-2 cells were stimulated with LPS/interferon γ and subjected to migration assay and nanoparticle uptake. Cell survival, proliferation and the expression pattern of different microglial activation markers (cFOS, iNOS) as well as transcription factors (PPARγ, YB1) were analyzed. In organotypic cultures, high-dose GP supported survival of motor neurons and especially of the neuronal fiber network. Despite reduced neurodegeneration, however, there was a GP-mediated activation of astro- and microglia. In NSC-34 cells, high-dosed GP had degenerative and anti-proliferative effects, but only in normal medium. Moreover, GP supported the neuro-differentiation ability. In BV-2 cells, high-dosed GP was toxic. In lower dosages, GP affected cell survival and proliferation when combined with LPS/interferon γ. Nanoparticle uptake, migration ability, and the transcription factor PPARγ, however, GP affected directly. The data suggest positive effects of GP on injured spinal motor neurons. Moreover, GP activated microglial cells. The dual role of microglia (protective/detrimental) in neurodegenerative processes required further experiments to enhance the knowledge about GP effects. Therefore, a possible clinical use of GP in spinal cord injuries is still a long way off.

Immuno-histological detection of resistant columnar units and vulnerable networks in the rat retina after asphyxia-induced transient cardiac arrest.

BACKGROUND: Stroke-related loss of vision is one of the residual impairments, restricting the quality of life. However, studies of the ocular manifestations of asphyxia cardiac arrest/resuscitation (ACA/R) have reported very heterogeneous results. OBJECTIVE: We aimed to evaluate the ACA/R-induced degeneration pattern of the different retinal cell populations in rats using different immuno-histological stainings. METHODS: The staining pattern of toluidine blue and the ganglion cell markers ß-III-tubulin and NeuN; the calcium-binding protein parvalbumin, indicating ganglion, amacrine, and horizontal cells; calretinin D28k, indicating ganglion and amacrine cells; calbindin, indicating horizontal cells; Chx 10, indicating cone bipolar cells; PKCα, indicating ON-type rod bipolar cells; arrestin, indicating cones; and rhodopsin, a marker of rods, as well as the glial cell markers GFAP (indicating astroglia and Müller cells) and IBA1 (indicating microglia), were evaluated after survival times of 7 and 21 days in an ACA/R rat model. Moreover, quantitative morphological analysis of the optic nerve was performed. The ACA/R specimens were compared with those from sham-operated and completely naïve rats. RESULTS: ACA/R-induced effects were: (i) a significant reduction of retinal thickness after long-term survival; (ii) ganglion cell degeneration, including their fiber network in the inner plexiform layer; (iii) degeneration of amacrine and cone bipolar cells; (iv) degeneration of cone photoreceptors; (v) enhanced resistance to ACA/R by rod photoreceptors, ON-type rod bipolar and horizontal cells, possibly caused by the strong upregulation of the calcium-binding proteins calretinin, parvalbumin, and calbindin, counteracting the detrimental calcium overload; (vi) significant activation of Müller cells as further element of retinal anti-stress self-defense mechanisms; and (vii) morphological alterations of the optic nerve in form of deformed fibers. CONCLUSIONS: Regardless of the many defects, the surviving neuronal structures seemed to be able to maintain retinal functionality, which can be additionally improved by regenerative processes true to the "use it or lose it" dogma.

The implications of hypothalamic abnormalities for schizophrenia.

Until a few years ago, the hypothalamus was believed to play only a marginal role in schizophrenia pathophysiology. However, recent findings show that this rather small brain region involved in many pathways found disrupted-in schizophrenia. Gross anatomic abnormalities (volume changes of the third ventricle, the hypothalamus, and its individual nuclei) as well as alterations at the cellular level (circumscribed loss of neurons) can be observed. Further, increased or decreased expression of hypothalamic peptides such as oxytocin, vasopressin, several factors involved in the regulation of appetite and satiety, endogenous opiates, products of schizophrenia susceptibility genes as well as of enzymes involved in neurotransmitter and neuropeptide metabolism have been reported in schizophrenia and/or animal models of the disease. Remarkably, although profound disturbances of the hypothalamus-pituitary-adrenal axis, hypothalamus-pituitary-thyroid axis, and the hypothalamus-pituitary-gonadal axis are typical signs of schizophrenia, there is currently no evidence for alterations in the expression of hypothalamic-releasing and inhibiting factors that control these hormonal axes. Finally, the implications of hypothalamus for disease-related disturbances of the sleep-wakefulness cycle and neuroimmune dysfunctions in schizophrenia are outlined.

Polyamines and polyamine-metabolizing enzymes in schizophrenia: Current knowledge and concepts of therapy.

Polyamines play preeminent roles in a variety of cellular functions in the central nervous system and other organs. A large body of evidence suggests that the polyamine pathway is prominently involved in the etiology and pathology of schizophrenia. Alterations in the expression and activity of polyamine metabolizing enzymes, as well as changes in the levels of the individual polyamines, their precursors and derivatives, have been measured in schizophrenia and animal models of the disease. Additionally, neuroleptic treatment has been shown to influence polyamine concentrations in brain and blood of individuals with schizophrenia. Thus, the polyamine system may appear to be a promising target for neuropharmacological treatment of schizophrenia. However, for a number of practical reasons there is currently only limited hope for a polyamine-based schizophrenia therapy.

The Spinal Cord Damage in a Rat Asphyxial Cardiac Arrest/Resuscitation Model.

BACKGROUND: After cardiac arrest/resuscitation (CA/R), animals often had massive functional restrictions including spastic paralysis of hind legs, disturbed balance and reflex abnormalities. Patients who have survived CA also develop movement restrictions/disorders. A successful therapy requires detailed knowledge of the intrinsic damage pattern and the respective mechanisms. Beside neurodegenerations in the cerebellum and cortex, neuronal loss in the spinal cord could be a further origin of such movement artifacts. METHODS: Thus, we aimed to evaluate the CA/R-induced degeneration pattern of the lumbar medulla spinalis by immunocytochemical expression of SMI 311 (marker of neuronal perikarya and dendrites), IBA1 (microglia marker), GFAP (marker of astroglia), calbindin D28k (marker of the cellular neuroprotective calcium-buffering system), MnSOD (neuroprotective antioxidant), the transcription factor PPARγ and the mitochondrial marker protein PDH after survival times of 7 and 21 days. The CA/R specimens were compared with those from sham-operated and completely naïve rats. RESULTS & CONCLUSION: The main ACA/R-mediated results were: (1) degeneration of lumbar spinal cord motor neurons, characterized by neuronal pyknotization and peri-neuronal tissue artifacts; (2) attendant activation of microglia in the short-term group; (3) attendant activation of astroglia in the long-term group; (4) degenerative pattern in the intermediate gray matter; (5) activation of the endogenous anti-oxidative defense systems calbindin D28k and MnSOD; (6) activation of the transcription factor PPARγ, especially in glial cells of the gray matter penumbra; and (7) activation of mitochondria. Moreover, marginal signs of anesthesia-induced cell stress were already evident in sham animals when compared with completely naïve spinal cords. A correlation between the NDS and the motor neuronal loss could not be verified. Thus, the NDS appears to be unsuitable as prognostic tool.

From putative brain tumor marker to high cognitive abilities: Emerging roles of a disintegrin and metalloprotease (ADAM) 12 in the brain.

ADAM (a disintergin and metalloprotease) 12 is a member of the large family of multidomain metalloprotease-disintegrins, which possess cell-binding and metalloprotease properties. The enzyme is responsible for the shedding of a number of membrane-bound proteins (heparin-binding-EGF, insulin-like growth factor 2-binding proteins 3 and 5, oxytocinase, glycoprotein non-metastatic melanoma protein B and basigin). In rat and human CNS, ADAM12 is predominantly localized in white and gray matter oligodendrocytes. In addition it can be detected in astrocytes, neurons and endothelial cells. Its function in healthy brain is not well established yet, but prominent roles in CNS development, myelination and high cognitive abilities are discussed. There is increasing evidence that ADAM12 is involved in numerous major diseases of the CNS, which are summarized in the present review (brain tumors, multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer´s disease, stroke, schizophrenia, autism and bipolar disorder).

Differentiation of NSC-34 cells is characterized by expression of NGF receptor p75, glutaminase and NCAM L1, activation of mitochondria, and sensitivity to fatty acid intervention.

Motor neuronal damage due to diseases, traumatic insults or de-afferentation of the spinal cord is often incurable because of poor intrinsic regenerative capacity. Hence, medical basic research has to provide a better understanding of development-/regeneration-related cellular processes as only way to develop new and successful therapeutic strategies. Here, we investigated the neuronal differentiation of the NSC-34 hybrid cell line, which is an accepted model for spinal cord motor neurons. Their differentiation was stimulated by switching from normal to differentiation medium and by supplementation with palmitic and oleic acid. To characterize neuro-differentiation of NSC-34 cells, expression of nicotinic acetylcholine receptor alpha 4, NGF p75 receptor, IGF I alpha receptor, glutaminase, NCAM L1, ADAM10 and myelin basic protein as well as activation of mitochondria were analyzed. Both switch from normal to differentiation medium and fatty acid application stimulated NSC-34 differentiation. Differentiation was characterized by diminishing expression of the nicotinic acetylcholine receptor alpha 4 and enhancing expression of the NGF receptor p75, of glutaminase, of NCAM L1 and it's partially transformation from the cell surface into the cell. Fatty acid intervention stabilized the expression of the nicotinic acetylcholine receptor alpha 4, diminished the expression of the NGF receptor p75, consolidated the expression profile of NCAM L1, and intensified the expression of the relevant for NCAM L1 cleavage ADAM10. However, NCAM L1 cleavage itself was unaffected by fatty acid intervention, as was the differentiation-relevant activation of mitochondria and their transformation into neuronal filopodia.

Normoxic post-ROSC ventilation delays hippocampal CA1 neurodegeneration in a rat cardiac arrest model, but does not prevent it.

The European Resuscitation Guidelines recommend that survivors of cardiac arrest (CA) be resuscitated with 100% O2 and undergo subsequent-post-return of spontaneous circulation (ROSC)-reduction of O2 supply to prevent hyperoxia. Hyperoxia produces a "second neurotoxic hit," which, together with the initial ischemic insult, causes ischemia-reperfusion injury. However, heterogeneous results from animal studies suggest that normoxia can also be detrimental. One clear reason for these inconsistent results is the considerable heterogeneity of the models used. In this study, the histological outcome of the hippocampal CA1 region following resuscitation with 100% O2 combined with different post-ROSC ventilation regimes (21%, 50%, and 100% O2) was investigated in a rat CA/resuscitation model with survival times of 7 and 21 days. Immunohistochemical stainings of NeuN, MAP2, GFAP, and IBA1 revealed a neuroprotective potency of post-ROSC ventilation with 21% O2, although it was only temporary. This limitation should be because of the post-ROSC intervention targeting only processes of ischemia-induced secondary injury. There were no ventilation-dependent effects on either microglial activation, reduction of which is accepted as being neuroprotective, or astroglial activation, which is accepted as being able to enhance neurons' resistance to ischemia/reperfusion injury. Furthermore, our findings verify the limited comparability of animal studies because of the individual heterogeneity of the animals, experimental regimes, and evaluation procedures used.

Binding varicella zoster virus: an underestimated facet of insulin-degrading enzyme´s implication for Alzheimer´s disease pathology?

We shortly discuss a possible contribution of insulin-degrading enzyme to Alzheimer´s disease pathology by binding varicella zoster virus glycoprotein E, which increases the infectivity and cell-cell spread of the virus.

Relative Resilience of Cerebellar Purkinje Cells in a Cardiac Arrest/Resuscitation Rat Model.

BACKGROUND: In studies on cardiac arrest (CA)/resuscitation (R) injury, Purkinje cell degeneration was described, however, with inconsistent data concerning severity and time point of manifestation. Moreover, CA/R studies paid only limited attention to inhibitory stellate interneurons. To this aim, the hypothesis that cerebellar could be relatively resilient toward CA/R because of diverse cellular defense mechanisms including interaction with stellate cells was tested. METHODS: We examined rats with survival times of 6, 24, and 48 h, and 7 and 21 days in comparison with sham- and nonoperated animals. Thereby, we focused on the immunohistochemical expression of cfos, MnSOD, Bcl2, caspase 3, parvalbumin, calbindin D28 k, MAP2, IBA1, and GFAP, especially in the particular sensitivity to CA/R cerebellar lobule IX. Hippocampal CA1 degeneration was demonstrated by expression patterns of MAP2 and NeuN in combination with IBA1 and GFAP. RESULTS/CONCLUSIONS: Comparative analysis of hippocampal CA1 pyramidal cells and cerebellar Purkinje cells confirmed a relative resil-ience of Purkinje cells to CA/R. We found only a notable degeneration of Purkinje cell neuronal fiber network, which, however, not necessarily led to neuronal cell death. To induce significant Purkinje cell loss, a stronger ischemic trigger seems to be needed. As possible Purkinje cell-protecting mechanisms, we would propose: (1) activation of inhibitory stellate cells, shown by cfos, MnSOD, and Bcl2 expression, balancing out ischemia-induced excitation and inhibition of Purkinje cells; (2) translocation of the calcium-buffering system, shown by parvalbumin and calbindin D28 k expression, protecting Purkinje cells from detrimental calcium overload; (3) activation of the neuron-astrocyte cross talk, protecting Purkinje cells from over-excitation by removing potassium and neurotransmitters from the extracellular space; (4) activation of the effective and long-lasting MnSOD defense system; and (5) of the anti-apoptotic protein Bcl2 in Purkinje cells itself. Moreover, the results emphasize the limited comparability of animal CA/R studies because of the heterogeneity of the used experimental regimes.

Enhanced mitochondrial autophagy (mitophagy) in oligodendrocytes might play a role in white matter pathology in schizophrenia.

Disrupted white matter integrity is a typical feature of brain pathologic alterations in schizophrenia, which includes impaired myelination, decreased oligodendrocyte densities, distortion of their spatial distribution and deviations from normal oligodendrocyte cell morphology. While most genes expressed "in the remaining" oligodendrocytes are downregulated in schizophrenia, only a few are upregulated. To the latter group belong prohibitin 2 and DISC 1, which were recently identified as mitochondria-located mitophagy receptors. Their overexpression, together with greatly reduced numbers and densities of oligodendroglial mitochondria and the structurally "normal appearance of the remaining mitochondria" in these cells as reported by Uranova's group (Uranova et al., 2001, 2004, 2018), point to enhanced mitophagy in oligodendrocytes in schizophrenia, which is possibly even cell protective by preventing apoptosis. Since massive loss of white matter oligodendrocytes is a characteristic feature of schizophrenia, we assume that increased mitophagy is a late event in the development and/or further progression of white matter pathologic changes. Moreover, altered oligodendroglial mitophagy might in part result from antipsychotic treatment. Further studies are clearly needed to substantiate our hypothesis on enhanced mitochondrial autophagy in schizophrenia, whereby the "drug-naïve state" and the possible influence of antipsychotic treatment could be elegantly simulated using animal models of the disease.

Perineuronal oligodendrocytes in health and disease: the journey so far.

Perineuronal oligodendrocytes (pn-Ols) are located in the cerebral gray matter in close proximity to neuronal perikarya and less frequently near dendrites and neurites. Although their morphology is indistinguishable from that of other oligodendrocytes, it is not known if pn-Ols have a similar or different cell signature from that of typical myelinating oligodendroglial cells. In this review, we discussed the potential roles of these cells in myelination under normal and pathophysiologic conditions as functional and nutritional supporters of neurons, as restrainers of neuronal firing, and as possible players in glutamate-glutamine homeostasis. We also highlighted the occurrences in which perineuronal oligodendroglia are altered, such as in experimental demyelination, multiple sclerosis, cerebral ischemia, epilepsy, Alzheimer's disease, schizophrenia, major depression, and bipolar disorder.

The Differentiation of Spinal Cord Motor Neurons is Associated with Changes of the Mitochondrial Phospholipid Cardiolipin.

Motor neuron damage caused by diseases, traumatic insults or de-afferentation of the spinal cord is often incurable due to the poor intrinsic regenerative capacity. Moreover, regenerated peripheral nerves often do not reach normal functionality. Here, we investigated cardiolipin in the process of neuro-differentiation, since cardiolipin is closely linked to the mitochondrial energy supply in cells. The NSC-34 hybrid cell line, produced by fusing neuroblastoma cells with primary spinal cord motor neurons, was used, since it shares several morphological and physiological characteristics with mature primary motor neurons. Their neuro-differentiation was supported by switching from normal to differentiation medium or by fatty acid supplementation. Differentiation was evaluated by measuring neurite-sprouting parameters and PPARα expression. Cellular fatty acid distribution was analyzed to indicate changes in lipid metabolism during differentiation. Cardiolipin was characterized by acyl-chain composition and the distribution of molecular cardiolipin species. Both, the switch from normal to differentiation medium as well as the administration of palmitic and oleic acid promoted neuro-differentiation. Stimulated differentiation was accompanied by changes in cardiolipin content and composition. The positive correlation between neuro-differentiation and concentration of those molecular cardiolipin species containing palmitic and oleic acid implied a link between differentiation of NSC-34 cells and cardiolipin metabolism. We further demonstrated the impact of cellular lipid metabolism, and particularly cardiolipin metabolism, during and NSC-34 neuritogenesis. Thus, cardiolipin may represent a new therapeutic target for axon regeneration after peripheral nerve injuries or when axon sprouting is required to compensate for motor neuron loss in response to aging and/or disease.

The hypothalamus and neuropsychiatric disorders: psychiatry meets microscopy.

The past decades have witnessed an explosion of knowledge on brain structural abnormalities in schizophrenia and depression. Focusing on the hypothalamus, we try to show how postmortem brain microscopy has contributed to our understanding of mental disease-related pathologic alterations of this brain region. Gross anatomical abnormalities (volume changes of the third ventricle, the hypothalamus, and its nuclei) and alterations at the cellular level (loss of neurons, increased or decreased expression of hypothalamic peptides such as oxytocin, vasopressin, corticotropin-releasing hormone, and other regulatory factors as well as of enzymes involved in neurotransmitter and neuropeptide metabolism) have been reported in schizophrenia and/or depression. While histologic research has mainly concentrated on neurons, little is currently known about the impact of non-neuronal cells for hypothalamus pathology in mental disorders. Their study would be a rewarding task for the future.