Chronic mild stress influences nerve growth factor through a matrix metalloproteinase-dependent mechanism

FK506 contributes to peripheral nerve regeneration by inhibiting neuroinflammatory responses and promoting neuron survival

JOURNAL/nrgr/04.03/01300535-202507000-00031/figure1/v/2024-09-09T124005Z/r/image-tiff FK506 (Tacrolimus) is a systemic immunosuppressant approved by the U.S. Food and Drug Administration. FK506 has been shown to promote peripheral nerve regeneration, however, its precise mechanism of action and its pathways remain unclear. In this study, we established a rat model of sciatic nerve injury and found that FK506 improved the morphology of the injured sciatic nerve, increased the numbers of motor and sensory neurons, reduced inflammatory responses, markedly improved the conduction function of the injured nerve, and promoted motor function recovery. These findings suggest that FK506 promotes peripheral nerve structure recovery and functional regeneration by reducing the intensity of inflammation after neuronal injury and increasing the number of surviving neurons.

Low-carbohydrate diet as a nutritional intervention in a major depression disorder: focus on relapse prevention

OBJECTIVES

Mood disorders are trending to be among the leading causes of years lived with disability. Despite multiple treatment options, around 30% patients with major depressive disorder (MDD) develop treatment resistant depression (TRD) and fail to respond to current pharmacological therapies. This study aimed to explore the potential benefits of nutritional treatment strategies, along with their molecular mechanisms of action, focusing especially on low-carbohydrate diet (LCHD), ketogenic diet (KD) and other strategies based on carbohydrates intake reduction.

METHODS

A comprehensive literature review was conducted to determine the impact of LCHD on alleviating depressive symptoms in patients with MDD, along with an explanation of its mode of action.

RESULTS

The study revealed significant impact of nutritional interventions based on restriction in carbohydrate intake such as LCHD, KD or sugar-sweetened beverages (SSB) exclusion on anxiety or depression symptoms reduction, mood improvement and lower risk of cognitive impairment or depression. The efficacy of these approaches is further substantiated by their underlying molecular mechanisms, mainly brain-derived neurotrophic factor (BDNF) which is a potential key target of sugar restriction diets in terms of neuroplasticity.

DISCUSSION

Healthcare professionals may consider implementing LCHD strategies for MDD and TRD patients to modify the disease process, maintain euthymia, and prevent depressive episode relapses. Ranging from the exclusion of SSB to the adherence to rigorous LCHD regimens, these nutritional approaches are safe, straightforward to implement, and may confer benefits for well-being and relapse prevention in this specific patient population.

Convergence of endothelial dysfunction, inflammation and glucocorticoid resistance in depression-related cardiovascular diseases

Major Depressive Disorder, or depression, has been extensively linked to dysregulated HPA axis function, chronic inflammation and cardiovascular diseases. While the former two have been studied in depth, the mechanistic connection between depression and cardiovascular disease is unclear. As major mediators of vascular homeostasis, vascular pathology and immune activity, endothelial cells represent an important player connecting the diseases. Exaggerated inflammation and glucocorticoid function are important topics to explore in the endothelial response to MDD. Glucocorticoid resistance in several cell types strongly promotes inflammatory signaling and results in worsened severity in many diseases. However, endothelial health and inflammation in chronic stress and depression are rarely considered from the perspective of glucocorticoid signaling and resistance. In this review, we aim to discuss (1) endothelial dysfunction in depression, (2) inflammation in depression, (3) general glucocorticoid resistance in depression and (4) endothelial glucocorticoid resistance in depression co-morbid inflammatory diseases. We will first describe vascular pathology, inflammation and glucocorticoid resistance separately in depression and then describe their potential interactions with one another in depression-relevant diseases. Lastly, we will hypothesize potential mechanisms by which glucocorticoid resistance in endothelial cells may contribute to vascular disease states in depressed people. Overall, endothelial-glucocorticoid signaling may play an important role in connecting depression and vascular pathology and warrants further study.

Glucocorticoids, their uses, sexual dimorphisms, and diseases: new concepts, mechanisms, and discoveries

The normal stress response in humans is governed by the hypothalamic-pituitary-adrenal (HPA) axis through heightened mechanisms during stress, raising blood levels of the glucocorticoid hormone cortisol. Glucocorticoids are quintessential compounds that balance the proper functioning of numerous systems in the mammalian body. They are also generated synthetically and are the preeminent therapy for inflammatory diseases. They act by binding to the nuclear receptor transcription factor glucocorticoid receptor (GR), which has two main isoforms (GRα and GRβ). Our classical understanding of glucocorticoid signaling is from the GRα isoform, which binds the hormone, whereas GRβ has no known ligands. With glucocorticoids being involved in many physiological and cellular processes, even small disruptions in their release via the HPA axis, or changes in GR isoform expression, can have dire ramifications on health. Long-term chronic glucocorticoid therapy can lead to a glucocorticoid-resistant state, and we deliberate how this impacts disease treatment. Chronic glucocorticoid treatment can lead to noticeable side effects such as weight gain, adiposity, diabetes, and others that we discuss in detail. There are sexually dimorphic responses to glucocorticoids, and women tend to have a more hyperresponsive HPA axis than men. This review summarizes our understanding of glucocorticoids and critically analyzes the GR isoforms and their beneficial and deleterious mechanisms and the sexual differences that cause a dichotomy in responses. We also discuss the future of glucocorticoid therapy and propose a new concept of dual GR isoform agonist and postulate why activating both isoforms may prevent glucocorticoid resistance.

Neuropathic pain; what we know and what we should do about it

Neuropathic pain can result from injury to, or disease of the nervous system. It is notoriously difficult to treat. Peripheral nerve injury promotes Schwann cell activation and invasion of immunocompetent cells into the site of injury, spinal cord and higher sensory structures such as thalamus and cingulate and sensory cortices. Various cytokines, chemokines, growth factors, monoamines and neuropeptides effect two-way signalling between neurons, glia and immune cells. This promotes sustained hyperexcitability and spontaneous activity in primary afferents that is crucial for onset and persistence of pain as well as misprocessing of sensory information in the spinal cord and supraspinal structures. Much of the current understanding of pain aetiology and identification of drug targets derives from studies of the consequences of peripheral nerve injury in rodent models. Although a vast amount of information has been forthcoming, the translation of this information into the clinical arena has been minimal. Few, if any, major therapeutic approaches have appeared since the mid 1990's. This may reflect failure to recognise differences in pain processing in males vs. females, differences in cellular responses to different types of injury and differences in pain processing in humans vs. animals. Basic science and clinical approaches which seek to bridge this knowledge gap include better assessment of pain in animal models, use of pain models which better emulate human disease, and stratification of human pain phenotypes according to quantitative assessment of signs and symptoms of disease. This can lead to more personalized and effective treatments for individual patients. Significance statement: There is an urgent need to find new treatments for neuropathic pain. Although classical animal models have revealed essential features of pain aetiology such as peripheral and central sensitization and some of the molecular and cellular mechanisms involved, they do not adequately model the multiplicity of disease states or injuries that may bring forth neuropathic pain in the clinic. This review seeks to integrate information from the multiplicity of disciplines that seek to understand neuropathic pain; including immunology, cell biology, electrophysiology and biophysics, anatomy, cell biology, neurology, molecular biology, pharmacology and behavioral science. Beyond this, it underlines ongoing refinements in basic science and clinical practice that will engender improved approaches to pain management.

Lower Nerve Growth Factor Levels in Major Depression and Suicidal Behaviors: Effects of Adverse Childhood Experiences and Recurrence of Illness

Major depressive disorder (MDD) and its severe subtype, major dysmood disorder (MDMD), are distinguished by activation of inflammatory and growth factor subnetworks, which are associated with recurrence of illness (ROI) and adverse childhood experiences (ACEs). Nerve growth factor (NGF) plays a crucial role in facilitating neuro-immune communications and may regulate the inflammatory response.

METHODS

The present study examined the effects of ACEs and ROI on culture supernatant NGF, stem cell factor (SCF), stem cell GF (SCGF), hepatocyte GF (HGF), and macrophage colony-stimulating factor (M-CSF), in relation to a neurotoxicity (NT) cytokine profile.

RESULTS

NGF levels are lower in MDD (p = 0.003), particularly MDMD (p < 0.001), as compared with normal controls. ROI and ACE were significantly and inversely associated with NGF (≤0.003) and the NGF/NT ratio (≤0.001), whereas there are no effects of ACEs and ROI on SCF, SCGF, HGF, or M-CSF. Lowered NGF (p = 0.003) and the NGF/NT ratio (p < 0.001) are highly significantly and inversely associated with the severity of the current depression phenome, conceptualized as a latent vector extracted from the current severity of depression, anxiety, and suicidal behaviors. We found that one validated and replicable latent vector could be extracted from NGF, ROI, and the depression phenome, which therefore constitutes a novel ROI-NGF-pathway-phenotype. ACEs explained 59.5% of the variance in the latter pathway phenotype (p < 0.001).

CONCLUSIONS

The imbalance between decreased NGF and increased neurotoxic cytokines during the acute phase of severe depression may contribute to decreased neuroprotection, increased neuro-affective toxicity, and chronic mild inflammation.

Exploring brain glutathione and peripheral blood markers in posttraumatic stress disorder: a combined [1H]MRS and peripheral blood study

Introduction

Oxidative stress has been implicated in psychiatric disorders, including posttraumatic stress disorder (PTSD). Currently, the status of glutathione (GSH), the brain's most abundant antioxidant, in PTSD remains uncertain. Therefore, the current study investigated brain concentrations of GSH and peripheral concentrations of blood markers in individuals with PTSD vs. Healthy Controls (HC).

Methods

GSH spectra was acquired in the anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex (DLPFC) using MEGA-PRESS, a J-difference-editing acquisition method. Peripheral blood samples were analyzed for concentrations of metalloproteinase (MMP)-9, tissue inhibitors of MMP (TIMP)-1,2, and myeloperoxidase (MPO).

Results

There was no difference in GSH between PTSD and HC in the ACC (n = 30 PTSD, n = 20 HC) or DLPFC (n = 14 PTSD, n = 18 HC). There were no group differences between peripheral blood markers (P > 0.3) except for (non-significantly) lower TIMP-2 in PTSD. Additionally, TIMP-2 and GSH in the ACC were positively related in those with PTSD. Finally, MPO and MMP-9 were negatively associated with duration of PTSD.

Conclusions

We do not report altered GSH concentrations in the ACC or DLPFC in PTSD, however, systemic MMPs and MPO might be implicated in central processes and progression of PTSD. Future research should investigate these relationships in larger sample sizes.

Antidepressant effect of 4-Butyl-a-agarofuran via HPA axis and serotonin system

Depression is a leading cause of disability worldwide and the psychiatric diagnosis most commonly associated with suicide. 4-Butyl-a-agarofuran (AF-5), a derivative of agarwood furan, is currently in phase III clinical trials for generalized anxiety disorder. Herein, we explored the antidepressant effect and its possible neurobiological mechanisms in animal models. In present study, AF-5 administration markedly decreased the immobility time in mouse forced swim test and tail suspension test. In the sub-chronic reserpine-induced depressive rats, AF-5 treatment markedly increased the rectal temperature and decreased the immobility time of model rats. In addition, chronic AF-5 treatment markedly reversed the depressive-like behaviors in chronic unpredictable mild stress (CUMS) rats by reducing immobility time of forced swim test. Single treatment with AF-5 also potentiated the mouse head-twitch response induced by 5-hydroxytryptophan (5-HTP, a metabolic precursor to serotonin), and antagonized the ptosis and motor ability triggered by reserpine. However, AF-5 had no effect on yohimbine toxicity in mice. These results indicated that acute treatment with AF-5 produced serotonergic, but not noradrenergic activation. Furthermore, AF-5 reduced adrenocorticotropic hormone (ACTH) level in serum and normalized the neurotransmitter changes, including the decreased serotonin (5-HT) in hippocampus of CUMS rats. Moreover, AF-5 affected the expressions of CRFR1 and 5-HT2C receptor in CUMS rats. These findings confirm the antidepressant effect of AF-5 in animal models, which may be primarily related to CRFR1 and 5-HT2C receptor. AF-5 appears to be promising as a novel dual target drug for depression treatment.

Neurotrophin Signaling Impairment by Viral Infections in the Central Nervous System

Neurotrophins, such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin 3 (NT-3), NT-4, and NT-5, are proteins involved in several important functions of the central nervous system. The activation of the signaling pathways of these neurotrophins, or even by their immature form, pro-neurotrophins, starts with their recognition by cellular receptors, such as tropomyosin receptor kinase (Trk) and 75 kD NT receptors (p75NTR). The Trk receptor is considered to have a high affinity for attachment to specific neurotrophins, while the p75NTR receptor has less affinity for attachment with neurotrophins. The correct functioning of these signaling pathways contributes to proper brain development, neuronal survival, and synaptic plasticity. Unbalanced levels of neurotrophins and pro-neurotrophins have been associated with neurological disorders, illustrating the importance of these molecules in the central nervous system. Furthermore, reports have indicated that viruses can alter the normal levels of neurotrophins by interfering with their signaling pathways. This work discusses the importance of neurotrophins in the central nervous system, their signaling pathways, and how viruses can affect them.

Matrix Metalloproteinase-9 as an Important Contributor to the Pathophysiology of Depression

Matrix metalloproteinases (MMPs) are physiologically expressed in the central nervous system in neurons, astrocytes and microglia, and their aberrant elevation contributes to a number of diseases. Amongst the MMP members, MMP−9 has generated considerable attention because of its possible involvement in inflammatory responses, blood-brain barrier permeability, the regulation of perineuronal nets, demyelination, and synaptic long-term potentiation. Emerging evidence indicate an association between MMP−9 and the syndrome of depression. This review provides an updated and comprehensive summary of the probable roles of MMP−9 in depression with an emphasis on the mechanisms and potential of MMP−9 as a biomarker of depression.

Evolution of an increased performance under acute challenge does not exacerbate vulnerability to chronic stress

An adequate stress response plays a vital role in coping with challenges. However, if selection for improved coping with an acute challenge affects the entire stress response system, susceptibility to adverse effects of chronic stressors can be deepened. Here, we used bank voles from lines selected for high swim-induced aerobic metabolism (A) and unselected control (C), and asked if the selection affected sensitivity to chronic mild stress (CMS). The voles were first habituated to daily weighing and feces collection for three weeks, and then for two weeks were exposed to CMS or remained undisturbed. The habituation itself resulted in an increased swim-induced oxygen consumption in both line types, and a decreased body mass. The CMS treatment caused reduction of food consumption in the second week of the experiment, and, in males, a decline in the metabolic rate. Paradoxically, fecal corticosterone metabolites decreased in the CMS-treated group. The response to CMS did not differ between the line types. Thus, the selection for increased performance was not traded off by increased vulnerability to chronic stress. The counter-intuitive results may even lead to a speculation that bank voles—and perhaps also other animals—prefer experiencing unpredictable, unpleasant stressors over the monotony of standard laboratory housing.

The role of pro- and mature neurotrophins in the depression

Neurotrophic factors, which can provide nutritional support to neurons and neuronal cells, also played an important role in their proliferation and survival. As signaling molecules, it also mediated the learning, memory and other activities in the brain. The latest study shows that neurotrophic factors have diametrically opposing effects of the pro- and mature form through distinct receptors. In this review, we summarize the different forms of neurotrophic factors, related receptors, and the corresponding biological effects. More importantly, we expounded the physiology and pathology mechanisms of brain-derived neurotrophic factor(BDNF)in depression. It is hopefully to provide new idea on the relationship of neurotrophic factors and depression.

Cell Type-Specific Methylome-wide Association Studies Implicate Neurotrophin and Innate Immune Signaling in Major Depressive Disorder

BACKGROUND

We sought to characterize methylation changes in brain and blood associated with major depressive disorder (MDD). As analyses of bulk tissue may obscure association signals and hamper the biological interpretation of findings, these changes were studied on a cell type-specific level.

METHODS

In 3 collections of human postmortem brain (n = 206) and 1 collection of blood samples (N = 1132) of MDD cases and controls, we used epigenomic deconvolution to perform cell type-specific methylome-wide association studies within subpopulations of neurons/glia for the brain data and granulocytes/T cells/B cells/monocytes for the blood data. Sorted neurons/glia from a fourth postmortem brain collection (n = 58) were used for validation purposes.

RESULTS

Cell type-specific methylome-wide association studies identified multiple findings in neurons/glia that were detected across brain collections and were reproducible in physically sorted nuclei. Cell type-specific analyses in blood samples identified methylome-wide significant associations in T cells, monocytes, and whole blood that replicated findings from a past methylation study of MDD. Pathway analyses implicated p75 neurotrophin receptor/nerve growth factor signaling and innate immune toll-like receptor signaling in MDD. Top results in neurons, glia, bulk brain, T cells, monocytes, and whole blood were enriched for genes supported by genome-wide association studies for MDD and other psychiatric disorders.

CONCLUSIONS

We both replicated and identified novel MDD-methylation associations in human brain and blood samples at a cell type-specific level. Our results provide mechanistic insights into how the immune system may interact with the brain to affect MDD susceptibility. Importantly, our findings involved associations with MDD in human samples that implicated many closely related biological pathways. These disease-linked sites and pathways represent promising new therapeutic targets for MDD.

Direct and indirect evidences of BDNF and NGF as key modulators in depression: role of antidepressants treatment

PURPOSE

Depression is one of the most prevalent, recurrent and life-threatening mental illnesses. However, the precise mechanism underlying the disorder is not yet clearly understood. It is therefore, essential to identify the novel biomarkers which may help in the development of effective treatment.

METHODS

In this milieu, the profile of the brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) were considered as biomarkers in the light of pathophysiology of depression and its treatment.

RESULTS

Previously, we have reported that BDNF level in the postmortem brain of suicide victims was significantly lower than those of normal controls. We also found decreased BDNF levels in the specific brain regions of the learned helplessness model of depression in rat, and was found to increase normal level following chronic fluoxetine hydrochloride treatment. NGF is another important member of neurotrophin, which is dysregulated in the pathophysiology of depression in some models of peripheral nerve damage and stress. The results shown evidences of the effect of antidepressants on modulating depression via the NGF in preclinical and clinical models of depression, but conflicted, therefore make it currently difficult to affirm the therapeutic role of antidepressants.

CONCLUSIONS

Here, we review some of the preclinical and clinical studies aimed at disclosing the role of BDNF and NGF mediated pathophysiological mechanisms of depression and the new therapeutic approaches targeting those key molecules. In addition, an important link between BDNF, NGF and depression has been discussed in the light of current existing knowledge.

The reduced level of growth factors in an animal model of depression is accompanied by regulated necrosis in the frontal cortex but not in the hippocampus

In the present study, we asked if the different types of stress alter neuronal plasticity markers distinctively in the frontal cortex (FCx) and in the hippocampus (Hp). To do so, we implemented various stress regimens to analyze changes evoked in these rat brain structures. We utilized several molecular techniques, including western blot, ELISA, quantitative RT-PCR, and various biochemical assays, to examine a range of proteins and subjected rats to behavioral tests to evaluate potential maladaptive alterations. A decrease in the level of growth factors in the FCx was accompanied by changes suggesting damage of this structure in the manner of regulated necrosis, while the Hp appeared to be protected. The observed changes in the brain region-specific alterations in neurotrophin processing may also depend on the period of life, in which an animal experiences stress and the duration of the stressful stimuli. We conclude that chronic stress during pregnancy can result in serious alterations in the functioning of the FCx of the progeny, facilitating the development of depressive behavior later in life. We also suggest that the altered energy metabolism may redirect pro-NGF/p75^NTR/ATF2 signaling in the cortical neurons towards cellular death resembling regulated necrosis, rather than apoptosis.

Effects and mechanisms of matrix metalloproteinase2 on neural differentiation of induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) possess the potential to differentiate into neural lineage cells. Matrix metalloproteinase 2 (MMP2), an endopeptidase in the extracellular matrix, has been shown to protect neural cells from injury. However, the mechanisms and effects of MMP2 on neural differentiation of iPSCs remain poorly understood. Here, we demonstrated a role for MMP2 in the differentiation of iPSCs to neurons via the AKT pathway. Treatment of iPSCs with MMP2 promoted their proliferation and differentiation into neural stem cells (NSCs), and then into neurons. The transcript and protein expression of Nestin and microtubule-associated protein 2 (MAP2) increased. Moreover, MMP2 markedly induced the expression of phospho-AKT (pAKT) during these differentiation stages. Consistently, silencing MMP2 using siRNA attenuated the expression of Nestin, MAP2 and pAKT, compared with the control group. In addition, the increasing levels of Nestin, MAP2 and pAKT in the MMP2 group were declined by pretreatment with the phosphoinositide 3-kinase (PI3K)/AKT inhibitor, LY294002. Furthermore, the study detected that TrkA and TrkB were perhaps the potential receptors for these effects of MMP2 on neural differentiation through PI3K/AKT signaling pathway. Taken together, these results suggest that MMP2 induces the differentiation of iPSCs into neurons by regulating the AKT signaling pathway.