Exercise rather than fluoxetine promotes oligodendrocyte differentiation and myelination in the hippocampus in a male mouse model of depression

Treadmill Training-Induced Remyelination Rescues Cognitive Impairment After Acute Hypoxia

Acute and chronic exposure to high altitude causes multiple negative neurological consequences. Further research has shown the efficacy of targeted drugs after acute hypoxia. However, the effects and mechanisms of physical therapy like exercise, on after exposed-induced myelin repair and functional improvements have remained unclear. Here, we explored the efficacy of treadmill training at different intensities on recovery in a rat model of acute hypobaric hypoxia (HH) injury. A 4-week treadmill training scheme was used at 30%, 50%, and 70% of maximum speed. The evolution of oligodendrocyte morphometry was observed by immunofluorescence, and the expressions of myelin-related proteins were detected by western blotting. Transmission electron microscopy (TEM) is used to study fine myelin structure. In addition, the open field test (OFT), elevated plus maze (EPM) and Morris water maze (MWM) were used for the observation of cognitive function recovery. Our study revealed varying degrees of demyelination changes in the cortex and hippocampus following acute hypoxia exposure. Additionally, high-intensity treadmill training enhances oligodendrocyte (OL) maturation, improves myelin-related proteins, and increases myelin sheath thickness, thus facilitating myelin repair, rescuing cognitive function and mood disorders, and preserving normal nerve conduction. Finally, the upregulation of peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1α) and key enzymes of cholesterol synthesis (HMGCR/FDPS) induced by high-intensity treadmill training was detected. Our results demonstrate that high-intensity treadmill training as a physical therapy via PGC1α and cholesterol synthesis enhances myelin repair and functional restoration, which should provide new insight for the rehabilitation of remyelination by exercise.

Exercise alleviates CUS-induced depressive-like behaviors by modulating paracellular and transcellular permeability of the blood-brain barrier in the prefrontal cortex

BACKGROUND

Increased blood-brain barrier (BBB) permeability is implicated in the pathophysiology of major depressive disorder (MDD). While aerobic exercise has shown promise in mitigating MDD symptoms by potentially preserving BBB integrity, the detailed mechanisms remain unclear. This study explores these mechanisms to assess aerobic exercise's therapeutic potential for MDD.

METHODS

Male C57BL/6 J mice were used in this study to investigate the effects of aerobic exercise on CUS-induced BBB permeability and depressive-like behaviors. Chronic unpredictable stress (CUS)-induced MDD mouse models were divided into three groups: Control, CUS, and CUS+Exercise. We monitored body weight, blood S100β levels, and cytokines via ELISA. Claudin-5 and Caveolin-1 (CAV-1) expressions in the medial prefrontal cortex were evaluated using Western blotting and immunofluorescence. BBB permeability was assessed using biocytin-TMR and Alb-Alexa 594 tracers. Transmission electron microscopy was used to observe ultrastructural changes in the BBB directly. Depression-related behaviors were tested through several behavioral assays.

RESULTS

CUS significantly increased CAV-1 expression and Alb-Alexa 594 leakage, suggesting enhanced transcellular BBB permeability. Despite unchanged Claudin-5 levels, its tight junction ultrastructure was altered, leading to increased biocytin-TMR leakage. Aerobic exercise ameliorated these disruptions, reduced inflammatory cytokines, and improved behavioral outcomes in CUS mice.

CONCLUSION

Disruptions in both paracellular and transcellular BBB pathways are pivotal in depression development. Aerobic exercise offers potential therapeutic benefits for MDD linked with BBB dysfunction by mitigating stress-induced structural and functional changes.

NADPH mimics the antidepressant effects of exercise in a chronic unpredictable stress rat model

Exercise is known to be an effective intervention for depression. NADPH has been demonstrated to have neuroprotective effects in our previous studies. This study aimed to investigate if NADPH has antidepressant effects and can mimic the effects of exercise in a chronic unpredictable stress (CUS) rat model. CUS rats underwent an 8-week swimming exercise (30 min/d, 5d/w) or were intraperitoneally administered 4 mg/kg or 8 mg/kg NADPH. The open field test (OFT), sucrose preference test (SPT), novelty-suppressed feeding test (NSFT), and forced swimming test (FST) were used to examine the antidepressant-like behaviors of the rats. Exercise, 4 mg/kg, and 8 mg/kg NADPH similarly reduced anxiety, as demonstrated by the number of fecal pellets. Meanwhile, exercise and 8 mg/kg NADPH significantly increased locomotion activity in the OFT. Exercise, 4 mg/kg, and 8 mg/kg NADPH effectively reversed CUS-induced anhedonia in rats in the SPT. Exercise, 4 mg/kg, and 8 mg/kg NADPH had no impact on appetite of depressed rats; however, 8 mg/kg NADPH increased the rats' exploratory activity in the NSFT. Exercise, 4 mg/kg, and 8 mg/kg NADPH significantly reduced the immobility time of CUS model rats, while exercise and 8 mg/kg NADPH postponed the early CUS-induced "immobility" in the FST. These results demonstrated that NADPH has similar antidepressant-like effects to exercise in CUS-induced depression model rats and is a potential exercise-mimicking antidepressant.

Running exercise alleviates hippocampal neuroinflammation and shifts the balance of microglial M1/M2 polarization through adiponectin/AdipoR1 pathway activation in mice exposed to chronic unpredictable stress

Running exercise has been shown to alleviate depressive symptoms. However, the mechanism underlying the antidepressant effects of running exercise is not fully understood. The imbalance of M1/M2 microglia phenotype/polarization and concomitant dysregulation of neuroinflammation play crucial roles in the pathogenesis of depression. Running exercise increases circulating levels of adiponectin which is known to cross the blood‒brain barrier and suppress inflammatory responses. AdipoR1 is an adiponectin receptor that is involved in regulating microglial phenotypes and activation states. However, whether running exercise regulates hippocampal microglial phenotypes and neuroinflammation through adiponectin/AdipoR1 to exert its antidepressant effects remains unclear. In the current study, 4 weeks of running exercise significantly alleviated the depressive-like behaviors of chronic unpredictable stress (CUS)-exposed mice. Moreover, running exercise decreased the microglial numbers and altered microglial morphology in three subregions of the hippocampus to restore the M1/M2 balance; these effects were accompanied by regulation of pro-/anti-inflammatory cytokine production and secretion in CUS-exposed mice. These effects may involve elevation of peripheral tissue (adipose tissue and muscle) and plasma adiponectin levels, and hippocampal AdipoR1 levels as well as activation of the AMPK-NF-κB/STAT3 signaling pathway by running exercise. When an adeno-associated virus was used to knock down hippocampal AdipoR1, mice showed depressive-like behaviors and alterations in microglia and inflammatory factor expression in the hippocampus that were similar to those observed in CUS-exposed mice. Together, these results suggest that running exercise maintains the M1/M2 balance and inhibits neuroinflammation in the hippocampus of CUS-exposed mice. These effects might occur via adiponectin/AdipoR1-mediated activation of the AMPK-NF-κB/STAT3 signaling pathway.

Running exercise improves astrocyte loss, morphological complexity and astrocyte-contacted synapses in the hippocampus of CUS-induced depression model mice

Although the antidepressant effects of running exercise have been widely reported, further research is still needed to determine the structural bases for these effects. Astrocyte processes physically contact many synapses and directly regulate the numbers of synapses, but it remains unclear whether running exercise can modulate astrocyte morphological complexity and astrocyte-contacted synapses in the hippocampus of the mice with depressive-like behavior. Male C57BL/6 J mice underwent four weeks of running exercise after four weeks of chronic unpredictable stress (CUS). The sucrose preference test (SPT), tail suspension test (TST) and forced swim test (FST) were used to assess anhedonia in mice. Western blotting was used to measure the expression of astrocyte- and synapse-related proteins. Immunofluorescence and 3D reconstruction were used to quantify the density and morphology of astrocytes, and astrocyte-contacted synapses in each hippocampal subregion. Four weeks of running exercise alleviated depressive-like symptoms in mice. The expression of astrocyte- and synapse-related proteins in the hippocampus; astrocyte process lengths, process numbers, and dendritic arborization; and the number of astrocyte-contacted PSD95 positive synapses in the CA2-3 and DG regions were significantly decreased in the mice with depressive-like behavior, and running exercise successfully reserved these changes. Running exercise improved the decreases in astrocyte morphological complexity and astrocyte-contacted PSD95 positive synapses in the CA2-3 and DG regions of the mice with depressive-like behavior, suggesting that the physical interactions between astrocytes and synapses can be increased by running exercise, which might be an important structural basis for the antidepressant effects of running exercise.

Antidepressant effect of teriflunomide via oligodendrocyte protection in a mouse model

Addressing the treatment of depression is crucial; nevertheless, the etiology and pathogenesis remain unelucidated. Therefore, this study investigated the effects of teriflunomide (TF) on corticosterone (CORT)-induced depression-like behaviors in mice. Notably, TF administration resulted in a substantial amelioration of anxiety and depression-like behaviors observed in CORT-treated mice. This was evidenced by behavioral assessments conducted via the sucrose preference test (SPT), open-field test (OFT), novelty-suppressed feeding test (NSFT), forced swimming test (FST), and tail suspension test (TST). The administration of CORT inflicts damage upon oligodendrocytes and neurons within the hippocampus. Our findings indicate that TF offers significant protective effects on oligodendrocytes, mitigating apoptosis both invivo and invitro. Additionally, TF was found to counteract the CORT-induced neuronal loss and synaptic damage, as demonstrated by an increase in Nissl-positive cells across hippocampal regions CA1, CA3, and the dentate gyrus (DG) alongside elevated levels of synapse-related proteins including PSD-95 and synaptophysin. Additionally, TF treatment facilitated a reduction in the levels of apoptosis-related proteins while simultaneously augmenting the levels of Bcl2. Our findings indicate that TF administration effectively mitigates CORT-induced depression-like behaviors and reverses damage to oligodendrocytes and neurons in the hippocampus, suggesting TF as a promising candidate for depression.

Agomelatine prevented depression in the chronic restraint stress model through enhanced catalase activity and halted oxidative stress

BACKGROUND

Agomelatine (AGO) is an antidepressant with unique pharmacological effects; however, its underlying mechanisms remain unknown. In this study, we examined agomelatine's effects on catalase activity, oxidative stress, and inflammation.

METHODS

Chronic restraint stress (CRS) model mice were established over 4 weeks, and AGO 50 mg/kg was administered to different groups alongside a deferasirox (DFX) 10 mg/kg gavage treatment. Behavioral tests were performed to assess the effect of AGO on the remission of depression-like behaviors. Meanwhile, the expression of CAT, the oxidative stress signaling pathway and inflammatory protein markers were assessed using ELISA, qRT-PCR, Western blot, and immunohistochemistry.

RESULTS

Four weeks of AGO treatment significantly improved depression-like behavior in mice through the activation of catalase in the hippocampus and serum of the model mice, increased superoxide dismutase expression, reduced malondialdehyde expression, and reduced oxidative stress damage. Deferasirox was found to offset this therapeutic effect partially. In addition, the inflammatory pathway (including nuclear factor-κB and nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor, alpha) was not significantly altered.

CONCLUSIONS

AGO can exert antidepressant effects by altering oxidative stress by modulating catalase activity.

Digital Therapeutics for Improving Effectiveness of Pharmaceutical Drugs and Biological Products: Preclinical and Clinical Studies Supporting Development of Drug + Digital Combination Therapies for Chronic Diseases

Limitations of pharmaceutical drugs and biologics for chronic diseases (e.g., medication non-adherence, adverse effects, toxicity, or inadequate efficacy) can be mitigated by mobile medical apps, known as digital therapeutics (DTx). Authorization of adjunct DTx by the US Food and Drug Administration and draft guidelines on "prescription drug use-related software" illustrate opportunities to create drug + digital combination therapies, ultimately leading towards drug-device combination products (DTx has a status of medical devices). Digital interventions (mobile, web-based, virtual reality, and video game applications) demonstrate clinically meaningful benefits for people living with Alzheimer's disease, dementia, rheumatoid arthritis, cancer, chronic pain, epilepsy, depression, and anxiety. In the respective animal disease models, preclinical studies on environmental enrichment and other non-pharmacological modalities (physical activity, social interactions, learning, and music) as surrogates for DTx "active ingredients" also show improved outcomes. In this narrative review, we discuss how drug + digital combination therapies can impact translational research, drug discovery and development, generic drug repurposing, and gene therapies. Market-driven incentives to create drug-device combination products are illustrated by Humira® (adalimumab) facing a "patent-cliff" competition with cheaper and more effective biosimilars seamlessly integrated with DTx. In conclusion, pharma and biotech companies, patients, and healthcare professionals will benefit from accelerating integration of digital interventions with pharmacotherapies.

Circadian misalignment impairs oligodendrocyte myelination via Bmal1 overexpression leading to anxiety and depression-like behaviors

Circadian misalignment (CM) caused by shift work can increase the risk of mood impairment. However, the pathological mechanisms underlying these deficits remain unclear. In the present study, we used long-term variable photoperiod (L-VP) in wild-type mice to better simulate real-life shift patterns and study its effects on the prefrontal cortex (PFC) and hippocampus, which are closely related to mood function. The results showed that exposure to L-VP altered the activity/rest rhythms of mice, by eliciting phase delay and decreased amplitude of the rhythms. Mice with CM developed anxiety and depression-like manifestations and the number of mature oligodendrocytes (OL) was reduced in the medial prefrontal cortex and hippocampal CA1 regions. Mood impairment and OL reduction worsened with increased exposure time to L-VP, while normal photoperiod restoration had no effect. Mechanistically, we identified upregulation of Bmal1 in the PFC and hippocampal regions of CM mice at night, when genes related to mature OL and myelination should be highly expressed. CM mice exhibited significant inhibition of the protein kinase B (AKT)/mTOR signaling pathway, which is directly associated to OL differentiation and maturation. Furthermore, we demonstrated in the OL precursor cell line Oli-Neu that overexpression of Bmal1 inhibits AKT/mTOR pathway and reduces the expression of genes OL differentiation. In conclusion, BMAL1 might play a critical role in CM, providing strong research evidence for BMAL1 as a potential target for CM therapy.

MPFC PV+ interneurons are involved in the antidepressant effects of running exercise but not fluoxetine therapy

Depression is a complex psychiatric disorder. Previous studies have shown that running exercise reverses depression-like behavior faster and more effectively than fluoxetine therapy. GABAergic interneurons, including the PV⁺ interneuron subtype, in the medial prefrontal cortex (MPFC) are involved in pathological changes of depression. It was unknown whether running exercise and fluoxetine therapy reverse depression-like behavior via GABAergic interneurons or the PV⁺ interneurons subtype in MPFC. To address this issue, we subjected mice with chronic unpredictable stress (CUS) to a 4-week running exercise or fluoxetine therapy. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that running exercise enriched GABAergic synaptic pathways in the MPFC of CUS-exposed mice. However, the number of PV⁺ interneurons but not the total number of GABAergic interneurons in the MPFC of mice exposed to CUS reversed by running exercise, not fluoxetine therapy. Running exercise increased the relative gene expression levels of the PV gene in the MPFC of CUS-exposed mice without altering other subtypes of GABAergic interneurons. Moreover, running exercise and fluoxetine therapy both significantly improved the length, area and volume of dendrites and the spine morphology of PV⁺ interneurons in the MPFC of mice exposed to CUS. However, running exercise but not fluoxetine therapy improved the dendritic complexity level of PV⁺ interneurons in the MPFC of mice exposed to CUS. In summary, the number and dendritic complexity level of PV⁺ interneurons may be important therapeutic targets for the mechanism by which running exercise reverses depression-like behavior faster and more effectively than fluoxetine therapy.

Repetitive transcranial magnetic stimulation and fluoxetine reverse depressive-like behavior but with differential effects on Olig2-positive cells in chronically stressed mice

Depression is a mood disorder coursing with several behavioral, cellular, and neurochemical alterations. The negative impact of chronic stress may precipitate this neuropsychiatric disorder. Interestingly, downregulation of oligodendrocyte-related genes, abnormal myelin structure, and reduced numbers and density of oligodendrocytes in the limbic system have been identified in patients diagnosed with depression, but also in rodents exposed to chronic mild stress (CMS). Several reports have emphasized the importance of pharmacological or stimulation-related strategies in influencing oligodendrocytes in the hippocampal neurogenic niche. Repetitive transcranial magnetic stimulation (rTMS) has gained attention as an intervention to revert depression. Here, we hypothesized that 5 Hz (Hz) of rTMS or Fluoxetine (Flx) would revert depressive-like behaviors by influencing oligodendrocytes and revert neurogenic alterations caused by CMS in female Swiss Webster mice. Our results showed that 5 Hz rTMS or Flx revert depressive-like behavior. Only rTMS influenced oligodendrocytes by increasing the number of Olig2-positive cells in the hilus of the dentate gyrus and the prefrontal cortex. However, both strategies exerted effects on some events of the hippocampal neurogenic processes, such as cell proliferation (Ki67-positive cells), survival (CldU-positive cells), and intermediate stages (doublecortin-positive cells) along the dorsal-ventral axis of this region. Interestingly, the combination of rTMS-Flx exerted antidepressant-like effects, but the increased number of Olig2-positive cells observed in mice treated only with rTMS was canceled. However, rTMS-Flx exerted a synergistic effect by increasing the number of Ki67-positive cells. It also increased the number of CldU- and doublecortin-positive cells in the dentate gyrus. Our results demonstrate that 5 Hz rTMS has beneficial effects, as it reverted depressive-like behavior by increasing the number of Olig2-positive cells and reverting the decrement in hippocampal neurogenesis in CMS-exposed mice. Nevertheless, the effects of rTMS on other glial cells require further investigation.

Physical exercise mediates a cortical FMRP-mTOR pathway to improve resilience against chronic stress in adolescent mice

Aerobic exercise effectively relieves anxiety disorders via modulating neurogenesis and neural activity. The molecular mechanism of exercise-mediated anxiolysis, however, remains incomplete. On a chronic restrain stress (CRS) model in adolescent mice, we showed that 14-day treadmill exercise profoundly maintained normal neural activity and axonal myelination in the medial prefrontal cortex (mPFC), in association with the prevention of anxiety-like behaviors. Further interrogation of molecular mechanisms revealed the activation of the mechanistic target of the rapamycin (mTOR) pathway within mPFC under exercise training. At the upstream of mTOR, exercise-mediated brain RNA methylation inhibited the expression of Fragile X mental retardation protein (FMRP) to activate the mTOR pathway. In summary, treadmill exercise modulates an FMRP-mTOR pathway to maintain cortical neural activity and axonal myelination, contributing to improved stress resilience. These results extended our understanding of the molecular substrate of exercise-mediated anxiolytic effect during adolescent period.

Activation of liver X receptors protects oligodendrocytes in CA3 of stress-induced mice

Depression is a complex disorder that is associated with various structural abnormalities. Oligodendrocyte (OL) dysfunction is associated with the pathogenesis of depression and the promotion of hippocampal oligodendrocyte maturation and myelination could be a novel therapeutic strategy for ameliorating depressive behaviors. Recent studies have shown that activation of liver X receptors (LXRs) by GW3965 improves depressive phenotypes, but the effects of GW3965 on OL function and myelination in the hippocampus of depression remain relatively unclear. To address this issue, we investigated the effects of GW3965 on mature OL in the hippocampus and on the myelin sheaths of mice subjected to chronic unpredictable stress (CUS). Behavioral tests were performed to assess depressive behaviors. Then, the number of mature OLs (CC1⁺) in each hippocampal subregion was precisely quantified with immunohistochemical and stereological methods, and the density of newborn mature OLs (BrdU⁺/Olig2⁺/CC1⁺ cells) in each hippocampal subregion was quantified with immunofluorescence. In addition, myelin basic protein (MBP) staining intensity in the cornu ammonis 3 (CA3) region was assessed by using immunofluorescence. We found that both the number of CC1⁺ OLs and the density of BrdU⁺/Olig2⁺/CC1⁺ cells were obviously decreased in each hippocampal subregion of mice subjected to CUS, and 4 weeks of GW3965 treatment reversed these effects only in the CA3 region. Furthermore, the decreased MBP expression in the CA3 region of mice subjected to CUS was ameliorated by GW3965 treatment. Collectively, these results suggested that improvement of OL maturation and enhancement of myelination may be structural mechanisms underlying the antidepressant effects of LXR agonists.

A translational mouse model for investigation of the mechanism of preterm diffuse white matter injury

BACKGROUND

The increasing incidence of preterm birth has led to a global problem of adverse neurodevelopmental outcomes in preterm neonates as a result of brain injury. There is still a lack of models mimicking diffuse white matter injury (WMI) in preterm neonates that can be applied to transgenic mice.

METHODS

The right common carotid artery of the neonatal mouse was ligated on postnatal day 3 (P3) C57BL/6 mice and followed by 80, 90, or 100 min of hypoxia using a mixture of 10%±0.2% oxygen-nitrogen. The most suitable model was chosen by characterizing the effects of this hypoxic-ischemic insult on development of myelin, glial cell conditions, and neurological outcomes by hematoxylin-eosin (HE) staining performed at postnatal day 17 (P17), western blot measuring myelin basic protein (MBP) at postnatal day 10 (P10) and P17, immunofluorescence staining of MBP-neurofilament protein heavy chain (NFH), oligodendrocyte transcription factor-2 (Olig2)-adenomatous polyposis coli clone (CC1), glial fibrillary acidic protein (GFAP) and ionic calcium linker protein (Iba-1) at P17, electron microscopy observing myelin microstructure at postnatal day 52 (P52) and behavioral testing at postnatal day 45-50 (P45-P50).

RESULTS

The 90-min group showed neuroanatomical changes in the ipsilateral side of the brain, the 80-min group showed minor changes, and the 100-min group showed severe injury. Mice in the 90-min group subsequently showed marked activation of astrocytes, augmentation of microglia, a notable decrease in expression of MBP with a normal level of NFH, long-term cognitive dysfunction, and impairment of the myelin ultrastructure in adulthood.

CONCLUSIONS

In conclusion, a mouse model of preterm diffuse WMI rather than cystic periventricular leukomalacia was successfully achieved by ligating one of the common carotid arteries on P3 followed by 90 min of hypoxia in a mixture of 10%±0.2% oxygen-nitrogen. The attempt provides an adequate translational animal model for elucidating the underlying mechanism.

The Relevance of Circadian Clocks to Stem Cell Differentiation and Cancer Progression

The molecular mechanism of circadian clocks depends on transcription-translation feedback loops (TTFLs) that have known effects on key cellular processes. However, the distinct role of circadian TTFLs in mammalian stem cells and other less differentiated cells remains poorly understood. Neural stem cells (NSCs) of the brain generate neurons and glia postnatally but also may become cancer stem cells (CSCs), particularly in astrocytomas. Evidence indicates clock TTFL impairment is needed for tumor growth and progression; although, this issue has been examined primarily in more differentiated cancer cells rather than CSCs. Similarly, few studies have examined circadian rhythms in NSCs. After decades of research, it is now well recognized that tumors consist of CSCs and a range of other cancer cells along with noncancerous stromal cells. The circadian properties of these many contributors to tumor properties and treatment outcome are being widely explored. New molecular tools and ones in development will likely enable greater discrimination of important circadian and non-circadian cells within malignancies at multiple stages of cancer progression and following therapy. Here, we focus on adult NSCs and glioma CSCs to address how cells at different stages of differentiation may harbor unique states of the molecular circadian clock influencing differentiation and cell fate.

Rapid treatments for depression: Endocannabinoid system as a therapeutic target

Current first-line treatments for major depressive disorder (MDD), i.e., antidepressant drugs and psychotherapy, show delayed onset of therapeutic effect as late as 2-3 weeks or more. In the clinic, the speed of beginning of the actions of antidepressant drugs or other interventions is vital for many reasons. Late-onset means that depression, its related disability, and the potential danger of suicide remain a threat for some patients. There are some rapid-acting antidepressant interventions, such as sleep deprivation, ketamine, acute exercise, which induce a significant response, ranging from a few hours to maximally one week, and most of them share a common characteristic that is the activation of the endocannabinoid (eCB) system. Activation of this system, i.e., augmentation of eCB signaling, appears to have anti-depressant-like actions. This article puts the idea forward that the activation of eCB signaling represents a critical mechanism of rapid-acting therapeutic interventions in MDD, and this system might contribute to the development of novel rapid-acting treatments for MDD.