Chronic stress hinders sensory axon regeneration via impairing mitochondrial cristae and OXPHOS

Peripheral mitochondrial DNA as a neuroinflammatory biomarker for major depressive disorder

In the pathogenesis of major depressive disorder, chronic stress-related neuroinflammation hinders favorable prognosis and antidepressant response. Mitochondrial DNA may be an inflammatory trigger, after its release from stress-induced dysfunctional central nervous system mitochondria into peripheral circulation. This evidence supports the potential use of peripheral mitochondrial DNA as a neuroinflammatory biomarker for the diagnosis and treatment of major depressive disorder. Herein, we critically review the neuroinflammation theory in major depressive disorder, providing compelling evidence that mitochondrial DNA release acts as a critical biological substrate, and that it constitutes the neuroinflammatory disease pathway. After its release, mitochondrial DNA can be carried in the exosomes and transported to extracellular spaces in the central nervous system and peripheral circulation. Detectable exosomes render encaged mitochondrial DNA relatively stable. This mitochondrial DNA in peripheral circulation can thus be directly detected in clinical practice. These characteristics illustrate the potential for mitochondrial DNA to serve as an innovative clinical biomarker and molecular treatment target for major depressive disorder. This review also highlights the future potential value of clinical applications combining mitochondrial DNA with a panel of other biomarkers, to improve diagnostic precision in major depressive disorder.

Electrical stimulation promotes peripheral nerve regeneration by upregulating glycolysis and oxidative phosphorylation

Peripheral nerve injury (PNI) frequently results in motor and sensory dysfunction due to the limited regenerative capacity of axonal neurons and Schwann cells. Electrical stimulation (ES) has emerged as a promising strategy to enhance nerve regeneration; however, the underlying mechanisms, particularly those related to energy metabolism, remain poorly understood. This study aimed to investigate whether ES could promote nerve regeneration in a mouse model of PNI by modulating energy metabolism. ES was applied to the gastrocnemius and posterior thigh muscles post-sciatic nerve injury. Motor functional recovery was evaluated using gait analysis and electrophysiological test. Molecular and cellular changes in the distal nerve stumps were evaluated through Western blot and immunofluorescence staining. Nerve regeneration was assessed by neurostructural protein staining and nerve ultrastructure visualized by transmission electron microscopy. Our findings indicate that ES significantly accelerated both morphological and functional recovery following PNI. Specifically, ES upregulated energy metabolism in the sciatic nerve post-PNI by enhancing glucose uptake, glycolysis, and oxidative phosphorylation. Furthermore, ES increased the expression of neurotrophic factors and modulated the AMPK/mTOR/p70S6K signaling pathway, which are crucial for cellular metabolism and nerve regeneration. Collectively, these findings underscore the critical role of ES in modulating energy metabolism to support nerve regeneration, highlighting its potential as a clinical strategy for treating peripheral neuropathy.

Transcriptomics of Various Diseases Reveals the Core Role of Immune System Pathways in Retinal Damage Repair and Nerve Regeneration

Retinal ganglion cells (RGCs) are the only neuronal bridges connecting retinal inputs to the brain's visual processing centers, enabling visual perception. The axon of RGCs forms the optic nerve, which transmits visual information to the visual cortex. Damage to RGCs and their axons results in irreversible visual impairment. Acute retinal damage is commonly induced by conditions such as optic nerve compression, glaucoma, and optic neuritis, for which effective clinical treatments are currently unavailable. Therefore, understanding the response of RGCs and their axons to injury is crucial for the development of potential treatments. This study utilizes multiple models including optic nerve crush (ONC), acute intraocular pressure (IOP) elevation, and local lipopolysaccharide (LPS) injection into the optic nerve to mimic eye diseases. Three days post-surgery, mice underwent retinal isolation followed by bulk-RNA sequencing to analyze differential gene expression among models. Using thresholds of |Log2 fold change (FC)|> 2 and p-value < 0.05, the significant gene expression changes observed in each model were as follows: ONC (upregulated, 456; downregulated, 84), IOP (upregulated, 1946; downregulated, 655), and LPS (upregulated, 219; downregulated, 94). Gene ontology (GO) analysis of the upregulated genes unexpectedly revealed that immune system pathways were the primary shared targets across all three models. In contrast, the downregulated genes exhibited model-specific enrichment: synaptic components and functions in IOP, neurogenesis and neuronal development in ONC, and inflammation and antioxidant in LPS. These findings were further confirmed by Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. This suggests that managing immune activation is essential for treating acute retinal injury, and therapeutic strategies should address model-specific targets as well. Notably, 39 genes intersected across the models, and the protein-protein interaction (PPI) network identified Ccl5 as a key hub gene, underscoring its critical role in the pathophysiology of all three diseases.

Carmiseconapine A as a Promising Antidepressant Candidate: An Adenosine 5'-Monophosphate-Activated Protein Kinase Agonist with an Unprecedented Chemical Skeleton

A novel rearranged C20-diterpenoid alkaloid, carmiseconapline A (1), featuring a unique 10,20:11,12-di-seco-napelline skeleton with a fused 5/6/5/6/7 pentacyclic ring system, was isolated from Aconitum carmichaelii Debeaux. Compound 1 exhibited remarkable antidepressive activity, being twice as potent as fluoxetine (10 mg/kg) at 0.06 mg/kg in mice. Further mechanism studies showed that 1 effectively activated adenosine 5'-monophosphate-activated protein kinase (AMPK), protected HT22 cells from mitochondrial dysfunction, and inhibited apoptosis. These findings suggested 1 as a potential AMPK activator for antidepressant development.

Corticosterone effects induced by stress and immunity and inflammation: mechanisms of communication

The body instinctively responds to external stimuli by increasing energy metabolism and initiating immune responses upon receiving stress signals. Corticosterone (CORT), a glucocorticoid (GC) that regulates secretion along the hypothalamic-pituitary-adrenal (HPA) axis, mediates neurotransmission and humoral regulation. Due to the widespread expression of glucocorticoid receptors (GR), the effects of CORT are almost ubiquitous in various tissue cells. Therefore, on the one hand, CORT is a molecular signal that activates the body's immune system during stress and on the other hand, due to the chemical properties of GCs, the anti-inflammatory properties of CORT act as stabilizers to control the body's response to stress. Inflammation is a manifestation of immune activation. CORT plays dual roles in this process by both promoting inflammation and exerting anti-inflammatory effects in immune regulation. As a stress hormone, CORT levels fluctuate with the degree and duration of stress, determining its effects and the immune changes it induces. The immune system is essential for the body to resist diseases and maintain homeostasis, with immune imbalance being a key factor in the development of various diseases. Therefore, understanding the role of CORT and its mechanisms of action on immunity is crucial. This review addresses this important issue and summarizes the interactions between CORT and the immune system.

Extracellular vesicles lay the ground for neuronal plasticity by restoring mitochondrial function, cell metabolism and immune balance

Extracellular vesicles (EVs) convey complex signals between cells that can be used to promote neuronal plasticity and neurological recovery in brain disease models. These EV signals are multimodal and context-dependent, making them unique therapeutic principles. This review analyzes how EVs released from various cell sources control neuronal metabolic function, neuronal survival and plasticity. Preferential sites of EV communication in the brain are interfaces between pre- and postsynaptic neurons at synapses, between astrocytes and neurons at plasma membranes or tripartite synapses, between oligodendrocytes and neurons at axons, between microglial cells/macrophages and neurons, and between cerebral microvascular cells and neurons. At each of these interfaces, EVs support mitochondrial function and cell metabolism under physiological conditions and orchestrate neuronal survival and plasticity in response to brain injury. In the injured brain, the promotion of neuronal survival and plasticity by EVs is tightly linked with EV actions on mitochondrial function, cell metabolism, oxidative stress and immune responses. Via the stabilization of cell metabolism and immune balance, neuronal plasticity responses are activated and functional neurological recovery is induced. As such, EV lay the ground for neuronal plasticity.

Glucose metabolism impairment in major depressive disorder

Major depressive disorder (MDD) is a common mental disorder with chronic tendencies that seriously affect regular work, life, and study. However, its exact pathogenesis remains unclear. Patients with MDD experience systemic and localized impairments in glucose metabolism throughout the disease course, disrupting various processes such as glucose uptake, glycoprotein transport, glycolysis, the tricarboxylic acid cycle (TCA), and oxidative phosphorylation (OXPHOS). These impairments may result from mechanisms including insulin resistance, hyperglycemia-induced damage, oxidative stress, astrocyte abnormalities, and mitochondrial dysfunction, leading to insufficient energy supply, altered synaptic plasticity, neuronal cell death, and functional and structural damage to reward networks. These mechanical changes contribute to the pathogenesis of MDD and severely interfere with the prognosis. Herein, we summarized the impairment of glucose metabolism and its pathophysiological mechanisms in patients with MDD. In addition, we briefly discussed potential pharmacological interventions for glucose metabolism to alleviate MDD, including glucagon-like peptide-1 receptor agonists, metformin, topical insulin, liraglutide, and pioglitazone, to encourage the development of new therapeutics.

Reversing Persistent PTEN Activation after Traumatic Brain Injury Fuels Long-Term Axonal Regeneration via Akt/mTORC1 Signaling Cascade

Traumatic brain injury (TBI) often leads to enduring axonal damage and persistent neurological deficits. While PTEN's role in neuronal growth is recognized, its long-term activation changes post-TBI and its effects on sensory-motor circuits are not well understood. Here, it is demonstrated that the neuronal knockout of PTEN (PTEN-nKO) significantly enhances both structural and functional recovery over the long term after TBI. Importantly, in vivo, DTI-MRI revealed that PTEN-nKO promotes white matter repair post-TBI. Additionally, calcium imaging and electromyographic recordings indicated that PTEN-nKO facilitates cortical remapping and restores sensory-motor pathways. Mechanistically, PTEN negatively regulates the Akt/mTOR pathway by inhibiting Akt, thereby suppressing mTOR. Raptor is a key component of mTORC1 and its suppression impedes axonal regeneration. The restoration of white matter integrity and the improvements in neural function observed in PTEN-nKO TBI-treated mice are reversed by a PTEN/Raptor double knockout (PTEN/Raptor D-nKO), suggesting that mTORC1 acts as a key mediator. These findings highlight persistent alterations in the PTEN/Akt/mTORC1 axis are critical for neural circuit remodeling and cortical remapping post-TBI, offering new insights into TBI pathophysiology and potential therapeutic targets.

Preclinical Insights into the Role of Kir4.1 in Chronic Pain and Depression: Mechanisms and Therapeutic Potential

Chronic pain and mental health disorders, such as depression and anxiety, frequently co-occur and share underlying mechanisms involving neuronal excitability and synaptic transmission. The inwardly rectifying potassium channel 4.1 (Kir4.1), predominantly expressed in glial cells, is crucial for maintaining extracellular potassium and glutamate homeostasis. Dysregulation of Kir4.1 leads to altered neuronal activity, contributing to both chronic pain and mental health disorders. In chronic pain, downregulation of Kir4.1 impairs potassium buffering and glutamate clearance, increasing neuronal excitability and enhancing pain signaling through peripheral and central sensitization. In mental health disorders, impaired Kir4.1 function disrupts neurotrophic factor secretion and neuroinflammatory pathways, leading to mood disturbances. This review primarily summarizes findings from preclinical studies to examine the relationship between Kir4.1 and the pathogenesis of chronic pain and mental health disorders, discussing its molecular structure, expression patterns, and functional roles. Furthermore, we explore therapeutic strategies targeting Kir4.1, including pharmacological modulators and gene therapy approaches, emphasizing its potential as a novel therapeutic target.

Mind the GAPS: Glia associated with psychological stress

Glial cells are an integral component of the nervous system, performing crucial functions that extend beyond structural support, including modulation of the immune system, tissue repair, and maintaining tissue homeostasis. Recent studies have highlighted the importance of glial cells as key mediators of stress responses across different organs. This review focuses on the roles of glial cells in peripheral tissues in health and their involvement in diseases linked to psychological stress. Populations of glia associated with psychological stress ("GAPS") emerge as a promising target cell population in our basic understanding of stress-associated pathologies, highlighting their role as mediators of the deleterious effects of psychological stress on various health conditions. Ultimately, new insights into the impact of stress on glial cell populations in the periphery may support clinical efforts aimed at improving the psychological state of patients for improved health outcomes.

Hepatic kynurenic acid mediates phosphorylation of Nogo-A in the medial prefrontal cortex to regulate chronic stress-induced anxiety-like behaviors in mice

Exercise training effectively relieves anxiety disorders via modulating specific brain networks. The role of post-translational modification of proteins in this process, however, has been underappreciated. Here we performed a mouse study in which chronic restraint stress-induced anxiety-like behaviors can be attenuated by 14-day persistent treadmill exercise, in association with dramatic changes of protein phosphorylation patterns in the medial prefrontal cortex (mPFC). In particular, exercise was proposed to modulate the phosphorylation of Nogo-A protein, which drives the ras homolog family member A (RhoA)/ Rho-associated coiled-coil-containing protein kinases 1(ROCK1) signaling cascade. Further mechanistic studies found that liver-derived kynurenic acid (KYNA) can affect the kynurenine metabolism within the mPFC, to modulate this RhoA/ROCK1 pathway for conferring stress resilience. In sum, we proposed that circulating KYNA might mediate stress-induced anxiety-like behaviors via protein phosphorylation modification within the mPFC, and these findings shed more insights for the liver-brain communications in responding to both stress and physical exercise.

Lipin1 depletion coordinates neuronal signaling pathways to promote motor and sensory axon regeneration after spinal cord injury

Adult central nervous system (CNS) neurons down-regulate growth programs after injury, leading to persistent regeneration failure. Coordinated lipids metabolism is required to synthesize membrane components during axon regeneration. However, lipids also function as cell signaling molecules. Whether lipid signaling contributes to axon regeneration remains unclear. In this study, we showed that lipin1 orchestrates mechanistic target of rapamycin (mTOR) and STAT3 signaling pathways to determine axon regeneration. We established an mTOR-lipin1-phosphatidic acid/lysophosphatidic acid-mTOR loop that acts as a positive feedback inhibitory signaling, contributing to the persistent suppression of CNS axon regeneration following injury. In addition, lipin1 knockdown (KD) enhances corticospinal tract (CST) sprouting after unilateral pyramidotomy and promotes CST regeneration following complete spinal cord injury (SCI). Furthermore, lipin1 KD enhances sensory axon regeneration after SCI. Overall, our research reveals that lipin1 functions as a central regulator to coordinate mTOR and STAT3 signaling pathways in the CNS neurons and highlights the potential of lipin1 as a promising therapeutic target for promoting the regeneration of motor and sensory axons after SCI.

Human neural stem cell-derived artificial organelles to improve oxidative phosphorylation

Oxidative phosphorylation (OXPHOS) in the mitochondrial inner membrane is a therapeutic target in many diseases. Neural stem cells (NSCs) show progress in improving mitochondrial dysfunction in the central nervous system (CNS). However, translating neural stem cell-based therapies to the clinic is challenged by uncontrollable biological variability or heterogeneity, hindering uniform clinical safety and efficacy evaluations. We propose a systematic top-down design based on membrane self-assembly to develop neural stem cell-derived oxidative phosphorylating artificial organelles (SAOs) for targeting the central nervous system as an alternative to NSCs. We construct human conditionally immortal clone neural stem cells (iNSCs) as parent cells and use a streamlined closed operation system to prepare neural stem cell-derived highly homogenous oxidative phosphorylating artificial organelles. These artificial organelles act as biomimetic organelles to mimic respiration chain function and perform oxidative phosphorylation, thus improving ATP synthesis deficiency and rectifying excessive mitochondrial reactive oxygen species production. Conclusively, we provide a framework for a generalizable manufacturing procedure that opens promising prospects for disease treatment.

FBXL20 promotes synaptic impairment in depression disorder via degrading vesicle-associated proteins

BACKGROUND

Synaptic plasticity changes in presynaptic terminals or postsynaptic membranes play a critical role in cognitive impairments and emotional disorders, but the underlying molecular mechanisms in depression remain largely unknown.

METHODS

The regulation effects of F-box and leucine-rich repeat protein 20 (FBXL20), vesicular glutamate transporter 1 (VGLUT1) and vesicle-associated membrane protein 1 (VAMP1) on synaptic plasticity and depressive-like behaviors examined by proteomics analysis, viral stereotaxic injection, transmission electron microscope and biochemical methods. The glutamate release detected by fluorescent probe in cultured primary pyramidal neurons.

RESULTS

We found that chronic unpredictable mild stress (CUMS) induced significant synaptic deficits within hippocampus of depressed rats, accompanied with the decreased expression of VGLUT1 and VAMP1. Moreover, knockdown of VGLUT1 or VAMP1 in hippocampal pyramidal neurons resulted in abnormal glutamatergic neurotransmitter release. In addition, we found that the E3 ubiquitin ligase FBXL20 was increased within hippocampus, which may promote ubiquitination and degradation of VGLUT1 and VAMP1, and thus resulted in the reduction of glutamatergic neurotransmitter release, the disruptions of synaptic transmission and the induction of depression-like behaviors in rats. In contrast, shRNA knockdown of FBXL20 within the hippocampus of depressed rats significantly ameliorated synaptic damage and depression-like behaviors.

LIMITATION

Only one type of depression model was used in the present study, while other animal models should be used in the future to confirm the underlying mechanisms reported here.

CONCLUSIONS

This study provides new insights that inhibiting FBXL20 pathway in depressed rats may be an effective strategy to rescue synaptic transmission and depression-like behaviors.