Mitochondrial biogenesis in developing astrocytes regulates astrocyte maturation and synapse formation

Synaptic Plasticity Dysfunctions in the Pathophysiology of 22q11 Deletion Syndrome: Is There a Role for Astrocytes?

The 22q11 deletion syndrome (DS) is the most common microdeletion syndrome in humans and gives a high probability of developing psychiatric disorders. Synaptic and neuronal malfunctions appear to be at the core of the symptoms presented by patients. In fact, it has long been suggested that the behavioural and cognitive impairments observed in 22q11DS are probably due to alterations in the mechanisms regulating synaptic function and plasticity. Often, synaptic changes are related to structural and functional changes observed in patients with cognitive dysfunctions, therefore suggesting that synaptic plasticity has a crucial role in the pathophysiology of the syndrome. Most interestingly, among the genes deleted in 22q11DS, six encode for mitochondrial proteins that, in mouse models, are highly expressed just after birth, when active synaptogenesis occurs, therefore indicating that mitochondrial processes are strictly related to synapse formation and maintenance of a correct synaptic signalling. Because correct synaptic functioning, not only requires correct neuronal function and metabolism, but also needs the active contribution of astrocytes, we summarize in this review recent studies showing the involvement of synaptic plasticity in the pathophysiology of 22q11DS and we discuss the relevance of mitochondria in these processes and the possible involvement of astrocytes.

Translocator Protein (TSPO) Alleviates Neuropathic Pain by Activating Spinal Autophagy and Nuclear SIRT1/PGC-1α Signaling in a Rat L5 SNL Model

Purpose

Recent studies showed promotion of astrocyte autophagy in the spinal cord would provide analgesic effects. Silent information regulator T1 (SIRT1) and α subunit of peroxisome proliferator-activated receptor-γ coactivator-1 (PGC-1α) are two master regulators of endogenous antioxidant defense and mitochondrial biogenesis. They play vital roles in both autophagy and neuropathic pain (NP). Our previous study showed that TSPO agonist Ro5-4864 elicited potent analgesic effects against NP, but the mechanisms remain unclear. This study aims to investigate the effects of TSPO agonist Ro5-4864 on autophagy and nuclear SIRT1/PGC-1α signaling in spinal dorsal horn.

Methods

A rat model of L5 spinal nerve ligation (SNL) was adopted. Rats were randomly assigned to the Sham group, the SNL group, the Ro (TSPO agonist Ro5-4864) group and the Ro+3-MA group. The behavior assessments were conducted at baseline, on Day 1, 3, 7 and 14 after SNL. The autophagy-related proteins (ATG7, Beclin1, LC3, and P62) in spinal dorsal horn were assayed and the nuclear SIRT1/PGC-1α and downstream factors were analyzed.

Results

Ro5-4864 alleviated the mechanical allodynia induced by SNL (P < 0.01 vs the SNL group), which could be totally abrogated by autophagy inhibitor 3-MA (P < 0.01 vs the Ro group). SNL induced elevated ATG7 (P < 0.01), Beclin1 (P < 0.01) and LC3-II/LC3-I (P < 0.01) contents and P62 accumulation (P < 0.01) on Day 7 and Day 14, which suggested an autophagy flux impairment. Ro5-4864 augmented ATG7 (P < 0.01), Beclin1 (P < 0.01) and LC3-II/LC3-I (P < 0.05) with decreased P62 (P < 0.01), which indicated a more fluent autophagic process. These effects were also totally abrogated by 3-MA (P < 0.01). Furthermore, Ro5-4864 activated the spinal nuclear SIRT1/PGC-1α signaling pathway.

Conclusion

TSPO improved both autophagy impairment and mitochondrial biogenesis, which may provide a new strategy for the treatment of NP.

Transcranial photobiomodulation therapy ameliorates perioperative neurocognitive disorder through modulation of mitochondrial function in aged mice

Perioperative neurocognitive disorder (PND) is a serious nervous system complication characterized by progressive cognitive impairment, especially in geriatric population. However, the neuropathogenesis of PND is complex, and there are no approved disease-modifying therapeutic options. Mitochondrial dysfunction has been demonstrated to contribute to the occurrence and development of PND. Transcranial near-infrared (tNIR) light treatment helps to improve mitochondrial dysfunction and enhance cognition, but its effect on PND remains unclear. Here, we evaluated the effect of tNIR light treatment on PND caused by anesthesia and surgery in aged mice. We built the PND models with 18-month C57BL/6 male mice by exploratory laparotomy under isoflurane inhalation anesthesia, and treated by tNIR light with wavelength 810 nm for 2 weeks. The short-term and long-term changes in cognitive function were analyzed by behavioral tests. We further explored the effects of tNIR light on mitochondria, synapses, neurons, and signaling pathways through different experimental methods. The results demonstrated that the cognitive impairment and mitochondrial dysfunction in PND mice were ameliorated after tNIR light treatment. Further experiments demonstrated that photobiomodulation therapy (PBMT) increased synapse-related protein expression, neuronal survival, and protected synapse from depletion. Moreover, downregulated sirtuin 1 (SIRT1) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) were increased after tNIR light treatment. Our results suggested that tNIR light was an effective treatment of PND through PBMT effect, accompanied by synaptic and neuronal improvement. The improvement of mitochondrial dysfunction mediated by SIRT1/PGC-1α signaling pathway might participate in this process. Those findings might provide a novel and noninvasive therapeutic target for PND.

Covering the Role of PGC-1α in the Nervous System

The peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) is a well-known transcriptional coactivator involved in mitochondrial biogenesis. PGC-1α is implicated in the pathophysiology of many neurodegenerative disorders; therefore, a deep understanding of its functioning in the nervous system may lead to the development of new therapeutic strategies. The central nervous system (CNS)-specific isoforms of PGC-1α have been recently identified, and many functions of PGC-1α are assigned to the particular cell types of the central nervous system. In the mice CNS, deficiency of PGC-1α disturbed viability and functioning of interneurons and dopaminergic neurons, followed by alterations in inhibitory signaling and behavioral dysfunction. Furthermore, in the ALS rodent model, PGC-1α protects upper motoneurons from neurodegeneration. PGC-1α is engaged in the generation of neuromuscular junctions by lower motoneurons, protection of photoreceptors, and reduction in oxidative stress in sensory neurons. Furthermore, in the glial cells, PGC-1α is essential for the maturation and proliferation of astrocytes, myelination by oligodendrocytes, and mitophagy and autophagy of microglia. PGC-1α is also necessary for synaptogenesis in the developing brain and the generation and maintenance of synapses in postnatal life. This review provides an outlook of recent studies on the role of PGC-1α in various cells in the central nervous system.

Mitochondria in neurogenesis: Implications for mitochondrial diseases

Mitochondria are organelles with recognized key roles in cellular homeostasis, including bioenergetics, redox, calcium signaling, and cell death. Mitochondria are essential for neuronal function, given the high energy demands of the human brain. Consequently, mitochondrial diseases affecting oxidative phosphorylation (OXPHOS) commonly exhibit neurological impairment. Emerging evidence suggests that mitochondria are important not only for mature postmitotic neurons but also for the regulation of neural progenitor cells (NPCs) during the process of neurogenesis. These recent findings put mitochondria as central regulator of cell fate decisions during brain development. OXPHOS mutations may disrupt the function of NPCs and thereby impair the metabolic programming required for neural fate commitment. Promoting the mitochondrial function of NPCs could therefore represent a novel interventional approach against incurable mitochondrial diseases.

Impaired Mitophagy in Neurons and Glial Cells during Aging and Age-Related Disorders

Aging is associated with a decline in cognitive function, which can partly be explained by the accumulation of damage to the brain cells over time. Neurons and glia undergo morphological and ultrastructure changes during aging. Over the past several years, it has become evident that at the cellular level, various hallmarks of an aging brain are closely related to mitophagy. The importance of mitochondria quality and quantity control through mitophagy is highlighted by the contribution that defects in mitochondria-autophagy crosstalk make to aging and age-related diseases. In this review, we analyze some of the more recent findings regarding the study of brain aging and neurodegeneration in the context of mitophagy. We discuss the data on the dynamics of selective autophagy in neurons and glial cells during aging and in the course of neurodegeneration, focusing on three mechanisms of mitophagy: non-receptor-mediated mitophagy, receptor-mediated mitophagy, and transcellular mitophagy. We review the role of mitophagy in neuronal/glial homeostasis and in the molecular pathogenesis of neurodegenerative disorders, such as Parkinson's disease, Alzheimer's disease, and other disorders. Common mechanisms of aging and neurodegeneration that are related to different mitophagy pathways provide a number of promising targets for potential therapeutic agents.

Erythropoietin promotes hippocampal mitochondrial function and enhances cognition in mice

Erythropoietin (EPO) improves neuronal mitochondrial function and cognition in adults after brain injury and in those afflicted by psychiatric disorders. However, the influence of EPO on mitochondria and cognition during development remains unexplored. We previously observed that EPO stimulates hippocampal-specific neuronal maturation and synaptogenesis early in postnatal development in mice. Here we show that EPO promotes mitochondrial respiration in developing postnatal hippocampus by increasing mitochondrial content and enhancing cellular respiratory potential. Ultrastructurally, mitochondria profiles and total vesicle content were greater in presynaptic axon terminals, suggesting that EPO enhances oxidative metabolism and synaptic transmission capabilities. Behavioural tests of hippocampus-dependent memory at early adulthood, showed that EPO improves spatial and short-term memory. Collectively, we identify a role for EPO in the murine postnatal hippocampus by promoting mitochondrial function throughout early postnatal development, which corresponds to enhanced cognition by early adulthood.

Robert Jacobs, Mostafa Aboouf, et al. examined the effect of erythropoietin (EPO) in hippocampal mitochondrial function and memory in two mouse models: one overexpressing EPO in the brain, and juvenile mice treated during three days with a high dose of intraperitoneal EPO. Their results suggest that erythropoietin in the neonatal brain may impact spatial memory by increasing mitochondrial content.

Astrocyte-Neuron Signaling in Synaptogenesis

Astrocytes are the key component of the central nervous system (CNS), serving as pivotal regulators of neuronal synapse formation and maturation through their ability to dynamically and bidirectionally communicate with synapses throughout life. In the past 20 years, numerous astrocyte-derived molecules promoting synaptogenesis have been discovered. However, our understanding of the cell biological basis underlying intra-neuron processes and astrocyte-mediated synaptogenesis is still in its infancy. Here, we provide a comprehensive overview of the various ways astrocytes talk to neurons, and highlight astrocytes’ heterogeneity that allow them to displays regional-specific capabilities in boosting synaptogenesis. Finally, we conclude with promises and future directions on how organoids generated from human induced pluripotent stem cells (hiPSCs) effectively address the signaling pathways astrocytes employ in synaptic development.

Reduced mGluR5 Activity Modulates Mitochondrial Function

The metabotropic glutamate receptor 5 (mGluR5) is an essential modulator of synaptic plasticity, learning and memory; whereas in pathological conditions, it is an acknowledged therapeutic target that has been implicated in multiple brain disorders. Despite robust pre-clinical data, mGluR5 antagonists failed in several clinical trials, highlighting the need for a better understanding of the mechanisms underlying mGluR5 function. In this study, we dissected the molecular synaptic modulation mediated by mGluR5 using genetic and pharmacological mouse models to chronically and acutely reduce mGluR5 activity. We found that next to dysregulation of synaptic proteins, the major regulation in protein expression in both models concerned specific processes in mitochondria, such as oxidative phosphorylation. Second, we observed morphological alterations in shape and area of specifically postsynaptic mitochondria in mGluR5 KO synapses using electron microscopy. Third, computational and biochemical assays suggested an increase of mitochondrial function in neurons, with increased level of NADP/H and oxidative damage in mGluR5 KO. Altogether, our observations provide diverse lines of evidence of the modulation of synaptic mitochondrial function by mGluR5. This connection suggests a role for mGluR5 as a mediator between synaptic activity and mitochondrial function, a finding which might be relevant for the improvement of the clinical potential of mGluR5.