Non-motor Behavioral Alterations of PGC-1α-Deficient Mice - A Peculiar Phenotype With Slight Male Preponderance and No Apparent Progression

Discovering functional interactions among schizophrenia-risk genes by combining behavioral genetics with cell biology

Despite much progress in identifying risk genes for polygenic brain disorders, their core pathogenic mechanisms remain poorly understood. In particular, functions of many proteins encoded by schizophrenia risk genes appear diverse and unrelated, complicating the efforts to establish the causal relationship between genes and behavior. Using various mouse lines, recent studies indicate that alterations of parvalbumin-positive (PV+) GABAergic interneurons can lead to schizophrenia-like behavior. PV+ interneurons display fast spiking and contribute to excitation-inhibition balance and network oscillations via feedback and feedforward inhibition. Here, we first summarize different lines of genetically modified mice that display motor, cognitive, emotional, and social impairments used to model schizophrenia and related mental disorders. We highlight ten genes, encoding either a nuclear, cytosolic, or membrane protein. Next, we discuss their functional relationship in regulating fast spiking and other aspects of PV+ interneurons and in the context of other domains of schizophrenia. Future investigations combining behavioral genetics and cell biology should elucidate functional relationships among risk genes to identify the core pathogenic mechanisms underlying polygenic brain disorders.

Indole-3-Propionic Acid, a Gut Microbiota Metabolite, Protects Against the Development of Postoperative Delirium

OBJECTIVE

The aim was to determine preoperative gut microbiota metabolites that may be associated with postoperative delirium (POD) development in patients and further study in rodents.

SUMMARY BACKGROUND DATA

POD occurs in 9% to 50% of older patients undergoing anesthesia/surgery but lacks effective treatments or prevention. High-throughput metabolomics using liquid chromatography with tandem mass spectrometry has accelerated disease-related biomarkers discovery. We performed metabolomic studies in humans to identify potential metabolite biomarkers linked to POD and examined potential mechanisms in rodents.

METHODS

We performed a prospective observational cohort study to examine the metabolomic changes that were associated with the development of POD. Then the gut microbiota-related metabolomic changes were recapitulated by gut microbiota perturbation in rodents. POD was assessed in mice using a battery of behavioral tests including novel objective test, Y-maze test, open-field test, and buried food test. The mechanisms through which gut microbiota-related metabolomic changes influenced POD were examined using chemogenetics.

RESULTS

Indole-3-propionic acid (IPA) is a gut microbiota metabolite that belongs to the indole family. Baseline plasma levels of IPA were significantly inversely correlated with the onset of POD in 103 (17 cases) human individuals. This relationship was validated in preclinical mouse models for POD: reducing IPA levels through gut microbiota perturbation promoted POD-like behavior. More importantly, IPA administration deterred POD-like behavior. Colonization of germ-free mice with mutant Clostridium sporogenes that did not produce IPA-promoted POD-like behavior. Chemogenetic studies revealed that the protective effect of IPA in mice was mediated, in part, by peroxisome proliferator-activated receptor gamma coactivator 1-alpha in hippocampal interneurons.

CONCLUSIONS

Gut microbiota-derived IPA is an important molecule implicated in the pathogenesis of POD, which could potentially be harnessed for POD prevention.

Effects of glycogen synthase kinase-3β activity inhibition on cognitive, behavioral, and hippocampal ultrastructural deficits in adulthood associated with adolescent methamphetamine exposure

Objective

Glycogen synthase kinase-3β (GSK3β) has been implicated in the maintenance of synaptic plasticity, memory process, and psychostimulant-induced behavioral effects. Hyperactive GSK3β in the Cornu Ammonis 1 (CA1) subregion of the dorsal hippocampus (DHP) was associated with adolescent methamphetamine (METH) exposure-induced behavioral and cognitive deficits in adulthood. This study aimed to evaluate the possible therapeutic effects of GSK3β inhibition in adulthood on adolescent METH exposure-induced long-term neurobiological deficits.

Methods

Adolescent male mice were treated with METH from postnatal day (PND) 45-51. In adulthood, three intervention protocols (acute lithium chloride systemic administration, chronic lithium chloride systemic administration, and chronic SB216763 administration within CA1) were used for GSK3β activity inhibition. The effect of GSK3β intervention on cognition, behavior, and GSK3β activity and synaptic ultrastructure in the DHP CA1 subregion were detected in adulthood.

Results

In adulthood, all three interventions reduced adolescent METH exposure-induced hyperactivity (PND97), while only chronic systemic and chronic within CA1 administration ameliorated the induced impairments in spatial (PND99), social (PND101) and object (PND103) recognition memory. In addition, although three interventions reversed the aberrant GSK3β activity in the DHP CA1 subregion (PND104), only chronic systemic and chronic within CA1 administration rescued adolescent METH exposure-induced synaptic ultrastructure changes in the DHP CA1 subregion (PND104) in adulthood.

Conclusion

Rescuing synaptic ultrastructural abnormalities in the dHIP CA1 subregion by chronic administration of a GSK3β inhibitor may be a suitable therapeutic strategy for the treatment of behavioral and cognitive deficits in adulthood associated with adolescent METH abuse.

Interferon beta attenuates recognition memory impairment and improves brain glucose uptake in a rat model of Alzheimer's disease: Involvement of mitochondrial biogenesis and PI3K pathway

Interferon beta (IFNβ) is a cytokine with anti-apoptotic and anti-inflammatory properties, and its beneficial effects on Alzheimer's disease (AD) have been recently shown. The alterations in cerebral glucose uptake are closely linked to memory deficit and AD progression. The current study was designed to determine if IFNβ can improve recognition memory and brain glucose uptake in a rat model of AD. The lentiviruses expressing mutant human amyloid precursor protein were injected bilaterally to the rat hippocampus. From day 23 after virus injection, rats were intranasally treated with recombinant IFNβ protein (68,000 IU/rat) every other day until day 50. Recognition memory performance was evaluated by novel object recognition test on days 46-49. The 18F-2- fluoro-deoxy-d-glucose positron emission tomography (18F-FDG-PET) was used to determine changes in brain glucose metabolism on day 50. The expression of the PI3K/Akt pathway components, neurotrophins and mitochondrial biogenesis factors were also measured by qPCR in the hippocampus. Our results showed that IFNβ treatment improves recognition memory performance in parallel with increased glucose uptake and neuronal survival in the hippocampus of the AD rats. The neuroprotective effect of IFNβ could be attributed, at least partly, to activation of PI3K-Akt-mTOR signaling pathway, increased expression of NGF, and mitochondrial biogenesis. Taken together, our findings suggest the therapeutic potential of IFNβ for AD.

A brain-specific pgc1α fusion transcript affects gene expression and behavioural outcomes in mice

This study shows that loss of a brain-specific fusion isoform of PGC1a leads to up-regulation of genes and motor impairments in mice, suggesting functional differences between PGC1 isoforms in the brain.

PGC1α is a transcriptional coactivator in peripheral tissues, but its function in the brain remains poorly understood. Various brain-specific Pgc1α isoforms have been reported in mice and humans, including two fusion transcripts (FTs) with non-coding repetitive sequences, but their function is unknown. The FTs initiate at a simple sequence repeat locus ∼570 Kb upstream from the reference promoter; one also includes a portion of a short interspersed nuclear element (SINE). Using publicly available genomics data, here we show that the SINE FT is the predominant form of Pgc1α in neurons. Furthermore, mutation of the SINE in mice leads to altered behavioural phenotypes and significant up-regulation of genes in the female, but not male, cerebellum. Surprisingly, these genes are largely involved in neurotransmission, having poor association with the classical mitochondrial or antioxidant programs. These data expand our knowledge on the role of Pgc1α in neuronal physiology and suggest that different isoforms may have distinct functions. They also highlight the need for further studies before modulating levels of Pgc1α in the brain for therapeutic purposes.

Multiple Roles in Neuroprotection for the Exercise Derived Myokine Irisin

Exercise has multiple beneficial effects on health including decreasing the risk of neurodegenerative diseases. Such effects are thought to be mediated (at least in part) by myokines, a collection of cytokines and other small proteins released from skeletal muscles. As an endocrine organ, skeletal muscle synthesizes and secretes a wide range of myokines which contribute to different functions in different organs, including the brain. One such myokine is the recently discovered protein Irisin, which is secreted into circulation from skeletal muscle during exercise from its membrane bound precursor Fibronectin type III domain-containing protein 5 (FNDC5). Irisin contributes to metabolic processes such as glucose homeostasis and browning of white adipose tissue. Irisin also crosses the blood brain barrier and initiates a neuroprotective genetic program in the hippocampus that culminates with increased expression of brain derived neurotrophic factor (BDNF). Furthermore, exercise and FNDC5/Irisin have been shown to have several neuroprotective effects against injuries in ischemia and neurodegenerative disease models, including Alzheimer's disease. In addition, Irisin has anxiolytic and antidepressant effects. In this review we present and summarize recent findings on the multiple effects of Irisin on neural function, including signaling pathways and mechanisms involved. We also discuss how exercise can positively influence brain function and mental health via the "skeletal muscle-brain axis." While there are still many unanswered questions, we put forward the idea that Irisin is a potentially essential mediator of the skeletal muscle-brain crosstalk.

A New Perspective on Ameliorating Depression-Like Behaviors: Suppressing Neuroinflammation by Upregulating PGC-1α

Inflammation plays an important role in depression pathology, making it a promising target for ameliorating depression-like behaviors. The peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) is a transcriptional coactivator being able to constrain inflammatory events through NF-κB signaling. However, the role of PGC-1α in depression is not yet clear. This study was designed to investigate the role of PGC-1α in depression and explore the underlying mechanisms. Mice modeled with chronic unpredictable mild stimulation (CUMS) were explored for the relationship between depression-like behaviors and PGC-1α. Baicalin was used to evaluate the effect regulating PGC-1α. Furthermore, the anti-neuroinflammatory effect of baicalin was investigated both in BV2-SH-SY5Y co-culture system and in mice by LPS challenge. The role of PGC-1α in neuroinflammation was explored in cell co-culture systems under gene silencing conditions targeting NF-κB signaling. We found that the expression of PGC-1α was inhibited in the hippocampus of mice exposed to CUMS or LPS, while baicalin could increase the expression of PGC-1α and alleviate the depression-like behaviors. Furthermore, baicalin attenuated neuroinflammation in the hippocampus of mice and BV2-SH-SY5Y co-culture system by LPS challenge via regulating NF-κB signaling; however, knockdown of the PGC-1α could reverse the effect of baicalin on neuroinflammation and NF-κB signaling. Our results revealed a vital role for PGC-1α in attenuating neuroinflammation in depression, indicating that PGC-1α might be a therapeutic target for depression.

Exploiting the Therapeutic Potential of Endogenous Immunomodulatory Systems in Multiple Sclerosis-Special Focus on the Peroxisome Proliferator-Activated Receptors (PPARs) and the Kynurenines

Multiple sclerosis (MS) is a progressive neurodegenerative disease, characterized by autoimmune central nervous system (CNS) demyelination attributable to a disturbed balance between encephalitic T helper 1 (Th1) and T helper 17 (Th17) and immunomodulatory regulatory T cell (Treg) and T helper 2 (Th2) cells, and an alternatively activated macrophage (M2) excess. Endogenous molecular systems regulating these inflammatory processes have recently been investigated to identify molecules that can potentially influence the course of the disease. These include the peroxisome proliferator-activated receptors (PPARs), PPARγ coactivator-1alpha (PGC-1α), and kynurenine pathway metabolites. Although all PPARs ameliorate experimental autoimmune encephalomyelitis (EAE), recent evidence suggests that PPARα, PPARβ/δ agonists have less pronounced immunomodulatory effects and, along with PGC-1α, are not biomarkers of neuroinflammation in contrast to PPARγ. Small clinical trials with PPARγ agonists have been published with positive results. Proposed as immunomodulatory and neuroprotective, the therapeutic use of PGC-1α activation needs to be assessed in EAE/MS. The activation of indolamine 2,3-dioxygenase (IDO), the rate-limiting step of the kynurenine pathway of tryptophan (Trp) metabolism, plays crucial immunomodulatory roles. Indeed, Trp metabolites have therapeutic relevance in EAE and drugs with structural analogy to kynurenines, such as teriflunomide, are already approved for MS. Further studies are required to gain deeper knowledge of such endogenous immunomodulatory pathways with potential therapeutic implications in MS.