Polygenic burden associated to oligodendrocyte precursor cells and radial glia influences the hippocampal volume changes induced by aerobic exercise in schizophrenia patients

Canonical and non-canonical roles of oligodendrocyte precursor cells in mental disorders

Psychiatric research has shifted from a neuroncentric view to understanding mental disorders as disturbances of heterogeneous brain networks. Oligodendrocyte precursor cells (OPCs)- actively involved in the modulation of neuronal functions - are altered in psychiatric patients, but the extent and related consequences are unclear. This review explores canonical and non-canonical OPC-related pathways in schizophrenia, bipolar disorder, post-traumatic stress disorder, and depression in humans, highlighting potential mechanisms shared across diagnostic entities.

Glial cell deficits are a key feature of schizophrenia: implications for neuronal circuit maintenance and histological differentiation from classical neurodegeneration

Dysfunctional glial cells play a pre-eminent role in schizophrenia pathophysiology. Post-mortem studies have provided evidence for significantly decreased glial cell numbers in different brain regions of individuals with schizophrenia. Reduced glial cell numbers are most pronounced in oligodendroglia, but reduced astrocyte cell densities have also been reported. This review highlights that oligo- and astroglial deficits are a key histopathological feature in schizophrenia, distinct from typical changes seen in neurodegenerative disorders. Significant deficits of oligodendrocytes in schizophrenia may arise in two ways: (i) demise of mature functionally compromised oligodendrocytes; and (ii) lack of mature oligodendrocytes due to failed maturation of progenitor cells. We also analyse in detail the controversy regarding deficits of astrocytes. Regardless of their origin, glial cell deficits have several pathophysiological consequences. Among these, myelination deficits due to a reduced number of oligodendrocytes may be the most important factor, resulting in the disconnectivity between neurons and different brain regions observed in schizophrenia. When glial cells die, it appears to be through degeneration, a process which is basically reversible. Thus, therapeutic interventions that (i) help rescue glial cells (ii) or improve their maturation might be a viable option. Since antipsychotic treatment alone does not seem to prevent glial cell loss or maturation deficits, there is intense search for new therapeutic options. Current proposals range from the application of antidepressants and other chemical agents as well as physical exercise to engrafting healthy glial cells into brains of schizophrenia patients.

Aerobic Exercise Improves the Overall Outcome of Type 2 Diabetes Mellitus Among People With Mental Disorders

The escalating global prevalence of type 2 diabetes mellitus (T2DM) and mental disorder (MD) including schizophrenia, bipolar disorder, major depressive disorder, and anxiety highlights the urgency for comprehensive therapeutic strategies. Aerobic exercise (AE) is a viable adjunct therapy, providing significant benefits for individuals dealing with both T2DM and MD. This review consolidates evidence on AE's role in alleviating the physiological and psychological effects of these comorbid conditions. It delves into the pathophysiological connections between T2DM and various MD, including depression, schizophrenia, anxiety, and bipolar disorder-emphasizing their reciprocal exacerbation. Key neurophysiological mechanisms through which AE confers benefits are explored, including neuroinflammation modulation, brain structure and neuroplasticity enhancement, growth factor expression regulation, and hypothalamic-pituitary-adrenal (HPA)/microbiota-gut-brain (MGB) axis normalization. Clinical results indicate that AE significantly improves both metabolic and psychological parameters in patients with T2DM and MD, providing a substantial argument for integrating AE into comprehensive treatment plans. Future research should aim to establish detailed, personalized exercise prescriptions and explore the long-term benefits of AE in this population. This review underscores the potential of AE to complement existing therapeutic modalities and enhance the management of patients with T2DM and MD.

Effects of aerobic exercise on hippocampal formation volume in people with schizophrenia - a systematic review and meta-analysis with original data from a randomized-controlled trial

BACKGROUND

The hippocampal formation represents a key region in the pathophysiology of schizophrenia. Aerobic exercise poses a promising add-on treatment to potentially counteract structural impairments of the hippocampal formation and associated symptomatic burden. However, current evidence regarding exercise effects on the hippocampal formation in schizophrenia is largely heterogeneous. Therefore, we conducted a systematic review and meta-analysis to assess the impact of aerobic exercise on total hippocampal formation volume. Additionally, we used data from a recent multicenter randomized-controlled trial to examine the effects of aerobic exercise on hippocampal formation subfield volumes and their respective clinical implications.

METHODS

The meta-analysis comprised six studies that investigated the influence of aerobic exercise on total hippocampal formation volume compared to a control condition with a total of 186 people with schizophrenia (100 male, 86 female), while original data from 29 patients (20 male, 9 female) was considered to explore effects of six months of aerobic exercise on hippocampal formation subfield volumes.

RESULTS

Our meta-analysis did not demonstrate a significant effect of aerobic exercise on total hippocampal formation volume in people with schizophrenia (g = 0.33 [-0.12 to 0.77]), p = 0.15), but our original data suggested significant volume increases in certain hippocampal subfields, namely the cornu ammonis and dentate gyrus.

CONCLUSIONS

Driven by the necessity of better understanding the pathophysiology of schizophrenia, the present work underlines the importance to focus on hippocampal formation subfields and to characterize subgroups of patients that show neuroplastic responses to aerobic exercise accompanied by corresponding clinical improvements.

Effects of aerobic training on brain architecture, hippocampal volume, cardiorespiratory parameters, and health-related quality of life among patients with schizophrenia: A systematic review

Background

Schizophrenia is considered to be a condition that usually manifests at any age but commonly seen in young people and is associated with a genetic propensity in brain development.

Aim

The study explores the impact of aerobic training on brain architecture, hippocampal volume, cardiorespiratory parameters, and quality of life in young individuals with schizophrenia. The investigation focuses on the correlation between genetic predisposition, hippocampal atrophy, and diminished cardiorespiratory fitness, aiming to discern potential benefits of aerobic exercise on both physical and mental health outcomes.

Methods

A systematic search was conducted in major online databases, such as Cochrane, Embase, PEDro, Web of science and PubMed (Medline). Two authors independently evaluated possibilities of bias, retrieved data and decided which trials should be included in the analysis. Total of 13 published articles (randomized clinical and controlled trials) with 656 patients was included from January 2010 to December 2020.

Results

Following aerobic exercise training, people with schizophrenia presented with an increased hippocampus volume and enhanced cardiorespiratory endurance (P ˂0.05). Due to a lack of information, we rated the majority of the studies' risk of bias in relation to random sequence creation, allocation concealment, and selective reporting as uncertain.

Conclusion

Findings from the present review propose aerobic exercise program as a meaningful therapeutic intervention for schizophrenia patients in terms of maintaining appropriate brain architecture, increasing the hippocampal volume, improving cardiorespiratory parameters and health related quality of life.

Disturbed Oligodendroglial Maturation Causes Cognitive Dysfunction in Schizophrenia: A New Hypothesis

BACKGROUND AND HYPOTHESIS

Cognitive impairment is a hallmark of schizophrenia, but no effective treatment is available to date. The underlying pathophysiology includes disconnectivity between hippocampal and prefrontal brain regions. Supporting evidence comes from diffusion-weighted imaging studies that suggest abnormal organization of frontotemporal white matter pathways in schizophrenia.

STUDY DESIGN

Here, we hypothesize that in schizophrenia, deficient maturation of oligodendrocyte precursor cells (OPCs) into mature oligodendrocytes substantially contributes to abnormal frontotemporal macro- and micro-connectivity and subsequent cognitive deficits.

STUDY RESULTS

Our postmortem studies indicate a reduced oligodendrocyte number in the cornu ammonis 4 (CA4) subregion of the hippocampus, and others have reported the same histopathological finding in the dorsolateral prefrontal cortex. Our series of studies on aerobic exercise training showed a volume increase in the hippocampus, specifically in the CA4 region, and improved cognition in individuals with schizophrenia. The cognitive effects were subsequently confirmed by meta-analyses. Cell-specific schizophrenia polygenic risk scores showed that exercise-induced CA4 volume increase significantly correlates with OPCs. From animal models, it is evident that early life stress and oligodendrocyte-related gene variants lead to schizophrenia-related behavior, cognitive deficits, impaired oligodendrocyte maturation, and reduced myelin thickness.

CONCLUSIONS

Based on these findings, we propose that pro-myelinating drugs (e.g., the histamine blocker clemastine) combined with aerobic exercise training may foster the regeneration of myelin plasticity as a basis for restoring frontotemporal connectivity and cognition in schizophrenia.

Sports Therapy for Schizophrenia Psychoses: from the Idea to the Guideline

Schizophrenia psychoses can be treated much better today due to the introduction of antipsychotics about 70 years ago in conjunction with the implementation of specific psychotherapies. However, current treatment options are still limited in the area of negative symptoms and disease-associated cognitive deficits. In the last 15 years, randomised controlled trials (RCTs) have been able to show that physical training and especially endurance training could represent a comprehensive complementary treatment approach and could lead to a significant improvement in positive, but especially also in negative symptoms and cognitive deficits. As a result, sports therapy for schizophrenia psychoses has found its way not only into the national treatment guidelines of the German Society for Psychiatry, Psychotherapy, Psychosomatics and Neurology (DGPPN), but also into European recommendations such as those of the European Psychiatric Association (EPA). With the introduction of the "Living guideline" format (here an update takes place at least once a year), a broader implementation in health care will be easier in the future. Based on a narrative review, this paper describes the process of implementing sports therapy for schizophrenia psychoses from its beginnings to its incorporation into guidelines and can be applied analogously to other forms of therapy.

Pathological potential of oligodendrocyte precursor cells: terra incognita

Adult oligodendrocyte precursor cells (aOPCs), transformed from fetal OPCs, are idiosyncratic neuroglia of the central nervous system (CNS) that are distinct in many ways from other glial cells. OPCs have been classically studied in the context of their remyelinating capacity. Recent studies, however, revealed that aOPCs not only contribute to post-lesional remyelination but also play diverse crucial roles in multiple neurological diseases. In this review we briefly present the physiology of aOPCs and summarize current knowledge of the beneficial and detrimental roles of aOPCs in different CNS diseases. We discuss unique features of aOPC death, reactivity, and changes during senescence, as well as aOPC interactions with other glial cells and pathological remodeling during disease. Finally, we outline future perspectives for the study of aOPCs in brain pathologies which may instigate the development of aOPC-targeting therapeutic strategies.

A Systematic Review of the Human Accelerated Regions in Schizophrenia and Related Disorders: Where the Evolutionary and Neurodevelopmental Hypotheses Converge

Schizophrenia is a psychiatric disorder that results from genetic and environmental factors interacting and disrupting neurodevelopmental trajectories. Human Accelerated Regions (HARs) are evolutionarily conserved genomic regions that have accumulated human-specific sequence changes. Thus, studies on the impact of HARs in the context of neurodevelopment, as well as with respect to adult brain phenotypes, have increased considerably in the last few years. Through a systematic approach, we aim to offer a comprehensive review of HARs' role in terms of human brain development, configuration, and cognitive abilities, as well as whether HARs modulate the susceptibility to neurodevelopmental psychiatric disorders such as schizophrenia. First, the evidence in this review highlights HARs' molecular functions in the context of the neurodevelopmental regulatory genetic machinery. Second, brain phenotypic analyses indicate that HAR genes' expression spatially correlates with the regions that suffered human-specific cortical expansion, as well as with the regional interactions for synergistic information processing. Lastly, studies based on candidate HAR genes and the global "HARome" variability describe the involvement of these regions in the genetic background of schizophrenia, but also in other neurodevelopmental psychiatric disorders. Overall, the data considered in this review emphasise the crucial role of HARs in human-specific neurodevelopment processes and encourage future research on this evolutionary marker for a better understanding of the genetic basis of schizophrenia and other neurodevelopmental-related psychiatric disorders. Accordingly, HARs emerge as interesting genomic regions that require further study in order to bridge the neurodevelopmental and evolutionary hypotheses in schizophrenia and other related disorders and phenotypes.

Fitness is positively associated with hippocampal formation subfield volumes in schizophrenia: a multiparametric magnetic resonance imaging study

Hippocampal formation (HF) volume loss is a well-established finding in schizophrenia, with select subfields, such as the cornu ammonis and dentate gyrus, being particularly vulnerable. These morphologic alterations are related to functional abnormalities and cognitive deficits, which are at the core of the insufficient recovery frequently seen in this illness. To counteract HF volume decline, exercise to improve aerobic fitness is considered as a promising intervention. However, the effects of aerobic fitness levels on HF subfields are not yet established in individuals with schizophrenia. Therefore, our study investigated potential associations between aerobic fitness and HF subfield structure, functional connectivity, and related cognitive impact in a multiparametric research design. In this cross-sectional study, 53 participants diagnosed with schizophrenia (33 men, 20 women; mean [SD] age, 37.4 [11.8] years) underwent brain structural and functional magnetic resonance imaging and assessments of aerobic fitness and verbal memory. Multivariate multiple linear regressions were performed to determine whether aerobic fitness was associated with HF subfield volumes and functional connections. In addition, we explored whether identified associations mediated verbal memory functioning. Significant positive associations between aerobic fitness levels and volumes were demonstrated for most HF subfields, with the strongest associations for the cornu ammonis, dentate gyrus, and subiculum. No significant associations were found for HF functional connectivity or mediation effects on verbal memory. Aerobic fitness may mitigate HF volume loss, especially in the subfields most affected in schizophrenia. This finding should be further investigated in longitudinal studies.Clinical Trials Registration: The study on which the manuscript is based was registered in the International Clinical Trials Database, ClinicalTrials.gov (NCT number: NCT03466112 ) and in the German Clinical Trials Register (DRKS-ID: DRKS00009804).

Associations between aerobic fitness, negative symptoms, cognitive deficits and brain structure in schizophrenia-a cross-sectional study

Negative symptoms and cognitive deficits are common in individuals with schizophrenia, greatly affect their outcome, and have been associated with alterations in cerebral gray and white matter volume (GMV, WMV). In the last decade, aerobic endurance training has emerged as a promising intervention to alleviate these symptoms and improved aerobic fitness has been suggested as a key moderator variable. In the present study, we investigated, whether aerobic fitness is associated with fewer cognitive deficits and negative symptoms and with GMVs and WMVs in individuals with schizophrenia in a cross-sectional design. In the largest study to date on the implications of fitness in individuals with schizophrenia, 111 participants at two centers underwent assessments of negative symptoms, cognitive functioning, and aerobic fitness and 69 underwent additional structural magnetic resonance imaging. Multilevel Bayesian partial correlations were computed to quantify relationships between the variables of interest. The main finding was a positive association of aerobic fitness with right hippocampal GMV and WMVs in parahippocampal and several cerebellar regions. We found limited evidence for an association of aerobic fitness with cognitive functioning and negative symptoms. In summary, our results strengthen the notion that aerobic fitness and hippocampal plasticity are interrelated which holds implications for the design of exercise interventions in individuals with schizophrenia.

Failed regeneration and inflammation in schizophrenia: two sides of the same coin?

More than 100 years after its conceptual definition as 'Dementia Praecox' by Emil Kraepelin, which was changed to schizophrenia by Eugen Bleuler, this is still a serious and debilitating psychiatric illness. The neurodevelopmental hypothesis of schizophrenia, introduced more than 30 years ago, states that schizophrenia is a consequence of failed neurodevelopmental processes leading to a dysfunctional neuronal network forming the basis for a psychosis proneness. Subsequently, significant research efforts were made to prove the neurodevelopmental or the neurodegenerative perspective. This review summarizes key arguments speaking for or against the two hypotheses leading to a concept with both aspects position side by side.

Aerobic exercise in severe mental illness: requirements from the perspective of sports medicine

Major depression, bipolar disorder, and schizophrenia are severe mental illnesses. Despite receiving psychopharmacological and psychosocial treatments, about half of patients develop a chronic course with residual cognitive and negative symptoms and have a high risk for cardiovascular disease and reduced life expectancy. Therefore, add-on innovative treatment approaches are needed to improve outcome. Aerobic exercise interventions have been shown to improve global functioning, cognition, and negative and depressive symptoms in these patients. The basic mechanism of these exercise-related changes has been reported to be improved brain plasticity, e.g., increased volume of disease-related brain regions such as the hippocampus. The optimal type, duration, and frequency of exercise have not yet been determined and need to be addressed in supervised physical exercise studies. Because of the low physical activity levels, lack of drive related to negative and depressive symptoms, and high prevalence of cardiovascular comorbidities in patients with severe mental illness, besides aiming to improve symptoms of mental illness, exercise interventions should also aim to increase cardiorespiratory fitness, which they should comprehensively assess by direct measurements of maximal oxygen uptake. Based on the recommendations for developing cardiorespiratory fitness by the American College of Sports Medicine, 150 min moderate-intensity training per week or vigorous-intensity exercise training for 75 min per week are appropriate. Most studies have had relatively short intervention periods, so future studies should focus on long-term adherence to exercise by implementing motivational strategies supported by telemedicine and by identifying and targeting typical barriers to exercise in this patient population.

Aerobic endurance training to improve cognition and enhance recovery in schizophrenia: design and methodology of a multicenter randomized controlled trial

Even today, patients with schizophrenia often have an unfavorable outcome. Negative symptoms and cognitive deficits are common features in many patients and prevent recovery. In recent years, aerobic endurance training has emerged as a therapeutic approach with positive effects on several domains of patients' health. However, appropriately sized, multicenter randomized controlled trials that would allow better generalization of results are lacking. The exercise study presented here is a multicenter, rater-blind, two-armed, parallel-group randomized clinical trial in patients with clinically stable schizophrenia being conducted at five German tertiary hospitals. The intervention group performs aerobic endurance training on bicycle ergometers three times per week for 40-50 min/session (depending on the intervention week) for a total of 26 weeks, and the control group performs balance and tone training for the same amount of time. Participants are subsequently followed up for 26 weeks. The primary endpoint is all-cause discontinuation; secondary endpoints include psychopathology, cognition, daily functioning, cardiovascular risk factors, and explorative biological measures regarding the underlying mechanisms of exercise. A total of 180 patients will be randomized. With currently 162 randomized participants, our study is the largest trial to date to investigate endurance training in patients with schizophrenia. We hypothesize that aerobic endurance training has beneficial effects on patients' mental and physical health, leading to lower treatment discontinuation rates and improving disease outcomes. The study results will provide a basis for recommending exercise interventions as an add-on therapy in patients with schizophrenia.The study is registered in the International Clinical Trials Database (ClinicalTrials.gov identifier [NCT number]: NCT03466112) and in the German Clinical Trials Register (DRKS-ID: DRKS00009804).

Shi-Zhen-An-Shen Decoction, a Herbal Medicine That Reverses Cuprizone-Induced Demyelination and Behavioral Deficits in Mice Independent of the Neuregulin-1 Pathway

Shi-Zhen-An-Shen decoction (SZASD), a Chinese herbal medicine that is a liquor extracted from plants by boiling, has been reported to be effective in treating schizophrenia. However, the mechanism is unclear. Abnormal demyelination has been implicated in schizophrenia. The aim of this study was to investigate the effect of SZASD on myelin in demyelinated mice exhibiting schizophrenia-like behaviors. Sixty male C57BL/6 mice were randomly divided into six groups (n = 10 per group): (1) control group, (2) cuprizone (CPZ, a copper chelator that induced demyelination, 0.2% w/w)+saline, (3) CPZ+low-dose SZASD (8.65 g·kg⁻¹·d⁻¹), (4) CPZ+medium-dose SZASD (17.29 g·kg⁻¹·d⁻¹), (5) CPZ+high-dose SZASD (25.94 g·kg⁻¹·d⁻¹), and (6) CPZ+quetiapine (QTP, an atypical antipsychotic that served as a positive treatment control, 10 mg·kg⁻¹·d⁻¹). Mice in groups 2-6 were treated with CPZ added to rodent chow for six weeks to induce demyelination. During the last two weeks, these mice were given an oral gavage of sterile saline, SZASD, or quetiapine. Behavioral tests and brain analyses were conducted after the last treatment. The brain expression of myelin basic protein (MBP) and neuregulin-1 (NRG-1) was assessed using immunohistochemistry and Western blots. CPZ induced significant schizophrenia-like behaviors in the mice, including reduced nest-building activity and sensory gating deficits. Hyperlocomotor activity was accompanied by significant reductions in MBP expression in the corpus callosum, hippocampus, and cerebral cortex. However, both QTP and SZASD significantly reversed the schizophrenia-like behaviors and demyelination in CPZ-fed mice. The QTP and medium-dose SZASD resulted in better therapeutic effects compared to the low and high SZASD doses. Reduced NRG-1 expression was observed in CPZ-fed mice compared with controls, but neither QTP nor SZASD showed significant influence on NRG-1 expression in the hippocampus. Together, SZASD showed a therapeutic effect on demyelinated mice, and the improvement of demyelination might not be through the NRG-1 pathway.

FreeSurfer ‐based segmentation of hippocampal subfields: A review of methods and applications, with a novel quality control procedure for ENIGMA studies and other collaborative efforts

Structural hippocampal abnormalities are common in many neurological and psychiatric disorders, and variation in hippocampal measures is related to cognitive performance and other complex phenotypes such as stress sensitivity. Hippocampal subregions are increasingly studied, as automated algorithms have become available for mapping and volume quantification. In the context of the Enhancing Neuro Imaging Genetics through Meta Analysis Consortium, several Disease Working Groups are using the FreeSurfer software to analyze hippocampal subregion (subfield) volumes in patients with neurological and psychiatric conditions along with data from matched controls. In this overview, we explain the algorithm's principles, summarize measurement reliability studies, and demonstrate two additional aspects (subfield autocorrelation and volume/reliability correlation) with illustrative data. We then explain the rationale for a standardized hippocampal subfield segmentation quality control (QC) procedure for improved pipeline harmonization. To guide researchers to make optimal use of the algorithm, we discuss how global size and age effects can be modeled, how QC steps can be incorporated and how subfields may be aggregated into composite volumes. This discussion is based on a synopsis of 162 published neuroimaging studies (01/2013–12/2019) that applied the FreeSurfer hippocampal subfield segmentation in a broad range of domains including cognition and healthy aging, brain development and neurodegeneration, affective disorders, psychosis, stress regulation, neurotoxicity, epilepsy, inflammatory disease, childhood adversity and posttraumatic stress disorder, and candidate and whole genome (epi‐)genetics. Finally, we highlight points where FreeSurfer‐based hippocampal subfield studies may be optimized.

Oligodendrocytes as A New Therapeutic Target in Schizophrenia: From Histopathological Findings to Neuron-Oligodendrocyte Interaction

Imaging and postmortem studies have revealed disturbed oligodendroglia-related processes in patients with schizophrenia and provided much evidence for disturbed myelination, irregular gene expression, and altered numbers of oligodendrocytes in the brains of schizophrenia patients. Oligodendrocyte deficits in schizophrenia might be a result of failed maturation and disturbed regeneration and may underlie the cognitive deficits of the disease, which are strongly associated with impaired long-term outcome. Cognition depends on the coordinated activity of neurons and interneurons and intact connectivity. Oligodendrocyte precursors form a synaptic network with parvalbuminergic interneurons, and disturbed crosstalk between these cells may be a cellular basis of pathology in schizophrenia. However, very little is known about the exact axon-glial cellular and molecular processes that may be disturbed in schizophrenia. Until now, investigations were restricted to peripheral tissues, such as blood, correlative imaging studies, genetics, and molecular and histological analyses of postmortem brain samples. The advent of human-induced pluripotent stem cells (hiPSCs) will enable functional analysis in patient-derived living cells and holds great potential for understanding the molecular mechanisms of disturbed oligodendroglial function in schizophrenia. Targeting such mechanisms may contribute to new treatment strategies for previously treatment-resistant cognitive symptoms.