Psychological stress induces depressive-like behavior associated with bone marrow-derived monocyte infiltration into the hippocampus independent of blood-brain barrier disruption

Chronic emotional stress and mediating role of Interleukine-6 in the association with cardiometabolic disorders in a multiethnic middle-aged and older US-population

Introduction

Chronic emotional stress is a well-recognized risk factor for psychiatric and cardiometabolic disorders. The mediating role of low-grade inflammation in older, ethnically diverse populations has never been studied.

Methods

The multiethnic ≥ 50-year-old study population is a subset of the Health and Aging Brain Study: Health Disparities (HABS-HD) study. Adjusted logistic and linear regression were used to assess associations. Statistical mediation analysis with non-parametric bootstrapping was used to determine the intermediate role of Interleukine-6 (IL-6).

Results

The study included 2,173 participants (50-92 years). Hispanic and Black participants disclosed higher chronic stress levels than White participants. Having a chronic stress total score ≥ six points is associated with 53% higher odds of disclosing concomitant cardiovascular disease (CVD) (adj.OR=1.53 [1.1-2.53]), 31% of Type-2 diabetes (T2DM) (adj.OR=1.31[1.06-1.62]), 23% of hypertension (adj.OR=1.23 [1.02-1.49]), and 30% obesity (adj.OR=1.3[1.09-1.55]). These associations were statistically mediated by IL-6 (12% ( p-value FDR =0.012) of the association with CVD, 17% T2DM ( p-value FDR <0.001), 18% hypertension ( p-value FDR <0.001), and 29% obesity ( p-value FDR =0.005)).

Conclusions

The study highlights a further aspect of the pathophysiological mechanisms involved in brain-body communication. While IL-6 partially explains statistical associations between chronic emotional stress and major cardiometabolic disorders, potential causal effects need to be explored in larger longitudinal studies.

Microglia Sing the Prelude of Neuroinflammation-Associated Depression

Major depressive disorder (MDD) is a psychiatric condition characterized by sadness and anhedonia and is closely linked to chronic low-grade neuroinflammation, which is primarily induced by microglia. Nonetheless, the mechanisms by which microglia elicit depressive symptoms remain uncertain. This review focuses on the mechanism linking microglia and depression encompassing the breakdown of the blood-brain barrier, the hypothalamic-pituitary-adrenal axis, the gut-brain axis, the vagus and sympathetic nervous systems, and the susceptibility influenced by epigenetic modifications on microglia. These pathways may lead to the alterations of microglia in cytokine levels, as well as increased oxidative stress. Simultaneously, many antidepressant treatments can alter the immune phenotype of microglia, while anti-inflammatory treatments can also have antidepressant effects. This framework linking microglia, neuroinflammation, and depression could serve as a reference for targeting microglia to treat depression.

Gut-derived trimethylamine N-oxide promotes CCR2-mediated macrophage infiltration in acute kidney injury

BACKGROUND

Inflammation is crucial in the development of acute kidney injury (AKI) and subsequent chronic kidney disease (CKD) following renal ischaemia-reperfusion (IR) injury. Gut microbiota metabolites trigger inflammation and affect IR-induced renal damage. Yet the driving factors and mechanisms are unclear. Trimethylamine N-oxide (TMAO), a gut-derived choline metabolite, is a strong pro-inflammatory factor that increases in patients with AKI and CKD. We hypothesized that TMAO can promote renal injury caused by IR.

METHODS

Mice subjected to unilateral renal IR to induce AKI and CKD were fed a high-choline diet to observe the effects of TMAO on kidney inflammation, fibrosis and macrophage dynamics.

RESULTS

A choline-rich diet altered the gut microbiota and elevated TMAO levels, exacerbating IR-induced AKI and subsequent CKD. Single-cell analysis identified a distinct subset of CCR2+ macrophages derived from monocytes as key responders to TMAO, intensifying immune cell interactions and worsening renal injury. TMAO promoted sustained CCR2 expression after IR, increasing macrophage infiltration. CCR2 deletion and antagonist RS-102895 improved TMAO-induced inflammation and fibrosis and alleviated renal injury induced by IR.

CONCLUSIONS

Our study provides valuable insights into the link between TMAO and IR-induced renal inflammation and fibrosis, emphasizing the critical role of TMAO-mediated macrophage infiltration via CCR2 as a key therapeutic target in the acute and chronic phases after IR.

Curcumin/pEGCG-encapsulated nanoparticles enhance spinal cord injury recovery by regulating CD74 to alleviate oxidative stress and inflammation

Spinal cord injury (SCI) often accompanies impairment of motor function, yet there is currently no highly effective treatment method specifically for this condition. Oxidative stress and inflammation are pivotal factors contributing to severe neurological deficits after SCI. In this study, a type of curcumin (Cur) nanoparticle (HA-CurNPs) was developed to address this challenge by alleviating oxidative stress and inflammation. Through non-covalent interactions, curcumin (Cur) and poly (-)-epigallocatechin-3-gallate (pEGCG) are co-encapsulated within hyaluronic acid (HA), resulting in nanoparticles termed HA-CurNPs. These nanoparticles gradually release curcumin and pEGCG at the SCI site. The released pEGCG and curcumin not only scavenge reactive oxygen species (ROS) and prevents apoptosis, thereby improving the neuronal microenvironment, but also regulate CD74 to promote microglial polarization toward an M2 phenotype, and inhibits M1 polarization, thereby suppressing the inflammatory response and fostering neuronal regeneration. Moreover, in vivo experiments on SCI mice demonstrate that HA-CurNPs effectively protect neuronal cells and myelin, reduce glial scar formation, thereby facilitating the repair of damaged spinal cord tissues, restoring electrical signaling at the injury site, and improving motor functions. Overall, this study demonstrates that HA-CurNPs significantly reduce oxidative stress and inflammation following SCI, markedly improving motor function in SCI mice. This provides a promising therapeutic approach for the treatment of SCI.

Looking Back to Move Forward: Research in Stress, Behavior, and Immune Function

BACKGROUND

From the original studies investigating the effects of adrenal gland secretion to modern high-throughput multidimensional analyses, stress research has been a topic of scientific interest spanning just over a century.

SUMMARY

The objective of this review was to provide historical context for influential discoveries, surprising findings, and preclinical models in stress-related neuroimmune research. Furthermore, we summarize this work and present a current understanding of the stress pathways and their effects on the immune system and behavior. We focus on recent work demonstrating stress-induced immune changes within the brain and highlight studies investigating stress effects on microglia. Lastly, we conclude with potential areas for future investigation concerning microglia heterogeneity, bone marrow niches, and sex differences.

KEY MESSAGES

Stress is a phenomenon that ties together not only the central and peripheral nervous system, but the immune system as well. The cumulative effects of stress can enhance or suppress immune function, based on the intensity and duration of the stressor. These stress-induced immune alterations are associated with neurobiological changes, including structural remodeling of neurons and decreased neurogenesis, and these contribute to the development of behavioral and cognitive deficits. As such, research in this field has revealed important insights into neuroimmune communication as well as molecular and cellular mediators of complex behaviors relevant to psychiatric disorders.

Repetitive Administration of Low-Dose Lipopolysaccharide Improves Repeated Social Defeat Stress-Induced Behavioral Abnormalities and Aberrant Immune Response

Repetitive exposure of innate immune cells to a subthreshold dosage of endotoxin components may modulate inflammatory responses. However, the regulatory mechanisms in the interactions between the central nervous system (CNS) and the immune system remain unclear. This study aimed to investigate the effects of lipopolysaccharide (LPS) preconditioning in repeated social defeat stress (RSDS)-induced abnormal immune responses and behavioral impairments. This study aimed to elucidate the mechanisms that underlie the protective effects of repeated administration of a subthreshold dose LPS on behavioral impairments using the RSDS paradigm. LPS preconditioning improved abnormal behaviors in RSDS-defeated mice, accompanied by decreased monoamine oxidases and increased glucocorticoid receptor expression in the hippocampus. In addition, pre-treated with LPS significantly decreased the recruited peripheral myeloid cells (CD11b+CD45hi), mainly circulating inflammatory monocytes (CD11b+CD45hiLy6ChiCCR2+) into the brain in response to RSDS challenge. Importantly, we found that LPS preconditioning exerts its protective properties by regulating lipocalin-2 (LCN2) expression in microglia, which subsequently induces expressions of chemokine CCL2 and pro-inflammatory cytokine. Subsequently, LPS-preconditioning lessened the resident microglia population (CD11b+CD45intCCL2+) in the brains of the RSDS-defeated mice. Moreover, RSDS-associated expressions of leukocytes (CD11b+CD45+CCR2+) and neutrophils (CD11b+CD45+Ly6G+) in the bone marrow, spleen, and blood were also attenuated by LPS-preconditioning. In particular, LPS preconditioning also promoted the expression of endogenous antioxidants and anti-inflammatory proteins in the hippocampus. Our results demonstrate that LPS preconditioning ameliorates lipocalin 2-associated microglial activation and aberrant immune response and promotes the expression of endogenous antioxidants and anti-inflammatory protein, thereby maintaining the homeostasis of pro-inflammation/anti-inflammation in both the brain and immune system, ultimately protecting the mice from RSDS-induced aberrant immune response and behavioral changes.

Bone marrow-derived myeloid cells transiently colonize the brain during postnatal development and interact with glutamatergic synapses

Although the roles of embryonic yolk sac-derived, resident microglia in neurodevelopment were extensively studied, the possible involvement of bone marrow-derived cells remains elusive. In this work, we used a fate-mapping strategy to selectively label bone marrow-derived cells and their progeny in the brain (FLT3+IBA1+). FLT3+IBA1+ cells were confirmed to be transiently present in the healthy brain during early postnatal development. FLT3+IBA1+ cells have a distinct morphology index at postnatal day(P)0, P7, and P14 compared with neighboring microglia. FLT3+IBA1+ cells also express the microglial markers P2RY12 and TMEM119 and interact with VGLUT1 synapses at P14. Scanning electron microscopy indeed showed that FLT3+ cells contact and engulf pre-synaptic elements. Our findings suggest FLT3+IBA1+ cells might assist microglia in their physiological functions in the developing brain including synaptic pruning which is performed using their purinergic sensors. Our findings stimulate further investigation on the involvement of peripheral macrophages during homeostatic and pathological development.

Neurodevelopmental and Neuropsychiatric Disorders

This chapter will focus on microglial involvement in neurodevelopmental and neuropsychiatric disorders, particularly autism spectrum disorder (ASD), schizophrenia and major depressive disorder (MDD). We will describe the neuroimmune risk factors that contribute to the etiopathology of these disorders across the lifespan, including both in early life and adulthood. Microglia, being the resident immune cells of the central nervous system, could play a key role in triggering and determining the outcome of these disorders. This chapter will review preclinical and clinical findings where microglial morphology and function were examined in the contexts of ASD, schizophrenia and MDD. Clinical evidence points out to altered microglial morphology and reactivity, as well as increased expression of pro-inflammatory cytokines, supporting the idea that microglial abnormalities are involved in these disorders. Indeed, animal models for these disorders found altered microglial morphology and homeostatic functions which resulted in behaviours related to these disorders. Additionally, as microglia have emerged as promising therapeutic targets, we will also address in this chapter therapies involving microglial mechanisms for the treatment of neurodevelopmental and neuropsychiatric disorders.

Interplay of G-proteins and Serotonin in the Neuroimmunoinflammatory Model of Chronic Stress and Depression: A Narrative Review

INTRODUCTION

This narrative review addresses the clinical challenges in stress-related disorders such as depression, focusing on the interplay between neuron-specific and pro-inflammatory mechanisms at the cellular, cerebral, and systemic levels.

OBJECTIVE

We aim to elucidate the molecular mechanisms linking chronic psychological stress with low-grade neuroinflammation in key brain regions, particularly focusing on the roles of G proteins and serotonin (5-HT) receptors.

METHODS

This comprehensive review of the literature employs systematic, narrative, and scoping review methodologies, combined with systemic approaches to general pathology. It synthesizes current research on shared signaling pathways involved in stress responses and neuroinflammation, including calcium-dependent mechanisms, mitogen-activated protein kinases, and key transcription factors like NF-κB and p53. The review also focuses on the role of G protein-coupled neurotransmitter receptors (GPCRs) in immune and pro-inflammatory responses, with a detailed analysis of how 13 of 14 types of human 5-HT receptors contribute to depression and neuroinflammation.

RESULTS

The review reveals a complex interaction between neurotransmitter signals and immunoinflammatory responses in stress-related pathologies. It highlights the role of GPCRs and canonical inflammatory mediators in influencing both pathological and physiological processes in nervous tissue.

CONCLUSION

The proposed Neuroimmunoinflammatory Stress Model (NIIS Model) suggests that proinflammatory signaling pathways, mediated by metabotropic and ionotropic neurotransmitter receptors, are crucial for maintaining neuronal homeostasis. Chronic mental stress can disrupt this balance, leading to increased pro-inflammatory states in the brain and contributing to neuropsychiatric and psychosomatic disorders, including depression. This model integrates traditional theories on depression pathogenesis, offering a comprehensive understanding of the multifaceted nature of the condition.

Interplay between stress and cancer-A focus on inflammation

Stress is an integral part of life. While acute responses to stress are generally regarded as beneficial in dealing with immediate threats, chronic exposure to threatening stimuli exerts deleterious effects and can be either a contributing or an aggravating factor for many chronic diseases including cancer. Chronic psychological stress has been identified as a significant factor contributing to the development and progression of cancer, but the mechanisms that link chronic stress to cancer remain incompletely understood. Psychological stressors initiate multiple physiological responses that result in the activation of the hypothalamic-pituitary-adrenal (HPA) axis, sympathetic nervous system, and the subsequent changes in immune function. Chronic stress exposure disrupts the homeostatic communication between the neuroendocrine and immune systems, shifting immune signaling toward a proinflammatory state. Stress-induced chronic low-grade inflammation and a decline in immune surveillance are both implicated in cancer development and progression. Conversely, tumor-induced inflammatory cytokines, apart from driving a tumor-supportive inflammatory microenvironment, can also exert their biological actions distantly via circulation and therefore adversely affect the stress response. In this minireview, we summarize the current findings on the relationship between stress and cancer, focusing on the role of inflammation in stress-induced neuroendocrine-immune crosstalk. We also discuss the underlying mechanisms and their potential for cancer treatment and prevention.