TREM Receptors Connecting Bowel Inflammation to Neurodegenerative Disorders

Glymphatic system: a gateway for neuroinflammation

The glymphatic system is a relatively recently identified fluid exchange and transport system in the brain. Accumulating evidence indicates that glymphatic function is impaired not only in central nervous system disorders but also in systemic diseases. Systemic diseases can trigger the inflammatory responses in the central nervous system, occasionally leading to sustained inflammation and functional disturbance of the central nervous system. This review summarizes the current knowledge on the association between glymphatic dysfunction and central nervous system inflammation. In addition, we discuss the hypothesis that disease conditions initially associated with peripheral inflammation overwhelm the performance of the glymphatic system, thereby triggering central nervous system dysfunction, chronic neuroinflammation, and neurodegeneration. Future research investigating the role of the glymphatic system in neuroinflammation may offer innovative therapeutic approaches for central nervous system disorders.

Probiotics and the microbiota-gut-brain axis in neurodegeneration: Beneficial effects and mechanistic insights

Neurodegenerative diseases (NDs) are a group of heterogeneous disorders with a high socioeconomic burden. Although pharmacotherapy is currently the principal therapeutic approach for the management of NDs, mounting evidence supports the notion that the protracted application of available drugs would abate their dopaminergic outcomes in the long run. The therapeutic application of microbiome-based modalities has received escalating attention in biomedical works. In-depth investigations of the bidirectional communication between the microbiome in the gut and the brain offer a multitude of targets for the treatment of NDs or maximizing the patient's quality of life. Probiotic administration is a well-known microbial-oriented approach to modulate the gut microbiota and potentially influence the process of neurodegeneration. Of note, there is a strong need for further investigation to map out the mechanistic prospects for the gut-brain axis and the clinical efficacy of probiotics. In this review, we discuss the importance of microbiome modulation and hemostasis via probiotics, prebiotics, postbiotics and synbiotics in ameliorating pathological neurodegenerative events. Also, we meticulously describe the underlying mechanism of action of probiotics and their metabolites on the gut-brain axis in different NDs. We suppose that the present work will provide a functional direction for the use of probiotic-based modalities in promoting current practical treatments for the management of neurodegenerative-related diseases.

Herbal medicines in Alzheimer's disease and the involvement of gut microbiota

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by memory loss and cognitive impairment. It severely affects the quality of life of victims. The prevalence of AD has been increasing in recent years. Therefore, it is of great importance to elucidate the pathogenic mechanism of AD and search for effective therapeutic approaches. Gut microbiota dysbiosis, an altered state of gut microbiota, has been well known for its involvement in the pathogenesis of AD. Much effort has been made in searching for approaches capable of modulating the composition of gut microbiota in recent years. Herbal medicines have attracted extensive attention in recent decades for the prevention and treatment of AD. Here, we gave an overview of the recent research progress on the modulatory effects of herbal medicines and herbal formulae on gut microbiota as well as the possible beneficial effects on AD, which may provide new insights into the discovery of anti-AD agents and their therapeutic potential for AD through modulating the composition of gut microbiota.

Microbiota-Gut-Brain Axis Dysregulation in Alzheimer's Disease: Multi-Pathway Effects and Therapeutic Potential

An essential regulator of neurodegenerative conditions like Alzheimer's disease (AD) is the gut microbiota. Alterations in intestinal permeability brought on by gut microbiota dysregulation encourage neuroinflammation, central immune dysregulation, and peripheral immunological dysregulation in AD, as well as hasten aberrant protein aggregation and neuronal death in the brain. However, it is unclear how the gut microbiota transmits information to the brain and how it influences brain cognition and function. In this review, we summarized the multiple pathways involved in the gut microbiome in AD and provided detailed treatment strategies based on the gut microbiome. Based on these observations, this review also discusses the problems, challenges, and strategies to address current therapeutic strategies.

Alzheimer's disease as a causal risk factor for diabetic retinopathy: a Mendelian randomization study

Objectives

This study aims to investigate the causal relationship between Alzheimer's Disease (AD) and Diabetic Retinopathy (DR).

Methods

Employing Mendelian Randomization (MR), Generalized Summary-data-based Mendelian Randomization (GSMR), and the MR-Steiger test, this study scrutinizes the genetic underpinnings of the hypothesized causal association between AD and DR, as well as its Proliferative DR (PDR) and Non-Proliferative DR (NPDR) subtypes. Comprehensive data from Genome-Wide Association Studies (GWAS) were analyzed, specifically AD data from the Psychiatric Genomics Consortium (71,880 cases/383,378 controls), and DR, PDR, and NPDR data from both the FinnGen consortium (FinnGen release R8, DR: 5,988 cases/314,042 controls; PDR: 8,383 cases/329,756 controls; NPDR: 3,446 cases/314,042 controls) and the IEU OpenGWAS (DR: 14,584 cases/176,010 controls; PDR: 8,681 cases/204,208 controls; NPDR: 2,026 cases/204,208 controls). The study also incorporated Functional Mapping and Annotation (FUMA) for an in-depth analysis of the GWAS results.

Results

The MR analyses revealed that genetic susceptibility to AD significantly increases the risk of DR, as evidenced by GWAS data from the FinnGen consortium (OR: 2.5090; 95% confidence interval (CI):1.2102-5.2018, false discovery rate P-value (PFDR)=0.0201; GSMR: bxy=0.8936, bxy_se=0.3759, P=0.0174), NPDR (OR: 2.7455; 95% CI: 1.3178-5.7197, PFDR=0.0166; GSMR: bxy=0.9682, bxy_se=0.3802, P=0.0126), and PDR (OR: 2.3098; 95% CI: 1.2411-4.2986, PFDR=0.0164; GSMR: bxy=0.7962, bxy_se=0.3205, P=0.0129) using DR GWAS from FinnGen consortium. These results were corroborated by DR GWAS datasets from IEU OpenGWAS. The MR-Steiger test confirmed a significant association of all identified instrumental variables (IVs) with AD. While a potential causal effect of DR and its subtypes on AD was identified, the robustness of these results was constrained by a low power value. FUMA analysis identified OARD1, NFYA, TREM1 as shared risk genes between DR and AD, suggesting a potential genetic overlap between these complex diseases.

Discussion

This study underscores the contribution of AD to an increased risk of DR, as well as NPDR and PDR subtypes, underscoring the necessity of a holistic approach in the management of patients affected by these conditions.

Connecting the Dots: The Cerebral Lymphatic System as a Bridge Between the Central Nervous System and Peripheral System in Health and Disease

As a recently discovered waste removal system in the brain, cerebral lymphatic system is thought to play an important role in regulating the homeostasis of the central nervous system. Currently, more and more attention is being focused on the cerebral lymphatic system. Further understanding of the structural and functional characteristics of cerebral lymphatic system is essential to better understand the pathogenesis of diseases and to explore therapeutic approaches. In this review, we summarize the structural components and functional characteristics of cerebral lymphatic system. More importantly, it is closely associated with peripheral system diseases in the gastrointestinal tract, liver, and kidney. However, there is still a gap in the study of the cerebral lymphatic system. However, we believe that it is a critical mediator of the interactions between the central nervous system and the peripheral system.

Systemic neutrophils are triggered by respiratory Bacillus Calmette- Guérin and mediate pulmonary mycobacterial clearance in synergy with the triggering receptor expressed on myeloid cells 1

Tuberculosis remains a threat to public health. The only approved vaccine, Bacillus Calmette-Guérin (BCG), is administered intradermally and provides limited protection, and its effect on innate immunity via the respiratory route has not been fully elucidated. A mouse model with genetically depleted TREM1 and seven-color flow cytometry staining were used to characterize the comprehensive immune response induced by respiratory BCG, through evaluating organ bacterial loads, lung histopathology, and lung immunohistochemistry. During respiratory BCG infection, the murine lungs displayed effective bacterial clearance. Notably, marked differences in neutrophils were observed between thymus and bone marrow cells, characterized by a significant increase in the expression of the triggering receptor expressed on myeloid cells 1 (TREM1). Subsequently, upon depletion of TREM1, a reduction in pulmonary neutrophils was observed, which further exacerbated bacterial loads and resulted in worsened pathology following respiratory BCG infection. In summary, up-regulated expression of TREM1 in rapidly increasing circulating neutrophil by pulmonary BCG is required for an efficient host response to BCG infection, and suggests the important role of TREM1 in neutrophil-related pulmonary bacteria clearance and pathology.

Contribution of Complement, Microangiopathy and Inflammation in Idiopathic Inflammatory Myopathies

PURPOSE OF REVIEW

Idiopathic inflammatory myopathies (IIMs) are a heterogeneous group characterized by muscle weakness and skin symptoms and are categorized into six subtypes: dermatomyositis (DM), polymyositis (PM), anti-synthetase syndrome (ASS), immune-mediated myopathy (IMNM), inclusion body myopathy (IBM), and overlap myositis. Myositis-specific autoantibodies were detected for the diagnosis and classification of IIM. This review highlights the pathogenic contributions of the complement system, microangiopathy, and inflammation in IIM.

RECENT FINDINGS

Deposition of complement around capillaries and/or the sarcolemma was observed in muscle biopsy specimens from patients with DM, ASS, and IMNM, suggesting the pathomechanism of complement-dependent muscle and endothelial cell injury. A recent study using human muscle microvascular endothelial cells showed that Jo-1 antibodies from ASS induce complement-dependent cellular cytotoxicity in vitro. Based on both clinical and pathological observations, antibody- and complement-mediated microangiopathy may contribute to the development of DM and anti-Jo-1 ASS. Juvenile DM is characterized by the loss of capillaries, perivascular inflammation, and small-vessel angiopathies, which may be related to microinfarction and perifascicular atrophy. Several serum biomarkers that reflect the IFN1 signature and microangiopathy are elevated in patients with DM. The pathological observation of myxovirus resistance protein A (MxA), which suggests a type 1 interferon (IFN1) signature in DM, supports the diagnosis and further understanding of the pathomechanism of IIM. A recent report showed that an increase in triggering receptor expressed on myeloid cells (TREM-1) around perimysial blood vessels and muscles in patients with IIM plays a role in triggering inflammation and promoting the migration of inflammatory cells by secreting proinflammatory cytokines, such as tumor necrosis factor α.

SUMMARY

The deposition of complement in muscles and capillaries is a characteristic feature of DM, ASS, and IMNM. Microangiopathy plays a pathogenic role in DM, possibly resulting in perifascicular atrophy. Further understanding of the detailed pathomechanism regarding complement, microangiopathy, and inflammation may lead to novel therapeutic approaches for IIM.

Prognostic utility of sTREM-1 in predicting early neurological deterioration in patients with acute ischemic stroke treated without reperfusion therapy

OBJECTIVE

Serum triggering receptor expressed on myeloid cells type 1 (sTREM-1) is a new type of immunoglobulin superfamily receptor related to inflammation that aggravates brain injury. This study aimed to assess the clinical value of sTREM-1 in predicting early neurological deterioration in patients with acute ischemic stroke (AIS) treated without reperfusion therapy.

METHODS

This prospective cohort study enrolled 315 patients with acute ischemic stroke admitted to the Affiliated Taizhou People's Hospital of Nanjing Medical University between October 2020 and October 2022. The study excluded patients treated with reperfusion therapy. sTREM-1 levels were evaluated within 24 h of the acute ischemic stroke. Early neurological deterioration (END) was defined as an increase in the National Institutes of Health Stroke Scale (NIHSS) score ≥ 4 points within three days after admission. Multivariable analyses were used to investigate the relationship between sTREM-1 levels and END.

RESULTS

A total of 81 (25.7 %) patients had early neurological deterioration. Patients in the END group had a higher NIHSS score at admission (P =0.007), CRP levels (P =0.011), white blood cell count (P =0.002), fasting blood glucose levels (P =0.028), and sTREM-1 levels (P <0.001). After adjusting for confounders, higher sTREM-1 levels were significantly associated with an increased risk of early neurological deterioration (OR, 1.98; 95 % CI, 1.17-3.38, P=0.012). Moreover, sTREM-1 levels efficiently differentiated END (area under the curve: 0.779; 95 % CI: 0.731-0.822). Furthermore, the results showed significant differences between the high sTREM-1 group and the low sTREM-1 group in NIHSS scores (P=0.019), C-reactive protein (P=0.018), white blood cell count (P=0.013), and the incidence of early neurological deterioration (P<0.001). According to the multivariate logistic regression model, we discovered that the high sTREM-1 group was a significant independent predictor of early neurological deterioration incidence (OR, 4.19; 95 % CI, 1.46-9.84; P= 0.003).

CONCLUSION

sTREM-1 could be a potential biomarker for predicting early neurological deterioration in AIS patients not treated with reperfusion therapy.

Unveiling the role of gut-brain axis in regulating neurodegenerative diseases: A comprehensive review

Emerging evidence have shown the importance of gut microbiota in regulating brain functions. The diverse molecular mechanisms involved in cross-talk between gut and brain provide insight into importance of this communication in maintenance of brain homeostasis. It has also been observed that disturbed gut microbiota contributes to neurological diseases such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis and aging. Recently, gut microbiome-derived exosomes have also been reported to play an essential role in the development and progression of neurodegenerative diseases and could thereby act as a therapeutic target. Further, pharmacological interventions including antibiotics, prebiotics and probiotics can influence gut microbiome-mediated management of neurological diseases. However, extensive research is warranted to better comprehend this interconnection in maintenance of brain homeostasis and its implication in neurological diseases. Thus, the present review is aimed to provide a detailed understanding of gut-brain axis followed by possibilities to target the gut microbiome for improving neurological health.

The Impact of Microbiota on the Gut-Brain Axis: Examining the Complex Interplay and Implications

The association and interaction between the central nervous system (CNS) and enteric nervous system (ENS) is well established. Essentially ENS is the second brain, as we call it. We tried to understand the structure and function, to throw light on the functional aspect of neurons, and address various disease manifestations. We summarized how various neurological disorders influence the gut via the enteric nervous system and/or bring anatomical or physiological changes in the enteric nervous system or the gut and vice versa. It is known that stress has an effect on Gastrointestinal (GI) motility and causes mucosal erosions. In our literature review, we found that stress can also affect sensory perception in the central nervous system. Interestingly, we found that mutations in the neurohormone, serotonin (5-HT), would result in dysfunctional organ development and further affect mood and behavior. We focused on the developmental aspects of neurons and cognition and their relation to nutritional absorption via the gastrointestinal tract, the development of neurodegenerative disorders in relation to the alteration in gut microbiota, and contrariwise associations between CNS disorders and ENS. This paper further summarizes the synergetic relation between gastrointestinal and neuropsychological manifestations and emphasizes the need to include behavioral therapies in management plans.

Jo-1 Antibodies From Myositis Induce Complement-Dependent Cytotoxicity and TREM-1 Upregulation in Muscle Endothelial Cells

BACKGROUND AND OBJECTIVES

Muscle microangiopathy due to dysfunction of endothelial cells because of inflammation is a critical hallmark of dermatomyositis (DM); however, its pathomechanism remains unclear. The aim of this study was to evaluate the effect of immunogloblin G (IgG) from patients with idiopathic inflammatory myopathies (IIM) on muscle endothelial cells in vitro.

METHODS

Using a high-content imaging system, we analyzed whether IgG purified from sera from patients with IIM (n = 15), disease controls (DCs: n = 7), and healthy controls (HCs: n = 7) can bind to muscle endothelial cells and induce complement-dependent cellular cytotoxicity.

RESULTS

IgGs from Jo-1 antibody myositis could bind to muscle endothelial cells and caused complement-dependent cell cytotoxicity. RNA-seq demonstrated the upregulation of genes associated with tumor necrosis factor (TNF)-α, triggering receptor expressed on myeloid cells-1 (TREM-1), CD25, and mitochondria pathways after exposure to IgG from the Jo-1, signal recognition particle (SRP), and polymyositis (PM) groups. The high-content imaging system showed that TREM-1 expression in the Jo-1, SRP, and PM groups was increased in comparison with DCs and HCs and that the TNF-α expression in the Jo-1 group was higher in comparison with the SRP, PM, DC, and HC groups. The expression of TREM-1 was observed in biopsied capillaries and the muscle membrane from patients with Jo-1 and in biopsied muscle fiber and capillaries from patients with DM and SRP. The depletion of Jo-1 antibodies by IgG of patients with Jo-1 antibody myositis reduced the Jo-1 antibody-induced complement-dependent cellular cytotoxicity in muscle endothelial cells.

DISCUSSION

Jo-1 antibodies from Jo-1 antibody myositis show complement-dependent cellular cytotoxicity in muscle endothelial cells. IgGs from patients with Jo-1, SRP, and DM increase the TREM-1 expression in endothelial cells and muscles.

The microglial innate immune receptors TREM-1 and TREM-2 in the anterior cingulate cortex (ACC) drive visceral hypersensitivity and depressive-like behaviors following DSS-induced colitis

Inflammatory bowel disease (IBD) is a chronic condition with a high recurrence rate. To date, the clinical treatment of IBD mainly focuses on inflammation and gastrointestinal symptoms while ignoring the accompanying visceral pain, anxiety, depression, and other emotional symptoms. Evidence is accumulating that bi-directional communication between the gut and the brain is indispensable in the pathophysiology of IBD and its comorbidities. Increasing efforts have been focused on elucidating the central immune mechanisms in visceral hypersensitivity and depression following colitis. The triggering receptors expressed on myeloid cells-1/2 (TREM-1/2) are newly identified receptors that can be expressed on microglia. In particular, TREM-1 acts as an immune and inflammatory response amplifier, while TREM-2 may function as a molecule with a putative antagonist role to TREM-1. In the present study, using the dextran sulfate sodium (DSS)-induced colitis model, we found that peripheral inflammation induced microglial and glutamatergic neuronal activation in the anterior cingulate cortex (ACC). Microglial ablation mitigated visceral hypersensitivity in the inflammation phase rather than in the remission phase, subsequently preventing the emergence of depressive-like behaviors in the remission phase. Moreover, a further mechanistic study revealed that overexpression of TREM-1 and TREM-2 remarkably aggravated DSS-induced neuropathology. The improved outcome was achieved by modifying the balance of TREM-1 and TREM-2 via genetic and pharmacological means. Specifically, a deficiency of TREM-1 attenuated visceral hyperpathia in the inflammatory phase, and a TREM-2 deficiency improved depression-like symptoms in the remission phase. Taken together, our findings provide insights into mechanism-based therapy for inflammatory disorders and establish that microglial innate immune receptors TREM-1 and TREM-2 may represent a therapeutic target for the treatment of pain and psychological comorbidities associated with chronic inflammatory diseases by modulating neuroinflammatory responses.

TREM-1 triggers necroptosis of macrophages through mTOR-dependent mitochondrial fission during acute lung injury

BACKGROUND

Necroptosis of macrophages is a necessary element in reinforcing intrapulmonary inflammation during acute lung injury (ALI). However, the molecular mechanism that sparks macrophage necroptosis is still unclear. Triggering receptor expressed on myeloid cells-1 (TREM-1) is a pattern recognition receptor expressed broadly on monocytes/macrophages. The influence of TREM-1 on the destiny of macrophages in ALI requires further investigation.

METHODS

TREM-1 decoy receptor LR12 was used to evaluate whether the TREM-1 activation induced necroptosis of macrophages in lipopolysaccharide (LPS)-induced ALI in mice. Then we used an agonist anti-TREM-1 Ab (Mab1187) to activate TREM-1 in vitro. Macrophages were treated with GSK872 (a RIPK3 inhibitor), Mdivi-1 (a DRP1 inhibitor), or Rapamycin (an mTOR inhibitor) to investigate whether TREM-1 could induce necroptosis in macrophages, and the mechanism of this process.

RESULTS

We first observed that the blockade of TREM-1 attenuated alveolar macrophage (AlvMs) necroptosis in mice with LPS-induced ALI. In vitro, TREM-1 activation induced necroptosis of macrophages. mTOR has been previously linked to macrophage polarization and migration. We discovered that mTOR had a previously unrecognized function in modulating TREM-1-mediated mitochondrial fission, mitophagy, and necroptosis. Moreover, TREM-1 activation promoted DRP1^Ser616 phosphorylation through mTOR signaling, which in turn caused surplus mitochondrial fission-mediated necroptosis of macrophages, consequently exacerbating ALI.

CONCLUSION

In this study, we reported that TREM-1 acted as a necroptotic stimulus of AlvMs, fueling inflammation and aggravating ALI. We also provided compelling evidence suggesting that mTOR-dependent mitochondrial fission is the underpinning of TREM-1-triggered necroptosis and inflammation. Therefore, regulation of necroptosis by targeting TREM-1 may provide a new therapeutic target for ALI in the future.

The CDR3 region as the major driver of TREM-1 interaction with its ligands, an in silico characterization

The triggering receptor expressed on myeloid cells-1 (TREM-1) is a pattern recognition receptor heavily investigated in infectious and non-infectious diseases. Because of its role in amplifying inflammation, TREM-1 has been explored as a diagnostic/prognostic biomarker. Further, as the receptor has been implicated in the pathophysiology of several diseases, therapies aiming at modulating its activity represent a promising strategy to constrain uncontrolled inflammatory or infectious diseases. Despite this, several aspects concerning its interaction with ligands and activation process, remain unclear. Although many molecules have been suggested as TREM-1 ligands, only five have been confirmed to interact with the receptor: actin, eCIRP, HMGB1, Hsp70 and PGLYRP1. However, the domains involved in the interaction between the receptor and these proteins are not clarified yet. Therefore, here we used in silico approaches to investigate the putative binding domains in the receptor, using hot spots analysis, molecular docking and molecular dynamics simulations between TREM-1 and its five known ligands. Our results indicated the complementarity-determining regions (CDRs) of the receptor as the main mediators of antigen recognition, especially the CDR3 loop. We believe that our study could be used as structural basis for the elucidation of TREM-1's recognition process, and may be useful for prospective in silico and biological investigations exploring the receptor in different contexts.

Macrophage-Targeted Sodium Chlorite (NP001) Slows Progression of Amyotrophic Lateral Sclerosis (ALS) through Regulation of Microbial Translocation

Amyotrophic lateral sclerosis (ALS) is a heterogeneous, progressive, and universally fatal neurodegenerative disease. A subset of ALS patients has measurable plasma levels of lipopolysaccharide (LPS) and C-reactive protein (CRP) consistent with low-grade microbial translocation (MT). Unless interrupted, MT sets up a self-perpetuating loop of inflammation associated with systemic macrophage activation. To test whether MT contributed to ALS progression, blood specimens from a phase 2 study of NP001 in ALS patients were evaluated for changes in activity in treated patients as compared to controls over the 6-month study. In this post hoc analysis, plasma specimens from baseline and six-month timepoints were analyzed. Compared with baseline values, biomarkers related to MT were significantly decreased (LPS, LPS binding protein (LBP), IL-18, Hepatocyte growth factor (HGF), soluble CD163 (sCD163)) in NP001-treated patients as compared to controls, whereas wound healing and immunoregulatory factors were increased (IL-10, Epidermal growth factor (EGF), neopterin) by the end of study. These biomarker results linked to the positive clinical trial outcome confirm that regulation of macrophage activation may be an effective approach for the treatment of ALS and, potentially, other neuroinflammatory diseases related to MT.

Manipulation of the diet-microbiota-brain axis in Alzheimer's disease

Several studies investigating the pathogenesis of Alzheimer's disease have identified various interdependent constituents contributing to the exacerbation of the disease, including Aβ plaque formation, tau protein hyperphosphorylation, neurofibrillary tangle accumulation, glial inflammation, and the eventual loss of proper neural plasticity. Recently, using various models and human patients, another key factor has been established as an influential determinant in brain homeostasis: the gut-brain axis. The implications of a rapidly aging population and the absence of a definitive cure for Alzheimer's disease have prompted a search for non-pharmaceutical tools, of which gut-modulatory therapies targeting the gut-brain axis have shown promise. Yet multiple recent studies examining changes in human gut flora in response to various probiotics and environmental factors are limited and difficult to generalize; whether the state of the gut microbiota in Alzheimer's disease is a cause of the disease, a result of the disease, or both through numerous feedback loops in the gut-brain axis, remains unclear. However, preliminary findings of longitudinal studies conducted over the past decades have highlighted dietary interventions, especially Mediterranean diets, as preventative measures for Alzheimer's disease by reversing neuroinflammation, modifying the intestinal and blood-brain barrier (BBB), and addressing gut dysbiosis. Conversely, the consumption of Western diets intensifies the progression of Alzheimer's disease through genetic alterations, impaired barrier function, and chronic inflammation. This review aims to support the growing body of experimental and clinical data highlighting specific probiotic strains and particular dietary components in preventing Alzheimer's disease via the gut-brain axis.

Phase 2B randomized controlled trial of NP001 in amyotrophic lateral sclerosis: pre‐specified and post‐hoc analyses

Introduction/Aims

ALS is a heterogeneous disease that may be complicated or in part driven by inflammation. NP001, a regulator of macrophage activation, was associated with slowing disease progression in those with higher levels of the plasma inflammatory marker C‐reactive protein (CRP) in phase 2A studies in ALS. Here, we evaluate the effects of NP001 in a phase 2B trial, and perform a post hoc analysis with combined data from the preceding phase 2A trial.

Methods

The phase 2B trial enrolled 138 participants within 3 y of symptom onset and with plasma hs‐CRP values >1.13 mg/L. They were randomized 1:1 to receive either placebo or NP001 for 6 mo. Change from baseline ALSFRS‐R scores was the primary efficacy endpoint. Secondary endpoints included vital capacity (VC) change from baseline and percentage of participants showing no decline of ALSFRS‐R score over 6 mo (non‐progressor).

Results

The phase 2B study did not show significant differences between placebo and active treatment with respect to change in ALSFRS‐R scores, or VC. The drug was safe and well tolerated. A post hoc analysis identified a 40‐ to 65‐y‐old subset in which NP001‐treated patients demonstrated slower declines in ALSFRS‐R score by 36% and VC loss by 51% compared with placebo. A greater number of non‐progressors were NP001‐treated compared with placebo (p = .004).

Discussion

Although the phase 2B trial failed to meet its primary endpoints, post hoc analyses identified a subgroup whose decline in ALSFRS‐R and VC scores were significantly slower than placebo. Further studies will be required to validate these findings.

Targeting TREM2 for Parkinson's Disease: Where to Go?

Parkinson’s disease (PD) is one of most common neurodegenerative disorders caused by a combination of environmental and genetic risk factors. Currently, numerous population genetic studies have shown that polymorphisms in myeloid cell-triggered receptor II (TREM2) are associated with a variety of neurodegenerative disorders. Recently, TREM2 has been verified to represent a promising candidate gene for PD susceptibility and progression. For example, the expression of TREM2 was apparently increased in the prefrontal cortex of PD patients. Moreover, the rare missense mutations in TREM2 (rs75932628, p.R47H) was confirmed to be a risk factor of PD. In addition, overexpression of TREM2 reduced dopaminergic neurodegeneration in the 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine mouse model of PD. Due to the complex pathogenesis of PD, there is still no effective drug treatment. Thus, TREM2 has received increasing widespread attention as a potential therapeutic target. This review focused on the variation of TREM2 in PD and roles of TREM2 in PD pathogenesis, such as excessive-immune inflammatory response, α-Synuclein aggregation and oxidative stress, to further provide evidence for new immune-related biomarkers and therapies for PD.

Differential expression of Triggering Receptor Expressed on Myeloid cells 2 (Trem2) in tissue eosinophils

No longer regarded simply as end-stage cytotoxic effectors, eosinophils are now recognized as complex cells with unique phenotypes that develop in response stimuli in the local microenvironment. In our previous study, we documented eosinophil infiltration in damaged muscle characteristic of dystrophin-deficient (mdx) mice that model Duchenne muscular dystrophy. Specifically, we found that eosinophils did not promote the generation of muscle lesions, as these persisted in eosinophil-deficient mdx.PHIL mice. To obtain additional insight into these findings, we performed RNA sequencing of eosinophils isolated from muscle tissue of mdx, IL5tg, and mdx.IL5tg mice. We observed profound up-regulation of classical effector proteins (major basic protein-1, eosinophil peroxidase, and eosinophil-associated ribonucleases) in eosinophils isolated from lesion-free muscle from IL5tg mice. By contrast, we observed significant up-regulation of tissue remodeling genes, including proteases, extracellular matrix components, collagen, and skeletal muscle precursors, as well as the immunomodulatory receptor, Trem2, in eosinophils isolated from skeletal muscle tissue from the dystrophin-deficient mdx mice. Although the anti-inflammatory properties of Trem2 have been described in the monocyte/macrophage lineage, no previous studies have documented its expression in eosinophils. We found that Trem2 was critical for full growth and differentiation of bone marrow-derived eosinophil cultures and full expression of TLR4. Immunoreactive Trem2 was also detected on human peripheral blood eosinophils at levels that correlated with donor body mass index and total leukocyte count. Taken together, our findings provide important insight into the immunomodulatory and remodeling capacity of mouse eosinophils and the flexibility of their gene expression profiles in vivo.

The Gut-Brain Axis in Inflammatory Bowel Disease-Current and Future Perspectives

The gut–brain axis is a bidirectional communication system driven by neural, hormonal, metabolic, immunological, and microbial signals. Signaling events from the gut can modulate brain function and recent evidence suggests that the gut–brain axis may play a pivotal role in linking gastrointestinal and neurological diseases. Accordingly, accumulating evidence has suggested a link between inflammatory bowel diseases (IBDs) and neurodegenerative, as well as neuroinflammatory diseases. In this context, clinical, epidemiological and experimental data have demonstrated that IBD predisposes a person to pathologies of the central nervous system (CNS). Likewise, a number of neurological disorders are associated with changes in the intestinal environment, which are indicative for disease-mediated gut–brain inter-organ communication. Although this axis was identified more than 20 years ago, the sequence of events and underlying molecular mechanisms are poorly defined. The emergence of precision medicine has uncovered the need to take into account non-intestinal symptoms in the context of IBD that could offer the opportunity to tailor therapies to individual patients. The aim of this review is to highlight recent findings supporting the clinical and biological link between the gut and brain, as well as its clinical significance for IBD as well as neurodegeneration and neuroinflammation. Finally, we focus on novel human-specific preclinical models that will help uncover disease mechanisms to better understand and modulate the function of this complex system.

Immunoinflammatory role of apolipoprotein E4 in malnutrition and enteric infections and the increased risk for chronic diseases under adverse environments

Apolipoprotein E plays a crucial role in cholesterol metabolism. The immunomodulatory functions of the human polymorphic APOE gene have gained particular interest because APOE4, a well-recognized risk factor for late-onset Alzheimer's disease, has also been recently linked to increased risk of COVID-19 infection severity in a large UK biobank study. Although much is known about apoE functions in the nervous system, much less is known about APOE polymorphism effects on malnutrition and enteric infections and the consequences for later development in underprivileged environments. In this review, recent findings are summarized of apoE's effects on intestinal function in health and disease and the role of APOE4 in protecting against infection and malnutrition in children living in unfavorable settings, where poor sanitation and hygiene prevail, is highlighted. The potential impact of APOE4 on later development also is discussed and gaps in knowledge are identified that need to be addressed to protect children's development under adverse environments.

The Baseline Structure of the Enteric Nervous System and Its Role in Parkinson's Disease

The gastrointestinal (GI) tract is provided with a peculiar nervous network, known as the enteric nervous system (ENS), which is dedicated to the fine control of digestive functions. This forms a complex network, which includes several types of neurons, as well as glial cells. Despite extensive studies, a comprehensive classification of these neurons is still lacking. The complexity of ENS is magnified by a multiple control of the central nervous system, and bidirectional communication between various central nervous areas and the gut occurs. This lends substance to the complexity of the microbiota–gut–brain axis, which represents the network governing homeostasis through nervous, endocrine, immune, and metabolic pathways. The present manuscript is dedicated to identifying various neuronal cytotypes belonging to ENS in baseline conditions. The second part of the study provides evidence on how these very same neurons are altered during Parkinson’s disease. In fact, although being defined as a movement disorder, Parkinson’s disease features a number of degenerative alterations, which often anticipate motor symptoms. Among these, the GI tract is often involved, and for this reason, it is important to assess its normal and pathological structure. A deeper knowledge of the ENS is expected to improve the understanding of diagnosis and treatment of Parkinson’s disease.

TREM1 Blockade Ameliorates Lipopolysaccharide-Induced Acute Intestinal Dysfunction through Inhibiting Intestinal Apoptosis and Inflammation Response

OBJECTIVE

The lipopolysaccharide- (LPS-) induced acute intestinal dysfunction model has been widely applied in recent years. Here, our aim was to investigate the effect of triggering receptor expressed on myeloid cells-1 (TREM1) inhibitor in LPS-induced acute intestinal dysfunction.

METHODS

Male rats were randomly assigned into normal (saline injection), model (LPS and saline injection), and LP17 (LPS and LP17 (a synthetic TREM1 inhibitor) injection) groups. The levels of intestinal TREM1 expression were evaluated by immunohistochemistry and western blot. Intestinal permeability and apoptosis were separately assessed by the lactulose/mannitol (L/M) ratio and TUNEL assay. The levels of soluble TREM1 (sTREM1), TNF-α, IL-6, and IL-1β were measured in the plasma and intestinal tissues by ELISA. The expression levels of NF-κB, high-mobility group box 1 (HMGB1), and toll-like receptor 4 (TLR-4) were measured with RT-qPCR and western blot. After transfection with si-TREM1 in LPS-induced intestinal epithelium-6 (IEC-6) cells, p-p65 and p-IκBα levels were detected by western blot.

RESULTS

LP17-mediated TREM1 inhibition alleviated the intestine tissue damage in rats with LPS-induced acute intestinal dysfunction. LP17 attenuated the LPS-induced increase in sTREM1, TNF-α, IL-6, and IL-1β levels in the plasma and intestinal tissues. Furthermore, intestine permeability and epithelial cell apoptosis were ameliorated by LP17. LP17 attenuated the LPS-induced increase in the expression of TREM1, HMGB1, TLR-4, and NF-κB in the intestine tissues. In vitro, TREM1 knockdown inactivated the NF-κB signaling in LPS-induced IEC-6 cells.

CONCLUSION

LP17 could ameliorate LPS-induced acute intestinal dysfunction, which was associated with inhibition of intestinal apoptosis and inflammation response.

Microglia Specific Drug Targeting Using Natural Products for the Regulation of Redox Imbalance in Neurodegeneration

Microglia, a type of innate immune cell of the brain, regulates neurogenesis, immunological surveillance, redox imbalance, cognitive and behavioral changes under normal and pathological conditions like Alzheimer's, Parkinson's, Multiple sclerosis and traumatic brain injury. Microglia produces a wide variety of cytokines to maintain homeostasis. It also participates in synaptic pruning and regulation of neurons overproduction by phagocytosis of neural precursor cells. The phenotypes of microglia are regulated by the local microenvironment of neurons and astrocytes via interaction with both soluble and membrane-bound mediators. In case of neuron degeneration as observed in acute or chronic neurodegenerative diseases, microglia gets released from the inhibitory effect of neurons and astrocytes, showing activated phenotype either of its dual function. Microglia shows neuroprotective effect by secreting growths factors to heal neurons and clears cell debris through phagocytosis in case of a moderate stimulus. But the same microglia starts releasing pro-inflammatory cytokines like TNF-α, IFN-γ, reactive oxygen species (ROS), and nitric oxide (NO), increasing neuroinflammation and redox imbalance in the brain under chronic signals. Therefore, pharmacological targeting of microglia would be a promising strategy in the regulation of neuroinflammation, redox imbalance and oxidative stress in neurodegenerative diseases. Some studies present potentials of natural products like curcumin, resveratrol, cannabidiol, ginsenosides, flavonoids and sulforaphane to suppress activation of microglia. These natural products have also been proposed as effective therapeutics to regulate the progression of neurodegenerative diseases. The present review article intends to explain the molecular mechanisms and functions of microglia and molecular dynamics of microglia specific genes and proteins like Iba1 and Tmem119 in neurodegeneration. The possible interventions by curcumin, resveratrol, cannabidiol, ginsenosides, flavonoids and sulforaphane on microglia specific protein Iba1 suggest possibility of natural products mediated regulation of microglia phenotypes and its functions to control redox imbalance and neuroinflammation in management of Alzheimer's, Parkinson's and Multiple Sclerosis for microglia-mediated therapeutics.

Glymphatic System as a Gateway to Connect Neurodegeneration From Periphery to CNS

The classic concept of the absence of lymphatic vessels in the central nervous system (CNS), suggesting the immune privilege of the brain in spite of its high metabolic rate, was predominant until recent times. On the other hand, this idea left questioned how cerebral interstitial fluid is cleared of waste products. It was generally thought that clearance depends on cerebrospinal fluid (CSF). Not long ago, an anatomically and functionally discrete paravascular space was revised to provide a pathway for the clearance of molecules drained within the interstitial space. According to this model, CSF enters the brain parenchyma along arterial paravascular spaces. Once mixed with interstitial fluid and solutes in a process mediated by aquaporin-4, CSF exits through the extracellular space along venous paravascular spaces, thus being removed from the brain. This process includes the participation of perivascular glial cells due to a sieving effect of their end-feet. Such draining space resembles the peripheral lymphatic system, therefore, the term "glymphatic" (glial-lymphatic) pathway has been coined. Specific studies focused on the potential role of the glymphatic pathway in healthy and pathological conditions, including neurodegenerative diseases. This mainly concerns Alzheimer's disease (AD), as well as hemorrhagic and ischemic neurovascular disorders; other acute degenerative processes, such as normal pressure hydrocephalus or traumatic brain injury are involved as well. Novel morphological and functional investigations also suggested alternative models to drain molecules through perivascular pathways, which enriched our insight of homeostatic processes within neural microenvironment. Under the light of these considerations, the present article aims to discuss recent findings and concepts on nervous lymphatic drainage and blood-brain barrier (BBB) in an attempt to understand how peripheral pathological conditions may be detrimental to the CNS, paving the way to neurodegeneration.

TREM-1 isoforms in bacterial infections: to immune modulation and beyond

The triggering receptor expressed on myeloid cells 1 (TREM-1) is an innate immunity receptor associated with the amplification of inflammation in sterile and non-sterile inflammatory disorders. Since its first description, the two isoforms of the receptor, membrane and soluble (mTREM-1 and sTREM-1, respectively) have been largely explored in the immunopathogenesis of several bacterial diseases and sepsis. The role of the receptor in these scenarios seems to be at least partly dependent on the source/type of bacteria, host and context. As uncontrolled inflammation is a result of several bacterial infections, the inhibition of the receptor has been considered as a promising approach to treat such conditions. Further, sTREM-1 has been explored as a biomarker for diagnosis and/or prognosis of several bacterial diseases. Therefore, this review aims to provide an updated insight into how the receptor influences and is influenced by bacterial infections, highlighting the advances regarding the use/manipulation of TREM-1 isoforms in biomedical research and clinical practice.

The Immunopathogenesis of Alzheimer's Disease Is Related to the Composition of Gut Microbiota

The microbiota-gut-brain axis plays an important role in the development of neurodegenerative diseases. Commensal and pathogenic enteric bacteria can influence brain and immune system function by the production of lipopolysaccharides and amyloid. Dysbiosis of the intestinal microbiome induces local and consecutively systemic immune-mediated inflammation. Proinflammatory cytokines then trigger neuroinflammation and finally neurodegeneration. Immune-mediated oxidative stress can lead to a deficiency of vitamins and essential micronutrients. Furthermore, the wrong composition of gut microbiota might impair the intake and metabolization of nutrients. In patients with Alzheimer's disease (AD) significant alterations of the gut microbiota have been demonstrated. Standard Western diet, infections, decreased physical activity and chronic stress impact the composition and diversity of gut microbiota. A higher abundancy of "pro-inflammatory" gut microbiota goes along with enhanced systemic inflammation and neuroinflammatory processes. Thus, AD beginning in the gut is closely related to the imbalance of gut microbiota. Modulation of gut microbiota by Mediterranean diet, probiotics and curcumin can slow down cognitive decline and alter the gut microbiome significantly. A multi-domain intervention approach addressing underlying causes of AD (inflammation, infections, metabolic alterations like insulin resistance and nutrient deficiency, stress) appears very promising to reduce or even reverse cognitive decline by exerting positive effects on the gut microbiota.

Dexmedetomidine attenuates sepsis-associated inflammation and encephalopathy via central α2A adrenoceptor

Sepsis-associated encephalopathy (SAE) is a significant clinical issue that is associated with increased mortality and cost of health care. Dexmedetomidine, an α2 adrenoceptor agonist that is used to provide sedation, has been shown to induce neuroprotection under various conditions. This study was designed to determine whether dexmedetomidine protects against SAE and whether α2 adrenoceptor plays a role in this protection. Six- to eight-week old CD-1 male mice were subjected to cecal ligation and puncture (CLP). They were treated with intraperitoneal injection of dexmedetomidine in the presence or absence of α2 adrenoceptor antagonists, atipamezole or yohimbine, or an α2A adrenoceptor antagonist, BRL-44408. Hippocampus and blood were harvested for measuring cytokines. Mice were subjected to Barnes maze and fear conditioning 14 days after CLP to evaluate their learning and memory. CLP significantly increased the proinflammatory cytokines including tumor necrosis factor α, interleukin (IL)-6 and IL-1β in the blood and hippocampus. CLP also increased the permeability of blood-brain barrier (BBB) and impaired learning and memory. These CLP detrimental effects were attenuated by dexmedetomidine. Intracerebroventricular application of atipamezole, yohimbine or BRL-44408 blocked the protection of dexmedetomidine on the brain but not on the systemic inflammation. Astrocytes but not microglia expressed α2A adrenoceptors. Microglial depletion did not abolish the protective effects of dexmedetomidine. These results suggest that dexmedetomidine reduces systemic inflammation, neuroinflammation, injury of BBB and cognitive dysfunction in septic mice. The protective effects of dexmedetomidine on the brain may be mediated by α2A adrenoceptors in the astrocytes.

Serum Levels of Soluble Triggering Receptor Expressed on Myeloid Cells-1 Associated with the Severity and Outcome of Acute Ischemic Stroke

Stroke is a neurological emergency, where the mechanism of the blood supply to the brain is impaired, resulting in brain cell ischemia and death. Neuroinflammation is a key component in the ischemic cascade that results in cell damage and death after cerebral ischemia. The triggering receptor expressed on myeloid cells-1 (TREM-1) modulates neuroinflammation after acute ischemic stroke. In the present study, 60 patients with acute ischemic stroke, who had been subjected to neurological examinations and National Institutes of Health Stroke Scale (NIHSS) and brain magnetic resonance imaging studies, were enrolled in the emergency room of Kaohsiung Chang Gung Memorial Hospital. Twenty-four healthy volunteers were recruited as controls. The serum levels of soluble TREM-1 (sTREM-1), human S100 calcium-binding protein B (S100B), and proinflammatory cytokines and chemokines, including tumor necrosis α (TNF-α), interleukin 1β, interleukin 6 (IL-6), interleukin 8, and interferon-γ were measured immediately after acute ischemic stroke. The serum levels of sTREM-1, TNFα, IL-6, and S100B were correlated with the stroke volume and NIHSS, after acute ischemic stroke. Additionally, the serum levels of sTREM-1 were significantly positively correlated with S100B. The functional outcomes were evaluated 6 months after ischemic stroke by the Barthel index, which was correlated with the age and levels of sTREM-1 and S100B. We suggest that acute ischemic stroke induces neuroinflammation by the activation of the TREM-1 signaling pathway and the downstream inflammatory machinery that modulates the inflammatory response and ischemic neuronal cell death. From a translational perspective, our results may allow for the development of a new therapeutic strategy for acute ischemic stroke by targeting the TREM-1 signaling pathway.