Alzheimer's disease: The role of T lymphocytes in neuroinflammation and neurodegeneration

Peripheral lymphocyte counts and regional cerebral blood flow on brain SPECT correlate in Alzheimer's disease: A retrospective cross-sectional study

BACKGROUND

Given emerging evidence of immune involvement in Alzheimer's disease (AD), we aimed to clarify whether peripheral lymphocyte counts are associated with regional cerebral blood flow (rCBF) as measured by brain single-photon emission computed tomography (SPECT). Identifying such a relationship may help to establish early, accessible biomarkers of disease progression.

METHODS

Participants were 111 patients diagnosed with AD at the Yokohama City University Hospital Medical Center for Dementia Diseases between January 2021 and December 2023 and who underwent blood tests and brain SPECT. Sex, age, cognitive function tests, peripheral blood values, and rCBF on brain SPECT were investigated retrospectively. Neutrophil and lymphocyte counts were extracted from blood values. In addition, the rCBF in each region (frontal, parietal, temporal, occipital, and limbic system) was calculated from brain SPECT, and correlation analysis between lymphocytes and rCBF was performed.

RESULTS

Significant positive correlations between lymphocyte counts in peripheral blood and rCBF were found in all regions except the left frontal lobe. In particular, the correlation coefficient between rCBF and lymphocyte count was highest in the right temporal lobe (ρ = 0.311, P = 0.001).

CONCLUSIONS

Peripheral blood lymphocyte counts are positively related to rCBF on brain SPECT, and lymphocytes can be an early biomarker that can be tested inexpensively and easily. Limitations include the retrospective cross-sectional design and single-center setting, which preclude analysis of causality and changes over time.

Rejuvenation of thymus and modulation of local and systemic T cell responses in animal model of Alzheimer's disease following cell therapy using sperm head

In Alzheimer's disease (AD), the balance of T cell response in the brain is dysregulated due to increase of T-helper 1 (Th1) and Th17 over Th2 response. Considering the link between local and systemic immune response, it is important to modulate brain pattern of T cell in harmony with the systemic immune system. Some studies also attempted to rejuvenate thymus which is affected in AD. Based on immunologic properties of sperm, previous studies demonstrated significant therapeutic effects of sperm head on the brain AD animal models. In this study, pattern of T cell response was determined locally in the brain and systemically in the cervical lymph nodes, and spleen. Thymus health status was also evaluated using forkhead box N1 (FOXN1). The results were compared between control and sperm head-treated AD model animals. In the brain, cervical lymph nodes, and spleen, treatment with sperm head significantly decreased interferon-gamma (IFN-γ) along with interleukin-17 (IL-17) and increased IL-4, representative of Th1, Th17, and Th2, respectively. Surprisingly, in the sperm head-treated AD model animals, significant decrease was observed in regulatory T cells (Treg), represented by cluster of designation 4 (CD4), CD25, and FOXP3 high expression. Interestingly, sperm head had significant rejuvenation effects on the thymus represented by increase in FOXN1. The results show that sperm head could deviate chronic inflammation towards a constructive inflammation. Results suggest revision of our attitude towards the inflammation as the results suggest that boosting inflammation can be more efficient than suppressing inflammation for treatment of AD.

Unmasking a Paradox: Roles of the PD-1/PD-L1 Axis in Alzheimer's Disease-Associated Neuroinflammation

Alzheimer's disease (AD) represents the most prevalent form of dementia, characterized by progressive cognitive impairment and chronic neuroinflammation. Immune checkpoint inhibitors (ICIs), including anti-programmed cell death (PD)-1 and anti-PD-L1, signify a revolutionary advancement in cancer treatment by preventing T-cell exhaustion; however, their therapeutic application in AD presents a conundrum. Hypothesis: Recent preclinical studies indicate that PD-1 inhibition in AD mouse models induces an interferon-gamma (IFN-γ)-mediated response, leading to increased recruitment of monocyte-derived macrophages into the brain, enhanced clearance of amyloid-beta (Aβ) plaques, and improved cognitive performance. Nonetheless, this therapeutic effect is counterbalanced by the potential for exacerbated neuroinflammation, as PD-1/PD-L1 blockade may potentiate pro-inflammatory T helper (Th)1 and Th17 responses. In this review, we critically discuss the pertinent pro-inflammatory and neuroprotective facets of T cell biology in the pathogenesis of AD, emphasizing the potential for modulation of the PD-1/PD-L1 axis to influence both Aβ clearance and the dynamics of neuroinflammatory processes. In summary, we determine that ICIs are promising tools for reducing AD pathology and improving cognition. However, it is essential to refine treatment protocols and carefully select patients to optimize neuroprotective effects while adequately considering inflammatory risks.

Controversies and insights into cytokine regulation of neurogenesis and behavior in adult rodents

Adult learning, memory, and social interaction partially depend on neurogenesis in two regions: the hippocampus and the subventricular zone. There is evidence that the immune system is important for these processes in pathological situations, but there is no review of its role in non-pathological or near-physiological conditions. Although further research is warranted in this area, some conclusions can be drawn. Intrusive LyC6hi monocytes and autoreactive CD4+ T cells have a positive impact on neurogenesis and behavior, but the latter are deleterious if specific to external antigens. Mildly activated microglia play a crucial role in promoting these processes, by eliminating apoptotic neuronal progenitors and producing low levels of interleukins, which increase if the cells are activated, leading to inhibition of neurogenesis. Chemokines are poorly studied, but progenitor cells and neurons express their receptors, which appear important for migration and maturation. The few works that jointly analyzed neurogenesis and behavior showed congruent effects of immune cells and cytokines. In conclusion, the immune system components -mostly local- seem of utmost importance for the control of behavior under non-pathological conditions.

T-regulatory cells and extracellular vesicles in Alzheimer's disease: New therapeutic concepts and hypotheses

Cell-based treatment has experienced exponential expansion in recent years in terms of clinical application and market share among pharmaceutical companies. When malignant cells in a healthy individual produce antigenic peptides derived from mutant or improperly synthesized proteins, the immune system attacks and kills the transforming cells. This process is carried out continuously by immune cells scanning the body for altered cells that could cause some harm. T-regulatory cells (Tregs), which preserve immunological tolerance and can exert neuroprotective benefits in numerous disorders, including animal models of Alzheimer's disease (AD), have demonstrated considerable therapeutic potential. Evidence also suggests that not only Tregs, but extracellular vesicles (EVs) are involved in a wide range of diseases, such as cellular homoeostasis, infection propagation, cancer development and heart disease, and have become a promisor cell-based therapeutic field too. Nevertheless, despite significant recent clinical and commercial breakthroughs, cell-based medicines still confront numerous challenges that hinder their general translation and commercialization. These challenges include, but are not limited to, choosing the best cell source, and creating a product that is safe, adequately viable, and fits the needs of individual patients and diseases. Here, we summarize what we know about Tregs and EVs and their potential therapeutic usage in AD.

Influence of immune cells and inflammatory factors on Alzheimer's disease axis: evidence from mediation Mendelian randomization study

BACKGROUND

Alzheimer's disease (AD) is one of the most common forms of dementia in the elderly, characterized by progressive neurodegeneration. While the exact etiology of AD remains unclear, immune inflammation is known to play a significant role in the disease.

METHODS

This study utilized a two-sample Mendelian randomization (MR) approach to assess the causal relationship between different types of immune cells and AD, while considering inflammatory factors as intermediate variables. Data were collected from three sources: immune cell data (731 phenotypes), inflammatory factors (48 cytokines from 8,293 individuals), and AD data (35,274 cases, 59,163 controls). Multiple MR methods were employed to minimize bias, and detailed descriptions of instrumental variable selection and statistical methods were provided.

RESULTS

The study findings suggest potential causal relationships between six different types of immune cells and AD, as well as causal relationships between 13 immune cells and inflammatory factors. Additionally, two statistically significant inflammatory factors were found to have potential causal relationships with AD. Specifically, immune cells CD33-HLA DR + and CD45 on CD33-HLA DR + may further influence AD by regulating Interleukin-2 levels.

CONCLUSION

This study provides valuable insights into the immunoinflammatory pathogenesis of AD and offers partial guidance for the development of relevant interventions, thereby contributing beneficial information for the prevention and treatment of related diseases.

Uric Acid: A Biomarker and Pathogenic Factor of Affective Disorders and Neurodegenerative Diseases

Uric acid (UA), the end-product of purine metabolism, has a complicated physiological role in the body, showing the combination of regulating inflammatory response, promoting oxidation/anti-oxidation, and modifying autophagy activity in vivo. Meanwhile, various research and theories support that inflammation, oxidative stress, and other risk factors promote the onset and progression of affective disorders and neurodegenerative diseases. Existing studies suggest that UA may be involved in the pathophysiological processes of affective disorders in various ways, and there has been a gradual advance in the understanding of the interplay between UA levels and affective disorders and neurodegenerative diseases. This review summarized the role of UA in the process of inflammation, oxidative stress, and autophagy. On this basis, we discussed the correlation between UA and affective disorders and several neurodegenerative diseases, and simultaneously analyzed the possible mechanism of its influence on affective disorders and neurodegenerative diseases, to provide a theoretical basis for UA as a biomarker or therapeutic target for the diagnosis of these diseases.

Peripheral immune profile and neutrophil-to-lymphocyte ratio in progressive supranuclear palsy: Case-control study and meta-analysis

BACKGROUND AND PURPOSE

Peripheral inflammation is probably involved in the pathogenesis of progressive supranuclear palsy (PSP) and it may be a common feature with Parkinson's disease (PD). The peripheral immune profile in PSP remains unclear, as well as whether the inflammatory pathways differ from those in PD. The neutrophil-to-lymphocyte ratio (NLR) has been proven to be a well-established biomarker of systemic inflammation. This study aimed to evaluate the peripheral immune profile in PSP compared with PD.

METHODS

A cross-sectional study was conducted including patients with PSP and PD and healthy controls (HCs). Leukocyte subpopulations and the NLR were measured in peripheral blood. Multivariate linear regression and post hoc tests were applied. Electronic databases were searched in November 2023 to perform meta-analyses to clarify the peripheral immune profile in PSP.

RESULTS

Our cohort included 121 patients with PSP, 127 patients with PD and 266 HCs. The NLR was higher in PSP and PD compared with HCs. PSP had a higher neutrophil count compared with HCs. Whilst a lower lymphocyte count was found in PD compared with HCs, the lymphocyte count did not differ between PSP and HCs. The meta-analyses supported this immune profile.

CONCLUSIONS

PSP and PD show an increased peripheral inflammation and a higher NLR compared with HCs. Different pathogenic inflammatory mechanisms are probably involved in PSP and PD, since in PSP this altered peripheral immune profile is mainly driven by neutrophils. Understanding the neutrophils' role in PSP may allow for the development of targeted therapies.

β-Amyloids and Immune Responses Associated with Alzheimer's Disease

Alzheimer's disease (AD) is associated with the accumulation of β-amyloids (Aβs) and the formation of Aβ plaques in the brain. Various structural forms and isoforms of Aβs that have variable propensities for oligomerization and toxicity and may differentially affect the development of AD have been identified. In addition, there is evidence that β-amyloids are engaged in complex interactions with the innate and adaptive immune systems, both of which may also play a role in the regulation of AD onset and progression. In this review, we discuss what is currently known about the intricate interplay between β-amyloids and the immune response to Aβs with a more in-depth focus on the possible roles of B cells in the pathogenesis of AD.

Brainstem transcriptomic changes in male Wistar rats after acute stress, comparing the use of duplex specific nuclease (DSN)

In this work, we have analyzed the transcriptomic changes in the brainstem of male Wistar rats 2 h after an acute stress exposure. We performed duplex-specific nuclease normalization of cDNA libraries and compared the results back-to-back for the first time. Based on our RNAseq data, we selected reference genes for RT-qPCR that are best suited for acute stress experiments. Most genes were upregulated. We detected a massive shift in neuropeptide Crh, Trh,Cga, Tshb, Uts2b, Tac4, Lep and neuropeptide receptor Hcrtr1, Sstr5, Bdkrb2, Crhr2 signaling, as well as glutamate Grin3b, Grm2 and GABA Gpr156, acetylcholine Chrm4,Chrne, adrenergic Adra2b receptors expression. A strong increase in the expression of intermediate filaments Krt83/Krt86/Krt80/Krt84/Krt87/Krt4/Krt76 and motor proteins Myo7a, Klc3 was detected. Remarkably, in the absence of astrocyte activation, we also observed signs of microglial activation at this time point. Both expression of anti-inflammatory cytokines Il13, Ccl24 and pro-inflammatory cytokine receptors Il9r, Il12rb1, Tnfrsf14, Tnfrsf13c, Tnfrsf25, Tnfrsf1b were increased. In the Wnt signaling pathway, we observed increased expression of ligands-receptors Wnt1, Wnt11, Ror2 and also negative regulators Notum, Sfrp5, Sost. RNAseq results after DSN treatment correlated at a high level with RNAseq results without DSN, but there was a proportion of genes that shifted their logFC values. They are mostly rare transcripts TPM 1-10 with higher 0.5-0.9 GC content.

Dysregulated expression of miR-140 and miR-122 compromised microglial chemotaxis and led to reduced restriction of AD pathology

BACKGROUND

Deposition of amyloid β, which is produced by amyloidogenic cleavage of APP by β- and γ-secretase, is one of the primary hallmarks of AD pathology. APP can also be processed by α- and γ-secretase sequentially, to generate sAPPα, which has been shown to be neuroprotective by promoting neurite outgrowth and neuronal survival, etc. METHODS: The global expression profiles of miRNA in blood plasma samples taken from 11 AD patients as well as from 14 age and sex matched cognitively normal volunteers were analyzed using miRNA-seq. Then, overexpressed miR-140 and miR-122 both in vivo and in vitro, and knock-down of the endogenous expression of miR-140 and miR-122 in vitro. Used a combination of techniques, including molecular biology, immunohistochemistry, to detect the impact of miRNAs on AD pathology.

RESULTS

In this study, we identified that two miRNAs, miR-140-3p and miR-122-5p, both targeting ADAM10, the main α-secretase in CNS, were upregulated in the blood plasma of AD patients. Overexpression of these two miRNAs in mouse brains induced cognitive decline in wild type C57BL/6J mice as well as exacerbated dyscognition in APP/PS1 mice. Although significant changes in APP and total Aβ were not detected, significantly downregulated ADAM10 and its non-amyloidogenic product, sAPPα, were observed in the mouse brains overexpressing miR-140/miR-122. Immunohistology analysis revealed increased neurite dystrophy that correlated with the reduced microglial chemotaxis in the hippocampi of these mice, independent of the other two ADAM10 substrates (neuronal CX3CL1 and microglial TREM2) that were involved in regulating the microglial immunoactivity. Further in vitro analysis demonstrated that both the reduced neuritic outgrowth of mouse embryonic neuronal cells overexpressing miR-140/miR-122 and the reduced Aβ phagocytosis in microglia cells co-cultured with HT22 cells overexpressing miR-140/miR-122 could be rescued by overexpressing the specific inhibitory sequence of miR-140/miR-122 TuD as well as by addition of sAPPα, rendering these miRNAs as potential therapeutic targets.

CONCLUSIONS

Our results suggested that neuroprotective sAPPα was a key player in the neuropathological progression induced by dysregulated expression of miR-140 and miR-122. Targeting these miRNAs might serve as a promising therapeutic strategy in AD treatment.

Genetic correlation, shared loci, but no causality between bipolar disorder and inflammatory bowel disease: A genome-wide pleiotropic analysis

BACKGROUND AND AIMS

The comorbidity between bipolar disorder (BD) and inflammatory bowel disease (IBD) has been widely reported in observational studies. However, unclear whether this comorbidity reflects a shared genetic architecture.

METHODS

Leveraging large-scale genome-wide association study (GWAS) summary statistics of BD, IBD and its subtypes, ulcerative colitis (UC) and Crohn's disease (CD), we performed a genome-wide pleiotropic analysis to estimate heritability and genetic correlation, identify pleiotropy loci/genes, and explore the shared biological pathway. Mendelian randomization (MR) studies were subsequently employed to infer whether the potential causal relationship is present.

RESULTS

We found a positive significant genetic correlation between BD and IBD (rg = 0.10, P = 7.00 × 10-4), UC (rg = 0.09, P = 2.90 × 10-3), CD (rg = 0.08, P = 6.10 × 10-3). In cross-trait meta-analysis, a total of 29, 24, and 23 independent SNPs passed the threshold for significant association between BD and IBD, UC, and CD, respectively. We identified five novel pleiotropy genes including ZDHHC2, SCRN1, INPP4B, C1orf123, and BRD3 in both BD and IBD, as well as in its subtypes UC and CD. Pathway enrichment analyses revealed that those pleiotropy genes were mainly enriched in several immune-related signal transduction pathways and cerebral disease-related pathways. MR analyses provided no evidence for a causal relationship between BD and IBD.

CONCLUSION

Our findings corroborated that shared genetic basis and common biological pathways may explain the comorbidity of BD and IBD. These findings further our understanding of shared genetic mechanisms underlying BD and IBD, and potentially provide points of intervention that may allow the development of new therapies for these co-occurrent disorders.