Vitamin D deficiency decreases survival of bacterial meningoencephalitis in mice

Biological agents and the aging brain: glial inflammation and neurotoxic signaling

Neuroinflammation is a universal characteristic of brain aging and neurological disorders, irrespective of the disease state. Glial inflammation mediates this signaling, through astrocyte and microglial polarization from neuroprotective to neurotoxic phenotypes. Glial reactivity results in the loss of homeostasis, as these cells no longer provide support to neurons, in addition to the production of chronically toxic pro-inflammatory mediators. These glial changes initiate an inflammatory brain state that injures the central nervous system (CNS) over time. As the brain ages, glia are altered, including increased glial cell numbers, morphological changes, and either a pre-disposition or inability to become reactive. These alterations induce age-related neuropathologies, ultimately leading to neuronal degradation and irreversible damage associated with disorders of the aged brain, including Alzheimer's Disease (AD) and other related diseases. While the complex interactions of these glial cells and the brain are well studied, the role additional stressors, such as infectious agents, play on age-related neuropathology has not been fully elucidated. Both biological agents in the periphery, such as bacterial infections, or in the CNS, including viral infections like SARS-CoV-2, push glia into neuroinflammatory phenotypes that can exacerbate pathology within the aging brain. These biological agents release pattern associated molecular patterns (PAMPs) that bind to pattern recognition receptors (PRRs) on glial cells, beginning an inflammatory cascade. In this review, we will summarize the evidence that biological agents induce reactive glia, which worsens age-related neuropathology.

Effects of Vitamin D-Deficient Diet on Intestinal Epithelial Integrity and Zonulin Expression in a C57BL/6 Mouse Model

Background and Aims: Vitamin D (VD) plays an important role not only in mineral balance and skeletal maintenance but also in immune modulation. VD status was found correlated with the pathophysiology and severity of inflammatory bowel diseases and other autoimmune disorders. Epithelial barrier function is primarily regulated by the tight-junction (TJ) proteins. In this study, we try to establish an animal model by raising mice fed VD-deficient diet and to investigate the effects of VD-deficient diet on gut integrity and zonulin expression.

Methods: Male C57BL/6 mice were administered either VD-deficient [VDD group, 25(OH)₂D₃ 0 IU/per mouse] or VD-sufficient [VDS group, 25(OH)₂D₃ 37.8 IU/per mouse] special diets for 7 weeks. Body weight and diet intake were recorded weekly. Serum VD levels were detected. After sacrifice, jejunum and colon specimens were collected. The villus length and crypt depth of the jejunum as well as mucosa thickness of the colon were measured. Various serum pro-inflammatory cytokines and intestinal TJ proteins were assessed. The serum level of zonulin and the mRNA expression of jejunum zonulin were also investigated.

Results: We found that mice fed a VDD diet had a lower serum level of VD after 7 weeks (p < 0.001). VDD mice gained significant less weight (p = 0.022) and took a similar amount of diet (p = 0.398) when compared to mice raised on a VDS diet. Significantly decreased colon mucosa thickness was found in VDD mice compared with the VDS group (p = 0.022). A marked increase in serum pro-inflammatory cytokine levels was demonstrated in VDD mice. All relative levels of claudin (CLD)-1 (p = 0.007), CLD-3 (p < 0.001), CLD-7 (p < 0.001), and zonulin-1 (ZO-1, p = 0.038) protein expressions were significantly decreased in the VDD group when compared to the VDS group. A significant upregulation of mRNA expression of jejunum zonulin (p = 0.043) and elevated serum zonulin (p = 0.001) were found in the VDD group.

Conclusions: We successfully demonstrated that VDD could lead to impaired barrier properties. We assume that sufficient VD could maintain intestinal epithelial integrity and prevent mucosal barrier dysfunction. VD supplementation may serve as part of a therapeutic strategy for human autoimmune and infectious diseases with intestinal barrier dysfunction (leaky gut) in the future. To our knowledge, this is the first study to demonstrate that VDD could lead to a significant upregulation in mRNA expression of the jejunum zonulin level and also a marked elevation of serum zonulin in a mouse model.

Vitamin D Deficiency Induces Chronic Pain and Microglial Phenotypic Changes in Mice

The bioactive form of vitamin D, 1,25-dihydroxyvitamin D (1,25D3), exerts immunomodulatory actions resulting in neuroprotective effects potentially useful against neurodegenerative and autoimmune diseases. In fact, vitamin D deficiency status has been correlated with painful manifestations associated with different pathological conditions. In this study, we have investigated the effects of vitamin D deficiency on microglia cells, as they represent the main immune cells responsible for early defense at central nervous system (CNS), including chronic pain states. For this purpose, we have employed a model of low vitamin D intake during gestation to evaluate possible changes in primary microglia cells obtained from postnatal day(P)2-3 pups. Afterwards, pain measurement and microglia morphological analysis in the spinal cord level and in brain regions involved in the integration of pain perception were performed in the parents subjected to vitamin D restriction. In cultured microglia, we detected a reactive-activated and proliferative-phenotype associated with intracellular reactive oxygen species (ROS) generation. Oxidative stress was closely correlated with the extent of DNA damage and increased β-galactosidase (B-gal) activity. Interestingly, the incubation with 25D3 or 1,25D3 or palmitoylethanolamide, an endogenous ligand of peroxisome proliferator-activated-receptor-alpha (PPAR-α), reduced most of these effects. Morphological analysis of ex-vivo microglia obtained from vitamin-D-deficient adult mice revealed an increased number of activated microglia in the spinal cord, while in the brain microglia appeared in a dystrophic phenotype. Remarkably, activated (spinal) or dystrophic (brain) microglia were detected in a prominent manner in females. Our data indicate that vitamin D deficiency produces profound modifications in microglia, suggesting a possible role of these cells in the sensorial dysfunctions associated with hypovitaminosis D.

High dose vitamin D exacerbates central nervous system autoimmunity by raising T-cell excitatory calcium

Poor vitamin D status is associated with a higher relapse rate and earlier disability in multiple sclerosis. Based on these associations, patients with multiple sclerosis are frequently supplemented with the vitamin D precursor cholecalciferol, although it is unclear whether this regimen is of therapeutic benefit. To model consequences of this common practice, mice were fed for more than 3 months with a low, medium or high dose of cholecalciferol, representative of vitamin D deficiency, modest and disproportionally high supplementation, respectively, in patients with multiple sclerosis. Compared to vitamin D-deprived mice, its moderate supplementation reduced the severity of subsequent experimental autoimmune encephalomyelitis, which was associated with an expansion of regulatory T cells. Direct exposure of murine or human T cells to vitamin D metabolites inhibited their activation. In contrast, mice with 25-(OH) vitamin D levels above 200 nmol/l developed fulminant experimental autoimmune encephalomyelitis with massive CNS infiltration of activated myeloid cells, Th1 and Th17 cells. When dissecting this unexpected outcome, we observed that high, but not medium dose vitamin D had caused mild hypercalcaemia, which rendered T cells more prone to pro-inflammatory activation. Exposing murine or human T cells to equivalent calcium concentrations in vitro enhanced its influx, triggering activation, upregulation of pro-inflammatory gene products and enhanced transmigration across a blood-brain barrier model. These findings suggest that vitamin D at moderate levels may exert a direct regulatory effect, while continuous high dose vitamin D treatment could trigger multiple sclerosis disease activity by raising mean levels of T-cell excitatory calcium.

Vitamin D was not associated with survival or cerebrospinal fluid cathelicidin levels in children with bacterial meningitis

AIM

Vitamin D deficiency impairs the immunological system and has been associated with worse outcomes of infectious diseases, but its role in bacterial meningitis remains unknown. We investigated whether serum 25-hydroxyvitamin D concentrations related to disease outcomes and to cerebrospinal fluid (CSF) cathelicidin concentrations in childhood bacterial meningitis.

METHODS

All consecutively enrolled patients in a clinical trial on childhood bacterial meningitis in Latin America in 1996-2003 were considered, and 142 children, with a median age of seven months who had a confirmed bacterial aetiology and frozen serum available for further analyses, were included in this study. Serum 25-hydroxyvitamin D concentrations were determined with a chemiluminescence immunoassay analyser, while CSF cathelicidin was measured by enzyme-linked immunosorbent assay.

RESULTS

The median serum 25-hydroxyvitamin D concentration was 96 (range 19-251) nmol/L. No relationship was found with patient survival, but children with any neurological sequelae had lower serum 25-hydroxyvitamin D levels than children without sequelae. Serum 25-hydroxyvitamin D was unrelated to cathelicidin concentrations in CSF.

CONCLUSION

Although serum 25-hydroxyvitamin D in children with bacterial meningitis was not associated with survival or CSF cathelicidin concentrations, its relationship with more detailed disease outcomes warrants further study.

1,25-Dihydroxyvitamin D3 Facilitates M2 Polarization and Upregulates TLR10 Expression on Human Microglial Cells

OBJECTIVE

To explore the effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], the active metabolite of vitamin D, on M1/M2 polarization of human microglia and the expression of Toll-like receptor 10 (TLR10) on these cells, which has been suggested to play an inhibitory role in inflammation previously.

METHODS

Microglial HMO6 cells were treated with 1,25(OH)2D3, and mRNA or protein levels of M1 and M2 cytokines and TLR10 were examined.

RESULTS

1,25(OH)2D3 upregulated TLR10 in HMO6 cells at both mRNA and protein level. 1,25(OH)2D3 enhanced basal mRNA expression of M2 cytokines, such as IL-10 and CCL17, but did not affect the expression of M1 cytokines, including IL-12 and TNF-α. 1,25(OH)2D3 downregulated the lipopolysaccharide (LPS)-induced mRNA expression of M1 cytokines IL-12 and TNF-α. Concomitantly, it upregulated not only the M2 cytokines IL-10 and CCL17, but also TLR10 in microglial cells treated with LPS, in a concentration-dependent manner.

CONCLUSIONS

Our results suggest that 1,25(OH)2D3 may exert anti-inflammatory action by facilitating the M2 polarization of human microglial cells.