Therapeutic Trem2 activation ameliorates amyloid-beta deposition and improves cognition in the 5XFAD model of amyloid deposition.

BACKGROUND: Triggering receptor expressed on myeloid cell-2 (TREM2) is a lipid and lipoprotein binding receptor expressed by cells of myeloid origin. Homozygous TREM2 mutations cause early onset progressive presenile dementia while heterozygous, point mutations triple the risk of Alzheimer's disease (AD). Although human genetic findings support the notion that loss of TREM2 function exacerbates neurodegeneration, it is not clear whether activation of TREM2 in a disease state would result in therapeutic benefits. To determine the viability of TREM2 activation as a therapeutic strategy, we sought to characterize an agonistic Trem2 antibody (AL002a) and test its efficacy and mechanism of action in an aggressive mouse model of amyloid deposition. METHODS: To determine whether agonism of Trem2 results in therapeutic benefits, we designed both intracranial and systemic administration studies. 5XFAD mice in the intracranial administration study were assigned to one of two injection groups: AL002a, a Trem2-agonizing antibody, or MOPC, an isotype-matched control antibody. Mice were then subject to a single bilateral intracranial injection into the frontal cortex and hippocampus and euthanized 72 h later. The tissue from the left hemisphere was histologically examined for amyloid-beta and microglia activation, whereas the tissue from the right hemisphere was used for biochemical analyses. Similarly, mice in the systemic administration study were randomized to one of the aforementioned injection groups and the assigned antibody was administered intraperitoneally once a week for 14 weeks. Mice underwent behavioral assessment between the 12- and 14-week timepoints and were euthanized 24 h after their final injection. The tissue from the left hemisphere was used for histological analyses whereas the tissue from the right hemisphere was used for biochemical analyses. RESULTS: Here, we show that chronic activation of Trem2, in the 5XFAD mouse model of amyloid deposition, leads to reversal of the amyloid-associated gene expression signature, recruitment of microglia to plaques, decreased amyloid deposition, and improvement in spatial learning and novel object recognition memory. CONCLUSIONS: These findings indicate that Trem2 activators may be effective for the treatment of AD and possibly other neurodegenerative disorders.

Time course of neuropathological events in hyperhomocysteinemic amyloid depositing mice reveals early neuroinflammatory changes that precede amyloid changes and cerebrovascular events.

BACKGROUND: Vascular contributions to cognitive impairment and dementia (VCID) are the second leading cause of dementia behind only Alzheimer's disease (AD); however, VCID is commonly found as a co-morbidity with sporadic AD. We have previously established a mouse model of VCID by inducing hyperhomocysteinemia in both wild-type and amyloid depositing mice. While we have shown the time course of neuropathological events in the wild-type mice with hyperhomocysteinemia, the effect of amyloid deposition on this time course remains unknown; therefore, in this study, we determined the time course of neuropathological changes in our mouse model of hyperhomocysteinemia-induced VCID in amyloid depositing mice. METHODS: APP/PS1 mice were placed on either a diet deficient in folate and vitamins B6 and B12 and enriched in methionine to induce hyperhomocysteinemia or a control diet for 2, 6, 10, 14, or 18 weeks. Immunohistochemistry and gene expression analysis were used to determine neuroinflammatory changes. Microhemorrhages and amyloid deposition were analyzed using histology and, finally, behavior was assessed using the 2-day radial arm water maze. RESULTS: Neuroinflammation, specifically a pro-inflammatory phenotype, was the first pathological change to occur. Specifically, we see a significant increase in gene expression of tumor necrosis factor alpha, interleukin 1 beta, interleukin 6, and interleukin 12a by 6 weeks. This was followed by cognitive deficits starting at 10 weeks. Finally, there is a significant increase in the number of microhemorrhages at 14 weeks on diet as well as redistribution of amyloid from the parenchyma to the vasculature. CONCLUSIONS: The time course of these pathologies points to neuroinflammation as the initial, key player in homocysteine-induced VCID co-morbid with amyloid deposition and provides a possible therapeutic target and time points.

Respiratory culture growth and 3-years lung health outcomes in children with bronchopulmonary dysplasia and tracheostomies.

BACKGROUND: While bacteria identification on respiratory cultures is associated with poor short-term outcomes in children with bronchopulmonary dysplasia (BPD) and tracheostomies, the influence on longer-term respiratory support needs remains unknown. OBJECTIVE: To determine if respiratory culture growth of pathogenic organisms is associated with ongoing need for respiratory support, decannulation, and death at 3 years posttracheostomy placement in children with BPD and tracheostomies. METHODS: This single center, retrospective cohort study included infants and children with BPD and tracheostomies placed 2010-2018 and ≥1 respiratory culture obtained in 36 months posttracheostomy. Primary predictor was any pathogen identified on respiratory culture. Additional predictors were any Pseudomonas aeruginosa and chronic P. aeruginosa identification. Outcomes included continued use of respiratory support (e.g., oxygen, positive pressure), decannulation, and death at 3 years posttracheostomy. We used Poisson regression models to examine the relationship between respiratory organisms and outcomes, controlling for patient-level covariates and within-patient clustering. RESULTS: Among 170 children, 59.4% had a pathogen identified, 28.8% ever had P. aeruginosa, and 3.5% had chronic P. aeruginosa. At 3 years, 33.1% of alive children required ongoing respiratory support and 24.8% achieved decannulation; 18.9% were deceased. In adjusted analysis, any pathogen and P. aeruginosa were not associated with ongoing respiratory support or mortality. However, P. aeruginosa was associated with decreased decannulation probability (adjusted risk ratio 0.48, 95% CI 0.23-0.98). Chronic P. aeruginosa was associated with lower survival probability. CONCLUSION: Our findings suggest that respiratory pathogens including P. aeruginosa may not promote long-term respiratory dysfunction, but identification of P. aeruginosa may delay decannulation.

Respiratory culture organism isolation and test characteristics in children with tracheostomies with and without acute respiratory infection.

BACKGROUND: Among children with tracheostomies, little is known about how respiratory culture results differ between states with and without acute respiratory infections (ARI), or the overall test performance of respiratory cultures. OBJECTIVE: To determine the association of respiratory culture organism isolation with diagnosis of ARI in children with tracheostomies, and assess test characteristics of respiratory cultures in the diagnosis of bacterial ARI (bARI). METHODS: This single-center, retrospective cohort study included respiratory cultures of children with tracheostomies obtained between 2010 and 2018. The primary predictor was ARI diagnosis code at the time of culture; the primary outcomes were respiratory culture organism isolation and species identified. Generalized estimating equations were used to assess for association between ARI diagnosis and isolation of any organism while controlling for potential confounders and accounting for within-patient clustering. A multinomial logistic regression equation assessed for association with specific species. Test characteristics were calculated using bARI diagnosis as the reference standard. RESULTS: Among 3578 respiratory cultures from 533 children (median 4 cultures/child, interquartile range (IQR): 1-9), 25.9% were obtained during ARI and 17.2% had ≥1 organism. Children with ARI diagnosis had higher odds of organism identification (adjusted odds ratio 1.29, 95%  confidence interval [CI] 1.16-1.44). When controlling for covariates, ARI was associated with isolation of Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pneumoniae, and Streptococcus pyogenes. Test characteristics revealed a 24.3% sensitivity, 85.2% specificity, 36.5% positive predictive value, and 76.3% negative predictive value in screening for bARI. CONCLUSION: The utility of respiratory culture testing to screen for, diagnose, and direct treatment of ARI in children with tracheostomies is limited.

Hyperhomocysteinemia-Induced Gene Expression Changes in the Cell Types of the Brain.

High plasma levels of homocysteine, termed hyperhomocysteinemia, are a risk factor for vascular cognitive impairment and dementia, which is the second leading cause of dementia. While hyperhomocysteinemia induces microhemorrhages and cognitive decline in mice, the specific effect of hyperhomocysteinemia on each cell type remains unknown. We took separate cultures of astrocytes, microglia, endothelial cells, and neuronal cells and treated each with moderate levels of homocysteine for 24, 48, 72, and 96 hr. We then determined the gene expression changes for cell-specific markers and neuroinflammatory markers including the matrix metalloproteinase 9 system. Astrocytes had decreased levels of several astrocytic end feet genes, such as aquaporin 4 and an adenosine triphosphate (ATP)-sensitive inward rectifier potassium channel at 72 hr, as well as an increase in matrix metalloproteinase 9 at 48 hr. Gene changes in microglia indicated a peak in proinflammatory markers at 48 hr followed by a peak in the anti-inflammatory marker, interleukin 1 receptor antagonist, at 72 hr. Endothelial cells had reduced occludin expression at 72 hr, while kinases and phosphatases known to alter tau phosphorylation states were increased in neuronal cells. This suggests that hyperhomocysteinemia induces early proinflammatory changes in microglia and astrocytic changes relevant to their interaction with the vasculature. Overall, the data show how hyperhomocysteinemia could impact Alzheimer's disease and vascular cognitive impairment and dementia.

Time-course of glial changes in the hyperhomocysteinemia model of vascular cognitive impairment and dementia (VCID).

Vascular cognitive impairment and dementia (VCID) is the second leading cause of dementia behind Alzheimer's disease (AD) and is a frequent co-morbidity with AD. Despite its prevalence, little is known about the molecular mechanisms underlying the cognitive dysfunction resulting from cerebrovascular disease. Astrocytic end-feet almost completely surround intraparenchymal blood vessels in the brain and express a variety of channels and markers indicative of their specialized functions in the maintenance of ionic and osmotic homeostasis and gliovascular signaling. These functions are mediated by end-foot enrichment of the aquaporin 4 water channel (AQP4), the inward rectifying potassium channel Kir4.1 and the calcium-dependent potassium channel MaxiK. Using our hyperhomocysteinemia (HHcy) model of VCID we examined the time-course of astrocytic end-foot changes along with cognitive and neuroinflammatory outcomes. We found that there were significant astrocytic end-foot disruptions in the HHcy model. AQP4 becomes dislocalized from the end-feet, there is a loss of Kir4.1 and MaxiK protein expression, as well as a loss of the Dp71 protein known to anchor the Kir4.1, MaxiK and AQP4 channels to the end-foot membrane. Neuroinflammation occurs prior to the astrocytic changes, while cognitive impairment continues to decline with the exacerbation of the astrocytic changes. We have previously reported similar astrocytic changes in models of cerebral amyloid angiopathy (CAA) and therefore, we believe astrocytic end-foot disruption could represent a common cellular mechanism of VCID and may be a target for therapeutic development.