The TREM2-APOE Pathway Drives the Transcriptional Phenotype of Dysfunctional Microglia in Neurodegenerative Diseases.

Microglia play a pivotal role in the maintenance of brain homeostasis but lose homeostatic function during neurodegenerative disorders. We identified a specific apolipoprotein E (APOE)-dependent molecular signature in microglia from models of amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), and Alzheimer's disease (AD) and in microglia surrounding neuritic ß-amyloid (Aß)-plaques in the brains of people with AD. The APOE pathway mediated a switch from a homeostatic to a neurodegenerative microglia phenotype after phagocytosis of apoptotic neurons. TREM2 (triggering receptor expressed on myeloid cells 2) induced APOE signaling, and targeting the TREM2-APOE pathway restored the homeostatic signature of microglia in ALS and AD mouse models and prevented neuronal loss in an acute model of neurodegeneration. APOE-mediated neurodegenerative microglia had lost their tolerogenic function. Our work identifies the TREM2-APOE pathway as a major regulator of microglial functional phenotype in neurodegenerative diseases and serves as a novel target that could aid in the restoration of homeostatic microglia.

ApoE4 markedly exacerbates tau-mediated neurodegeneration in a mouse model of tauopathy.

APOE4 is the strongest genetic risk factor for late-onset Alzheimer disease. ApoE4 increases brain amyloid-ß pathology relative to other ApoE isoforms. However, whether APOE independently influences tau pathology, the other major proteinopathy of Alzheimer disease and other tauopathies, or tau-mediated neurodegeneration, is not clear. By generating P301S tau transgenic mice on either a human ApoE knock-in (KI) or ApoE knockout (KO) background, here we show that P301S/E4 mice have significantly higher tau levels in the brain and a greater extent of somatodendritic tau redistribution by three months of age compared with P301S/E2, P301S/E3, and P301S/EKO mice. By nine months of age, P301S mice with different ApoE genotypes display distinct phosphorylated tau protein (p-tau) staining patterns. P301S/E4 mice develop markedly more brain atrophy and neuroinflammation than P301S/E2 and P301S/E3 mice, whereas P301S/EKO mice are largely protected from these changes. In vitro, E4-expressing microglia exhibit higher innate immune reactivity after lipopolysaccharide treatment. Co-culturing P301S tau-expressing neurons with E4-expressing mixed glia results in a significantly higher level of tumour-necrosis factor-α (TNF-α) secretion and markedly reduced neuronal viability compared with neuron/E2 and neuron/E3 co-cultures. Neurons co-cultured with EKO glia showed the greatest viability with the lowest level of secreted TNF-α. Treatment of P301S neurons with recombinant ApoE (E2, E3, E4) also leads to some neuronal damage and death compared with the absence of ApoE, with ApoE4 exacerbating the effect. In individuals with a sporadic primary tauopathy, the presence of an ε4 allele is associated with more severe regional neurodegeneration. In individuals who are positive for amyloid-ß pathology with symptomatic Alzheimer disease who usually have tau pathology, ε4-carriers demonstrate greater rates of disease progression. Our results demonstrate that ApoE affects tau pathogenesis, neuroinflammation, and tau-mediated neurodegeneration independently of amyloid-ß pathology. ApoE4 exerts a 'toxic' gain of function whereas the absence of ApoE is protective.

Characterization of Rhesus Macaque Liver-Resident CD49a+ NK Cells During Retrovirus Infections.

CD49a+ tissue resident NK cells have been implicated in memory-like NK cell responses, but while this population is well-characterized in mice and in humans, they are poorly described in non-human primates (NHP) which are particularly critical for modeling human viral infections. Others and we have shown that memory-like NK cells are enriched in the liver and because of the importance of NHP in modeling HIV infection, understanding the immunobiology of CD49a+ NK cells in SIV-infected rhesus macaques is critical to explore the role of this cell type in retroviral infections. In this study mononuclear cells isolated from livers, spleens, and peripheral whole blood were analyzed in acutely and chronically lentivirus-infected and experimentally-naïve Indian rhesus macaques (RM). NK cells were then identified as CD45+CD14-CD20-CD3-NKG2A/C+ cells and characterized using multiparametric flow-cytometry. Our data show that in RM, CD49a+ NK cells increase in the liver following retroviral infections [median = 5.2% (naïve) vs. median = 9.48% (SIV+) or median = 16.8% (SHIV+)]. In contrast, there is little change in CD49a+ NK frequencies in whole blood or spleens of matched animals. In agreement with human and murine data we also observed that CD49a+ NK cells were predominantly Eomeslow T-betlow, though these frequencies are elevated in infected animal cohorts. Functionally, our data suggests that infection alters TNF-α, IFN-γ, and CD107a expression in stimulated CD49a+ NK cells. Specifically, our analyses found a decrease in CD49a+ CD107a+ TNFα+ IFNγ- NK cells, with a simultaneous increase in CD49a+ CD107a+ TNFα- IFNγ+ NK cells and the non-responsive CD49a+ CD107a- TNFα- IFNγ- NK cell population following infection, suggesting both pathogenic and inflammatory changes in the NK cell functional profile. Our data also identified significant global differences in polyfunctionality between CD49a+ NK cells in the naïve and chronic (SHIV+) cohorts. Our work provides the first characterization of CD49a+ NK cells in tissues from RM. The significant similarities between CD49a+ NK cells from RM and what is reported from human samples justifies the importance of studying CD49a+ NK cells in this species to support preclinical animal model research.

Herd-level prevalence of Mycoplasma spp mastitis and characteristics of infected dairy herds in Utah as determined by a statewide survey.

OBJECTIVE: To determine herd-level prevalence of Mycoplasma spp mastitis in Utah dairy herds and characterize farms and management practices for positive herds. DESIGN: Epidemiologic study. SAMPLE POPULATION: Bulk tank milk samples from 222 of 285 (78%) dairy farms in Utah. PROCEDURES: Milk haulers or dairy producers collected 5 milk samples from all bulk tanks at 3- to 4-day intervals for mycoplasmal culture. Owners of all positive herds were offered follow-up visits. RESULTS: Milk samples from 16 of 222 (7%) herds had positive mycoplasmal culture results. Follow-up information was obtained from 14 of 16 herds; 12 provided complete data. Some characteristics of mycoplasma-positive herds included the following: 8 of 14 herds had > 750 lactating cows, 9 of 11 had bulk tank milk somatic cell count of 140,000 to 240,000 cells/mL, 7 of 11 had actual milk production of 9,535 to 11,622 kg (21,000 to 25,600 lb)/305 d, 11 of 12 had cows with clinical mastitis that was nonresponsive to treatment and involved >or= 2 mammary gland quarters, 9 of 12 had cows with clinical mastitis that spread from 1 mammary gland quarter to another, 8 of 12 had cows with droopy ears, 7 of 12 had cows with a head tilt, 7 of 12 used common milking towels, 2 of 12 were closed to replacement cattle for > 1 year, and 2 of 12 purchased bulls only. CONCLUSIONS AND CLINICAL RELEVANCE: Herd-level prevalence of mycoplasma mastitis in Utah was relatively high, compared with other areas of the United States.

Opposite microglial activation stages upon loss of PGRN or TREM2 result in reduced cerebral glucose metabolism.

Microglia adopt numerous fates with homeostatic microglia (HM) and a microglial neurodegenerative phenotype (MGnD) representing two opposite ends. A number of variants in genes selectively expressed in microglia are associated with an increased risk for neurodegenerative diseases such as Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD). Among these genes are progranulin (GRN) and the triggering receptor expressed on myeloid cells 2 (TREM2). Both cause neurodegeneration by mechanisms involving loss of function. We have now isolated microglia from Grn-/- mice and compared their transcriptomes to those of Trem2-/-mice Surprisingly, while loss of Trem2 enhances the expression of genes associated with a homeostatic state, microglia derived from Grn-/- mice showed a reciprocal activation of the MGnD molecular signature and suppression of gene characteristic for HM The opposite mRNA expression profiles are associated with divergent functional phenotypes. Although loss of TREM2 and progranulin resulted in opposite activation states and functional phenotypes of microglia, FDG (fluoro-2-deoxy-d-glucose)-µPET of brain revealed reduced glucose metabolism in both conditions, suggesting that opposite microglial phenotypes result in similar wide spread brain dysfunction.

Nonsteroidal anti-inflammatory drugs' impact on nonunion and infection rates in long-bone fractures.

BACKGROUND: There is a dearth of clinical data regarding the effect of nonsteroidal anti-inflammatory drugs (NSAIDs) on long-bone fracture (LBF) healing in the acute trauma setting. The orthopedic community believes that the use of NSAIDs in the postoperative period will result in poor healing and increased infectious complications. We hypothesized that, first, NSAID use would not increase nonunion/malunion and infection rates after LBF. Second, we hypothesized that tobacco use would cause higher rates of these complications. METHODS: A retrospective study of all patients with femur, tibia, and/or humerus fractures between October 2009 and September 2011 at a Level 1 academic trauma center was performed . In addition to nonunion/malunion and infection rates, patient records were reviewed for demographic data, mechanism of fracture, type of fracture, tobacco use, Injury Severity Score (ISS), comorbidities, and medications given. RESULTS: During the 24-month period, 1,901 patients experienced LBF; 231 (12.1%) received NSAIDs; and 351 (18.4%) were smokers. The overall complication rate including nonunion/malunion and infection was 3.2% (60 patients). Logistic regression analysis with adjusted odds ratios were calculated on the risk of complications given NSAID use and/or smoking, and we found that a patient is significantly more likely to have a complication if he or she received an NSAID (odds ratio, 2.17; 95% confidence interval, 1.15-4.10; p < 0.016) in the inpatient postoperative setting. Likewise, smokers are significantly more likely to have complications (odds ratio, 3.19; 95% confidence interval, 1.84-5.53; p < 0.001). CONCLUSION: LBF patients who received NSAIDs in the postoperative period were twice as likely and smokers more than three times likely to suffer complications such as nonunion/malunion or infection. We recommend avoiding NSAID in traumatic LBF. LEVEL OF EVIDENCE: Epidemiologic & therapeutic study; level II.