Anita R. Patel

Age- and location-related changes in microglial function

Inflammation in the central nervous system (CNS) is primarily regulated by microglia. No longer considered a homogenous population, microglia display a high degree of heterogeneity, immunological diversity and regional variability in function. Given their low rate of self-renewal, the microenvironment in which microglia reside may play an important role in microglial senescence. This study examines age-related changes in microglia in the brain and spinal cord. Using ex-vivo flow cytometry analyses, functional assays were performed to assess changes in microglial morphology, oxidative stress, cytokine production, and phagocytic activity with age in both the brain and spinal cord. The regional CNS environment had a significant effect on microglial activity with age. Blood-CNS barrier permeability was greater in the aging spinal cord compared with aging brain; this was associated with increased tissue cytokine levels. Aged microglia had deficits in phagocytosis at baseline and after stimulus-induced activation. The identification of age-specific, high scatter microglia together with the use of ex-vivo functional analyses provides the first functional characterization of senescent microglia. Age and regional-specificity of CNS disease should be taken into consideration when developing immune-modulatory treatments.

Age-Associated Resident Memory CD8 T Cells in the Central Nervous System Are Primed To Potentiate Inflammation after Ischemic Brain Injury

Aging is associated with an increase in basal inflammation in the CNS and an overall decline in cognitive function and poorer recovery following injury. Growing evidence suggests that leukocyte recruitment to the CNS is also increased with normal aging, but, to date, no systematic evaluation of these age-associated leukocytes has been performed. In this work, the effect of aging on CNS leukocyte recruitment was examined. Aging was associated with more CD45high leukocytes, primarily composed of conventional CD8+ T cells. These results were strain independent and seen in both sexes. Intravascular labeling and immunohistology revealed the presence of parenchymal CD8+ T cells in several regions of the brain, including the choroid plexus and meninges. These cells had effector memory (CD44+CD62L−) and tissue-resident phenotypes and expressed markers associated with TCR activation. Analysis of TCRvβ repertoire usage suggested that entry into the CNS is most likely stochastic rather than Ag driven. Correlational analyses revealed a positive association between CD8 T cell numbers and decreased proinflammatory function of microglia. However, the effects of cerebral ischemia and ex vivo stimulation of these cells dramatically increased production of TNF, IFN-γ, and MCP-1/CCL2. Taken together, we identified a novel population of resident memory, immunosurveillant CD8 T cells that represent a hallmark of CNS aging and appear to modify microglia homeostasis under normal conditions, but are primed to potentiate inflammation and leukocyte recruitment following ischemic injury.

Reversal of the Detrimental Effects of Post-Stroke Social Isolation by Pair-Housing is Mediated by Activation of BDNF-MAPK/ERK in Aged Mice.

Social isolation (SI) increases stroke-related mortality and morbidity in clinical populations. The detrimental effects of SI have been successfully modeled in the laboratory using young animals. Mechanistically, the negative effects of SI in young animals are primarily mediated by an enhanced inflammatory response to injury and a reduction in neurotrophic factors. However, the response to brain injury differs considerably in the aged. Given that SI is more prevalent in aged populations, we hypothesized that isolation, even when initiated after stroke, would delay recovery in aged mice. We found that aged isolated male mice had significantly increased infarct volume, neurological deficits, and serum IL-6 levels three days after stroke compared to pair housed (PH) mice. Using RT2 Profiler PCR Array and real-time quantitative PCR we found several important synaptic plasticity genes were differentially expressed in post-stroke SI mice. Furthermore, paired mice showed improved memory and neurobehavioral recovery four weeks after injury. Mechanistic and histological studies showed that the beneficial effects of pair housing are partially mediated by BDNF via downstream MAPK/ERK signaling and restoration of axonal basic myelin protein levels.

Multiparity improves outcomes after cerebral ischemia in female mice despite features of increased metabovascular risk.

Significance Stroke is an age-related disease that disproportionately affects women. Although experimental studies have identified several hormonal and genetic factors underlying these differences, little is known about how reproductive experience influences risk. This study examined the role of pregnancy and parturition on neurovascular function and behavior in both normal female mice and in females exposed to stroke. We found that reproductive experience increases systemic metabolic risk and results in significant behavioral deficits that are associated with CNS immunosuppression. After stroke, however, multiparous females exhibited smaller infarct volumes, attenuated inflammatory responses, enhanced angiogenesis, and improved behavioral recovery. Although the precise mechanisms underlying this paradoxical finding remain unknown, parity was associated with higher VEGF and improved postischemic vascular remodeling. Females show a varying degree of ischemic sensitivity throughout their lifespan, which is not fully explained by hormonal or genetic factors. Epidemiological data suggest that sex-specific life experiences such as pregnancy increase stroke risk. This work evaluated the role of parity on stroke outcome. Age-matched virgin (i.e., nulliparous) and multiparous mice were subjected to 60 min of reversible middle cerebral artery occlusion and evaluated for infarct volume, behavioral recovery, and inflammation. Using an established mating paradigm, fetal microchimeric cells present in maternal mice were also tracked after parturition and stroke. Parity was associated with sedentary behavior, weight gain, and higher triglyceride and cholesterol levels. The multiparous brain exhibited features of immune suppression, with dampened baseline microglial activity. After acute stroke, multiparous mice had smaller infarcts, less glial activation, and less behavioral impairment in the critical recovery window of 72 h. Behavioral recovery was significantly better in multiparous females compared with nulliparous mice 1 mo after stroke. This recovery was accompanied by an increase in poststroke angiogenesis that was correlated with improved performance on sensorimotor and cognitive tests. Multiparous mice had higher levels of VEGF, both at baseline and after stroke. GFP+ fetal cells were detected in the blood and migrated to areas of tissue injury where they adopted endothelial morphology 30 d after injury. Reproductive experience has profound and complex effects on neurovascular health and disease. Inclusion of female mice with reproductive experience in preclinical studies may better reflect the life-long patterning of ischemic stroke risk in women.

CD8 T cell recruitment in the normal aging CNS

not activated, and recruitment of inflammation-resolving monocytederived macrophages to the spinal cord parenchyma was limited. We further demonstrate that monocyte-derived macrophages locally regulated recruitment of thymic-derived Foxp3 regulatory T (Treg) cells to the injured spinal cord parenchyma at the subacute/chronic phase. These two inflammation-resolving populations,monocyte-derived macrophages and Tregs, were found to be pivotal and non-redundant in their activities at distinct stages of the recovery process. Importantly, an ablation protocol that resulted in reduced Tregs at the subacute/chronic stage interfered with tissue remodeling, in contrast to Treg transient ablation, restricted to the 4 day-period before the injury, which favored repair. The enhanced functional recovery observed following such a controlled decrease of Tregs suggests that reduced systemic immunosuppression at the time of the insult can enhance CNS repair. Overall, we established that sequential participation of immune cells, including Th1 cells, infiltrating resolving mo-MΦ and regulatory T cells, is needed for recovery fromCNS injury. Our results further highlight the delicate spatial and temporal dynamics of the effector and regulatory/resolving cells, the balance of which is pivotal for the CNS repair process.

Age-related changes in intestinal permeability and gut microbiota after ischemic stroke

Modafinil is awakefulness promoting agent used in the treatment of narcolepsy. It is also beneficial in patients with multiple sclerosis and with Parkinsons disease who complain of fatigue and sleepiness. We and others have shown that patients with MS-related fatigue have a deficit of arousal that can be corrected by modafinil. The mechanisms of action of modafinil are not clearly elucidated, but it is known to target the dopamine transporter, and to enhance the availability of dopamine and catecholamine neurotransmitters. The wakefulness promoting effect is dependent on the presence of Dopamine receptor 1. Functional magnetic resonance studies in humans have implicated the thalamus, a gray matter component of the brain known to degenerate in MS, in the effects of modafinil. Behavioural and histological evidence suggests a neuroprotective effect of modafinil in experimental models of Parkinsons disease, and is conformed in other models of neurodegeneration. Based on this we first performed a retrospective review of MS patients on long term modafinil compared with matched MS controls without modafinil treatment and showed a slower progression of disability on modafinil, supporting a neuroprotective effect. In the present study, we investigated the effect of modafinil on MOG35-55 induced EAE in C57Bl/6 mice. Modafinil 33 mg/kg twice weekly intraperitoneally from the day of immunization showed a trend towards reducing EAE scores in the chronic phase (p = 0.06). In a subsequent set of experiments modafinil given in daily doses of 100 or 50 mg/kg from the development of EAEwith a score of 1 or higher, significantly reduced disease severity (p = 0.008 and 0.021 respectively). Gene expression profiling in the thalamus showed up-regulated expression of a number of genes associated with neuroprotection, in particular genes involved in the ubiquitin–proteasome pathway. Further potential immunomodulatory and neuroprotective mechanisms are investigated and discussed.