Microglial activation, emergence of ED1-expressing cells and clusterin upregulation in the aging rat CNS, with special reference to the spinal cord

Extracellular Matrix and Oxidative Stress Following Traumatic Spinal Cord Injury: Physiological and Pathophysiological Roles and Opportunities for Therapeutic Intervention

Significance: Traumatic spinal cord injury (SCI) causes significant disruption to neuronal, glial, vascular, and extracellular elements. The spinal cord extracellular matrix (ECM) comprises structural and communication proteins that are involved in reparative and regenerative processes after SCI. In the healthy spinal cord, the ECM helps maintain spinal cord homeostasis. After SCI, the damaged ECM limits plasticity and contributes to inflammation through the expression of damage-associated molecules such as proteoglycans. Recent Advances: Considerable insights have been gained by characterizing the origins of the gliotic and fibrotic scars, which not only reduce the spread of injury but also limit neuroregeneration. These properties likely limit the success of therapies used to treat patients with SCI. The ECM, which is a major contributor to the scars and normal physiological functions of the spinal cord, represents an exciting therapeutic target to enhance recovery post-SCI. Critical Issue: Various ECM-based preclinical therapies have been developed. These include disrupting scar components, inhibiting activity of ECM metalloproteinases, and maintaining iron homeostasis. Biomaterials have also been explored. However, the majority of these treatments have not experienced successful clinical translation. This could be due to the ECM and scars' polarizing roles. Future Directions: This review surveys the complexity involved in spinal ECM modifications, discusses new ECM-based combinatorial strategies, and explores the biomaterials evaluated in clinical trials, which hope to introduce new treatments that enhance recovery after SCI. These topics will incorporate oxidative species, which are both beneficial and harmful in reparative and regenerative processes after SCI, and not often assessed in pertinent literature. Antioxid. Redox Signal. 37, 184-207.

Quantitative, structural and molecular changes in neuroglia of aging mammals: A review

The neuroglia of the central and peripheral nervous systems undergo numerous changes during normal aging. Astrocytes become hypertrophic and accumulate intermediate filaments. Oligodendrocytes and Schwann cells undergo alterations that are often accompanied by degenerative changes to the myelin sheath. In microglia, proliferation in response to injury, motility of cell processes, ability to migrate to sites of neural injury, and phagocytic and autophagic capabilities are reduced. In sensory ganglia, the number and extent of gaps between perineuronal satellite cells – that leave the surfaces of sensory ganglion neurons directly exposed to basal lamina – increase significantly. The molecular profiles of neuroglia also change in old age, which, in view of the interactions between neurons and neuroglia, have negative consequences for important physiological processes in the nervous system. Since neuroglia actively participate in numerous nervous system processes, it is likely that not only neurons but also neuroglia will prove to be useful targets for interventions to prevent, reverse or slow the behavioral changes and cognitive decline that often accompany senescence.

Systematic Quantification of Neurotrophic Adipokines RBP4, PEDF, and Clusterin in Human Cerebrospinal Fluid and Serum

CONTEXT

Data on the presence/quantification of the neurotrophic adipokines retinol-binding protein-4 (RBP4), clusterin, and pigment epithelium-derived factor (PEDF) in human cerebrospinal fluid (CSF) are scarce and migration of these adipokines across of the blood-brain barrier (BBB) is uncertain.

OBJECTIVE

This work aimed to quantify RBP4, PEDF, and clusterin in paired serum and CSF samples of patients undergoing neurological evaluation.

METHODS

A total of 268 patients (109 male, 159 female) were included. Adipokine serum and CSF concentrations were measured by enzyme-linked immunosorbent assay in duplicate.

RESULTS

RBP4 was abundant in serum (mean, 31.9 ± 24.2 μg/mL). The serum concentrations were approximately 145 times higher than in CSF (CSF to serum RBP4 ratio, 8.2 ± 4.3 × 10-3). PEDF was detectable in serum (mean, 30.2 ± 11.7 μg/mL) and concentrations were approximately 25 times higher than in CSF (CSF to serum PEDF ratio, 42.3 ± 15.6 × 10-3). Clusterin serum concentrations were abundant with mean levels of 346.0 ± 114.6 μg/mL, which were approximately 40 times higher than CSF levels (CSF to serum clusterin ratio, 29.6 ± 23.4 × 10-3). RBP4 and PEDF serum levels correlated positively with CSF levels, which were increased in overweight/obese patients and in type 2 diabetic patients. The CSF concentrations of all 3 adipokines increased with BBB dysfunction. RBP4 in CSF correlated positively with inflammatory parameters. In detail, only RBP4 showed the kinetics and associations that are mandatory for a putative mediator of the fat-brain axis.

CONCLUSION

RBP4, PEDF, and clusterin are permeable to the BBB and increase with the measure of BBB dysfunction. RBP4 represents an inflammatory neurotrophic adipokine and is a promising mediator of the fat-brain axis.

Spinal Cord Microglia in Health and Disease

The review summarizes data of recent experimental studies on spinal microglia, the least explored cells of the spinal cord. It focuses on the origin and function of microglia in mammalian spinal cord embryogenesis. The main approaches to the classification of microgliocytes based on their structure, function, and immunophenotypic characteristics are analyzed. We discuss the results of studies conducted on experimental models of spinal cord diseases such as multiple sclerosis, amyotrophic lateral sclerosis, systemic inflammation, and some others, with special emphasis on the key role of microglia in the pathogenesis of these diseases. The review highlights the need to detect the new microglia-specific marker proteins expressed at all stages of ontogeny. New sensitive and selective microglial markers are necessary in order to improve identification of spinal cord microgliocytes in normal and pathological conditions. Possible morphometric methods to assess the functional activity of microglial cells are presented.

Glial activation and inflammation along the Alzheimer's disease continuum

Background

Neuronal and glial cell interaction is essential for synaptic homeostasis and may be affected in Alzheimer’s disease (AD). We measured cerebrospinal fluid (CSF) neuronal and glia markers along the AD continuum, to reveal putative protective or harmful stage-dependent patterns of activation.

Methods

We included healthy controls (n = 36) and Aβ-positive (Aβ+) cases (as defined by pathological CSF amyloid beta 1-42 (Aβ42)) with either subjective cognitive decline (SCD, n = 19), mild cognitive impairment (MCI, n = 39), or AD dementia (n = 27). The following CSF markers were measured: a microglial activation marker—soluble triggering receptor expressed on myeloid cells 2 (sTREM2), a marker of microglial inflammatory reaction—monocyte chemoattractant protein-1 (MCP-1), two astroglial activation markers—chitinase-3-like protein 1 (YKL-40) and clusterin, a neuron-microglia communication marker—fractalkine, and the CSF AD biomarkers (Aβ42, phosphorylated tau (P-tau), total tau (T-tau)). Using ANOVA with planned comparisons, or Kruskal-Wallis tests with Dunn’s pairwise comparisons, CSF levels were compared between clinical groups and between stages of biomarker severity using CSF biomarkers for classification based on amyloid pathology (A), tau pathology (T), and neurodegeneration (N) giving rise to the A/T/N score.

Results

Compared to healthy controls, sTREM2 was increased in SCD (p < .01), MCI (p < .05), and AD dementia cases (p < .001) and increased in AD dementia compared to MCI cases (p < .05). MCP-1 was increased in MCI (p < .05) and AD dementia compared to both healthy controls (p < .001) and SCD cases (p < .01). YKL-40 was increased in dementia compared to healthy controls (p < .01) and MCI (p < .05). All of the CSF activation markers were increased in subjects with pathological CSF T-tau (A+T−N+ and A+T+N+), compared to subjects without neurodegeneration (A−T−N− and A+T−N−).

Discussion

Microglial activation as indicated by increased sTREM2 is present already at the preclinical SCD stage; increased MCP-1 and astroglial activation markers (YKL-40 and clusterin) were noted only at the MCI and AD dementia stages, respectively, and in Aβ+ cases (A+) with pathological T-tau (N+). Possible different effects of early and later glial activation need to be explored.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1399-2) contains supplementary material, which is available to authorized users.

SIRT1 deacetylase in aging-induced neuromuscular degeneration and amyotrophic lateral sclerosis

SIRT1 is an NAD+ -dependent deacetylase that functions in a variety of cells and tissues to mitigate age-associated diseases. However, it remains unknown if SIRT1 also acts to prevent pathological changes that accrue in motor neurons during aging and amyotrophic lateral sclerosis (ALS). In this study, we show that SIRT1 expression decreases in the spinal cord of wild-type mice during normal aging. Using mouse models either overexpressing or lacking SIRT1 in motor neurons, we found that SIRT1 slows age-related degeneration of motor neurons' presynaptic sites at neuromuscular junctions (NMJs). Transcriptional analysis of spinal cord shows an overlap of greater than 90% when comparing alterations during normal aging with changes during ALS, revealing a substantial upregulation in immune and inflammatory response genes and a downregulation of synaptic transcripts. In addition, overexpressing SIRT1 in motor neurons delays progression to end-stage disease in high copy SOD1G93A mice. Thus, our findings suggest that there are parallels between ALS and aging, and interventions to impede aging may also slow the progression of this devastating disease.

Microglia in dementia with Lewy bodies

Microglial activation (neuroinflammation) is often cited as a pathogenic factor in the development of neurodegenerative diseases. However, there are significant caveats associated with the idea that inflammation directly causes either α-synuclein pathology or neurofibrillary degeneration (NFD). We have performed immunohistochemical studies on microglial cells in five cases of dementia with Lewy bodies (DLB), median age 87, and nine cases of non-demented (ND) controls, median age 74, using tissue samples from the temporal lobe and the superior frontal gyrus. Three different antibodies known to label microglia and macrophages were employed: iba1, anti-CD68, and anti-ferritin. All DLB cases showed both α-synuclein pathology (Lewy bodies and neurites) and NFD ranging from Braak stage II to IV. In contrast, all controls were devoid of α-synuclein pathology but did show NFD ranging from Braak stage I to III. Using iba1 labeling, our current results show a notable absence of activated microglia in all cases with the exception of two controls that showed small focal areas of microglial activation and macrophage formation. Both iba1 and ferritin antibodies revealed a mixture of ramified and dystrophic microglial cells throughout the regions examined, and there were no measurable differences in the prevalence of dystrophic microglial cells between DLB and controls. Double-labeling for α-synuclein and iba1-positive microglia showed that cortical Lewy bodies were surrounded by both ramified and dystrophic microglial cells. We found an increase in CD68 expression in DLB cases relative to controls. Since microglial dystrophy has been linked to NFD and since it did not appear to be worse in DLB cases over controls, our findings support the idea that the additional Lewy body pathology in DLB is not the result of intensified microglial dystrophy. CD68 is likely associated with lipofuscin deposits in microglial cells which may be increased in DLB cases because of impaired proteostasis. Overall, we conclude that neurodegenerative changes in DLB are unlikely to result directly from activated microglia but rather from dysfunctional ones.

Perturbed cholesterol homeostasis in aging spinal cord

The spinal cord is vital for the processing of sensorimotor information and for its propagation to and from both the brain and the periphery. Spinal cord function is affected by aging, however, the mechanisms involved are not well-understood. To characterize molecular mechanisms of spinal cord aging, microarray analyses of gene expression were performed on cervical spinal cords of aging rats. Of the metabolic and signaling pathways affected, cholesterol-associated pathways were the most comprehensively altered, including significant downregulation of cholesterol synthesis-related genes and upregulation of cholesterol transport and metabolism genes. Paradoxically, a significant increase in total cholesterol content was observed-likely associated with cholesterol ester accumulation. To investigate potential mechanisms for the perturbed cholesterol homeostasis, we quantified the expression of myelin and neuroinflammation-associated genes and proteins. Although there was minimal change in myelin-related expression, there was an increase in phagocytic microglial and astrogliosis markers, particularly in the white matter. Together, these results suggest that perturbed cholesterol homeostasis, possibly as a result of increased inflammatory activation in spinal cord white matter, may contribute to impaired spinal cord function with aging.

Microglial P2 Purinergic Receptor and Immunomodulatory Gene Transcripts Vary By Region, Sex, and Age in the Healthy Mouse CNS

Inflammatory damage in many neurodegenerative diseases is restricted to certain regions of the CNS, and while microglia have long been implicated in the pathology of many of these disorders, information comparing their gene expression in different CNS regions is lacking. Here we tested the hypothesis that the expression of purinergic receptors, estrogen receptors and other neuroprotective and pro-inflammatory genes differed among CNS regions in healthy mice. Because neurodegenerative diseases vary in incidence by sex and age, we also examined the regional distribution of these genes in male and female mice of four different ages between 21 days and 12 months. We postulated that pro-inflammatory gene expression would be higher in older animals, and lower in young adult females. We found that microglial gene expression differed across the CNS. Estrogen receptor alpha (Esr1) mRNA levels were often lower in microglia from the brainstem/spinal cord than from the cortex, whereas tumor necrosis factor alpha (Tnfα) expression was several times higher. In addition, the regional pattern of gene expression often changed with animal age; for example, no regional differences in P2X7 mRNA levels were detected in 21 day-old animals, but at 7 weeks and older, expression was highest in cerebellar microglia. Lastly, the expression of some genes was sexually dimorphic. In microglia from 12 month-old animals, mRNA levels of inducible nitric oxide synthase, but not Tnfα, were higher in females than males. These data suggest that microglial gene expression is not uniformly more pro-inflammatory in males or older animals. Moreover, microglia from CNS regions in which neuronal damage predominates in neurodegenerative disease do not generally express more pro-inflammatory genes than microglia from regions less frequently affected. This study provides an in-depth assessment of regional-, sex- and age-dependent differences in key microglial transcripts from the healthy mouse CNS.

Neuroimmune and Neuropathic Responses of Spinal Cord and Dorsal Root Ganglia in Middle Age

Prior studies of aging and neuropathic injury have focused on senescent animals compared to young adults, while changes in middle age, particularly in the dorsal root ganglia (DRG), have remained largely unexplored. 14 neuroimmune mRNA markers, previously associated with peripheral nerve injury, were measured in multiplex assays of lumbar spinal cord (LSC), and DRG from young and middle-aged (3, 17 month) naïve rats, or from rats subjected to chronic constriction injury (CCI) of the sciatic nerve (after 7 days), or from aged-matched sham controls. Results showed that CD2, CD3e, CD68, CD45, TNF-α, IL6, CCL2, ATF3 and TGFβ1 mRNA levels were substantially elevated in LSC from naïve middle-aged animals compared to young adults. Similarly, LSC samples from older sham animals showed increased levels of T-cell and microglial/macrophage markers. CCI induced further increases in CCL2, and IL6, and elevated ATF3 mRNA levels in LSC of young and middle-aged adults. Immunofluorescence images of dorsal horn microglia from middle-aged naïve or sham rats were typically hypertrophic with mostly thickened, de-ramified processes, similar to microglia following CCI. Unlike the spinal cord, marker expression profiles in naïve DRG were unchanged across age (except increased ATF3); whereas, levels of GFAP protein, localized to satellite glia, were highly elevated in middle age, but independent of nerve injury. Most neuroimmune markers were elevated in DRG following CCI in young adults, yet middle-aged animals showed little response to injury. No age-related changes in nociception (heat, cold, mechanical) were observed in naïve adults, or at days 3 or 7 post-CCI. The patterns of marker expression and microglial morphologies in healthy middle age are consistent with development of a para-inflammatory state involving microglial activation and T-cell marker elevation in the dorsal horn, and neuronal stress and satellite cell activation in the DRG. These changes, however, did not affect the establishment of neuropathic pain.

Three-dimensional morphometric analysis of microglial changes in a mouse model of virus encephalitis: age and environmental influences

Many RNA virus CNS infections cause neurological disease. Because Piry virus has a limited human pathogenicity and exercise reduces activation of microglia in aged mice, possible influences of environment and aging on microglial morphology and behavior in mice sublethal encephalitis were investigated. Female albino Swiss mice were raised either in standard (S) or in enriched (EE) cages from age 2 to 6 months (young - Y), or from 2 to 16 months (aged - A). After behavioral tests, mice nostrils were instilled with Piry-virus-infected or with normal brain homogenates. Brain sections were immunolabeled for virus antigens or microglia at 8 days post-infection (dpi), when behavioral changes became apparent, and at 20 and 40 dpi, after additional behavioral testing. Young infected mice from standard (SYPy) and enriched (EYPy) groups showed similar transient impairment in burrowing activity and olfactory discrimination, whereas aged infected mice from both environments (EAPy, SAPy) showed permanent reduction in both tasks. The beneficial effects of an enriched environment were smaller in aged than in young mice. Six-hundred and forty microglial cells, 80 from each group were reconstructed. An unbiased, stereological sampling approach and multivariate statistical analysis were used to search for microglial morphological families. This procedure allowed distinguishing between microglial morphology of infected and control subjects. More severe virus-associated microglial changes were observed in young than in aged mice, and EYPy seem to recover microglial homeostatic morphology earlier than SYPy . Because Piry-virus encephalitis outcomes were more severe in aged mice, it is suggested that the reduced inflammatory response in those individuals may aggravate encephalitis outcomes.

Clusterin/Apolipoprotein J immunoreactivity is associated with white matter damage in cerebral small vessel diseases

AIM

Brain clusterin is known to be associated with the amyloid-β deposits in Alzheimer's disease (AD). We assessed the distribution of clusterin immunoreactivity in cerebrovascular disorders, particularly focusing on white matter changes in small vessel diseases.

METHODS

Post-mortem brain tissues from the frontal or temporal lobes of a total of 70 subjects with various disorders including cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), cerebral amyloid angiopathy (CAA) and AD were examined using immunohistochemistry and immunofluorescence. We further used immunogold electron microscopy to study clusterin immunoreactivity in extracellular deposits in CADASIL.

RESULTS

Immunostaining with clusterin antibodies revealed strong localization in arterioles and capillaries, besides cortical neurones. We found that clusterin immunostaining was significantly increased in the frontal white matter of CADASIL and pontine autosomal dominant microangiopathy and leukoencephalopathy subjects. In addition, clusterin immunostaining correlated with white matter pathology severity scores. Immunostaining in axons ranged from fine punctate deposits in single axons to larger confluent areas with numerous swollen axon bulbs, similar to that observed with known axon damage markers such as non-phosphorylated neurofilament H and the amyloid precursor protein. Immunofluorescence and immunogold electron microscopy experiments showed that whereas clusterin immunoreactivity was closely associated with vascular amyloid-β in CAA, it was lacking within the granular osmiophilic material immunolabelled by NOTCH3 extracelluar domain aggregates found in CADASIL.

CONCLUSIONS

Our results suggest a wider role for clusterin associated with white matter damage in addition to its ability to chaperone proteins for clearance via the perivascular drainage pathways in several disease states.

γδ T cells as a major source of IL-17 production during age-dependent RPE degeneration

PURPOSE

Chronic inflammation is a key factor contributing to the progression of age-related macular degeneration (AMD). The goals of the current study were to develop an improved mouse model with retinal pathologic features similar to those of AMD and to characterize the immunoreactive cells in the outer retina and choroid during degeneration of the retinal pigment epithelium (RPE).

METHODS

Mice deficient in nuclear erythroid 2-related factor 2 (Nrf2) at 12 months of age were fed a high-fat, cholesterol-rich diet for up to 16 weeks. Ocular phenotype was monitored by optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO) in live animals, and was further validated by retinal histopathology. Immunofluorescence staining of either cryosections or RPE flat mounts was used to define immunoreactive cells. Flow cytometry analyses were further performed to define the subsets of intraocular T lymphocytes.

RESULTS

After 16 weeks on a high-fat (HF) diet, 58% of the eyes from Nrf2-/- mice had progression of retinal lesions. Major histocompatibility complex class II (MHC II)-positive microglia, FoxP3+ regulatory T cells (Tregs), and CD3+ IL-17-producing T cells were detected in either the retina or sub-RPE space. Flow cytometry analyses further revealed that most of the IL-17-producing cells were CD3+ CD4- TCRγδ+ cells.

CONCLUSIONS

The results suggest that the T cell-mediated immune responses played important roles in controlling the progression of AMD-like phenotype in Nrf2-deficient mice.

Alterations of protein composition along the rostro-caudal axis after spinal cord injury: proteomic, in vitro and in vivo analyses

Based on proteomic analyses we investigated the differences of released molecules in the conditioned media (CM) from the spinal cord central lesion and adjacent rostral and caudal segments at 3, 7, and 10 days after spinal cord injury (SCI), in order to specify the molecular environment within greater extent of tissue damage. Proteins found in CM were analyzed by shot-gun MS using nanoLC coupled to an orbitrap. The results showed some specific proteins at each site of the lesion at 3days. Among the proteins from rostral and lesion segments, some are related to chemokines, cytokines or to neurogenesis factors. In contrast, proteins from caudal segments are more related to necrosis factors. The CM from each spinal segment were used in vitro, on microglial BV2 cell lines and DRGs explants, showing a lesion site-dependent impact on microglia activation and DRGs neurite outgrowth. In addition, while naive BV2 cells exhibited insignificant staining for CX3CR1 receptor, the level of CX3CR1 was strongly enhanced in some BV2 cells after their stimulation by CM collected from SCI. The molecular data might correlate with different polarization of activated microglia and macrophages along the rostro-caudal axis following acute injury. This was partially confirmed in vivo with CX3CR1 receptor, revealing higher expression in the rostral segment, with potential neuroprotective action. In addition, the neurotrophic factors released from rostral and lesion segments enhanced outgrowth of DRGs explants. Taken together these data suggest that regionalization in terms of inflammatory and neurotrophic responses may occur between rostral and caudal segments in acute SCI.

The effects of N-acetyl-cysteine and acetyl-L-carnitine on neural survival, neuroinflammation and regeneration following spinal cord injury

Traumatic spinal cord injury induces a long-standing inflammatory response in the spinal cord tissue, leading to a progressive apoptotic death of spinal cord neurons and glial cells. We have recently demonstrated that immediate treatment with the antioxidants N-acetyl-cysteine (NAC) and acetyl-l-carnitine (ALC) attenuates neuroinflammation, induces axonal sprouting, and reduces the death of motoneurons in the vicinity of the trauma zone 4weeks after initial trauma. The objective of the current study was to investigate the effects of long-term antioxidant treatment on the survival of descending rubrospinal neurons after spinal cord injury in rats. It also examines the short- and long-term effects of treatment on apoptosis, inflammation, and regeneration in the spinal cord trauma zone. Spinal cord hemisection performed at the level C3 induced a significant loss of rubrospinal neurons 8 weeks after injury. At 2 weeks, an increase in the expression of the apoptosis-associated markers BCL-2-associated X protein (BAX) and caspase 3, as well as the microglial cell markers OX42 and ectodermal dysplasia 1 (ED1), was seen in the trauma zone. After 8 weeks, an increase in immunostaining for OX42 and the serotonin marker 5HT was detected in the same area. Antioxidant therapy reduced the loss of rubrospinal neurons by approximately 50%. Treatment also decreased the expression of BAX, caspase 3, OX42 and ED1 after 2 weeks. After 8 weeks, treatment decreased immunoreactivity for OX42, whereas it was increased for 5HT. In conclusion, this study provides further insight in the effects of treatment with NAC and ALC on descending pathways, as well as short- and long-term effects on the spinal cord trauma zone.

Dietary approach to decrease aging-related CNS inflammation

We demonstrate that the spontaneously hypertensive rat stroke-prone rat (SHRsp) undergoes premature aging of the CNS compared to the related normotensive Wistar Kyoto rat (WKY) as demonstrated by presence of activated microglia/macrophages, increased expression of inducible nitric oxide synthase and increased astrogliosis. We tested the hypothesis that dietary intake of phase 2 protein inducers would decrease these aging-associated degenerative changes. The source of dietary phase 2 protein inducers was dried broccoli sprouts of a cultivar containing high amounts of glucoraphanin that gives rise to phase 2 protein-inducing isothiocyanate sulforaphane. This diet significantly decreased the aging-related degenerative changes in the SHRsp CNS. We conclude that modest changes in diet may have profound effects on the aging CNS.

The influence of aging and estradiol to progesterone ratio on rat macrophage phenotypic profile and NO and TNF-α production

The phenotype and function of tissue macrophages substantially depend on the cellular milieu and biological effector molecules, such as steroid hormones, to which they are exposed. Furthermore, in female rats, aging is associated with the altered macrophage functioning and the increased estrogen level is followed by a decrease in that of progesterone. Therefore, the present study aimed to investigate the influence of estradiol/progesterone balance on rat macrophage function and phenotype throughout whole adult lifespan. We ovariectomized rats at the late prepubertal age or at the very end of reproductive lifespan, and examined the expression of ED2 (CD163, a marker of mature resident macrophages related to secretion of inflammatory mediators) on peritoneal macrophages and their ability to produce TNF-α and NO upon LPS-stimulation at different age points. In addition, to delineate direct and indirect effects of estrogen, we assessed the in vitro influence of different concentrations of 17β-estradiol on LPS-induced macrophage TNF-α and NO production. Results showed that: (a) the low frequency of ED2(high) cells amongst peritoneal macrophages of aged rats was accompanied with the reduced TNF-α, but not NO production; (b) estradiol level gradually increased following ovariectomy; (c) macrophage ED2 expression and TNF-α production were dependent on estradiol/progesterone balance and they changed in the same direction; (d) changes in estradiol/progesterone balance differentially affected macrophages TNF-α and NO production; and (e) estradiol exerted pro-inflammatory and anti-inflammatory effects on macrophages in vivo and in vitro, respectively. Overall, our study discloses that estradiol/progesterone balance contributes to the fine-tuning of rat macrophage secretory capacity, and adds to a better understanding of the ovarian steroid hormone role in the regulation of macrophage function, and its significance for the age-associated changes in innate immunity.

Administration of glucosylceramide ameliorated the memory impairment in aged mice

The function and the role of glucosylceramide have not been well studied in the central nervous system. This study was aimed to investigate the possible roles of glucosylceramide in memory function in aged mice. Glucosylceramide (50 mg/kg, p.o.) showed memory enhancing activity after 3-month treatment in the aged mice (C56BL/6, 18–20 months old) through Y-maze, novel objective test, and Morris water maze test. Long-term treatment of glucosylceramide decreased the expression of iNOS and COX-2 in the brain of aged mice. The LPS-induced mRNA level of iNOS, COX-2, IL-1β, and TNF-α was reduced by the acute treatment with glucosylceramide in adult mice. These results suggest that glucosylceramide plays an important role in anti-inflammatory and memory enhancement, and it could be a potential new therapeutic agent for the treatment of neurodegenerative diseases such as Alzheimer's disease.

Immune marker CD68 correlates with cognitive impairment in normally aged rats

The relationship between heightened neuroinflammation and cognitive decline in the normally aged brain is still debatable, as most data are derived from insult-related models. Accordingly, the aim of the current study was to determine whether a link could be established for 2 immune markers at the post-transcriptional level; CD68 and MHC-II, in a normally aged (24-month-old) rat population discriminated for their learning abilities. Using the Morris Water Maze (MWM) task, aged rats were divided into aged learning-impaired (AI) or -unimpaired (AU) groups. Western immunoblots of hippocampal tissue revealed a significant increase of CD68 in AI rats compared to the AU group. Moreover, up-regulated CD68 expression correlated with increased latency times in the MWM task. Immunofluorescence for CD68 revealed intense staining in the white matter regions and CA3 subregion of the hippocampus in the AI group. Despite expression of MHC-II in the AI group, no correlation was found. Overall, these data suggest that CD68 could play a role associated with cognitive decline in a subgroup of the normally aged population.

Age related changes in microglial phenotype vary between CNS regions: grey versus white matter differences

Subtle regional differences in microglial phenotype exist in the adult mouse brain. We investigated whether these differences were amplified during ageing and following systemic challenge with lipopolysaccharide (LPS). We studied microglial morphology and phenotype in young (4mo) and aged (21mo) C57/BL6 mice using immunohistochemistry and quantified the expression levels of surface molecules on microglia in white and grey matter along the rostral-caudal neuraxis. We detected significant regional, age dependent differences in microglial phenotypes, with the microglia of white matter and caudal areas of the CNS exhibiting greater upregulation of CD11b, CD68, CD11c, F4/80 and FcγRI than grey matter and rostral CNS areas. Upregulation of CD11c with age was restricted to the white matter, as was the appearance of multinucleated giant cells. Systemic LPS caused a subtle upregulation of FcγRI after 24 h, but the other markers examined were not affected. Burrowing behaviour and static rod assays were used to assess hippocampal and cerebellar integrity. Aged mice exhibited exaggerated and prolonged burrowing deficits following systemic LPS injection, while in the absence of an inflammatory challenge aged mice performed significantly worse than young mice in the static rod test. Taken together, these findings show that the effects of age on microglial phenotype and functional integrity vary significantly between CNS compartments, as do, albeit to a lesser extent, the effects of systemic LPS.

Plasma apolipoprotein levels are associated with cognitive status and decline in a community cohort of older individuals

Objectives

Apolipoproteins have recently been implicated in the etiology of Alzheimer’s disease (AD). In particular, Apolipoprotein J (ApoJ or clusterin) has been proposed as a biomarker of the disease at the pre-dementia stage. We examined a group of apolipoproteins, including ApoA1, ApoA2, ApoB, ApoC3, ApoE, ApoH and ApoJ, in the plasma of a longitudinal community based cohort.

Methods

664 subjects (257 with Mild Cognitive Impairment [MCI] and 407 with normal cognition), mean age 78 years, from the Sydney Memory and Aging Study (MAS) were followed up over two years. Plasma apolipoprotein levels at baseline (Wave 1) were measured using a multiplex bead fluorescence immunoassay technique.

Results

At Wave 1, MCI subjects had lower levels of ApoA1, ApoA2 and ApoH, and higher levels of ApoE and ApoJ, and a higher ApoB/ApoA1 ratio. Carriers of the apolipoprotein E ε4 allele had significantly lower levels of plasma ApoE, ApoC3 and ApoH and a significantly higher level of ApoB. Global cognitive scores were correlated positively with ApoH and negatively with ApoJ levels. ApoJ and ApoE levels were correlated negatively with grey matter volume and positively with cerebrospinal fluid (CSF) volume on MRI. Lower ApoA1, ApoA2 and ApoH levels, and higher ApoB/ApoA1 ratio, increased the risk of cognitive decline over two years in cognitively normal individuals. ApoA1 was the most significant predictor of decline. These associations remained after statistically controlling for lipid profile. Higher ApoJ levels predicted white matter atrophy over two years.

Conclusions

Elderly individuals with MCI have abnormal apolipoprotein levels, which are related to cognitive function and volumetric MRI measures cross-sectionally and are predictive of cognitive impairment in cognitively normal subjects. ApoA1, ApoH and ApoJ are potential plasma biomarkers of cognitive decline in non-demented elderly individuals.

Propidium iodide staining: a new application in fluorescence microscopy for analysis of cytoarchitecture in adult and developing rodent brain

Immunohistochemical visualization of antigens in specimen has evolved to an indispensable technique in biomedical research for investigations of cell morphology and pathology both in bright field and fluorescence microscopy. While there are couple of staining methods that reveal entire cytoarchitecture in bright field microscopy such as Nissl or hemalaun-eosin, there are still limitations in visualizations of cytoarchitecture in fluorescence microscopy. The present study reports a simple staining method that provides the required illustration of cell allocations and cellular composition in fluorescence microscopy in adult and in developing rodent central nervous system using the fluorophore propidium iodide (PI, 5μg/mL). PI is a well-accepted marker for degenerating cells when applied prior to fixation (pre-fixation PI staining). Here, PI was added to the sections after the fixation (post-fixation PI staining). This revised labeling procedure led to similar cytoarchitectural staining patterns in fluorescence microscopy as observed with hemalaun in bright field microscopy. This finding was proven in organotypic hippocampal slice cultures (OHSC) and brain sections obtained from different postnatal developmental stages. Excitotoxically lesioned OHSC subjected to pre-fixation PI staining merely showed brightly labeled condensed nuclei of degenerating neurons. In contrast, post-fixation PI staining additionally revealed extensive labeling of neuronal cell bodies and glial cells within the OHSC, thus allowing visualization of stratification of neuronal layers and cell morphology. Furthermore, post-fixation PI staining was combined with NeuN, calbindin, calretinin, glial fibrillary acidic protein or Griffonia simplicifolia isolectin B4 (IB(4)) in post natal (p1 and p9) and adult rats. In early post-natal brain sections almost all mentioned cellular markers led to an incomplete staining of the native cell organization and resulted in an inaccurate estimation of cell morphology when compared to adult brains. In contrast, post-fixation PI staining allowed investigation of the whole cytoarchitecture independent of the developmental stage. Taken together, post-fixation PI staining provides a detailed insight in the morphology of both developing and adult brain tissues in fluorescence microscopy.

Aging microglia: relevance to cognition and neural plasticity

Over the years it has become evident that the immune system can affect the function of the central nervous system (CNS), including altering cognitive processes. The impact of immune activation on the CNS is particularly important for aged individuals, as the brain's resident immune cells, microglia, acquire a pro-inflammatory profile. The low-grade chronic neuroinflammation that develops with normal aging likely contributes to the susceptibility to cognitive deficits and a host of age-related pathologies. Understanding why microglia show increased inflammatory activity (i.e., neuroinflammation) and identifying effective treatments to reduce microglia activation is expected to have beneficial effects on cognitive performance and measures of neural plasticity. However, microglia also promote regeneration after injury. Therefore, effective treatments must dampen inflammatory activity while preserving microglia's neuroprotective function. Discovering factors that induce neuroinflammation and investigating potential preventative therapies is expected to uncover the ways of maintaining normal microglia activity in the aged brain.

Macrophage and microglia ontogeny in the mouse visual system can be traced by the expression of Cathepsins B and D

Here, we show a detailed chronotopographical analysis of cathepsin B and D expression during development of the mouse visual system. Both proteases were detected in large rounded/ameboid cells usually located in close relationship with prominent sites of extensive physiological cell death. In concordance with their morphological features and topographical distribution, we demonstrate that expressing cells corresponded with macrophages and microglial precursors. We found that as microglial precursors differentiated the expression of both cathepsins was down-regulated. Of interest, cathepsin B and D transcripts were never observed in degenerating cells. Our findings point to a role for cathepsin D and B in cell debris degradation after apoptotic processes rather than promoting cell death, as proposed for other developmental models. Additionally their pattern of expression suggests a role in the maturation of the microglial precursors.

Age-related alterations in the dynamic behavior of microglia

Microglia, the primary resident immune cells of the central nervous system (CNS), exhibit dynamic behavior involving rapid process motility and cellular migration that is thought to underlie key functions of immune surveillance and tissue repair. Although age-related changes in microglial activation have been implicated in the pathogenesis of neurodegenerative diseases of aging, how dynamic behavior in microglia is influenced by aging is not fully understood. In this study, we employed live imaging of retinal microglia in situ to compare microglial morphology and behavioral dynamics in young and aged animals. We found that aged microglia in the resting state have significantly smaller and less branched dendritic arbors, and also slower process motilities, which probably compromise their ability to survey and interact with their environment continuously. We also found that dynamic microglial responses to injury were age-dependent. While young microglia responded to extracellular ATP, an injury-associated signal, by increasing their motility and becoming more ramified, aged microglia exhibited a contrary response, becoming less dynamic and ramified. In response to laser-induced focal tissue injury, aged microglia demonstrated slower acute responses with lower rates of process motility and cellular migration compared with young microglia. Interestingly, the longer term response of disaggregation from the injury site was retarded in aged microglia, indicating that senescent microglial responses, while slower to initiate, are more sustained. Together, these altered features of microglial behavior at rest and following injury reveal an age-dependent dysregulation of immune response in the CNS that may illuminate microglial contributions to age-related neuroinflammatory degeneration.

Preparation and Analysis of the Central Nervous System

For many pathologists, neuropathology is intimidating. Practical approaches for nervous tissue histologic evaluations to meet both routine and advanced study designs can lead to rewarding neuropathology efforts. Cost-effective, high-quality histologic evaluations can occur if animals are exsanguinated quickly, brains removed carefully to maintain structural integrity and avoid dark neuron artifact, immersion-fixed quickly and thoroughly, and trimmed and processed to consistently survey multiple areas. While brightfield examination of H&E-stained sections is generally sufficient for survey evaluations, epifluorescent assessment of neuronal autofluorescence facilitates recognition of neurodegeneration in H&E-stained sections. Fluoro-Jade B or specialized immunohistochemical stains may be required to answer specific questions. Evaluations require that both technical staff and pathologists have a working knowledge of a few easily identified neuroanatomic landmarks and familiarity with use of a detailed brain atlas. At least four coronal sections should be routinely surveyed from young adult rats, with evaluation of comparable areas in other laboratory animal species. This number should be at least doubled if there is reason to suspect morphologic changes in the CNS. This article focuses on technical details of efficient specimen preparation for neuropathologic evaluations involving relatively large numbers of rodents, as well as a practical approach to basic neuroanatomic site identification.

Life and death of microglia

The importance of microglial cells in the maintenance of a well-functioning central nervous system (CNS) cannot be overstated. As descendants of the myelomonocytic lineage they are industrious housekeepers and watchful sentries that safeguard a homeostatic environment through a number of mechanisms designed to provide protection of fastidious neurons at all times. Microglia become particularly active after homeostasis has been perturbed by physical injury or other insults and they enter into a state of activation which is determined largely by the nature and severity of the lesion. Microglial activation is the main cellular event in acute neuroinflammation and essential for wound healing in the CNS. Recent studies from this laboratory have been focused on microglia in the aging brain and identified structural abnormalities, termed microglial dystrophy, that are consistent with cell senescence and progress to a form of accidental cell death that is marked by cytoplasmic degeneration and has been termed cytorrhexis. Cytorrhexis of microglia is infrequent in the normally aged human brain and non-detectable in aged rodents, but its occurrence increases dramatically during neurodegenerative conditions, including Alzheimer's disease (AD) in humans and motoneuron disease in transgenic rats. The identification of degenerating microglia has given rise to a novel theory of AD pathogenesis, the microglial dysfunction hypothesis, which views the loss of microglial neuroprotection as a central event in neurodegenerative disease development.

The multifaceted profile of activated microglia

Although relatively neglected previously, research efforts in the past decade or so have identified a pivotal role for glial cells in regulating neuronal function. Particular emphasis has been placed on increasing our understanding of the function of microglia because a change from the ramified "resting" state of these cells has been associated with the pathogenesis of several neurodegenerative diseases, notably Alzheimer's disease. However, it is not clear whether activation of microglia and the associated inflammatory changes play a part in triggering disease processes or whether cell activation is a response to the early changes associated with the disease. In either case, the possibility exists that modulation of microglial activation may be beneficial in some circumstances, underlying the need to pursue research in this area. The original morphological categorization of microglia by Del Rio Hortega into ameboid, ramified, and intermediate forms, must now be elaborated to encompass a functional description. The evidence which has been generated recently suggests that microglia are probably never in a "resting" state and that several intermediate transitional states, based on function and morphology, probably exist. A more complete understanding of these states and the triggers which lead to a change from one to another state, and the factors which modulate the molecular switch that determines the persistence of the "activated" state remain to be identified.

Neuroinflammatory changes increase the impact of stressors on neuronal function

In the last few years, several research groups have reported that neuroinflammation is one feature common to several neurodegenerative diseases and that similar, although perhaps less profound, neuroinflammatory changes also occur with age. Age is the greatest risk factor in many neurodegenerative diseases, and the possibility exists that the underlying age-related neuroinflammation may contribute to this increased risk. Several animal models have been used to examine this possibility, and it is now accepted that, under experimental conditions in which microglial activation is up-regulated, responses to stressors are exacerbated. In the present article, these findings are discussed and data are presented from in vitro and in vivo experiments which reveal that responses to Abeta (amyloid beta-peptide) are markedly up-regulated in the presence of LPS (lipopolysaccharide). These, and previous findings, point to a vulnerability associated with inflammation and suggest that, even though inflammation may not be the primary cause of neurodegenerative disease, its treatment may decelerate disease progression.

Glial responses, neuron death and lesion resolution after intracerebral hemorrhage in young vs. aged rats

Intracerebral hemorrhage (ICH) usually affects older humans but almost no experimental studies have assessed aged animals. We address how aging alters inflammation, neuron death and lesion resolution after a hemorrhage in the rat striatum. In the normal aged brain, microglia displayed a 'dystrophic' phenotype, with shorter cellular processes and large gaps between adjacent cells, and there was more astrocyte reactivity. The ICH injury was monitored as hematoma volume and number of dying neurons at 1 and 3 days, and the volume of the residual lesion, ventricles and lost tissue at 28 days. Inflammation at 1 and 3 days was assessed from densities of microglia with resting vs. activated morphologies, or expressing the lysosomal marker ED1. Despite an initial delay in neuron death in aged animals, by 28 days, there was no difference in neuron density or volume of tissue lost. However, lesion resolution was impaired in aged animals and there was less compensatory ventricular expansion. At 1 day after ICH, there were fewer activated microglia/macrophages in the aged brain, but by 3 days there were more of these cells at the edge of the hematoma and in the surrounding parenchyma. In both age groups a glial limitans had developed by 3 days, but astrocyte reactivity and the spread of activated microglia/macrophages into the surrounding parenchyma was greater in the aged. These findings have important implications for efforts to reduce secondary injury after ICH and to develop anti-inflammatory therapies to treat ICH in aged humans.

Phase 2 protein inducers in the diet promote healthier aging

Oxidative stress drives many aging-associated problems. Because oxidative stress can be decreased by induction of phase 2 proteins, we hypothesized that incorporating the phase 2 protein inducer 2(3)-tert-butyl-4-hydroxyanisole (tBHA) into the diet would result in healthier aging. C57BL/6 mice were placed either on control mouse chow diet or on chow containing tBHA and were examined at 6, 12, and 18 months. Dietary tBHA resulted in the antioxidant response activation, decreased both oxidative stress and pro-inflammatory gene expression in tissues examined, counteracted the decrease in the transcription factors peroxisome proliferator-activated receptor-gamma and increase in CCAAT/enhancer binding protein-alpha levels seen in liver with aging, and was associated with mice having less weight gain, despite having no differences in food consumption, and better locomotor function. We conclude that simple changes in the diet such as incorporation of phase 2 protein inducers can have a profound influence on health and, thereby, the aging process.

Age-dependent responses of glial cells and leptomeninges during systemic inflammation

Systemic inflammation causes the age-dependent differential glial responses, but little is known about how age influences the barrier function of leptomeninges during systemic inflammation. This study was conducted to elucidate the relationship between the glial responses and the levels of tight junction proteins, occludin and ZO-1, in adjuvant arthritis (AA) rats. In young AA rats, microglia and astrocytes localized to the proximity of the leptomeninges expressed interleukin (IL)-10 and transforming growth factor (TGF)-beta1. The level of occludin significantly increased. In middle-aged AA rats, however, glial cells expressed IL-1beta and prostaglandin E(2) (PGE(2))-synthesizing enzymes. Furthermore, occludin and ZO-1 significantly decreased, resulting in the increased permeability of leptomeninges. In the cultured leptomeningeal cells, IL-1beta and PGE(2) caused a marked loss of occludin and ZO-1, respectively. Pretreatment with IL-10 and TGF-beta1 significantly antagonized their effects. These findings establish that age strongly influences the barrier functions of the leptomeninges through the age-dependent differential glial responses during systemic inflammation.

Modulation of amyloid-beta-induced and age-associated changes in rat hippocampus by eicosapentaenoic acid

The age-related deficit in long-term potentiation (LTP) in the dentate gyrus is positively correlated with hippocampal concentration of the pro-inflammatory cytokine, interleukin-1beta (IL-1beta). Previous evidence also indicates that the inhibition of LTP induced by intracerebroventricular injection of amyloid-beta(1-40) (Abeta) is accompanied by increased hippocampal IL-1beta concentration and IL-1beta-stimulated signalling, specifically activation of the stress-activated protein kinase, c-jun N-terminal kinase (JNK). We considered that the underlying age-related neuroinflammation may render older rats more susceptible to Abeta administration and, to investigate this, young, middle-aged and aged rats were injected intracerebroventricularly with Abeta or vehicle. Hippocampal IL-1beta concentration, JNK phosphorylation, expression of the putative Abeta receptor, Receptor for advanced glycation end products (RAGE) and the microglial cell surface marker, CD40 were assessed. We report that Abeta inhibited LTP in a concentration-dependent manner in young rats and that this was accompanied by concentration-dependent increases in hippocampal IL-1beta and expression of phosphorylated JNK, RAGE and CD40. While 20 micromol/L Abeta exerted no significant effect on LTP in young rats, it inhibited LTP in middle-aged and aged rats and the increased vulnerability of aged rats was associated with increased IL-1beta concentration. Treatment of rats with eicosapentaenoic acid attenuated the inhibitory effect of 60 micromol/L Abeta on LTP in young rats and the effect of 20 micromol/L Abeta in middle-aged and aged rats. We present evidence which indicates that the effect of eicosapentaenoic acid may be linked with its ability to stimulate activation of peroxisome proliferator-activated receptor gamma.

Long-term cultured human umbilical cord neural-like cells transplanted into the striatum of NOD SCID mice

The use of stem cells and other cells as therapies is still in its infancy. One major setback is the limited survival of the grafts, possibly due to immune rejection. Studies were therefore performed with human umbilical cord blood cells (HUCB) to determine the ability of these cells to survive in vivo and the effect of the immune response on their survival by transplantation into the normal striatum of immunodeficient NOD SCID mice. Long-term culture of HUCB cells resulted in several different populations of cells, including one that possessed fine processes and cell bodies that resembled neurons. Their neuronal phenotype was confirmed by immunohistochemical staining for the early neuronal marker TuJ1 and the potentially neural marker Nestin. Five days after cell transplantation of this neuronal phenotype, immunohistochemical staining for human mitochondria confirmed the presence of living HUCB cells in the mouse striatum, with cells localized at the site of injection, expressing early neural and neuronal markers (Nestin and TuJ1) as well as exhibiting neuronal morphology. However, no evidence of surviving cells was apparent 1 month postgrafting. The absence of signs of T cell-mediated rejection, such as CD4 and CD8 lymphocytes and minimal changes in microglia and astrocytes, suggest that cell loss was not due to a T cell-mediated immune response. In conclusion HUCB cells can survive long-term in vitro and undergo neuron-like differentiation. In mice, these cells do not survive a month. This may relate to the differentiated state of the cells transplanted into the unlesioned striatum, rather than T cell-mediated immunological rejection.

Factors contributing to neuromuscular impairment and sarcopenia during aging

Motor disturbances and wasting of skeletal muscles (sarcopenia) causes significant impairment of daily life activities and is a major underlying cause for hospitalization in senescence. Herein we review data and present new findings on aging-specific changes in motoneurons, skeletal muscle and the interplay between motoneurons and target muscle fibers. Although many of the changes occurring during aging may be specific to motoneurons and myofibers, respectively, evidence indicates that myofiber regeneration in sarcopenic muscle is halted at the point where reinnervation is critical for the final differentiation into mature myofibers. Combined, evidence suggests that sarcopenia to a significant extent depend on a decreased capacity among motoneurons to innervate regenerating fibers. There are also conspicuous changes in the expression of several cytokines known to play important roles in establishing and maintaining neuromuscular connectivity during development and adulthood. We also present data showing the usefulness of rodent models in studies of successful and unsuccessful patterns of aging. Finally, we show that not only dietary restriction (DR) but also activity and social environment may modulate the pattern of aging.

Quantification of the rat spinal microglial response to peripheral nerve injury as revealed by immunohistochemical image analysis and flow cytometry

Microgliosis is implicated in the pathophysiology of several neurological disorders, including neuropathic pain. Consequently, perturbation of microgliosis is a mechanistic and drug development target in neuropathic pain, which highlights the requirement for specific, sensitive and reproducible methods of microgliosis measurement. In this study, we used the spinal microgliosis associated with L5 spinal nerve transection and minocycline-induced attenuation thereof to: (1) evaluate novel software based semi-quantitative image analysis paradigms for the assessment of immunohistochemical images. Microgliosis was revealed by immunoreactivity to OX42. Several image analysis paradigms were assessed and compared to a previously validated subjective categorical rating scale. This comparison revealed that grey scale measurement of the proportion of a defined area of spinal cord occupied by OX42 immunoreactive cells is a robust image analysis paradigm. (2) Develop and validate a flow cytometric approach for quantification of spinal microgliosis. The flow cytometric technique reliably quantified microgliosis in spinal cord cell suspensions, using OX42 and ED9 immunoreactivity to identify microglia.

The results suggest that image analysis of immunohistochemical revelation of microgliosis reliably detects the spinal microgliosis in response to peripheral nerve injury and pharmacological attenuation thereof. In addition, flow cytometry provides an alternative approach for quantitative analysis of spinal microgliosis elicited by nerve injury.

The age-related attenuation in long-term potentiation is associated with microglial activation

It is well established that inflammatory changes contribute to brain ageing, and an increased concentration of proinflammatory cytokine, interleukin-1beta (IL-1beta), has been reported in the aged brain associated with a deficit in long-term potentiation (LTP) in rat hippocampus. The precise age at which changes are initiated is unclear. In this study, we investigate parallel changes in markers of inflammation and LTP in 3-, 9- and 15-month-old rats. We report evidence of increased hippocampal concentrations of the proinflammatory cytokines IL-1alpha, IL-18 and interferon-gamma (IFNgamma), which are accompanied by deficits in LTP in the older rats. We also show an increase in expression of markers of microglial activation, CD86, CD40 and intercellular adhesion molecules (ICAM). Associated with these changes, we observed a significant impairment of hippocampal LTP in the same rats. The importance of microglial activation in the attenuation of long-term potentiation (LTP) was demonstrated using an inhibitor of microglial activation, minocycline; partial restoration of LTP in 15-month-old rats was observed following administration of minocycline. We propose that signs of neuroinflammation are observed in middle age and that these changes, which are characterized by microglial activation, may be triggered by IL-18.

Microglia in the aging brain

The aging brain is characterized by a demonstrable decrease in weight and volume, particularly after the age of 50. This atrophy, which affects both grey and white matter, is presumed to result from a loss of neurons and myelinated axons. Glial cells, on the other hand, appear to increase in the aging brain, which exhibits greater immunoreactivity with both astrocytic and microglial markers. This review is focused on the morphologic and phenotypic changes that occur in microglial cells with normal aging. Although there is a consistent aging-related upregulation of microglial activation markers in experimental animals and humans that could be interpreted as aging-related neuroinflammation, it is generally difficult to show a direct correlation between ostensible microglial activation and neurodegeneration. This raises questions about whether aging-related microglial activation indeed represents reactive gliosis in the conventional sense. As an alternative, we discuss the possibility that structural and phenotypic changes that occur in microglia are a direct reflection of the aging process on microglia. Thus, microglia cells themselves may be subject to cellular senescence in the sense that they no longer function efficiently. The concept of microglial senescence offers a novel perspective on aging-related neurodegeneration, namely that neurodegeneration could also occur secondary to microglial degeneration.

Eicosapentaenoic acid confers neuroprotection in the amyloid-beta challenged aged hippocampus

Among the changes that occur in the hippocampus with age, is a deficit in long-term potentiation (LTP). This impairment is associated with inflammatory changes, which are typified by increased concentration of the pro-inflammatory cytokine interleukin-1beta (IL-1beta). Activated microglia are the most likely cell source of IL-1beta, but data demonstrating an age-related increase in microglial activation is equivocal. Here we demonstrate that the age-related deficit in LTP is accompanied by increased expression of cell surface markers of activated microglia (major histocompatibility complex II and CD40) and increased IL-1beta production, and that these changes may be stimulated by interferon-gamma. Treatment of aged rats with eicosapentaenoic acid (EPA) attenuates these changes and we suggest that IL-4 mediates the action of EPA. We demonstrate that aged rats exhibit an exaggerated response to intracerebroventricular injection of beta-amyloid peptide 1-40 (Abeta). Thus Abeta inhibited LTP in aged, but not young, rats and induced a further increase in hippocampal IL-1beta concentration. Of particular significance is the demonstration that EPA protects the aged brain so that the increased vulnerability to Abeta is ameliorated in EPA-treated rats.

Interaction between interferon ? and insulin-like growth factor-1 in hippocampus impacts on the ability of rats to sustain long-term potentiation

There is compelling evidence to suggest that inflammation significantly contributes to neurodegenerative changes. Consistent with this is the observation that several neurodegenerative disorders are accompanied by an increase in the concentration of interleukin (IL)-1beta. IL-1beta has a negative impact on synaptic plasticity and therefore an increased concentration of IL-1beta, such as that in the hippocampus of the aged rat, is associated with a deficit in long-term potentiation (LTP). IL-1beta is derived mainly from activated microglia but the trigger leading to this activation, specifically in the aged brain, remains to be identified. Here we examined the possibility that interferon (IFN)gamma may stimulate microglial activation and increase IL-1beta concentration, thereby inhibiting LTP. The IFNgamma concentration was increased in hippocampus prepared from aged, compared with young, rats and inversely correlated with the ability of rats to sustain LTP. Intracerebroventricular injection of IFNgamma inhibited LTP, and increased microglial activation was observed in both IFNgamma-injected and aged rats. The age-related increase in IFNgamma was accompanied by a decrease in the hippocampal concentration of insulin-like growth factor (IGF)-1. The evidence presented suggests that IGF-1 acts to antagonize the IFNgamma-induced microglial activation, the accompanying increase in IL-1beta concentration and the consequent deficit in LTP.

Specific immunolabeling of brain macrophages and microglial cells in the developing and mature chick central nervous system

The present study showed that the HIS-C7 monoclonal antibody, which recognizes the chick form of CD45, is a specific marker for macrophages/microglial cells in the developing and mature chick central nervous system (CNS). HIS-C7-positive cells were characterized according to their morphological features and chronotopographical distribution patterns within developing and adult CNS, similar to those of macrophages/microglial cells in the quail CNS and confirmed by their histochemical labeling with Ricinus communis agglutinin I, a lectin that recognizes chick microglial cells. Therefore, the HIS-C7 antibody is a valuable tool to identify brain macrophage and microglial cells in studies of the function, development, and pathology of the chick brain. CD45 expression differed between chick microglia (as revealed with HIS-C7 antibody) and mouse microglial cells (as revealed with an antibody against mouse form of CD45). Thus, a discontinuous label was seen on mouse microglial cells with the anti-mouse CD45 immunostaining, whereas the entire surface of chick microglial cells was labeled with the anti-chick CD45 staining. The functional relevance of these differences between species has yet to be determined.

Effect of aging on the microglial response to peripheral nerve injury

Microglial morphology and immunophenotype have been studied extensively in aging-related neurodegenerative diseases, but to a lesser extent in the normally aged CNS, and little is known about how aging affects the ability of microglia to respond to neuronal injury. The goal of the current study was to determine if aging affects the ability of microglia to divide during the early response to facial nerve axotomy. In addition, we investigated the incidence of microglial cell death during later post-axotomy time points to determine if aging had an effect on microglial turnover. We employed DNA labeling with 3H-thymidine, TUNEL and lectin histochemistry after facial nerve axotomy in young (3 months), middle-aged (15 months), and old (30 months) Fisher344-Brown Norway hybrid rats. Proliferation of microglia in old rats remained significantly higher than in young rats 4 days after injury, suggesting that regulation of microglial proliferation changes with aging. There was no aging-related difference in microglial TUNEL staining at 7, 14 or 21 days post-axotomy. Lectin histochemistry in the unoperated facial nucleus revealed aging-related morphological changes in resting microglia, including hypertrophy of the cytoplasm with dense perinuclear staining. Aging-related differences in activated microglia on the lesioned side were more subtle, although many activated microglia of aged animals continued to exhibit dense perinuclear lectin reactivity. We propose that aging-related changes in morphology in conjunction with a less regulated proliferative response in the aged facial nucleus may be a reflection of microglial senescence.