Anatomical location of injected microglia in different activation states and time course of injury determines survival of retinal ganglion cells after optic nerve crush.

Background: Activated microglia release harmful substances to retinal ganglion cells (RGCs), but may also benefit by removing cellular debris and secreting neurotrophic factors. These paradoxical roles remain controversial because the nature and time-course of the injury that defines their role is unknown. The aim of this study was to determine if pharmacological manipulation of microglia to acquire a pro-inflammatory or pro-survival phenotype will exacerbate or enhance neuronal survival after injury.Material and methods: Treated HAP I (highly aggressively proliferating immortalized) microglia were injected into the vitreous or tail vein (T V) of female Sprague-Dawley rats. Retinas were examined at 4-14 days following optic nerve crush (ONC) and the number of surviving RGCs was determined.Results: Injection of untreated HAP I cells resulted in the greater loss of RGCs early after ONC when injected into the vitreous and later after ONC when injected into the T V. LP S activated HAP I cells injected into the vitreous resulted in greater RGC loss with and without injury. When injected into the T V with ONC there was no loss of RGCs 4 days after ONC but greater loss afterwards. Minocycline treated HAP I cells injected into the vitreous resulted in greater RGC survival than untreated HAP I cells. However, when injected into the T V with ONC there was greater loss of RGCs. These results suggest that optic nerve signals attract extrinsic microglia to the retina, resulting in a proinflammatory response.Conclusion: Neuroprotection or cytotoxicity of microglia depends on the type of activation, time course of the injury, and if they act on the axon or cell body.

We show here that neuroprotection is not solely determined by the microglial activation state but factors such as the environment and time-course of the injury.Culture microglia can be treated in vitro and then injected in vivo.The cells migrate to the site of injury, cell body of retinal ganglion cells if in the vitreous or to the optic nerve if injected in the tail vein.Retinal ganglion cell death is dependent on the location the microglia act, time-course of injury, and activation state.Proinflammatory microglia can be neuroprotective early in the injury when the primary site of action is on the axons whereas hypoactivated microglia are neuroprotective early in injury when they act on the soma. Later in the injury, both become detrimental.

Changes in parvalbumin immunoreactive retinal ganglion cells and amacrine cells after optic nerve injury.

Parvalbumin (PARV) is a Ca(2+)-binding protein that may offer resistance to cell death as it primarily functions to maintain Ca(2+) homeostasis. The purpose of this study was to investigate whether PARV expressing retinal ganglion cells (RGCs) would be more resistant to cell death than RGCs that do not express PARV. RGCs in Sprague-Dawley rats were retrogradely labeled with Fluorogold (FG). After 2-28 days following an optic nerve crush (ONC) injury immunohistochemistry was performed on the sections using antibodies against PARV and markers of RGCs. The proportion of retinal ganglion cell layer cells labeled with PARV colocalized with FG or Brn3a and labeled only with PARV (displaced amacrine cells; dACs) were analyzed. PARV staining intensity was measured in ACs, dACs, and RGCs. Double labeling studies revealed that 49% of RGCs and 22% of dACs expressed PARV. There was an immediate reduction in RGC PARV staining after ONC but the overall rate of cell death after 28 days was similar in PARV and non-PARV expressing RGCs. There was no change in PARV AC or dAC number or staining intensity. Although this study suggests that there is no selective survival of the subpopulation of RGCs that contain PARV, there is down-regulation of PARV expression by these RGCs. This suggests that down-regulation of PARV may contribute to RGC death due to a compromised Ca(2+) buffering capacity. Maintaining PARV expression after injury could be an important neuroprotective strategy to improve RGC survival after injury.

Downregulation of BM88 after optic nerve injury.

PURPOSE: BM88 is a cell-cycle exit and neuronal differentiation protein that has been used as a marker of surviving retinal ganglion cells (RGCs) after optic nerve injury. Thy1.1 has also been used as a marker for RGC loss, but after optic nerve crush (ONC) a decrease in Thy1.1 expression precedes the loss of RGCs. The purpose of this study was to determine if BM88 expression was correlated with RGC loss after ONC and optic nerve transection (ONT) injuries. METHODS: Rats were injected with Fluorogold (FG) into the superior colliculus to label RGCs and received ONC or ONT 7 days later. Eyes were collected 2 to 28 days after injury. Retinas were labeled with BM88 and intensity of the BM88 cell labeling was measured. RESULTS: In control retinas, 98.9% of RGCs were immunoreactive (-IR) for BM88. There was a significant downregulation of BM88 by 52% to 80% of RGCs 7 days after ONC or ONT. The staining intensity of the remaining labeled cells was reduced to 41% to 51% of the control after 28 days of optic nerve injury. However, early in the injury there was a significant increase in the staining intensity of BM88. CONCLUSIONS: Nearly all BM88-IR RGCs colocalized with FG-labeled RGCs in control retinas. However, both the number of BM88-IR RGCs and their intensity decreased gradually between 4 and 28 days, preceding the loss of FG-labeled cells. These findings indicate that BM88 is not a good marker of surviving RGCs but may indicate abnormal RGC functioning, which precedes cell death.

The relationship between exercise and osteoarthritis in the elderly.

OBJECTIVES: To review within a prescribed evidence-based framework (1) the relationship between intermittent or lifelong physical activity and the subsequent onset or progression of osteoarthritis (OA) in later life and (2) the effect of structured exercise routines on the management of OA in the elderly. DATA SOURCES: A systematic literature search of MEDLINE (1950 to April Week 2, 2008) and EMBASE (1980 to 2008 Week 16) was carried out using the Ovid interface. Relevant mapped terms addressing the identified objectives were combined and exploded according to a defined protocol. STUDY SELECTION: Studies that met relevancy criteria and were of high methodologic quality (prospective cohort studies for the risk factor component and systematic reviews and randomized controlled trials for the therapy component) were extracted and then hand searched for any additional studies. Final inclusion was based on agreement between two independent assessors, according to prescribed criteria. Any studies that were not in the English language, did not address the questions of interest in humans, or did not include a population that had at least a mean age of 55 years at the time of study termination, were excluded. Only land-based regimens were included in the therapy component of the review. DATA EXTRACTION: Pertinent information on subjects, risks, and outcomes (when assessing physical activity as a risk factor for OA in the elderly) and subjects, interventions, and outcomes (when evaluating the application of exercise in the management of OA in older persons) was extracted from the selected studies. DATA SYNTHESIS: Ten studies met entry criteria for examining the relationship between physical activity and the development or progression of OA. Likely because of study variations and differences in the nature, duration and intensities of exercise regimens, no clearcut consensus was apparent on whether or not physical activity was a risk factor for OA. Six scientific reviews and ten single blinded randomized controlled trials were included when evaluating the effect of exercise on OA management. Regardless of wide variability in the included studies, a majority demonstrated that structured exercise programs were effective in the management of older subjects with OA. CONCLUSIONS: : Nuances of study design, differences in age and type of target populations, variability in the intensity, duration, and nature of physical activity in the respective studies, and lack of standardization in the way radiographic data are interpreted are among the factors that prevent consensus regarding the effect of physical activity on later development of OA. Similarly, there is considerable heterogeneity in the studies that assessed exercise in the treatment of OA. Nonetheless, there is substantive evidence in support of the benefits of one or another strength training or aerobic exercise regimen in the management of OA in middle-aged and elderly subjects.

Is regular exercise a friend or foe of the aging immune system? A systematic review.

OBJECTIVE: The purpose of the current review is to synthesize the available evidence from prospective clinical trials that are relevant to the clinical question: "What, if any, are the effects of regular aerobic and/or resistance exercise on the immune system in healthy older adults?" DATA SOURCES: Electronic databases were searched, using terms pertaining to immunology, exercise, and aging. Using the Ovid interface, the following databases were explored: Allied and Complimentary Medicine (AMED) (1985 to 2008), Cumulative Index to Nursing and Allied Health Literature (CINAHL) (1982 to 2008), all EBM Reviews (Cochrane DSR, ACP Journal Club, DARE, CCTR, CMR, HTA, and NHSEED), EMBASE (1980 to 2008), and MEDLINE (1950 to 2008). The MEDLINE database was searched a second time through the PubMed interface. STUDY SELECTION: Prospective controlled clinical trials were selected for review if they investigated the effects of an exercise intervention (minimum 4 weeks in duration) on an immune outcome measure in an older but otherwise healthy population. A total of 19 articles representing 17 trials were identified. DATA EXTRACTION: Quality assessment of the relevant articles was performed using the Jadad et al criteria. Data extraction was performed using a standardized instrument. Data regarding the participants, interventions, and laboratory and clinical immunologic outcomes were synthesized. DATA SYNTHESIS: Available data provide no clear evidence of acute or chronic effects of exercise on lymphocyte or natural killer (NK) cell numbers or phenotype (ie, surface markers)/activity, with 2 exceptions: (1) strength or endurance exercise may cause an acute transient elevation in circulating CD8+ T cells, and (2) regular aerobic exercise appears to enhance immunologic memory in the context of vaccination. The effects of strength training on NK cell activity are unclear. Furthermore, regular aerobic exercise appears to be associated with a reduction in chronic inflammation. Finally, no prospective controlled trials have clearly documented clinical immunologic benefits of regular exercise, which may well relate to underpowering of these studies. CONCLUSIONS: Overall, in healthy older adults, regular, particularly aerobic, exercise appears to be a friend of the immune system, helping to offset diminished adaptive responses and chronic inflammation. The possibility exists that particularly strenuous exercise may cause acute immunologic changes, such as diminished NK cell activity, which could predispose to infection in certain individuals. However, given the possible benefits of regular exercise on the immune system and the many definite benefits on other systems, the evidence presented here should not dissuade practitioners from suggesting regular exercise to otherwise healthy older adults.