Browsing by Subject "microglia"

Alzheimer’s disease (AD) is the seventh leading cause of death worldwide. One hallmark of AD includes the amyloid beta (Aβ1-42) peptide that accumulates into oligomers, fibrils, and plaques. Aβ1-42 has been shown to be structurally and functionally similar to antimicrobial peptides (AMPs). Publications have reported that Borrelia burgdorferi can be found in the brain of AD patients. B. burgdorferi and B. garinii cause Lyme disease (LD). B. duttonii is responsible for relapsing fever (RF), a disease characterized by recurrent episodes of high fever. The aim of this research was to study whether synthetic Aβ1-42 binds to LD and RF Borrelia sp. and several bacterial molecules important for their virulence, and whether Borrelia sp. have evolved strategies to evade Aβ1-42-mediated killing. Binding of Aβ1-42 to B. burgdorferi, B. garinii and B. duttonii and several microbial molecules was studied by ELISA and immunoblotting. Bacterial culturing and microscopy were used to study survival, agglutination, and phagocytosis of Borrelia sp. in the presence of Aβ1-42 and microglia. In this research, Aβ1-42 was able to bind and agglutinate all of the three studied Borrelia sp. However, Aβ1-42 reduced the survival and increased the phagocytosis of B. duttonii. while B. burgdorferi and B. garinii were unaffected. In addition, potential Aβ1-42 binding molecules were detected from several bacterial species, including FhbA expressed by B. duttonii. In conclusion, this study suggests that some restricted species of bacteria may evade Aβ1-42 entrapment and thus may be involved in the ability of the species to invade the CNS that may trigger neuroinflammation related to AD.

Morphological features are considered as markers of microglial functionality, and they show regional heterogeneity in the brain. Recently the sleep-wake cycle was shown to affect microglial morphology in mice and correlate with cortical sleep slow wave activity (SWA). Microglial sizes and ramification increased during the dark period and decreased during the light period in cerebral areas associated with SWA, suggesting that neuronal activation could be affecting microglial morphology through SWA. I studied microglia in the hindbrain areas with and without functional connection to SWA to further investigate the association between SWA and alterations in morphology, and to investigate if there are differences in microglial morphology and their diurnal alterations in brain regions other than those commonly investigated. I examined three hindbrain areas (cerebellar cortex (CC), deep cerebellar nucleus (DCN) and medial vestibular nucleus (MVN)) and somatosensory cortex (SC) of mice (n=15) at two timepoints: 6 hours after the light onset (high SWA) and offset (low SWA). My aims were to answer if there are morphological differences in microglia between 1) the four brain areas at both timepoints and 2) between the two timepoints in each brain area. My hypotheses were that CC and DCN which have functional connections to cortical SWA, would show similar diurnal morphology alterations as demonstrated in the cerebral areas, and MVN that has no known cortical SWA connection, would lack significant alterations. As microglia are heterogenous throughout brain, I expected microglia to differ between different brain areas, especially the hindbrain and the SC. I found that microglial morphologies significantly differed between the hindbrain and the cortex, while the hindbrain areas were more similar in morphology. Moreover, the brain areas demonstrated diurnal morphology alterations of microglia with varying extent: CC and DCN microglial morphology did not correlate with SWA as clearly as SC did, and interestingly, morphological features of MVN microglia showed a pattern opposite to other areas, microglia being larger during the light period than the dark period. These results highlight the importance of the diurnal time to microglial morphology and the heterogeneity of microglia between different brain regions.

Cortical stroke induces a chain of events that results in secondary injury in the ipsilateral thalamus. Inflammation is a key player in the delayed injury. Microglia, the resident innate immune cells of the brain, seem to have an important role in the initiation and maintenance of the inflammation. After infarct they are rapidly activated and start to proliferate and release proinflammatory cytokines. They may even phagocytose viable neurons, a phenomenon called "phagoptosis". Many studies, which have aimed at inhibition of the the detrimental function of microglia, suggest that inhibition of microglia might offer promising therapeutical targets. However, microglia are also involved in the resolution and the repair phase after infarct, which makes development of novel therapies challenging. The only approved treatment for ischemic stroke, a fibrinolytic agent, has a very narrow therapeutic time window. Thus, new treatments are urgently needed. Modulation of inflammation may offer a wider therapeutic time window. In this study, we investigated the effects of two potentially neurotrophic factors, CDNF (cerebral dopamine neurotrophic factor) and MANF (mesencephalic astrocyte-derived neurotrophic factor), as well as a specific vitronectin receptor blocker, cRGDfV, on the prevention of neuronal death in thalamus in a transient murine cortical stroke model. MANF and CDNF are proteins released during stress of the endoplasmic reticulum (ER). They have been shown to protect neurons during ER stress and to reduce the production of some proinflammatory mediators. The vitronectin receptor blocker has in vitro inhibited microglial phagoptosis. The treatments were administered as single injections to the thalamus 7 days after the stroke onset. CDNF and MANF alleviated functional deficits, but did not protect thalamic neurons from death or affect the accumulation of phagocytic microglia. cRGDfV neither enhanced functional outcome nor protected neurons from death. The mechanisms of action were not investigated. In addition, we investigated, whether the death of thalamic neurons in the cortical stroke results in sensitization to pain. Central post-stroke pain has been reported on stroke patients and it has been associated with the death or the disturbances in the function of thalamic neurons. However, in spite of significant reduction in the number of neurons in the ipsilateral thalamus and the increase in the accumulation of phagocytic microglia on day 30 after stroke, we did not observe any significant sensitization to pain caused by thermal or mechanical stimuli on days 3, 14 and 28 after stroke. In conclusion, transient ischemic cortical stroke doesn't seem to induce sensitization to pain. MANF and CDNF seem to alleviate functional deficiencies, but they do not protect thalamic neurons from delayed death.

Microglia, the resident immune cells of the central nervous system, react to inflammatory stimuli in the brain in a variety of ways. These include migrating to the site of damage and releasing pro- and anti-inflammatory factors. Previous research indicates that these microglial functions require extensive intracellular calcium signaling. Microglial overactivation can exacerbate neuronal damage, especially in cases of chronic inflammation. The ability to modulate the microglial response to damage would therefore be of great clinical relevance. The endoplasmic reticulum (ER) acts as the cell’s main calcium store and regulates cellular calcium levels primarily through the activity of ryanodine receptors (RYR), inositol-triphosphate receptors (IP3R), and the sarco-endoplasmic reticulum calcium ATPase (SERCA) pump. Calcium depletion from the ER is associated with cellular stress and microglial reactivity and therefore the ER may be an important target for modulating the microglial reactive response. The aim of this study is to show whether ER calcium depletion in a microglial cell line causes changes in protein expression, cellular infiltration, and the release of key pro-inflammatory factors. Drugs that block the pumping of calcium from the cytosol via the SERCA pump, such as thapsigargin, effectively induce a state of calcium depletion in the ER. In the present study, treatment with the SERCA pump inhibitor thapsigargin was found to increase SERCA2 expression in BV2, but not SV40, microglial cell lines. Treatment of microglia with thapsigargin was associated with large increases in the release of pro-inflammatory factors IL-6 and TNF-alpha but had no effect on microglial migration.

The immune system is crucial in the central nervous system (CNS), protecting sensitive tissues, promoting regeneration, and maintaining homeostasis. It is involved in CNS-disorders, such as neurodegenerative diseases and neurological insults related to stroke. Critical myeloid leukocytes in the CNS are microglia, divided into pro-inflammatory M1 and anti-inflammatory M2 phenotypes. This polarization achieves modulation of the inflammatory response by amplifying or dampening it. Therefore, microglia are widely investigated in CNS-disorders. β2-integrins are adhesion proteins that mediate inflammation. They are expressed explicitly on leukocytes, including microglia. Important processes, such as phagocytosis and cell motility, are regulated by β2-integrins. They also relay downstream signals, altering inflammation in many settings, although their effects on microglial properties and stroke are currently poorly understood. We here aimed to investigate the role of β2-integrins in stroke-related injury and microglia polarization in vivo using knock-in (KI) mice, which lack functional β2-integrins. Our results show that in a mouse model of haemorrhagic stroke, the functional outcome was less severe in β2-integrin KI versus wild-type (WT) mice (P = 0.0147), suggesting that β2-integrins are involved in stroke pathophysiology. Furthermore, by using flow cytometry we observed significantly lower frequencies of M1 microglia in the KI mouse brain (P = 0.0096). Therefore, our findings reveal neuroprotective aspects by inhibiting β2-integrins in neuroinflammation. Investigating microglial properties mediated by β2-integrins could contribute to the understanding of neuroinflammatory events, leading to the development of therapies for poorly treated CNS-disorders. Our results suggest that β2-integrins should be further explored as molecular targets for novel stroke treatments.