Michael G. Kozoriz

Inhibition of cytokine-induced connexin43 hemichannel activity in astrocytes is neuroprotective

Astrocytes express high levels of connexin43, a protein that forms two types of channels: gap junction channels for direct intercellular communication, and hemichannels for exchanges with the extracellular space. Inflammation induces connexin43 hemichannel activation, which has been proposed to be involved in neuroglial interactions. Here, we investigated the contribution of connexin43 to NMDA-induced excitotoxicity in neuron/astrocyte co-cultures, after treatment with a pro-inflammatory cytokine mixture, containing TNF-alpha and IL1-beta (Mix), that stimulated astroglial connexin43 hemichannel activity. Interestingly, NMDA treatment induced a higher amount of neurotoxicity in Mix-treated co-cultures than in untreated ones, whereas this extent of neurotoxicity was absent in enriched neuron cultures or in co-cultures with connexin43 knock-out astrocytes. Furthermore, application of connexin43 hemichannel blockers or a synthetic cannabinoid prevented the Mix-induced potentiated NMDA neurotoxicity. Altogether, these data demonstrate that inflammation-induced astroglial hemichannel activation plays a critical role in neuronal death and suggest a neuroprotective role of connexin43 hemichannel blockade.

The connexin43 C-terminal region mediates neuroprotection during stroke.

Connexin43 plays an important role in neuroprotection in experimental stroke models; reducing the expression of this gap junction protein in astrocytes enhances injury upon middle cerebral artery occlusion (MCAO). Because the C-terminal region of connexin43 isimportant for channel activity, we carried out MCAO stroke experiments in mice expressing a truncated form of connexin43 (Cx43&Dgr;CT mice). Brain sections were analyzed for infarct volume, astrogliosis, and inflammatory cell invasion 4 days after MCAO. Adult cortices and astrocyte cultures were examined for connexin43 (Cx43) expression by immunohistochemistry and Western blot. Cultured astrocytes were also examined for dye coupling, channel conductance, hemichannel activity, and Ca2+ wave propagation. The Cx43&Dgr;CT mice exhibit enhanced cerebral injury after stroke. Astrogliosis was reduced and inflammatory cell invasion was increased inthe peri-infarct region in these mice compared with controls; Cx43 expression was also altered. Lastly, cultured astrocytes from Cx43&Dgr;CT mice were less coupled and displayed alterations in channel gating, hemichannel activity, and Ca2+ wave properties. These results suggest that astrocytic Cx43 contributed to the regulation of cell death after stroke and support the view that the Cx43 C-terminal region is important in protection in cerebral ischemia.

Policing the police: astrocytes modulate microglial activation.

Andy Y. Shih,1,2,3 Herman B. Fernandes,1,2,3 Fiona Y. Choi,1,2,3 Michael G. Kozoriz,4 Yingru Liu,1,3 Ping Li,1,2 Catherine M. Cowan,2,3 and Andis Klegeris2 1Graduate Program in Neuroscience, 2Kinsmen Laboratory of Neurological Research, 3Brain Research Centre, and 4Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3 Review of Min et al. (http://www.jneurosci.org/cgi/content/full/26/6/1880)

Temporary sequestration of potassium by mitochondria in astrocytes.

Increases in extracellular potassium concentration ([K+]o), which can occur during neuronal activity and under pathological conditions such as ischemia, lead to a variety of potentially detrimental effects on neuronal function. Although astrocytes are known to contribute to the clearance of excess K+o, the mechanisms are not fully understood. We examined the potential role of mitochondria in sequestering K+ in astrocytes. Astrocytes were loaded with the fluorescent K+ indicator PBFI and release of K+ from mitochondria into the cytoplasm was examined after uncoupling the mitochondrial membrane potential with carbonyl cyanide m-chlorophenylhydrazone (CCCP). Under the experimental conditions employed, transient applications of elevated [K+]o led to increases in K+ within mitochondria, as assessed by increases in the magnitudes of cytoplasmic [K+] ([K+]i) transients evoked by brief exposures to CCCP. When mitochondrial K+ sequestration was impaired by prolonged application of CCCP, there was a robust increase in [K+]i upon exposure to elevated [K+]o. Blockade of plasmalemmal K+ uptake routes by ouabain, Ba2+, or a mixture of voltage-activated K+ channel inhibitors reduced K+ uptake into mitochondria. Also, reductions in mitochondrial K+ uptake occurred in the presence of mito-KATP channel inhibitors. Rises in [K+]i evoked by brief applications of CCCP following exposure to high [K+]o were also reduced by gap junction blockers and in astrocytes isolated from connexin43-null mice, suggesting that connexins also play a role in K+ uptake into astrocyte mitochondria. We conclude that mitochondria play a key role in K+o handling by astrocytes.

Post-vaccination myositis and myocarditis in a previously healthy male

BackgroundThe immunological literature has been redefining clinical phenomena as hypotheses emerge regarding causal links between triggers, immunologic manifestations, and their specific inflammatory cascades. Of late, autoimmune manifestations that appear to be caused by an external adjuvant have been grouped into a complex syndrome referred to as autoimmune/inflammatory syndrome induced by adjuvants (ASIA). This syndrome may present with diverse clinical problems, which may include neurocognitive impairment, inflammatory musculoskeletal changes, and constitutional symptoms. There is evidence in the literature linking vaccines to different auto-immune manifestations. Vaccines have not traditionally been reported to trigger ASIA, although reports are emerging linking the human papilloma virus and hepatitis B vaccines to it.Case presentationWe report the first suspected case of ASIA in a previously healthy patient who received the Fluad seasonal influenza vaccine, which contains the MF59 adjuvant. He presented to hospital with profound weakness and was diagnosed with severe rhabdomyolysis. He also had elevated troponin-I and extensive cardiac investigations enabled the diagnosis of myocarditis. His infectious and rheumatologic work-ups were negative. He responded well to conservative management and did not require immune suppressive therapy.ConclusionGiven the benefits of the influenza vaccine, and the low incidence of clinically significant complications, we encourage ongoing seasonal influenza immunization. However, ongoing surveillance is required to evaluate the occurrence of rare adverse events, including ASIA.

Evaluating bone marrow oedema patterns in musculoskeletal injury

MRI is a common tool in the evaluation of musculoskeletal injury that allows the clinician to pinpoint specific pathologies. The patients history and physical exam play a critical role in the diagnosis of sports injuries, however, complementary imaging can play an important role in determining the nature and extent of injury. With the widespread use of MRI, attention has focused on the signals generated following injury. In particular, bone marrow oedema (BME) patterns can be used to aid in the diagnosis of musculoskeletal injury. In this pictorial essay, the authors will demonstrate common patterns of BME that accompany a wide range of musculoskeletal injuries. It is expected that by the end of this article, the reader will be able to (1) recognise BME is a phenomenon observed on MRI following sports injury; (2) recognise typical patterns of BME; (3) understand the relationship of oedema to the type of injury and (4) in the presence of oedema, understand other co-existing injuries that ultimately may have an impact on management.

Passing potassium with and without gap junctions.

Editors Note: These short reviews of a recent paper in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to mimic the journal clubs that exist in your own departments or institutions. For more information on the format and purpose of the Journal Club, please see Review of Wallraff et al. Glia, originally thought to play a passive role in the CNS, are now recognized as active regulators of CNS activity. For example , astrocytes are essential for the maintenance of extracellular ion concentrations , notably K ϩ , at physiological levels (Orkand et al., 1966). Any deviation of extracellular K ϩ concentration ([K ϩ ] o) from ϳ3 mM can affect neural activity. Elevated [K ϩ ] o occurs during seizure activity , ischemia, and spreading depression, in which [K ϩ ] o can reach 10 –50 mM (Walz, 2000; Somjen, 2002), with consequent effects on neuronal excitability and ultimately on cell viability. To limit increased [K ϩ ] o , astrocytes are equipped with a variety of K ϩ uptake mechanisms, including the Na ϩ-K ϩ-ATPase, Na ϩ-K ϩ-2Cl Ϫ cotransporters and voltage-activated K ϩ channels. Furthermore, local elevations in [K ϩ ] o shift the K ϩ equilibrium potential (E K) to more positive values relative to the membrane potential (V m), thus driving K ϩ into these cells along an electrochemical gradient. K ϩ can also be spatially buffered via diffusion through the astrocytic cytoplasm to areas of lower [K ϩ ] o , and then K ϩ is driven back out of the cell at distal sites at which E K is still more negative than the V m. Spatial redistribution of K ϩ is believed to be enhanced by gap junction coupling between astrocytes, although the experimental evidence for this mechanism is minimal (Walz, 2000; Kofuji and Newman, 2004). In their recent paper in The Journal of Neuroscience, Wallraff et al. (2006) examined the role of gap junction coupling between astrocytes in K ϩ buffer-ing and its subsequent physiological effect. Using hippocampal slices, the authors examined coupling in transgenic mice from which connexin43 (Cx43), the most abundant astrocytic Cx, had been conditionally deleted. Cx43/Cx30 double knockout (dko) mice were also used because Cx30 is the other major connexin in astrocytes. Dye coupling of the gap junction-permeable tracer biocytin was reduced in the Cx43 knockout and abolished in the dko [Wallraff et …

The Accuracy of Colorectal Cancer Detection by Computed Tomography in the Unprepared Large Bowel in a Community-Based Hospital

Purpose This retrospective study examined the performance of general radiologists in a community-based hospital in detecting colorectal cancer (CRC) with computed tomography (CT) in the unprepared large bowel. Methods The pathology database at a community hospital over the past 7 years (2009–2015) was retrospectively analysed for pathologically proven CRC (924 cases). The provincial hospital information profile for these patients was reviewed to determine if they had an abdominal CT for any reason in the year prior to biopsy. Metrics such as age, sex, time between the CT and biopsy or surgery, whether CRC was initially detected by the radiologist, and if this was an emergency presentation was evaluated. In the cases where CRC was not identified, the CT scans were reanalysed to determine if the CRC was identifiable in retrospect. The sensitivity of detecting CRC by CT scan in the unprepared large bowel was calculated. Results Of the 924 biopsy proven CRC cases, 22% (207 of 924) of the patients had a CT prior to biopsy. Of these cases, 47% (97 of 207) presented on an emergency basis. Of the cases with imaging in the year prior, about 60% (125 of 207) had cancer prospectively detected by the radiologist. Upon re-examination of the cases in which CRC was not initially detected, 59% were visualized in retrospect. Conclusions Community general radiologists can successfully detect CRC with a high degree of accuracy. Reformatted images, bowel wall thickening when regional nodes are prominent, and minimizing oral contrast were helpful in improving detection.

Post-Vaccination Myositis and Myocarditis in a Previously Healthy Male

Rhabdomyolysis is the breakdown of muscle cells leading to the release of cellular constituents such as electrolytes, enzymes and myoglobin. There is a broad differential diagnosis for this condition. In this report we describe a 65 year old male who presented with weakness, rhabdomyolysis, and acute kidney injury five days after receiving the seasonal flu vaccine. Laboratory investigations showed elevated creatine kinase and troponin-I, and extensive cardiac investigations yielded a diagnosis of myocarditis. The cause of his clinical picture is explored in this case report.