Specific ion channels contribute to key elements of pathology during secondary degeneration following neurotrauma

Background: Following partial injury to the central nervous system, cells beyond the initial injury site undergo secondary degeneration, exacerbating loss of neurons, compact myelin and function. Changes in Ca 2+ flux are associated with metabolic and structural changes, but it is not yet clear how flux through specific ion channels contributes to the various pathologies. Here, partial optic nerve transection in adult female rats was used to model secondary degeneration. Treatment with combinations of three ion channel inhibitors was used as a tool to investigate which elements of oxidative and structural damage related to long term functional outcomes. The inhibitors employed were the voltage gated Ca 2+ channel inhibitor Lomerizine (Lom), the Ca 2+ permeable AMPA receptor inhibitor YM872 and the P2X 7 receptor inhibitor oxATP. Results: Following partial optic nerve transection, hyper-phosphorylation of Tau and acetylated tubulin immunoreactivity were increased, and Nogo-A immunoreactivity was decreased, indicating that axonal changes occurred acutely. All combinations of ion channel inhibitors reduced hyper-phosphorylation of Tau and increased Nogo-A immunoreactivity at day 3 after injury. However, only Lom/oxATP or all three inhibitors in combination significantly reduced acetylated tubulin immunoreactivity. Most combinations of ion channel inhibitors were effective in restoring the lengths of the paranode and the paranodal gap, indicative of the length of the node of Ranvier, following injury. However, only all three inhibitors in combination restored to normal Ankyrin G length at the node of Ranvier. Similarly, HNE immunoreactivity and loss of oligodendrocyte precursor cells were only limited by treatment with all three ion channel inhibitors in combination. Conclusions: Data indicate that inhibiting any of a range of ion channels preserves certain elements of axon and node structure and limits some oxidative damage following injury, whereas ionic flux through all three channels must be inhibited to prevent lipid peroxidation and preserve Ankyrin G distribution and OPCs

Delayed treatment of secondary degeneration following acute optic nerve transection using a combination of ion channel inhibitors

Studies have shown that a combined application of several ion channel inhibitors immediately after central nervous system injury can inhibit secondary degeneration. However, for clinical use, it is necessary to determine how long after injury the combined treatment of several ion channel inhibitors can be delayed and efficacy maintained. In this study, we delivered Ca 2+ entry-inhibiting P2X7 receptor antagonist oxidized- ATP and AMPA receptor antagonist YM872 to the optic nerve injury site via an iPRECIO @ pump immediately, 6 hours, 24 hours and 7 days after partial optic nerve transection surgery. In addition, all of the ion channel inhibitor treated rats were administered with calcium channel antagonist lomerizine hydrochloride. It is important to note that as a result of implantation of the particular pumps required for programmable delivery of therapeutics directly to the injury site, seromas occurred in a significant proportion of animals, indicating infection around the pumps in these animals. Improvements in visual function were observed only when treatment was delayed by 6 hours; phosphorylated Tau was reduced when treatment was delayed by 24 hours or 7 days. Improvements in structure of node/paranode of Ranvier and reductions in oxidative stress indicators were also only observed when treatment was delayed for 6 hours, 24 hours, or 7 days. Benefits of ion channel inhibitors were only observed with time-delayed treatment, suggesting that delayed therapy of Ca 2+ ion channel inhibitors produces better neuroprotective effects on secondary degeneration, at least in the presence of seromas

Schematic diagram of dissection of retina for microarray studies.

<p>RGC somata whose axons are transected after PT of the optic nerve are located in the dorsal, temporal and central areas (indicated in blue), leaving RGCs in nasal and ventral retina initially intact but vulnerable to secondary degeneration[<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0192348#pone.0192348.ref026" target="_blank">26</a>]. The dashed line indicates where dorsal and ventral retinal tissue were separated.</p

Association between Retinal Arteriolar and Venule Calibre with Prevalent Heart Failure: A Cross-Sectional Study.

There is evidence to suggest that microvascular disease, particularly diabetic retinopathy, plays a role in the pathogenesis of HF. However, whether changes in retinal vessel calibre predicts HF is unclear. The purpose of this study was to examine the association of retinal microvascular structure with prevalent heart failure (HF).The Australian Heart Eye Study (AHES) is a cross-sectional study that surveyed 1680 participants who presented to a tertiary referral hospital for the evaluation of potential coronary artery disease by coronary angiography. Retinal vessel calibre was graded using retinal photography and participants' self-reported echocardiography-confirmed HF was obtained via an extensive medical questionnaire.There were 107 participants (8.1%) with prevalent self-reported HF. Persons with wider retinal arteriolar calibre (comparing highest versus lowest tertile or reference) were more likely to have prevalent HF (OR 3.5; 95% CI, 1.7-7.2) when adjusted for age and sex. After further adjustment for body mass index, hypertension, diabetes, smoking status, triglycerides and estimated glomerular filtration rate, this association remained significant (OR 4.5; 95% CI, 2.0-9.8). After further stratification, this association remained significant among participants with diabetes (OR 10.3; 95% CI, 2.7-39.3) but not in those without diabetes (OR 2.7; 95% CI, 0.9-7.5). The strength of this association was not dependent on the length of history of diabetes, or retinopathy status. There was no significant association between retinal venular calibre and prevalence of HF.Wider retinal arteriolar diameter was significantly and independently associated with prevalent HF in participants of a cross-sectional study. This association was significant stronger among participants with diabetes compared to without diabetes. No association was found between retinal venule calibre with prevalent HF

Immunoreactivity of Ecel 1 GFAP and ATF3 in retinal sections.

<p><b>(</b>A) Endothelin converting enzyme-like 1 (Ecel1), (B) Glial fibrillary acidic protein (GFAP) and (C) Activating transcription factor-3 (ATF3); representative images shown for dorsal and ventral retina. Semi-quantification of immunointensity was performed on the retinal ganglion cell layer (GCL) in dorsal, central and ventral retina on normal uninjured animals and the retina of animals at 1 and 7 days following PT. Error bars show the standard error of the mean (SEM) for each experiment. Statistically analysis conducted on each region and significant differences between retinal tissue of injured and uninjured ON are indicated by <i>asterisks</i> (* p-value < 0.05, ** p-value < 0.01, *** p-value <0.001). Scale bar = 10 μm.</p

GSEA of differentially expressed genes (FC > 1.4, p-value < 0.05) between dorsal and ventral retina, showing GO classified biological_functions at day 1 and day 7 after PT injury.

<p>All biological_function clusters are upregulated in dorsal retina when compared to ventral retina. Top 10 significant (p-value < 0.05) biological_functions shown for day 1 with a list of contributing genes that are differentially expressed by fold change > 2, p-value < 0.05. Only 2 clusters were enriched from differentially expressed genes between dorsal and ventral retina at day 7 after injury. The genes listed are differentially expressed by a FC > 1.5. The bar graph depicts the total number of genes that contribute to each functional cluster.</p