Pinin protects astrocytes from cell death after acute ischemic stroke via maintenance of mitochondrial anti-apoptotic and bioenergetics functions.

BACKGROUND: Stroke is the second most common cause of deaths worldwide. After an ischemic stroke, the proliferated reactive astrocytes in the peri-infarct areas play a beneficial role in neuronal survival. As such, astrocytes have gradually become a target for neuroprotection in stroke. The present study assessed the hypothesis that Pinin (Pnn), originally identified as a nuclear and desmosome-associated protein and is now known to possess anti-apoptotic capacity, protects astrocytes from cell death after ischemic stroke and delineated the underlying mechanisms. METHODS: In in vivo experiments, adult male Sprague-Dawley rats (12-week old) were used to induce acute focal cerebral ischemia employing the middle cerebral artery occlusion (MCAO) method. In in vitro experiments, postnatal day 1 (P1) Sprague-Dawley rat pups were used to prepare cultures of primary astrocytes. Oxygen-glucose deprivation (OGD) and re-oxygenation (OGD/R) procedures were employed to mimic the hypoxic-ischemic condition of stroke in those astrocytes. RESULTS: We found in the peri-infarct area of the ipsilateral cortex and striatum in Sprague-Dawley rats after transient MCAO an increase in Pnn expression that correlated positively with the time-course of infarction as detected by T2-weighted imaging and triphenyltetrazolium chloride staining, augmented number of reactive astrocytes that double-labelled with Pnn as determined by immunofluorescence, and enhanced cytotoxic edema as revealed by diffusion weighted imaging; but mirrored the decreased cleaved caspase-3 as measured by western blot. In an OGD and OGD/R model using primary cultured astrocytes, treatment with Pnn siRNA doubled the chance of surviving astrocytes to manifest cell death as revealed by flow cytometry, and blunted activated ERK signaling, reduced Bcl-2 expression and augmented cleaved caspase 3 detected by western blot in the normoxia, OGD or OGD/R group. Gene-knockdown of Pnn also impeded the reversal from decline in cell viability, elevation in lactate dehydrogenase leakage and decrease in ATP production in the OGD/R group. CONCLUSION: We conclude that the endogenous Pnn participates in neuroprotection after acute ischemic stroke by preserving the viability of astrocytes that survived the ischemic challenge via maintenance of mitochondrial anti-apoptotic and bioenergetics functions.

Baroreflex functionality in the eye of diffusion tensor imaging.

By applying diffusion tensor imaging (DTI) as a physiological tool to evaluate changes in functional connectivity between key brainstem nuclei in the baroreflex neural circuits of mice and rats, recent work has revealed several hitherto unidentified phenomena regarding baroreflex functionality. (1) The presence of robust functional connectivity between nucleus tractus solitarii (NTS) and nucleus ambiguus (NA) or rostral ventrolateral medulla (RVLM) offers a holistic view on the moment-to-moment modus operandi of the cardiac vagal baroreflex or baroreflex-mediated sympathetic vasomotor tone. (2) Under pathophysiological conditions (e.g. neurogenic hypertension), the disruption of functional connectivity between key nuclei in the baroreflex circuits is reversible. However, fatality ensues on progression from pathophysiological to pathological conditions (e.g. hepatic encephalopathy) when the functional connectivity between NTS and NA or RVLM is irreversibly severed. (3) The absence of functional connectivity between the NTS and caudal ventrolateral medulla (CVLM) necessitates partial rewiring of the classical neural circuit that includes CVLM as an inhibitory intermediate between the NTS and RVLM. (4) Sustained functional connectivity between the NTS and NA is responsible for the vital period between brain death and the inevitable cardiac death. (5) Reduced functional connectivity between the NTS and RVLM or NA points to inherent anomalous baroreflex functionality in floxed and Cre-Lox mice. (6) Disrupted NTS-NA functional connectivity in Flk-1 (VEGFR2) deficient mice offers an explanation for the hypertensive side-effect of anti-vascular endothelial growth factor therapy (anti-VEGF) therapy. These newly identified baroreflex functionalities revealed by DTI bear clinical and therapeutic implications.

Critical role for all-trans retinoic acid for optimal effector and effector memory CD8 T cell differentiation.

A plethora of work implicates important effects of the vitamin A derivative retinoic acid (RA) in myeloid differentiation, whereas fewer studies explore the role of RA in lymphoid cells. Most work on lymphoid cells has focused on the influence of RA on CD4 T cells. Little information about the role of RA in CD8 T cell differentiation is available, and even less on cell-intrinsic effects in the CD8 T cell. This study explores the role of RA in effector and memory differentiation in a cell-intrinsic manner in the context of vaccinia virus infection. We observed the loss of the short-lived effector cell phenotype (reduced KLRG1(+), T-bet(hi), granzyme B(hi)), accompanied by an enhanced memory precursor phenotype at the effector (increased CD127(hi), IL-2(+)) and contraction phases (increased CD127(hi), IL-2(+), eomesodermin(hi)) of the CD8 response in the absence of RA signaling. The lack of RA also increased the proportion of central memory CD8s. Collectively, these results introduce a new role for RA in CD8 T cell activation and differentiation. This new role may have significant implications for optimal vaccine design in which vitamin A supplementation is used to augment effector responses, but it may be to the detriment of the long-term central memory response.