Reversal of the Detrimental Effects of Post-Stroke Social Isolation by Pair-Housing is Mediated by Activation of BDNF-MAPK/ERK in Aged Mice

Abstract

Social isolation (SI) increases stroke-related mortality and morbidity in clinical populations. The detrimental effects of SI have been successfully modeled in the laboratory using young animals. Mechanistically, the negative effects of SI in young animals are primarily mediated by an enhanced inflammatory response to injury and a reduction in neurotrophic factors. However, the response to brain injury differs considerably in the aged. Given that SI is more prevalent in aged populations, we hypothesized that isolation, even when initiated after stroke, would delay recovery in aged mice. We found that aged isolated male mice had significantly increased infarct volume, neurological deficits, and serum IL-6 levels three days after stroke compared to pair housed (PH) mice. Using RT2 Profiler PCR Array and real-time quantitative PCR we found several important synaptic plasticity genes were differentially expressed in post-stroke SI mice. Furthermore, paired mice showed improved memory and neurobehavioral recovery four weeks after injury. Mechanistic and histological studies showed that the beneficial effects of pair housing are partially mediated by BDNF via downstream MAPK/ERK signaling and restoration of axonal basic myelin protein levels.

Deletion of the P2X4 receptor is neuroprotective acutely, but induces a depressive phenotype during recovery from ischemic stroke

“…We selected the three-day outcome because the infarct matures completely and shows minimal variation in its volume by that time. The 15- and 30-day time points represent sub-acute and chronic recovery as discussed previously (Verma et al, 2014, 2016). Briefly, we performed a midline ventral neck incision and unilateral right MCAo by advancing a 6.0 silicone rubber-coated monofilament (Doccol Corporation, CA) 10–11 mm from the internal carotid artery bifurcation via an external carotid artery stump.…”

“…We measured tissue infarct (day 3) or tissue atrophy (day 30) after stroke as described previously (Verma et al, 2016). Briefly, we sacrificed the mice after stroke surgery with an overdose of Avertin (250 mg/kg intraperitoneally, i.p).…”

“…After quick perfusion with 1xPBS, we rapidly removed the brain, and then separated and homogenized the frontal cortical region (perilesional cortex) of the right (ischemic) hemisphere as described previously (Verma et al, 2016). To determine the protein concentration, we used a bicinchoninic acid protein assay kit (Thermo Fisher Scientific Inc., Rockford, IL) and performed Western blot analysis.…”

“…We determined P2X4R expression in the ischemic or non-ischemic brain by both Western blot analysis using an anti-P2X4R antibody (1:500; Preoteintech Rosemont, IL) and immunolabeling with a different anti-P2X4R antibody (1:200 Alomone Labs, Jerusalem Israel). To determine cell-specific location, we co-labeled with target proteins using either NeuN (1:500, Abcam Cambridge, MA) or IbA-1 (1:500, Abcam, Cambridge, MA) antibodies as described (Verma et al, 2016). …”

“…Finally, P2X4R activation drives the release of brain-derived neurotrophic factor (BDNF) from microglial cells (Trang et al, 2009). BDNF is necessary for the maintenance of synaptic plasticity, enhances post-stroke recovery, and has an anti-depressant effect (Verma et al, 2014, 2016). Thus, microglial-induced neuroinflammation may be responsible for the depressive phenotype observed after stroke; this especially could be the case in immunocompromised animals, in which virus can rapidly gain access to the brain, infect microglia (but not neurons), and induce their activation (Kaul et al, 2001).…”