The aPKC-CBP Pathway Regulates Post-stroke Neurovascular Remodeling and Functional Recovery

Abstract

Epigenetic modifications have emerged as attractive molecular substrates that integrate extrinsic changes into the determination of cell identity. Since stroke-related brain damage releases micro-environmental cues, we examined the role of a signaling-induced epigenetic pathway, an atypical protein kinase C (aPKC)-mediated phosphorylation of CREB-binding protein (CBP), in post-stroke neurovascular remodeling. Using a knockin mouse strain (CbpS436A) where the aPKC-CBP pathway was defective, we show that disruption of the aPKC-CBP pathway in a murine focal ischemic stroke model increases the reprogramming efficiency of ischemia-activated pericytes (i-pericytes) to neural precursors. As a consequence of enhanced cellular reprogramming, CbpS436A mice show an increased transient population of locally derived neural precursors after stroke, while displaying a reduced number of i-pericytes, impaired vascular remodeling, and perturbed motor recovery during the chronic phase of stroke. Together, this study elucidates the role of the aPKC-CBP pathway in modulating neurovascular remodeling and functional recovery following focal ischemic stroke.

Keywords: aPKC-CBP pathway; cellular reprogramming; ischemic stroke; neural precursors; pericyte; vascular remodeling.

Figure 1

CbpS436A Enhances the Reprogramming Efficiency of i-Pericytes to NPCs in Culture (A) Schematic of experimental flowchart. (B) Images of i-pericytes cultured for 7 days, showing PDGFRβ+ (red)/NG2+ (green)/SOX2− (purple) cells. Scale bar, 25 μm. (C) A neurosphere reprogrammed from i-pericytes expressed Sox2 (red) after cytospin. Scale bar, 10 μm. (D) Differentiation of neurospheres that were reprogrammed from i-pericytes into βIII TUBULIN+ neurons (left panel), GFAP+ astrocytes (middle panel), and O4+ oligodendrocytes (right panel) in the presence of retinoic acid. Arrows denote positive cells for βIII TUBULIN, GFAP, or O4. Scale bar, 20 μm. (E and F) Images (E) and quantitative analysis (F) of the number of neurospheres reprogrammed from i-pericytes isolated from wild-type (WT) and CbpS436A-KI stroke tissues. Scale bar, 150 μm. ^∗p ≤ 0.05, n = 4/group. (G) Quantitative analysis of the number of neurospheres reprogrammed from i-pericytes in the absence and presence of compound C (1 μM). ^∗p ≤ 0.05, n = 4/group. Error bars in this figure represent the SEM.

Figure 2

CbpS436A Increases the Transient Population of Locally Derived NPCs that Are Reprogrammed from Pericytes in the Post-stroke Brain (A and B) Expression of SOX2+ (green)/TDT+ (red) NPCs in the SVZ of NestinCre-ER^T2/tdTomato^flx/Stop/flx mice, receiving tamoxifen before stroke, at 3 days (B) and 7 days (A) post stroke, while SOX2+NPCs in injured cortex layer I were negative for TDT 3 days post stroke. Arrows denote co-labeled cells, while arrowheads denote single-labeled cells with SOX2+. Scale bar, 100 μm (A); 40 μm (B). PM, pia mater; LV, lateral ventricle; TDT, TdTomato. (C) Expression of GFP+ (green) and SOX2+ (red) cells in injured cortex of Nestin-GFP mice 3 days post stroke. White boxed image is enlarged in the bottom panel. Scale bar, 25 μm. (D) Expression of GFP+ (green)/NESTIN+ (red) co-labeled NPCs that were adjacent to CD31+ (white) endothelial cells in injured cortex of Sox2-GFP mice 3 days post stroke. White boxed image is enlarged in the right panels. Arrows denote co-labeled GFP+/NESTIN+ cells. Scale bar, 25 μm. (E) NESTIN+ cells within the infarct core are co-labeled with other pericyte markers, NG2 (red, left panel) and PDGFRβ (red, right panel). Arrows denote co-labeled cells. Scale bar, 20 μm. (F and G) Images (F) and quantification (G) of SOX2 (green)/NESTIN+ (red, left panel) NPCs, PAX6 (green)/NESTIN+ (red, middle panel) NPCs and DCX+ (red, right panel) neuroblasts in injured cortex layer I 3, 7, and 14 days post stroke. Arrows represent positive cells that were quantified for (G). Scale bar, 20 μm. (H and I) Images (H) and quantification (I) of co-labeled SOX2+/NESTIN+ NPCs in WT and CbpS436A ipsilateral cortex 3 days post stroke. Arrows denote co-labeled cells. Scale bar, 20 μm. ^∗p < 0.05, n = 3–4/group. (J–M) Images (J and L) and quantification (K and M) of co-labeled PAX6+/EdU+ NPCs (J and K) and DCX+/EdU+ neuroblasts (L and M) in WT and CbpS436A ipsilateral cortex 14 days post stroke, injected with EdU days 2–5 post stroke. White boxed image is enlarged in the right panels. Arrows denote co-labeled cells. Scale bar, 25 μm. ^∗p < 0.05; ^∗∗p < 0.01, n = 3–4/group. Error bars in this figure represent the SEM.

Figure 3

CbpS436A regulates Post-stroke Vascular Remodeling (A and B) Images (A) and quantification (B) of co-labeled PDGFRβ+/EdU+ pericytes in WT and CbpS436A ipsilateral cortex 14 days post stroke. Arrows denote co-labeled cells. Scale bar, 50 μm. ^∗p < 0.05, n = 3/group. (C) Images of CD31 (green) in injured cortex from WT and CbpS436A mice 14 days post stroke (right panel). Scale bar, 100 μm. (D and E) Quantification of total blood vessel counts (D) and the percentage of vascular coverage (E) from ipsilateral and contralateral cortex of WT and CbpS436A mice as shown in (C), normalized to the average counts of the WT contralateral group. Data were analyzed by two-way ANOVA(Genotype × Hemisphere interaction F(1,24) = 1.116, p = 0.3022, Genotype F(1,24) = 18.52, p = 0.0003, n = 7/per group for total blood vessel counts; Genotype × Hemisphere interaction F(1,12) = 0.225, p = 0.649, Genotype F(1,12) = 0.58 p = 0.0001, n = 4/per group for vascular coverage), with Tukey's post hoc test, ^∗p < 0.05, n = 4–7/group. (F) Confocal images of cortex of WT and CbpS436A mice 25 days post stroke, stained for CD31 (green). Scale bar, 100 μm. (G and H) Quantitative analysis of vessel length (G) and branchpoints (H), normalized as fold change over contralateral (Genotype × Hemisphere interaction F(1,12) = 4.317, p = 0.3022 for vessel length; Genotype × Hemisphere interaction F(1,12) = 5.372, p = 0.0389 for branchpoints) (n = 5 for WT, n = 3 for KI), with Tukey's post hoc test, ^∗p < 0.05, n = 3–5/group. (I and J) Images (I) and quantification (J) of co-labeled CD31+/EdU+ endothelial cells in WT and CbpS436A ipsilateral cortex 14 days post stroke. Arrows denote co-labeled cells. Scale bar, 20 μm. ^∗p < 0.05, n = 3/group. Error bars in this figure represent the SEM.

Figure 4

CbpS436A Modulates Post-stroke Functional Recovery without Altering Stroke Volume (A and B) Images (A) and quantification (B) of infarct volumes at 3 and 14 days post stroke from WT and CbpS436A-KI mice. Scale bars, 50 μm (n = 6/group for 3 days; n = 9/group for 14 days). (C) The percentage of forelimb error step at 7 and 14 days post stroke in WT and CbpS436A mice, analyzed by two-way ANOVA (Time × Genotype with forelimbs F(6,168) = 0.76, p = 0.7587, n = 17 for WT, n = 13 for KI), with Tukey's post hoc test, ^∗p < 0.05 compared with WT, n = 13–17/group. (D) The ipsilateral preference in the cylinder test at 7 and 14 days post stroke in WT and CbpS436A-KI mice, analyzed by two-way ANOVA (Time × Genotype F(2,42) = 2.395, p = 0.1035, n = 17 for WT, n = 13 for KI) with Tukey's post hoc test, ^∗p < 0.05 compared with WT, n = 13–17/group. Error bars in this figure represent the SEM.