Abstract
MicroRNAs have gained popularity as a potential treatment for many diseases, including stroke. This study identifies and characterizes a specific member of the miR-17–92 cluster, miR-20a-3p, as a possible stroke therapeutic. A comprehensive microRNA screening showed that miR-20a-3p was significantly upregulated in astrocytes of adult female rats, which typically have better stroke outcomes, while it was profoundly downregulated in astrocytes of middle-aged females and adult and middle-aged males, groups that typically have more severe stroke outcomes. Assays using primary human astrocytes and neurons show that miR-20a-3p treatment alters mitochondrial dynamics in both cell types. To assess whether stroke outcomes could be improved by elevating astrocytic miR-20a-3p, we created a tetracycline (Tet)-induced recombinant adeno-associated virus (rAAV) construct where miR-20a-3p was located downstream a glial fibrillary acidic protein promoter. Treatment with doxycycline induced miR-20-3p expression in astrocytes, reducing mortality and modestly improving sensory motor behavior. A second Tet-induced rAAV construct was created in which miR-20a-3p was located downstream of a neuron-specific enolase (NSE) promoter. These experiments demonstrate that neuronal expression of miR-20a-3p is vastly more neuroprotective than astrocytic expression, with animals receiving the miR-20a-3p vector showing reduced infarction and sensory motor improvement. Intravenous injections, which are a therapeutically tractable treatment route, with miR-20a-3p mimic 4 h after middle cerebral artery occlusion (MCAo) significantly improved stroke outcomes including infarct volume and sensory motor performance. Improvement was not observed when miR-20a-3p was given immediately or 24 h after MCAo, identifying a unique delayed therapeutic window. Overall, this study identifies a novel neuroprotective microRNA and characterizes several key pathways by which it can improve stroke outcomes.
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Introduction
Stroke remains the leading cause of disability and the fifth leading cause of mortality in the USA. Ischemic stroke accounts for 80% of all strokes, and there is currently only one FDA-approved drug therapy, tissue plasminogen activator (tPA). tPA must be administered within a short time window of 3–4.5 h to be effective, which limits the proportion of patients eligible to receive this treatment (5.9–7.0%) [1, 2]. Therefore, there is an urgent need for the development of effective and safe therapeutics. Moreover, since stroke risk and stroke severity are modified by the age and biological sex of the patient, it is imperative for preclinical studies of potential stroke therapies to address both variables.
Epigenetic modifiers, such as small non-coding RNAs, have emerged as powerful candidates for several diseases including cancers and immune, infectious, cardiovascular, and neurodegenerative diseases [3,4,5,6]. MicroRNAs (miRNAs) are typically 18–25 nucleotides long and bind to complementary sequences in the 3′ UTR of multiple target mRNAs to regulate gene expression [7]. In the case of ischemic stroke, several studies have now shown that miRNA mimics or antagomirs can regulate acute and chronic stroke outcomes [8,9,10,11,12]. Previous work from our lab has shown that the efficacy of miRNA treatment may be restricted to specific age and sex groups. For example, anti-Let7f treatment after middle cerebral artery occlusion (MCAo) improved stroke outcomes in adult female rats but not older females or adult males [8, 13]. Similarly, miR-363-3p, identified by miRNA profiling of serum, modifies stroke outcomes only in females (adult and middle-aged) but not age-matched males [14]. In order to identify a more universally effective microRNA treatment, the present study used a novel approach by focusing on astrocytes.
Astrocytes are a crucial cell type for mediating brain energy homeostasis, providing neurotrophic support, and maintaining the blood–brain barrier [15]. Astrocytes have been shown to develop an “aging” phenotype, characterized by increased glial fibrillary acidic protein (GFAP) expression [16] and increased production of senescence-associated secretory phenotype (SASP) factors, such as interleukins (IL-1α [17], IL-6 [18, 19], IL-8 [20], IL-15 [21]) and matrix metalloproteases (MMP-1 [18], MMP-3, MMP-10 [20]). Astrocytes harvested from the ischemic cortex and striatum in middle-aged females show similar senescence-related changes, including reduced glutamate reuptake, decreased growth factor release, and increased chemokine release compared to adult females, all indicative of decreased neuroprotective capacity [22]. Furthermore, astrocytes from middle-aged females showed reduced trimethylation of histone H3K4, a transcriptional enhancer, as compared to adult females [23], indicating a global reduction in transcription potential, including the transcriptional start site for the miR-17a-92a cluster.
To assess the role of astrocytic miRNA in stroke outcomes, we compared miRNA profiles in astrocytes obtained from the ischemic forebrain of adult and middle-aged males and females. These groups were specifically selected because stroke outcomes are more severe in adult males and middle-aged males and females as compared to adult females, where stroke-induced infarction and sensory motor impairment is low. This approach confirmed the suppression of the miR-17–92 cluster observed in ChIP-seq analysis [23] and further identified miR-20a-3p as a uniquely age- and sex-regulated miRNA, whose expression was dramatically elevated in adult females as compared to all other groups. Bioinformatics identified mitochondrial and inflammation-associated genes as targets of miR-20a-3p, and select examples were confirmed in molecular and functional assays. A viral construct designed to conditionally elevated miR-20a-3p in astrocytes partially improved stroke outcomes. Subsequently, intravenous injection of fluorescently labeled miR-20a-3p after stroke was found to be preferentially taken up by neurons. A second viral construct was designed to conditionally express miR-20a-3p in neurons, resulting in robust neuroprotection. Finally, i.v. treatment of miR-20a-3p, a more translationally viable route of administration, was found to be neuroprotective in both middle-aged males and females. Together, these data indicate that while miR-20a-3p is produced by and profoundly alters the function of astrocytes after ischemia, stroke neuroprotection via this microRNA may depend on other cell types such as neurons receiving and utilizing miR-20a-3p.
Results
Expression of MicroRNA from the miR-17–92 Cluster in Astrocytes from Adult and Middle-Aged Males and Females
Astrocytes were extracted at 48 h post stroke from adult and middle-aged females and males using positive selection for GLAST. Based on our previous data showing increased trimethylation of the miR-17–92 cluster in adult females, we analyzed sex and age differences in this cluster by qRT-PCR (normalized to U6). Members of this miRNA cluster showed a complex regulation due to age and sex. As shown in Fig. 1a, miR-17-5p, miR-18a-5p, miR-19a, miR-19b, miR-20a-5p, and miR-20a-3p displayed a significant age × sex effects, such that each of these miRNAs was elevated in the adult female as compared to the adult male and middle-aged male or female. In the case of miR-17-3p, there were a main effect of age and a main effect of sex, while in the case of miR-92a-3p, there was a main effect of age, where adult animals had a higher expression of these miRNAs as compared to middle-aged animals. The most remarkable age × sex regulation was seen in miR-20a-3p expression, which demonstrated a > 240,000-fold elevation in adult female as compared to middle-aged females. A separate analysis of the entire miRnome panel controlling for false discovery rate (FDR) showed that miR-20a-3p was the only astrocytic miRNA that was significantly elevated by age and sex.
MiRnome analysis of miR expression from the miR-17–92 cluster. A histogram depicting the mean (± SEM) expression of microRNA from the miR-17–92 cluster in adult and middle-aged males and females. Bar above each set indicates main and interaction effects from two-way ANOVAs. a Main effect of age. b Main effect of sex. c Interaction effect (age × sex). B MiR-20a-3p expression in serum, whole brain, and astrocyte. Pre-stroke and 2-day post-stroke serum, brain, and astrocyte samples were evaluated for miR-20a expression. Key: asterisk, significantly different from pre stroke; number sign, significantly different from adult females at that time point. p < 0.05. n = 6 in most groups, n = 3 in pre-stroke astrocytes and post stroke brain samples. Red line, adult females; black line, middle-aged females
miR-20a-3p Expression in the Circulation, Brain, and Astrocytes in Adult and Middle-Aged Females
To determine if miR-20a-3p suppression is a tissue-specific response to stroke, miR-20a-3p expression was analyzed using qRT-PCR in serum, whole-brain homogenate, and astrocytes from adult and middle-aged females in sham animals and at 2 days post stroke. While basal expression of miR-20a-3p is similar at both ages, miR-20a-3p is altered in an age- and tissue-specific manner (Fig. 1b) during the early acute phase (2 days) of stroke. In circulation (serum), miR-20a-3p is significantly elevated at 2 days post stroke in both adult and middle-aged females (Fig. 1b(i)). In whole-brain homogenate (Fig. 1b(ii)) and in astrocytes (Fig. 1b(iii)), miR-20a-3p expression is preferentially elevated in adult females (red line) and profoundly suppressed in middle-aged females (black line) at 2 days post stroke.
Effect of MiR-20a-3p Treatment on Astrocyte Mitochondrial Function In Vitro
Bioinformatics analyses (using databases TargetScan and MiRWalk 2.0) indicate that miR-20a-3p regulates a large number of genes that are responsible for mediating mitochondrial function (Supplementary Fig. 1). In order to investigate specific mechanisms by which miR-20a-3p alters mitochondrial function, male and female human astrocytes were cultured and subjected to 6 h of oxygen glucose deprivation (OGD) (1% O2, 0 mM glucose) or normoxia (21% O2, 25 mM glucose) and treated with miR-20a-3p mimic, scrambled miR, or vehicle. Astrocyte cultures were confirmed by immunohistochemistry for GFAP (green) and co-labeled with nuclear dye DAPI (blue) (Supplementary Fig. 2a). Cultures that were incubated with 50 nM FAM-labeled miR-20a-3p mimic and MitoTracker Deep Red to stain living mitochondria for 6 h showed that the microRNA is readily taken up by astrocytes (Fig. 2a). In addition, qRT-PCR analysis indicates that female human astrocytes profoundly upregulate miR-20a-3p in response to ischemia, whereas the male astrocytes do not (Fig. 2b), recapitulating our in vivo observations.
Effect of miR20a-3p mimic on mitochondrial dynamics. a Primary human astrocytes stained with MitoTracker Deep Red and incubated with FAM-labeled miR-20a-3p for 6 h. b qRT-PCR expression of miR-20a-30 in primary human astrocytes. c Calcein assay on female and male human astrocytes. Histogram depicting the mean (± SEM) percent of viable cells relative to normoxic conditions. d FRAP analysis of female and male human astrocytes. The recovery was normalized to the level of bleaching in the cells (bleaching value was set at 1). e Seahorse XFe96 Mito Stress Test on human astrocytes. *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001, ****p ≤ 0.0001
To determine the effect of miR-20a-3p on astrocyte survival after OGD, cells were incubated with Calcein-AM dye (Life Technologies, CA) after OGD treatment. MiR-20a-3p treatment significantly increased cell viability in both male and female cells compared to scrambled miR treatment, but with different degrees of efficacy. In females, cell viability in the miR-20a-3p treatment group was virtually similar to that in normoxic controls, while cell viability in males that received miR-20a-3p was greater than that in cultures that received the scrambled oligo but was far lower than that in normoxic controls. Moreover, the female astrocytes demonstrated a greater degree of viability as compared to the male astrocytes after exposure to OGD (p = 0.002, Fig. 2c).
Two functional assays were used to explore the effect of miR-20a-3p treatment on astrocytic mitochondrial function. The first technique used was fluorescence recovery after photobleaching (FRAP), in which human astrocyte cultures were labeled with MitoTracker Deep Red and a small area of the cell was photobleached with a high intensity 405-nm laser and the subsequent fluorescent recovery was quantified using ImageJ. MiR-20a-3p treatment significantly increased recovery in both OGD and normoxic female groups immediately after bleaching (< 4 s), while the miR-20a-3p—treated male cells only exhibited significantly increased recovery in the OGD group after 18 s (Fig. 2d). Another functional assay used to assess mitochondrial dynamics is the Mito Stress Test using the Seahorse 96XFe Analyzer. This assay involves the serial injection of various drugs (oligomycin, FCCP, and rotenone + antimycin A) that target components of the electron transport chain. In normoxic conditions, female astrocytes show no difference between the miR-20a-3p—treated group and either of the control groups; however, the miR-20a-3p—treated male astrocytes show reduced oxygen consumption rate relative to both vehicle and scrambled oligo–treated cells (Fig. 2e). Moreover, miR-20a-3p treatment significantly reduces oxygen consumption rates in the male and female astrocytes in OGD conditions, though the male cells exhibit significantly more variability than the female cells (Fig. 2e). Increased oxygen consumption could be indicative of cell senescence induced by oxidative damage [24], and these data suggest that miR-20a-3p may reduce this senescent feature in an ischemic environment.
Astrocyte-Specific Enhancement of MiR-20a-3p Improves Select Stroke Outcomes in Middle-Aged Females
To assess the neuroprotective potential of astrocyte-derived miR-20a-3p in the context of stroke, a viral construct (rAAV5-TetOn-GFAP-miR-20a-3p-mCherry, SignaGen) under the control of a TetOn system with a GFAP promoter and conjugated with a mCherry reporter (Supplementary Figure 3a) and a control vector (Supplementary Figure 3b) was synthesized and injected into the left hemisphere of middle-aged female rat brains. Figure 3c demonstrates that the recombinant adeno-associated virus (rAAV) is activated by doxycycline and primarily co-localizes with GFAP. Two doses (2.5 × 1011 VP/ml; 2.5 × 1010 VP/ml) of the rAAV were used in pilot studies to determine the most effective dose to assess the effect of astrocyte-specific miR-20a-3p expression after stroke. Striatal injections of the high dose (2.5 × 1011 VP/ml) did not result in any adverse effects on body weight or spleen weight and were analyzed extensively for stroke outcomes (Fig. 3a–e). The Kaplan–Meier survival analysis (Fig. 3a) showed that the striatal injection of the rAAV containing miR-20a-3p reduced stroke-induced mortality (p = 0.0372). Infarct volume (Fig. 3b, c) assessed at 5 days after MCAo in animals that received the control vector was greater (53.42%) than that in animals that received the miR-20a-3p—containing vector (40.39%), although this difference did not meet the criteria for statistical significance (p = 0.1117). Sensory motor performance assessed by the adhesive removal test showed that both groups had increased latency at 2 days post stroke on the contralesional limb, while at 5 days post stroke, the miR-20a-3p group showed improved recovery and significantly reduced latency as compared to the control vector group (Fig. 3d). The vibrissae-evoked forelimb placement task did not demonstrate any improvement in the percentage of correct responses post MCAo when the same-side vibrissae were stimulated nor when the cross-midline vibrissae were stimulated (Supp. Fig. 4A).
Effect of rAAV-TetOn-GFAP-miR-20a-3p on stroke outcome in middle-aged females. A Kaplan–Meier survival plot shows significantly greater mortality in animals that received the control vector as compared to the miR-20a-3p–containing vector. B Representative images of TTC-stained sections obtained 5 days post MCAo. C Histogram depicting mean (± SEM) infarct volume. D Histogram of mean (± SEM) latency to remove the adhesive tape pre MCAo, 2 days post MCAo, and 5 days post MCAo. N = 12 (miR-20a-3p) and n = 11 (scrambled oligo) pre MCAo. *p ≤ 0.05, **p ≤ 0.01
FAM-Labeled miR-20a-3p Localizes to Neurons Rather Than Astrocytes After MCAo
We next examined the efficacy of intravenously injected miR-20a-3p. First, a FAM-labeled miR-20a-3p mimic was injected via tail vein 4 h after MCAo or sham surgery. The FAM-labeled mimic was chosen in order to visualize the localization of the miR-20a-3p mimic after intravenous treatment. FAM-labeled miR-20a-3p (green) preferentially co-localized with NeuN+ cells rather than GFAP+ cells in the animals that received MCAo (Fig. 4a, b). The proportion of FAM-labeled miR-20a-3p expressed in cells (co-labeled with dapi) that co-localized with NeuN+ cells compared to GFAP+ cells confirmed that neurons preferentially uptake the FAM-labeled miR (Fig. 4e). Interestingly, in animals that received the sham surgery, this preferential uptake by neurons is not observed (Fig. 4c–e). These data indicate that neurons may uptake this miRNA more readily under ischemic conditions.
Cellular localization of i.v. miR-20a-3p. Photomicrographs of coronal sections from animals injected with FAM-labeled miR-20a-3p after MCAo or sham surgery probed for glial and neuronal markers and counterstained for DAPI (blue). A MCAo: GFAP (red). B MCAo: NeuN (red). C Sham: GFAP (red). D Sham: NeuN (red). Arrows indicate FAM-labeled miR-20a-3p (green). E Quantification of FAM-miR-20a-3p co-localization. **p ≤ 0.01
Effect of MiR-20a-3p on Neuronal Mitochondrial Function In Vitro
In light of the cellular localization of i.v. FAM-miR-20a-3p injections, we decided to investigate the effects of miR-20a-3p on neuronal mitochondrial functions. Primary human neurons were cultured in identical conditions to the previously described astrocytes. Neuronal identify was confirmed via immunohistochemistry for NeuN (red) and co-labeled with the nuclear stain DAPI (Supplementary Fig. 2b). OGD was reduced to 30 min to account for greater cell death of the neurons relative to astrocytes in ischemic conditions. Confocal images indicate that the neurons uptake the FAM-labeled miR-20a-3p mimic after 30 min of OGD (Fig. 5a). qPCR analysis was performed to assess the expression of miR-20a-3p in normoxic and OGD conditions, and no differences in the expression of this microRNA were observed in either sex (Fig. 5b).
Effect of miR20a-3p mimic on neuronal mitochondrial dynamics. a Primary human neurons stained with MitoTracker Deep Red and incubated with FAM-labeled miR-20a-3p for 30 min. b qRT-PCR expression of miR-20a-30 in primary human neurons. c Calcein assay on female and male human neurons. Histogram depicting the mean (± SEM) percent of viable cells relative to normoxic conditions. d FRAP analysis of female and male human neurons. The recovery was normalized to the level of bleaching in the cells (bleaching value was set at 1). e Seahorse XFe96 Mito Stress Test on human neurons. *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001, ****p ≤ 0.0001
A cell viability assay, FRAP analysis, and the Seahorse Mito Stress Test assay were performed to assess the effect of miR-20a-3p on neuronal mitochondrial function. The cell viability assay did not show any improvement of neuronal survival after 30 min of OGD, though the female neurons did demonstrate a greater degree of viability as compared to the male neurons (p = 0.0007, Fig. 5c); however, key functional differences were elucidated in the FRAP and Seahorse assays. In all cases, neurons treated with miR-20a-3p significantly improved fluorescent recovery after photobleaching (Fig. 5d), similar to what was observed in the astrocytes. The Seahorse assay, however, demonstrated differences between neurons and astrocytes regarding the effect of miR-20a-3p on oxygen consumption. In normoxic conditions, male neurons treated with miR-20a-3p showed significantly elevated levels of oxygen consumption rate relative to control groups (Fig. 5e). The female neurons treated with miR-20a-3p exhibited greater oxygen consumption relative to vehicle, but there was not a significant difference between miR-20a-3p-treated and scrambled miR–treated groups. OGD reduced the rate of oxygen consumption in both sexes, though the difference between the miR-20a-3p–treated groups and the vehicle groups is not significant (Fig. 5e).
Neuron-Specific Enhancement of MiR-20a-3p is Neuroprotective in Middle-Aged Female Rats After Stroke
A second viral construct (rAAV5-TetOn-NSE-miR-20a-3p mCherry, SignaGen) was created to assess the effect of conditional neuronal miR-20a-3p expression. rAAV striatal injections and endothelin-1 (ET-1) surgeries were performed as indicated previously, and all procedures were identical to the previous rAAV experiment. However, unlike the GFAP vector, the neuron-specific enolase (NSE) vector showed significant reduction of infarct volume in animals that received the rAAV vector (Fig. 6b, c, p = 0.0087) and more significant improvement in the sensory motor tasks at both 2 days and 5 days post stroke (Fig. 6d, p < 0.0001). While post-stroke mortality in the rAAV-NSE-miR-20a-3p was almost half that of the group receiving the control vector, the Kaplan–Meier survival analysis only indicated a statistical trend in survival (Fig. 6a, p = 0.0805).
Effect of rAAV-TetOn-NSE-miR-20a-3p on stroke outcome in middle-aged females. a Kaplan–Meier survival plot shows a trend toward greater mortality in animals that received the control vector as compared to the miR-20a-3p—containing vector. b Representative images of TTC-stained sections obtained 5 days post MCAo. c Histogram depicting mean (± SEM) infarct volume. d Histogram of mean (± SEM) latency to remove the adhesive tape pre MCAo, 2 days post MCAo, and 5 days post MCAo. N = 10 (miR-20a-3p) and n = 9 (scrambled oligo) pre MCAo. *p ≤ 0.01, ****p ≤ 0.0001
MiR-20a-3p Treatment Significantly Reduced Infarct Volume in Middle-Aged Female and Male Rats
Although the rAAV experiments provide key insight into the cellular mechanism of neuroprotection of miR-20a-3p, i.v. treatment is much less invasive and therefore more translationally viable, so we next assessed the effect of i.v. miR-20a-3p on acute stroke outcomes. Animals were subjected to MCAo and injected via the tail vein with miR-20a-3p mimic either concurrent (immediate treatment (IT)) with the onset of ischemia, 4 h after ischemic onset (delayed treatment (DT)), or 24 h after the onset of ischemia (very delayed treatment (VDT)). As shown in Fig. 7a, triphenyl tetrazolium chloride (TTC)-stained images indicate that the cortico-striatal infarct is significantly reduced in middle-aged females in animals that received miR-20-3p 4 h after MCAo (DT) as compared to the age-matched counterparts that received i.v. injections of the scrambled oligos. Delayed miR-20a-3p treatment decreased infarct volume by 60% and improved performance on the adhesive removal test when measured 5 days post stroke (Fig. 7a). On the other hand, i.v. injections of miR-20a-3p–delivered concurrent with the onset of ischemia (IT) or 24 h after MCAo (VDT) did not show any decrease in infarct size or reduction in sensory motor deficits (Fig. 7b, c, Supp. Fig. 4c, d).
Effect of intravenous miR-20a-3p mimics on stroke outcomes in middle-aged females at IT, DT, and VDT: A(i)–C(i) TTC-stained coronal sections from middle-aged females treated with scrambled oligo or miR-20a-3p. a(ii)–c(ii) Histogram depicts average infarct volume (± SEM) normalized to the volume of the non-ischemic hemisphere. a(iii)–c(iii) Sensory motor performance on the adhesive removal test was evaluated before and after stroke. Histograms depict mean (± SEM) latency in seconds to remove the tape. DT, N = 6 (control or treatment); IT, N = 7 (control) and N = 8 (treatment); VDT, N = 8 (control) and N = 8 (treatment). *p ≤ 0.05, **p ≤ 0.01
Middle-aged males (a group that also sustains severe stroke outcomes) showed significantly reduced infarct following delayed miR-20a-3p mimic treatment (Supplementary Fig. 3A, B; p < 0.05) and significantly improved performance on the adhesive removal test, which is impaired after MCAo (Supplementary Fig. 3C). Collectively, these data indicate that, similar to middle-aged female rats, i.v. miR-20a-3p mimic to middle-aged male rats improved stroke outcomes.
Effect of DT MiR-20a-3p Treatment on Gene Targets Post MCAo
To assess whether i.v. treatment of miR-20a-3p affected astrocyte gene expression, astrocytes were isolated from the ischemic hemisphere for qRT-PCR analysis. In view of the improved stroke outcomes in the DT group, the analysis was only performed in this group. Several matrix metalloproteinases (MMPs) and mitochondrial gene targets of miR-20a-3p demonstrated altered regulation in the ischemic hemisphere of the animals that received DT as compared to the animal that received scrambled treatment. Gene expression of MMP-2, MMP-9, and MMP-14 was elevated in the ischemic hemisphere of animals that received scrambled oligo treatment, while this elevation was mitigated in the ischemic hemisphere of animals receiving miR-20a-3p (Fig. 8a–c, *p < 0.05). MMP activity was assessed by gelatin zymography. Protein was isolated from the ischemic hemisphere of animals subjected to MCAo that received either miR-20a-3p mimic or scrambled oligo (DT). Lytic activity was noted in the region between 50 and 70 kDa (Fig. 8e), which contains MMP-2 and MMP-14. This region was quantified for densitometry by ImageJ and revealed a significant reduction in MMP activity in the miR-20a-3p—treated animals (Fig. 8f). MMPs have been implicated in the blood–brain barrier (BBB) and cerebral microvasculature damage as well as hemorrhagic bleeds [25]. BBB damage was assessed by ELISA for serum GFAP, which is a surrogate measure of BBB leakiness. As shown in Fig. 8g, there was a trend (p = 0.12) toward decreased GFAP levels in the miR-20a-3p—treated groups. Hemorrhagic foci were inspected in TTC-stained sections (shown in Fig. 8h) by a code-blinded observer and were found to be present in all (100%) scrambled oligo-treated middle-aged female rats and in one-third of the miR-20a-3p—treated rats (chi-square; p < 0.0143), generally in the vicinity of striatal vessels. Collectively, these data suggest that miR-20a-3p treatment 4 h after MCAo may protect the brain against MMP-mediated BBB damage and subsequent hemorrhagic transformation.
Effect of intravenous miR-20a-3p on markers blood–brain barrier permeability. a–d qPCR analysis of MMPs from the ischemic and non-ischemic hemispheres of scrambled and miR-20a-3p–treated animals. e Representative image of gelatin Zymogram depicting MMP activity from protein lysates from the ischemic hemisphere. f Histogram showing the mean (±) of MMP activity from gelatin zymography. g ELISA analysis of GFAP expression in serum. h Representative TTC images of brain slices with hemorrhagic foci from females treated with miR-20a-3p mimic and scrambled oligo. Foci are indicated by white arrows. N = 6 (miR-20a-3p) and n = 6 (scrambled oligo). #p < 0.1, *p ≤ 0.05
IL-17A is a pro-inflammatory cytokine, which is a predicted target of miR-20a-3p and a therapeutic target for anti-inflammatory drugs to improve recovery post stroke [26]. Similar to the MMPs, IL-17A was elevated in the ischemic hemisphere of animals that received scrambled oligo treatment, while this elevation was mitigated in the ischemic hemisphere of animals receiving miR-20a-3p (Fig. 9a). This was further confirmed by ELISA assay, showing that IL-17A expression was significantly reduced in the ischemic hemisphere of the miR-20a-3p–treated middle-aged females as compared to the scrambled controls (Fig. 9b, p ≤ 0.05). Circulating (serum) levels of IL-17A were not different in the two groups (data not shown), suggesting that miR-20a-3p either has a brain-specific effect for this cytokine or regulates the blood–brain barrier to prevent extravasation of IL-17A or IL-17A–producing cells.
Effect of intravenous miR-20a-3p on predicted mitochondrial targets. a qPCR and b ELISA analysis of IL-17A expression from the ischemic and non-ischemic hemispheres of scrambled and miR-20a-3p–treated animals. c–e qPCR analysis of predicted mitochondrial genes from the ischemic and non-ischemic hemispheres of scrambled and miR-20a-3p–treated animals. f Protein from the ischemic hemisphere of scrambled and miR-20a-3p–treated animals probed for Drp1 by western blot and total protein stain. g Histogram of the mean (± SEM) of Drp1 normalized to total protein. N = 6 (miR-20a-3p) and n = 6 (scrambled oligo). *p ≤ 0.05, **p ≤ 0.01
Mitochondrial gene targets including Uqcfs1, Ndufa1, and Atp5s were reduced in the ischemic hemisphere of the scrambled oligo–treated animals, while there were no differences in the expression of these genes in the two hemispheres of the miR-20a-3p–treated animals (Fig. 9c–e), indicating that miR-20a-3p treatment preserved the expression of mitochondrial genes. Quantitative western blot analysis was performed on protein isolated from the ischemic hemisphere of animals subjected to MCAo that received DT of either miR-20a-3p mimic or scrambled oligo. The blot was probed with a Drp1 (mitochondrial fission protein) antibody (Fig. 9f) and normalized to the LiCOR Total Protein Stain. MiR-20a-3p–treated animals demonstrated significantly less expression of Drp1 as compared to scrambled oligo–treated animals (Fig. 9g).
Data Availability
This study includes no data deposited in external repositories. Requests for resources and reagents should be directed to the Corresponding Author, Farida Sohrabji (f-sohrabji@tamu.edu).
Code Availability
Not applicable.
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Acknowledgements
We would like to thank Dr. Kathiresh Mani, Yumna El-Hakim, Sivani Pandey, Macy Zardeneta, and Crystal Myers for their assistance with the experiments.
Funding
This work was supported by RFAG042189 to FS and 1F31NS118970-01A1 to TEB.
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TEB, AS, RS, and FS conceived and planned the experiments. TEB, AS, MJP, KEK, and KFK performed the experiments. TEB, AS, MJP, and FS analyzed the results. TEB, AS, RS, and FS wrote the manuscript.
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Supplementary file1 (TIFF 8792 kb)
Supplemental Fig. 1 Analysis of predicted miR-20a-3p targets. In silico analysis was performed on predicted gene targets of miR-20a-3p using the TargetScan and miRWalk database. Graph shows significant Gene Ontology pathways and the percentage of predicted miR-20a-3p target genes in each GO pathway.
Supplementary file2 (TIFF 8792 kb)
Supplemental Fig. 2 GFAP Immunohistochemistry of in vitro human cells. Representative image of human astrocytes (A) and human neurons (B) probed for antibodies to GFAP or NeuN, respectively (green). Control cultures incubated with (top right of panel) secondary antibody only (no primary) or (bottom right of panel) primary antibody only (no secondary). In all cases, cells were counter stained with the nuclear dye DAPI (blue).
Supplementary file3 (TIFF 8792 kb)
Supplemental Fig. 3 Characterization of astrocyte-specific viral vector for conditional expression of miR-20a-3p: (A) Schematic representation of the viral construct rAAV5 containing the miR-20a-3p gene downstream of the GFAP/Tet inducible promoter and linked to an mCherry reporter. (B) Schematic of the control vector. (C) Immunohistochemistry for GFAP, NeuN, and Iba1 on sections from rats injected with the rAAV construct and treated either with Dox (upper panel) or vehicle (lower panel). Arrows indicate mCherry localized to GFAP immunopositive cells.
Supplementary file4 (TIFF 8792 kb)
Supplemental Fig. 4 Characterization of neuron-specific viral vector for conditional expression of miR-20a-3p: (A) Schematic representation of the viral construct rAAV5 containing the miR-20a-3p gene downstream of the NSE/Tet inducible promoter and linked to an mCherry reporter. (B) Schematic of the control vector. (C) Immunohistochemistry for GFAP, NeuN, and Iba1 on sections from rats injected with the rAAV construct and treated either with Dox (upper panel) or vehicle (lower panel). Arrows indicate mCherry localized to NeuN immunopositive cells.
Supplementary file5 (TIFF 8792 kb)
Supplemental Fig. 5 Effect of intravenous miR20a-3p mimics treatment on stroke outcomes in middle-aged males: Middle-aged male rats were injected with miR-20a-3p mimics or scrambled oligos 4 h after MCAo. (A) Representative TTC-stained coronal sections from scrambled oligo and miR-20a-3p injected animals. (B) Histogram depicts average infarct volume (±SEM) normalized to the volume of the non-ischemic hemisphere. (C) Sensory motor performance on the adhesive removal test was evaluated before and after stroke. Histograms depict mean (±SEM) latency in seconds to remove the tape. *p ≤ 0.05. Middle-aged male N = 6 (control) and 5 (treatment).
Supplementary file6 (TIFF 8792 kb)
Supplemental Fig. 6 Vibrissae-evoked forelimb placement task: The vibrissae-evoked forelimb placement task was performed on all in vivo experiments: (A) GFAP rAAV animals. (B) NSE rAAV animals. (C) Delayed treatment. (D) Immediate treatment. (E) Very delayed treatment. For all groups, there is an effect of time on task performance. **p ≤ 0.01, ***p ≤ 0.001, ****p ≤ 0.0001.
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Branyan, T.E., Selvamani, A., Park, M.J. et al. Functional Assessment of Stroke-Induced Regulation of miR-20a-3p and Its Role as a Neuroprotectant. Transl. Stroke Res. 13, 432–448 (2022). https://doi.org/10.1007/s12975-021-00945-x
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DOI: https://doi.org/10.1007/s12975-021-00945-x