MRI Evaluation of Axonal Remodeling After Combination Treatment With Xiaoshuan Enteric-Coated Capsule and Enriched Environment in Rats After Ischemic Stroke

Buyang Huanwu Decoction promotes neurovascular remodeling by modulating astrocyte and microglia polarization in ischemic stroke rats

ETHNOPHARMACOLOGICAL RELEVANCE

Buyang Huanwu Decoction (BYHWD), one of the most commonly utilized traditional Chinese medicine prescription for treatment of cerebral ischemic stroke. However, the understanding of BYHWD on neurovascular repair following cerebral ischemia is so far limited.

AIM OF THE STUDY

This research investigated the influence of BYHWD on neurovascular remodeling by magnetic resonance imaging (MRI) technology and revealed the potential neurovascular repair mechanism underlying post-treatment with BYHWD after ischemic stroke.

MATERIALS AND METHODS

Male Sprague-Dawley rats were utilized as an ischemic stroke model by permanent occlusion of the middle cerebral artery (MCAO). BYHWD was intragastrically administrated once daily for 30 days straight. Multimodal MRI was performed to detect brain tissue injuries, axonal microstructural damages, cerebral blood flow and intracranial vessels on the 30th day after BYHWD treatment. Proangiogenic factors, axonal/synaptic plasticity-related factors, energy transporters and adenosine monophosphate-activated protein kinase (AMPK) signal pathway were evaluated using western blot. Double immunofluorescent staining and western blot were applied to evaluate astrocytes and microglia polarization.

RESULTS

Administration of BYHWD significantly alleviated infarct volume and brain tissue injuries and ameliorated microstructural damages, accompanied with improved axonal/synaptic plasticity-related factors, axonal growth guidance factors and decreased axonal growth inhibitors. Meanwhile, BYHWD remarkably improved cerebral blood flow, cerebral vascular signal and promoted the expression of proangiogenic factors. Particularly, treatment with BYHWD obviously suppressed astrocytes A1 and microglia M1 polarization accompanied with promoted astrocyte A2 and microglia M2 polarization. Furthermore, BYHWD effectively improved energy transporters. Especially, BYHWD markedly increased expression of phosphorylated AMPK, cyclic AMP-response element binding protein (CREB) and brain-derived neurotrophic factor (BDNF) accompanied by inactivation of the NF-κB.

CONCLUSION

Taken together, these findings identified that the beneficial roles of BYHWD on neurovascular remodeling were related to AMPK pathways -mediated energy transporters and NFκB/CREB pathways.

Environmental Enrichment for Stroke and Traumatic Brain Injury: Mechanisms and Translational Implications

Acquired brain injuries, such as ischemic stroke, intracerebral hemorrhage (ICH), and traumatic brain injury (TBI), can cause severe neurologic damage and even death. Unfortunately, currently, there are no effective and safe treatments to reduce the high disability and mortality rates associated with these brain injuries. However, environmental enrichment (EE) is an emerging approach to treating and rehabilitating acquired brain injuries by promoting motor, sensory, and social stimulation. Multiple preclinical studies have shown that EE benefits functional recovery, including improved motor and cognitive function and psychological benefits mediated by complex protective signaling pathways. This article provides an overview of the enriched environment protocols used in animal models of ischemic stroke, ICH, and TBI, as well as relevant clinical studies, with a particular focus on ischemic stroke. Additionally, we explored studies of animals with stroke and TBI exposed to EE alone or in combination with multiple drugs and other rehabilitation modalities. Finally, we discuss the potential clinical applications of EE in future brain rehabilitation therapy and the molecular and cellular changes caused by EE in rodents with stroke or TBI. This article aims to advance preclinical and clinical research on EE rehabilitation therapy for acquired brain injury. © 2024 American Physiological Society. Compr Physiol 14:5291-5323, 2024.

Tetramethylpyrazine promotes axonal remodeling and modulates microglial polarization via JAK2-STAT1/3 and GSK3-NFκB pathways in ischemic stroke

Ischemic stroke results in demyelination that underlies neurological disfunction. Promoting oligodendrogenesis will rescue the injured axons and accelerate remyelination after stroke. Microglia react to ischemia/hypoxia and polarize to M1/M2 phenotypes influencing myelin injury and repair. Tetramethylpyrazine (TMP) has neuroprotective effects in treating cerebrovascular disorders. This study aims to evaluate whether TMP promotes the renovation of damaged brain tissues especially on remyelination and modulates microglia phenotypes following ischemic stroke. Here magnetic resonance imaging (MRI)-diffusion tensor imaging (DTI) and histopathological evaluation are performed to characterize the process of demyelination and remyelination. Immunofluorescence staining is used to prove oligodendrogenesis and microglial polarization. Western blotting is conducted to examine interleukin (IL)-6, IL-10, transforming growth factor β (TGF-β) and Janus protein tyrosine kinase (JAK) 2-signal transducer and activator of transcription (STAT) 1/3-glycogen synthase kinase (GSK) 3-nuclear transcription factor κB (NFκB) signals. Results show TMP alleviates the injury of axons and myelin sheath, increases NG2+, Ki67+/NG2+, CNPase+, Ki67+/CNPase+, Iba1+/Arg-1+ cells and decreases Iba1+ and Iba1+/CD16+ cells in periinfarctions of rats. Particularly, TMP downregulates IL-6 and upregulates IL-10 and TGF-β expressions, besides, enhances JAK2-STAT3 and suppresses STAT1-GSK3-NFκB activation in middle cerebral artery occlusion (MCAo) rats. Then we demonstrate that TMP reverses M1/M2 phenotype via JAK2-STAT1/3 and GSK3-NFκB pathways in lipopolysaccharide (LPS) plus interferon-γ (IFN-γ)-stimulated BV2 microglia. Blocking JAK2 with AG490 counteracts TMP's facilitation on M2 polarization of microglia. This study warrants the promising therapy for stroke with TMP treatment.

Reactivation of corticogenesis-related transcriptional factors BCL11B and SATB2 after ischemic lesion of the adult mouse brain

The aim of this study was to characterize expression of corticogenesis-related transcription factors BCL11B and SATB2 after brain ischemic lesion in the adult mice, and to analyze their correlation to the subsequent brain recovery. Ischemic brain lesion was induced by transient middle cerebral artery occlusion followed by reperfusion, and the animals with ischemic lesion were compared to the sham controls. Progression of the brain damage and subsequent recovery was longitudinally monitored structurally, by magnetic resonance imaging, and functionally, by neurological deficit assessment. Seven days after the ischemic injury the brains were isolated and analyzed by immunohistochemistry. The results showed higher expression in the brain of both, BCL11B and SATB2 in the animals with ischemic lesion compared to the sham controls. The co-expression of both markers, BCL11B and SATB2, increased in the ischemic brains, as well as the co-expression of BCL11B with the beneficial transcriptional factor ATF3 but not its co-expression with detrimental HDAC2. BCL11B was mainly implicated in the ipsilateral and SATB2 in the contralateral brain hemisphere, and their level in these regions correlated with the functional recovery rate. The results indicate that the reactivation of corticogenesis-related transcription factors BCL11B and SATB2 is beneficial after brain ischemic lesion.

Tetramethylpyrazine promotes stroke recovery by inducing the restoration of neurovascular unit and transformation of A1/A2 reactive astrocytes

2,3,5,6-Tetramethylpyrazine (TMP) as an active ingredient extracted from a traditional Chinese herbal medicine Ligusticum chuanxiong Hort. has been proved to penetrate blood-brain barrier (BBB) and show neuroprotective effects on cerebral ischemia. However, whether TMP could regulate astrocytic reactivity to facilitate neurovascular restoration in the subacute ischemic stroke needs to be urgently verified. In this research, permanent occlusion of the middle cerebral artery (MCAO) model was conducted and TMP (10, 20, 40 mg/kg) was intraperitoneally administrated to rats once daily for 2 weeks. Neurological function was evaluated by motor deficit score (MDS). Magnetic resonance imaging (MRI) was implemented to analyze tissue injury and cerebral blood flow (CBF). Magnetic resonance angiography (MRA) was applied to exhibit vascular signals. Transmission electron microscopy (TEM) was performed to detect the neurovascular unit (NVU) ultrastructure. Haematoxylin and eosin (HE) staining was utilized to evaluate cerebral histopathological lesions. The neurogenesis, angiogenesis, A1/A2 reactivity, aquaporin 4 (AQP4) and connexin 43 (Cx43) of astrocytes were observed with immunofluorescent staining. Then FGF2/PI3K/AKT signals were measured by western blot. Findings revealed TMP ameliorated neurological functional recovery, preserved NVU integrity, and enhanced endogenous neurogenesis and angiogenesis of rats with subacute ischemia. Shifting A1 to A2 reactivity, suppressing excessive AQP4 and Cx43 expression of astrocytes, and activating FGF2/PI3K/AKT pathway might be potential mechanisms of promoting neurovascular restoration with TMP after ischemic stroke.

Enriched environment remodels the central immune environment and improves the prognosis of acute ischemic stroke in elderly mice with chronic ischemia

With the aging of many populations, cognitive and motor dysfunction caused by ischemic stroke (IS) secondary to long-term chronic cerebral ischemia presents a global problem. Enriched environment (EE), a classic paradigm of environment response and genetic interaction, has shown tremendous influence on the brain. This research aimed to investigate the potential effect of EE on cognitive and motor function in mice with chronic cerebral ischemia and secondary IS. In the chronic cerebral hypoperfusion (CCH) phase, EE treatment improved behavior performance by alleviating neuronal loss and white matter myelin damage, promoting the expression of brain-derived neurotrophic factor (BDNF) and phosphor-cAMP response element binding protein (p-CREB). Furthermore, infiltration of microglia/macrophages and astrocytes was inhibited, and the levels of IL-1β and TNFα were decreased. In the IS phase, EE altered the neuronal outcome on day 21 but not on day one after IS. In addition, EE inhibited IS-induced infiltration of microglia/macrophages and astrocytes, mediated the polarization of microglia/macrophages, and reduced pro-inflammatory factors. Importantly, EE improved IS-induced cognitive and motor deficits on day 21. Collectively, our work demonstrates that EE protects mice from cognitive and motor dysfunction and inhibits neuroinflammation caused by CCH and IS.

Magnetic Resonance Imaging Investigation of Neuroplasticity After Ischemic Stroke in Tetramethylpyrazine-Treated Rats

Ischemic stroke elicits white matter injury typically signed by axonal disintegration and demyelination; thus, the development of white matter reorganization is needed. 2,3,5,6-Tetramethylpyrazine (TMP) is widely used to treat ischemic stroke. This study was aimed to investigate whether TMP could protect the white matter and promote axonal repair after cerebral ischemia. Male Sprague–Dawley rats were subjected to permanent middle cerebral artery occlusion (MCAO) and treated with TMP (10, 20, 40 mg/kg) intraperitoneally for 14 days. The motor function related to gait was evaluated by the gait analysis system. Multiparametric magnetic resonance imaging (MRI) was conducted to noninvasively identify gray-white matter structural integrity, axonal reorganization, and cerebral blood flow (CBF), followed by histological analysis. The expressions of axonal growth-associated protein 43 (GAP-43), synaptophysin (SYN), axonal growth-inhibitory signals, and guidance factors were measured by Western blot. Our results showed TMP reduced infarct volume, relieved gray-white matter damage, promoted axonal remodeling, and restored CBF along the peri-infarct cortex, external capsule, and internal capsule. These MRI findings were confirmed by histopathological data. Moreover, motor function, especially gait impairment, was improved by TMP treatment. Notably, TMP upregulated GAP-43 and SYN and enhanced axonal guidance cues such as Netrin-1/DCC and Slit-2/Robo-1 but downregulated intrinsic growth-inhibitory signals NogoA/NgR/RhoA/ROCK-2. Taken together, our data indicated that TMP facilitated poststroke axonal remodeling and motor functional recovery. Moreover, our findings suggested that TMP restored local CBF, augmented guidance cues, and restrained intrinsic growth-inhibitory signals, all of which might improve the intracerebral microenvironment of ischemic areas and then benefit white matter remodeling.

Enriched Environment Effects on Myelination of the Central Nervous System: Role of Glial Cells

Myelination is regulated by various glial cells in the central nervous system (CNS), including oligodendrocytes (OLs), microglia, and astrocytes. Myelination of the CNS requires the generation of functionally mature OLs from OPCs. OLs are the myelin-forming cells in the CNS. Microglia play both beneficial and detrimental roles during myelin damage and repair. Astrocyte is responsible for myelin formation and regeneration by direct interaction with oligodendrocyte lineage cells. These glial cells are influenced by experience-dependent activities such as environmental enrichment (EE). To date, there are few studies that have investigated the association between EE and glial cells. EE with a complex combination of sensorimotor, cognitive, and social stimulation has a significant effect on cognitive impairment and brain plasticity. Hence, one mechanism through EE improving cognitive function may rely on the mutual effect of EE and glial cells. The purpose of this paper is to review recent research into the efficacy of EE for myelination and glial cells at cellular and molecular levels and offers critical insights for future research directions of EE and the treatment of EE in cognitive impairment disease.

Trillium tschonoskii rhizomes' saponins induces oligodendrogenesis and axonal reorganization for ischemic stroke recovery in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Trillium tschonoskii Maxim. is one of traditional Chinese medical herbs that has been utilized to treat brain damages and cephalalgia. The neuroprotective effect of total saponins from Trillium tschonoskii rhizome (TSTT) has been demonstrated efficacy in rats following ischemia. However, the axonal remodeling effect of TSTT and the detailed mechanisms after ischemic stroke have not been investigated.

AIM OF THE STUDY

We aimed to estimate therapeutic role of TSTT in axonal remodeling using magnetic resonance imaging (MRI) technique, and explored possible mechanisms underlying this process followed by histological assays in ischemic rats.

METHODS

Male Sprague-Dawley (SD) rats underwent permanently focal cerebral ischemia induced by occluding right permanent middle cerebral artery. TSTT was intragastrically administrated 6 h after surgery and once daily for consecutive 15 days. Neurological function was assessed by the motor deficit score and beam walking test. T2 relaxation mapping and diffusion tensor imaging (DTI) were applied for detecting cerebral tissues damages and microstructural integrity of axons. Luxol fast blue (LFB) and transmission electron microscope (TEM) were performed to evaluate histopathology in myelinated axons. Double immunofluorescent staining was conducted to assess oligodendrogenesis. Furthermore, the protein expressions regarding to axonal remodeling related signaling pathways were detected by Western blot assays.

RESULTS

TSTT treatment (65, 33 mg/kg) markedly improved motor function after ischemic stroke. T2 mapping MRI demonstrated that TSTT decreased lesion volumes, and DTI further confirmed that TSTT preserved axonal microstructure of the sensorimotor cortex and internal capsule. Meanwhile, diffusion tensor tractography (DTT) showed that TSTT elevated correspondent density and length of fiber in the internal capsule. These MRI measurements were confirmed by histological examinations. Notably, TSTT significantly increased Ki67/NG2, Ki67/CNPase double-labeled cells along the boundary zone of ischemic cortex and striatum. Meanwhile, TSTT treatment up-regulated the phosphorylation level of Ser 9 in GSK-3β, and down-regulated phosphorylated β-catenin and CRMP-2 expression.

CONCLUSION

Taken together, our findings indicated that TSTT (65, 33 mg/kg) enhanced post-stroke functional recovery, amplified endogenous oligodendrogenesis and promoted axonal regeneration. The beneficial role of TSTT might be correlated with GSK-3/β-catenin/CRMP-2 modulating axonal reorganization after ischemic stroke.

Effectiveness and mechanisms of enriched environment in post-stroke cognitive impairment

Post-stroke cognitive impairment (PSCI) is one of the most common complications of stroke, it is also an important reason for the poor prognosis in stroke patients with motor and speech dysfunction. Enriched Environment (EE), a novel and easy-to-implement rehabilitation treatment strategy, is thought to be a potential intervention for PSCI recently. In this paper, we review the therapeutic effects and related mechanisms of EE in PSCI from the level of animal research and clinical application. Besides, we further discuss the application prospects and limitations of EE in PSCI patients.

Enriched environment alleviates post-stroke cognitive impairment through enhancing α7-nAChR expression in rats

ABSTRACT Background: Enriched environment (EE) is a simple and effective intervention to improve cognitive function in post-stroke cognitive impairment (PSCI), partly due to the rebalancing of the cholinergic signaling pathway in the hippocampus. α7-nicotinic acetylcholine receptor (α7-nAChR) is a cholinergic receptor whose activation inhibits inflammation and promotes the recovery of neurological function in PSCI patients. However, it is still unclear whether EE can regulate α7-nAChR and activate the cholinergic anti-inflammatory pathway (CAP) in PSCI. Objective: To investigate the effects of EE on cognitive impairment, and the role of α7-nAChR in PSCI. Methods: A PSCI rat model was induced by middle cerebral artery occlusion and reperfusion (MCAO/R) and were reared in standard environment (SE) or EE for 28d, control group with sham surgery. Cognitive function was determined by Morris water maze test. The long-term potentiation (LTP) was assessed by Electrophysiology. Histopathological methods were used to determine infarct volume, α7-nAChR expression and the cytokines and cholinergic proteins expression. Results: Compared with SE group, rats in EE group had better cognitive function, higher expression of α7-nAChR positive neurons in hippocampal CA1 region. In addition, EE attenuated unfavorable changes induced by MCAO/R in cytokines and cholinergic proteins, and also enhanced LTP promoted by nicotine and attenuated by α-BGT; but showed no significantly difference in infarct volume. Conclusions: EE markedly improves cognitive impairment and enhances neuroplasticity in PSCI rats, which may be closely related to enhancement of α7-nAChR expression.