Tissue Clock Research Articles

The epidermal circadian clock integrates and subverts brain signals to guarantee skin homeostasis

In mammals, the circadian clock network drives daily rhythms of tissue-specific homeostasis. To dissect daily inter-tissue communication, we constructed a mouse minimal clock network comprising only two nodes: the peripheral epidermal clock and the central brain clock. By transcriptomic and functional characterization of this isolated connection, we identified a gatekeeping function of the peripheral tissue clock with respect to systemic inputs. The epidermal clock concurrently integrates and subverts brain signals to ensure timely execution of epidermal daily physiology. Timely cell-cycle termination in the epidermal stem cell compartment depends upon incorporation of clock-driven signals originating from the brain. In contrast, the epidermal clock corrects or outcompetes potentially disruptive feeding-related signals to ensure the optimal timing of DNA replication. Together, we present an approach for cataloging the systemic dependencies of daily temporal organization in a tissue and identify an essential gate-keeping function of peripheral circadian clocks that guarantees tissue homeostasis.

Enhanced Detection of Reversible Acute Ischemic Stroke: High-resolution Mapping of Net Water Uptake as a Tissue Clock in Non-contrast Computed Tomography Scans (P11-5.022)

Enhanced Detection of Reversible Acute Ischemic Stroke: High-resolution Mapping of Net Water Uptake as a Tissue Clock in Non-contrast Computed Tomography Scans (P11-5.022)

Investigating Neurologic Improvement After IV Thrombolysis: The Effect of Time From Stroke Onset vs Imaging-Based Tissue Clock.

Time from stroke onset is associated with clinical response to intravenous thrombolysis (IVT) with alteplase and is therefore used to select patients for treatment. Alternatively, neuroimaging may be used for treatment in the uncertain or extended time window. We hypothesized that the patient-specific imaging indicator of ischemic lesion progression ("tissue clock") using CT perfusion (CTP) or quantitative net water uptake (NWU) is a predictor of early neurologic improvement (ENI) independent of time. Observational study of anterior circulation ischemic stroke patients with proximal vessel occlusion and known time from symptom onset triaged by multimodal CT undergoing endovascular treatment. Quantitative NWU using an established threshold (11.5%) or CTP lesion core mismatch (EXTEND criteria) was used to estimate ischemic lesion progression. The treatment effect of IVT depending on lesion progression defined by tissue clock vs time clock was assessed by inverse probability weighting (IPW). End points were binarized ENI and functional independence at day 90. Four hundred nine patients were included, of which 223 (54.5%) received IVT. The proportion of patients within an early time window (<4.5hours), low NWU, and CTP mismatch were 45.0%, 86.5%, and 80.3%. In IPW, IVT was associated with higher rates of ENI (%-difference: 7.3%, p = 0.02). For patients with CTP mismatch or low NWU, IVT was associated with a 9.6% or 7.2% higher rate of ENI, which was different than the effect of IVT in patients without CTP mismatch or high NWU (-9.3%/-7.3%; p = 0.004/p = 0.03), whereas early treatment window did not modify the effect of IVT. CT-based measures of the "tissue clock" might identify patients who benefit from IVT more accurately than conventional time windows. Considering the high number of patients with early "tissue clock" (low NWU/CTP mismatch) within an extended time window, considerable benefit from IVT using imaging indicators of the "tissue clock" may be achieved.

Regulation of Pol II Pausing during Daily Gene Transcription in Mouse Liver.

Cell autonomous circadian oscillation is present in central and various peripheral tissues. The intrinsic tissue clock and various extrinsic cues drive gene expression rhythms. Transcription regulation is thought to be the main driving force for gene rhythms. However, how transcription rhythms arise remains to be fully characterized due to the fact that transcription is regulated at multiple steps. In particular, Pol II recruitment, pause release, and premature transcription termination are critical regulatory steps that determine the status of Pol II pausing and transcription output near the transcription start site (TSS) of the promoter. Recently, we showed that Pol II pausing exhibits genome-wide changes during daily transcription in mouse liver. In this article, we review historical as well as recent findings on the regulation of transcription rhythms by the circadian clock and other transcription factors, and the potential limitations of those results in explaining rhythmic transcription at the TSS. We then discuss our results on the genome-wide characteristics of daily changes in Pol II pausing, the possible regulatory mechanisms involved, and their relevance to future research on circadian transcription regulation.

Intravenous Thrombolysis for Acute Ischemic Stroke

This article reviews the history of IV thrombolysis, its current indications and implementation, the duality of the "time is brain" versus "tissue clock" approaches, the impact of endovascular thrombectomy on IV thrombolysis, the emergence of tenecteplase, and future research directions. The growing use of factor Xa inhibitors has increasingly caused patients with stroke to be excluded from treatment with IV thrombolysis. Important geographic, socioeconomic, sex, race, and ethnic disparities have been identified in the implementation of IV thrombolysis and need to be overcome. IV thrombolysis substantially improves outcomes when provided within the first golden hour after stroke onset in patients treated in mobile stroke units, supporting the "time is brain" concept and encouraging the possible value of more widespread implementation of the mobile stroke unit approach. At the same time, other studies have shown that IV thrombolysis can be successful in patients whose "tissue clock" is still ticking up to 9 hours after stroke onset or in patients who awaken with their stroke, as demonstrated by favorable imaging profiles. These considerations, along with the emergence of endovascular thrombectomy, have fostered examination of our care systems, including the "drip and ship" versus direct to comprehensive or endovascular thrombectomy stroke center approaches, as well as the possibility of skipping IV thrombolysis in certain patients treated with endovascular thrombectomy. Data suggesting that tenecteplase is at least noninferior to alteplase, as well as its more convenient dosing, has led to its increased use. Ongoing studies are evaluating newer thrombolytics and adding antithrombotic therapy to IV thrombolysis. IV thrombolysis remains the most common acute stroke treatment. Advances in acting faster to treat stroke have increased its efficacy, and advances in imaging have expanded its use. However, implementing these advances and overcoming disparities in IV thrombolysis use remain major challenges.

Abstract TP75: Waking Up To A New Wake-Up Stroke Protocol Is Feasible And Safe

Introduction: Up to 25% of strokes are recognized upon awakening. Recent studies have demonstrated that a “tissue clock” rather than a time clock can be used to identify patients who may benefit from intravenous thrombolytics (IVT) beyond 4.5 hours from last known well (LKW). Consistent access to hyperacute MRI limits many centers from treating wake-up stroke patients. We created a formal protocol of clinical and imaging criteria to standardize evaluation and management of wake-up strokes. Methods: This retrospective, observational study reviewed consecutive patients admitted to our Comprehensive Stroke Center who qualified for the wake-up protocol between February 2022 and June 2022. The implemented protocol, based on clinical trials’ inclusion criteria, is comprised of the following: 1) arrival within 12 hours from LKW and within 4.5 hours from symptom discovery; 2) high suspicion for acute ischemic stroke; 3) no contraindication to MRI; 4) NIHSS of at least 4; 5) baseline mRS 0-3; 6) no absolute contraindications to IVT. For patients meeting above inclusion criteria, emergent MRI with perfusion was performed. Diffusion-FLAIR mismatch (signal intensity ratio) and diffusion-perfusion mismatch were reviewed to determine thrombolysis eligibility by a trained neuroradiologist or vascular neurologist. Results: Ten patients qualified for the wake-up protocol in the first five months of protocol implementation. Median NIHSS was 7, median LKW to arrival time was 8 hours, and median door to MRI time was 72.5 minutes. A final diagnosis of ischemic stroke was made in 80% of these cases. Overall, 50% were eligible for IVT based on our criteria, and 30% received thrombolysis. Median door to needle time was 92 minutes (range 75-117). There were no symptomatic intracranial hemorrhages. All patients treated with IVT were discharged home with no to minimal residual deficits with mRS 0-1 and median NIHSS at discharge of 2 (range 0-4). Conclusion: A formal protocol for wake-up stroke management allowed a streamlined approach to expand the number of IVT-eligible cases. Continued efforts are needed to improve door to needle times in such cases and to follow clinical courses of treated patients.

The Management of Acute Ischaemic Stroke – A Review and South African Perspective

Abstract Reperfusion therapy in acute ischaemic stroke, namely intravenous thrombolysis and mechanical thrombectomy, have traditionally had strict time-based eligibility criteria. Recent advances in diagnostic and imaging modalities have resulted in a more dynamic view of eligibility for these therapies. The time clock concept may soon be superseded by the “tissue clock” concept, where accurate identification of the extent of the salvageable penumbra has been shown to result in favourable outcomes well beyond the traditional time limits in carefully selected patients. However in a low-middle income country like South Africa, the social, economic and geographic barriers to an effective acute stroke management service are often overwhelming. In this review we provide an update on the current evidence guiding management of acute ischaemic stroke, with a particular emphasis on the challenges faced in resource-constrained regions.

Snack timing affects tissue clock and metabolic responses in male mice.

Snacking of small quantities of palatable food items throughout the day is common in modern societies and is promoted by 24/7 lifestyles. Long-term mistimed high-caloric food intake disrupts endogenous circadian rhythms and supports the development of obesity and other metabolic disorders. However, less is known about the time-of-day dependent effects of snacking. We hypothesized that already a single snacking episode may affect the circadian regulation of metabolic parameters, in particular when the snack is consumed during the daily rest phase. We performed an acute snack experiment in mice by providing access to chow or chocolate either at day- or nighttime and assessed snack effects on core body temperature, locomotor activity, and gene expression in metabolic tissues. Our results show that daytime chocolate snacking leads to a higher body temperature and locomotor activity increase compared to chow and nighttime intake. This goes along with altered clock and metabolic gene expression in peripheral tissues. Changes in nutrient uptake transporter gene expression in the small intestine suggest increased glucose resorption after daytime snacking. Our results indicate an early mechanism for the adipogenic effect of mistimed high-calorie snacking.

Stroke: What's Sleep Got to Do With It?

Ischemic strokes most often occur between 6 am and 12 am after awakening from sleep but up to 30% occur during sleep. Wake-up strokes (WUS) are new focal neurological deficit(s) persisting for ≥ 24 hours attributable to an ischemic event present on patient awakening. Obstructive sleep apnea (OSA) is a major risk factor for WUS because it compounds the instability of the morning environment and increases the likelihood of cardiovascular events, including hypertension, atrial fibrillation, right-to-left shunts, and stroke. Circadian-driven alterations in structural, homeostatic, and serological factors also predispose to WUS. Also, WUS patients are often not considered candidates for time-dependent intravenous thrombolysis therapy because of an uncertain onset time. However, using the tissue clock (positive diffusion weighted imaging-negative fluid-attenuated inversion recovery mismatch) dates the WUS as 3 to 4.5 hours old and permits consideration for intravenous thrombolysis and if needed mechanical thrombectomy. Given the high prevalence of moderate/severe OSA in stroke patients and its impact on stroke outcomes, screening with overnight pulse oximetry and home sleep apnea test is needed. Treating OSA poststroke remains challenging. Polysomnographic changes in sleep architecture following acute/subacute stroke may also impact upon stroke outcome.

Studying Circadian Clock Entrainment by Hormonal Signals.

In mammals, molecular circadian clocks not only exist in the suprachiasmatic nucleus (SCN) but in almost all organ systems. Intriguingly, tissue clocks can operate in both isolated tissues and cell lines with endocrine signals mediating the circadian expression of local transcriptomes. This can be demonstrated by treating tissue explants with endocrine cues in a phase- and dose-dependent manner. In this chapter we provide an overview of methods to study the effects of candidate hormonal time cues on tissue clock resetting. We propose an experimental procedure based on an in vitro setup consisting of several consecutive steps in which organotypic tissue cultures or cells can be used. Our approach targets the potential resetting mechanism at three levels: the hormone, the direct clock gene target, and the tissue clock response.

A Semi-Supervised Learning Framework to Leverage Proxy Information for Stroke MRI Analysis.

Treating acute ischemic stroke (AIS) patients is a time-sensitive endeavor, as therapies target areas experiencing ischemia to prevent irreversible damage to brain tissue. Depending on how an AIS is progressing, thrombolytics such as tissue-plasminogen activator (tPA) may be administered within a short therapeutic window. The underlying conditions for optimal treatment are varied. While previous clinical guidelines only permitted tPA to be administered to patients with a known onset within 4.5 hours, clinical trials demonstrated that patients with signal intensity differences between diffusion-weighted imaging (DWI) and fluid-attenuated inversion recovery (FLAIR) sequences in an MRI study can benefit from thrombolytic therapy. This intensity difference, known as DWI-FLAIR mismatch, is prone to high inter-reader variability. Thus, a paradigm exists where onset time serves as a weak proxy for DWI-FLAIR mismatch. In this study, we sought to detect DWI-FLAIR mismatch in an automated fashion, and we compared this to assessments done by three expert neuroradiologists. Our approach involved training a deep learning model on MRI to classify tissue clock and leveraging time clock as a weak proxy label to supplement training in a semi-supervised learning (SSL) framework. We evaluate our deep learning model by testing it on an unseen dataset from an external institution. In total, our proposed framework was able to improve detection of DWI-FLAIR mismatch, achieving a top ROC-AUC of 74.30%. Our study illustrated that incorporating clinical proxy information into SSL can improve model optimization by increasing the fidelity of unlabeled samples included in the training process.

Fluid-Attenuated Inversion Recovery May Serve As a Tissue Clock in Patients Treated With Endovascular Thrombectomy.

We investigated whether the signal change on fluid-attenuated inversion recovery (FLAIR) can serve as a tissue clock that predicts the clinical outcome after endovascular thrombectomy (EVT), independently of the onset-to-admission time. Consecutive patients with acute stroke treated with EVT between September 2014 and December 2018 were enrolled. Based on the parenchymal signal change on FLAIR, patients were classified into FLAIR-negative and FLAIR-positive groups. The clinical characteristics, imaging findings, EVT parameters, and the intracranial hemorrhage defined as Heidelberg Bleeding Classification ≥1c hemorrhage (parenchymal hemorrhage, intraventricular hemorrhage, subarachnoid hemorrhage, and/or subdural hemorrhage) were compared between the 2 groups. A modified Rankin Scale score 0 to 1 at 3 months was considered to represent a good outcome. Of the 227 patients with EVT during the study period, 140 patients (62%) were classified into the FLAIR-negative group and 87 (38%) were classified into the FLAIR-positive group. In the FLAIR-negative group, the patients were older (P=0.011), the onset-to-image time was shorter (P<0.001), the frequency of cardioembolic stroke was higher (P=0.006), and the rate of intravenous thrombolysis was higher (P<0.001) in comparison to the FLAIR-positive group. Although the rate of complete recanalization after EVT did not differ between the 2 groups (P=0.173), the frequency of both any-intracranial hemorrhage and Heidelberg Bleeding Classification ≥1c hemorrhage were higher in the FLAIR-positive group (P=0.004 and 0.011). At 3 months, the percentage of patients with a good outcome (FLAIR-negative, 41%; FLAIR-positive, 27%) was significantly related to the FLAIR signal change (P=0.047), while the onset-to-image time was not significant (P=0.271). A multivariate regression analysis showed that a FLAIR-negative status was independently associated with a good outcome (odds ratio, 2.10 [95% CI, 1.02–4.31], P=0.044). A FLAIR-negative status may predict the clinical outcome more accurately than the onset-to-admission time, which may support the role of FLAIR as a tissue clock.

Imaging strategy for acute stroke patients, a review of literature

Background: This review article focused on the utilization and impact of current neuroimaging techniques for the patient with acute stroke, emphasizing how imaging builds upon clinical assessment to establish diagnosis or etiology and guide therapeutic decisions. When requesting imaging examinations in patients with stroke symptoms; it is crucial to evaluate four significant parameters of stroke; parenchyma, vessels, perfusion, and penumbra. Evaluation of all these four parameters, in their right request are essential to grasp the explanation and potential therapy decisions for stroke in a specific patient. Extensive neurovascular imaging conventions utilizing multimodality CT (NCCT, CT Angiography, and CT Perfusion) or multimodality MRI (DWI-perfusion mismatch or DWI-FLAIR mismatch, and MR Angiography) might be utilized to evaluate the acute stroke patients and provide all the needed data for treatment of them inside minutes after the patient lands at the emergency clinic. Using this approach will help to discriminate between hemorrhagic and ischemic stroke as presence of frank intracerebral hemorrhage contraindicates reperfusion treatment, permits the choice of patients with large vessel occlusion for endovascular treatment and answer the important “tissue clock” within 6 hours from symptom and even with late-presenting (&gt; 6 h) or wake-up stroke. Conclusions: As patients with acute cerebral stroke might be critically ill, the initial imaging scanning for acute stroke patients should be constrained to the procurement of useful data only, considering the accessible therapeutic options at a given place at any given time.

Epigenetic mutation load is weakly correlated with epigenetic age acceleration.

DNA methylation (DNAm) age estimators are widely used to study aging-related conditions. It is not yet known whether DNAm age is associated with the accumulation of stochastic epigenetic mutations (SEMs), which reflect dysfunctions of the epigenetic maintenance system. Here, we defined epigenetic mutation load (EML) as the total number of SEMs per individual. We assessed associations between EML and DNAm age acceleration estimators using biweight midcorrelations in four population-based studies (total n = 6,388). EML was not only positively associated with chronological age (meta r = 0.171), but also with four measures of epigenetic age acceleration: the Horvath pan tissue clock, intrinsic epigenetic age acceleration, the Hannum clock, and the GrimAge clock (meta-analysis correlation ranging from r = 0.109 to 0.179). We further conducted pathway enrichment analyses for each participant’s SEMs. The enrichment result demonstrated the stochasticity of epigenetic mutations, meanwhile implicated several pathways: signaling, neurogenesis, neurotransmitter, glucocorticoid, and circadian rhythm pathways may contribute to faster DNAm age acceleration. Finally, investigating genomic-region specific EML, we found that EMLs located within regions of transcriptional repression (TSS1500, TSS200, and 1stExon) were associated with faster age acceleration. Overall, our findings suggest a role for the accumulation of epigenetic mutations in the aging process.

The Tissue Clock Network: Driver and Gatekeeper of Circadian Physiology: Circadian rhythms are integrated outputs of central and peripheral tissue clocks interacting in a complex manner - from drivers to gatekeepers.

In mammals, a network of cellular circadian clocks organizes physiology and behavior along the 24-h day cycle. The traditional hierarchical model of circadian clock organization with a central pacemaker and peripheral slave oscillators has recently been challenged by studies combining tissue-specific mouse mutants with transcriptome analyses. First, a surprisingly small number of tissue rhythms are lost when only local clocks are ablated and, second, transcriptional circadian rhythms appear to be regulated by a complex mix of local and systemic factors. As reviewed here, these findings suggest a more integrated model of clock network interaction with the central pacemaker as the main source of behavioral and systemic-physiological rhythms and peripheral clocks controlling some local rhythms while at the same time acting as gatekeepers that temporally adjust cellular responses to external stimuli.

Regulation and function of extra-SCN circadian oscillators in the brain.

Most organisms evolved endogenous, so called circadian clocks as internal timekeeping mechanisms allowing them to adapt to recurring changes in environmental demands brought about by 24-hour rhythms such as the light-dark cycle, temperature variations or changes in humidity. The mammalian circadian clock system is based on cellular oscillators found in all tissues of the body that are organized in a hierarchical fashion. A master pacemaker located in the suprachiasmatic nucleus (SCN) synchronizes peripheral tissue clocks and extra-SCN oscillators in the brain with each other and with external time. Different time cues (so called Zeitgebers) such as light, food intake, activity and hormonal signals reset the clock system through the SCN or by direct action at the tissue clock level. While most studies on non-SCN clocks so far have focused on peripheral tissues, several extra-SCN central oscillators were characterized in terms of circadian rhythm regulation and output. Some of them are directly innervated by the SCN pacemaker, while others receive indirect input from the SCN via other neural circuits or extra-brain structures. The specific physiological function of these non-SCN brain oscillators as well as their role in the regulation of the circadian clock network remains understudied. In this review we summarize our current knowledge about the regulation and function of extra-SCN circadian oscillators in different brain regions and devise experimental approaches enabling us to unravel the organization of the circadian clock network in the central nervous system.

Elevated early lesion water uptake in acute stroke predicts poor outcome despite successful recanalization - When "tissue clock" and "time clock" are desynchronized.

Ischemic water uptake in acute stroke is a reliable indicator of lesion age. Nevertheless, inter-individually varying edema progression has been observed and elevated water uptake has recently been described as predictor of malignant infarction. We hypothesized that early-elevated lesion water uptake indicates accelerated "tissue clock" desynchronized with "time clock" and therefore predicts poor clinical outcome despite successful recanalization. Acute middle cerebral artery stroke patients with multimodal admission-CT who received successful thrombectomy (TICI 2b/3) were analyzed. Net water uptake (NWU), a quantitative imaging biomarker of ischemic edema, was determined in admission-CT and tested as predictor of clinical outcome using modified Rankin Scale (mRS) after 90 days. A binary outcome was defined for mRS 0-4 and mRS 5-6. Seventy-two patients were included. The mean NWU (SD) in patients with mRS 0-4 was lower compared to patients with mRS 5-6 (5.0% vs. 12.1%; p < 0.001) with similar time from symptom onset to imaging (2.6 h vs. 2.4 h; p = 0.7). Based on receiver operating curve analysis, NWU above 10% identified patients with very poor outcome with high discriminative power (AUC 0.85), followed by Alberta Stroke Program Early CT Score (ASPECTS) (AUC: 0.72) and National Institutes of Health Stroke Scale (NIHSS) (AUC: 0.72). Quantitative NWU may serve as an indicator of "tissue clock" and pronounced early brain edema with elevated NWU might suggest a desynchronized "tissue clock" with real "time clock" and therefore predict futile recanalization with poor clinical outcome.

Circadian clock network desynchrony promotes weight gain and alters glucose homeostasis in mice

ObjectiveA network of endogenous circadian clocks adapts physiology and behavior to recurring changes in environmental demands across the 24-hour day cycle. Circadian disruption promotes weight gain and type 2 diabetes development. In this study, we aim to dissect the roles of different tissue clocks in the regulation of energy metabolism. MethodsWe used mice with genetically ablated clock function in the circadian pacemaker of the suprachiasmatic nucleus (SCN) under different light and feeding conditions to study peripheral clock resetting and the role of the peripheral clock network in the regulation of glucose handling and metabolic homeostasis. ResultsIn SCN clock-deficient mice, behavioral and non-SCN tissue clock rhythms are sustained under rhythmic lighting conditions but deteriorate quickly in constant darkness. In parallel to the loss of behavioral and molecular rhythms, the animals develop adiposity and impaired glucose utilization in constant darkness. Restoring peripheral clock rhythmicity and synchrony by time-restricted feeding normalizes body weight and glucose metabolism. ConclusionsThese data reveal the importance of an overall synchronized circadian clockwork for the maintenance of metabolic homeostasis.

Pathophysiological, Molecular and Therapeutic Issues of Nonalcoholic Fatty Liver Disease: An Overview.

Nonalcoholic Fatty Liver Disease (NAFLD) represents the leading cause of liver disease in developed countries but its diffusion is currently also emerging in Asian countries, in South America and in other developing countries. It is progressively becoming one of the main diseases responsible for hepatic insufficiency, hepatocarcinoma and the need for orthotopic liver transplantation. NAFLD is linked with metabolic syndrome in a close and bidirectional relationship. To date, NAFLD is a diagnosis of exclusion, and liver biopsy is the gold standard for diagnosis. NAFLD pathogenesis is complex and multifactorial, mainly involving genetic, metabolic and environmental factors. New concepts are constantly arising in the literature promising new diagnostic and therapeutic tools. One of the challenges will be to better characterize not only NAFLD development but overall NAFLD progression, in order to better identify NAFLD patients at higher risk of metabolic, cardiovascular and neoplastic complications. This review analyses NAFLD epidemiology and the different prevalence of the disease in distinct groups, particularly according to sex, age, body mass index, type 2 diabetes and dyslipidemia. Furthermore, the work expands on the pathophysiology of NAFLD, examining multiple-hit pathogenesis and the role of different factors in hepatic steatosis development and progression: genetics, metabolic factors and insulin resistance, diet, adipose tissue, gut microbiota, iron deposits, bile acids and circadian clock. In conclusion, the current available therapies for NAFLD will be discussed.

Endovascular Stroke Therapy.

Ischemic stroke is a leading cause of death and disability throughout the world and is both preventable and treatable. This review focuses on the treatment of the most severe form of ischemic stroke, namely large-vessel ischemic stroke, using endovascular techniques. Such therapies were proven effective in 2015. These therapies are among the most beneficial surgical therapies ever subjected to randomized clinical trials. Recent research has explored treating patients up to 24h following the onset of stroke using advanced imaging techniques to select patients with brain tissue still at risk. These new findings suggest there exists a tissue clock rather than a time clock when selecting patients for therapy. Stroke systems throughout the world are now embracing endovascular stroke therapy. Improving regional stroke systems of care and expanding eligibility for patients are a major focus of current research.