Inhibition of Notch1 Signaling at the Subacute Stage of Stroke Promotes Endogenous Neurogenesis and Motor Recovery After Stroke

Sounds interesting. Now we just need to update the stroke strategy and followup with human clinical trials.  But that will never occur with our fucking failures of stroke associations along with NO stroke leadership and NO stroke strategy. Survivors are completely and totally fucking screwed until whatever passes for stroke leadership is replaced by stroke survivors.
https://www.frontiersin.org/articles/10.3389/fncel.2018.00245/full?

Xiao-Zhu Hao^1†, Le-Kang Yin^2†, Jia-Qi Tian¹, Chan-Chan Li¹, Xiao-Yuan Feng¹, Zhen-Wei Yao¹, Min Jiang³ and Yan-Mei Yang^1*

• ¹Department of Radiology, Huashan Hospital, Fudan University, Shanghai, China
• ²Department of Radiology, Shanghai Chest Hospital, Shanghai Jiaotong University, Shanghai, China
• ³Institutes of Brain Science and State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai, China

Background and Purpose: It is still not clear whether Notch1 signaling inhibition can promote functional outcomes after stroke, given that it plays time-dependent roles in the sequential process of endogenous neurogenesis. The purpose of this study was to identify the appropriate time frame for Notch1 signaling inhibition according to the temporal evolution of Notch1 signaling activation and the responses of neural stem cells (NSCs), in order to target it for therapeutic intervention and stimulate neurorestorative strategies after stroke.

Methods: Sprague-Dawley (SD) rats were subjected to 90-min of middle cerebral artery occlusion (MCAO). Rats were sacrificed before, and at day 1, day 2, day 3, day 4, and day 7 after ischemia for immunohistochemical analysis of the Notch intracellular domain (NICD), Nestin and doublecortin (Dcx). Next, MCAO rats were treated with the γ-secretase inhibitor N-[N-(3,5-di uorophenacetyl)-1-alanyl]-S-phenylglycine t-butylester (DAPT) or with saline at day 4 after ischemia, and subsequently evaluated with behavioral test analysis and magnetic resonance imaging (MRI). The rat brains were then harvested for immunohistochemical analysis of Dcx, NeuN and myelin basic protein (MBP) at 2, 3, 4, and 8 weeks.

Results: Notch1 signaling was maximally activated at day 3 after ischemia in parallel with the temporal evolution of NSCs. Inhibiting Notch1 signaling at day 4 after reperfusion with DAPT further promoted recovery of MRI parameters of the corticospinal tract (CST) and the functional outcomes, concomitantly with an increase in neuroblasts, their migration to the ischemic boundary, and potential differentiation to mature neurons, as well as the amelioration of axonal bundle integrity.

Conclusion: Inhibition of Notch1 signaling at the subacute stage of stroke could maximally promote endogenous neurogenesis and axonal reorganization.

Introduction

Stroke is one of the leading causes of death and serious long-term disability (Stinear et al., 2007; Smajlović, 2015). Importantly, a large number of stroke patients are permanently disabled in that only a minority of patients can benefit from thrombolysis given its limited therapeutic time window. Novel neurorestorative therapies with a wider therapeutic window that can promote brain repair, are thus, urgently needed to enhance functional neurological recovery following stroke (Barone, 2010; Zhan et al., 2011). Previous studies have demonstrated that cerebral ischemia induces proliferation of NSCs in the SVZ, which migrate into the damaged brain regions, differentiate into mature neurons and ultimately integrate into local as well as remote neural circuits (Arvidsson et al., 2002; Zhang et al., 2008; Wang L. et al., 2009; Sun et al., 2013), suggesting that endogenous neurogenesis could be a target for rehabilitative therapy in stroke patients.

In recent years, Notch1 signaling, which is critical for endogenous neurogenesis, has been regarded as a potential therapeutic target for promoting functional recovery after stroke (Wei et al., 2011). Notch1 is expressed in NSCs and neuroblasts and its activity is fundamental for neural development as well as neural specification by controlling maintenance, proliferation and differentiation of NSCs in young and aged brain in normal or pathological conditions (Zhang et al., 2008; Wang X. et al., 2009; Sun et al., 2013). Interestingly, while some studies have found that Notch1 signaling activation could promote neurogenesis (Oya et al., 2009; Wang X. et al., 2009), others support the idea that Notch1 signaling negatively regulates neurogenesis (Li et al., 2012). Notably, preventing Notch1 cleavage into the Notch intracellular domain (NICD) with the γ-secretase inhibitor N-[N-(3,5-diuorophenacetyl)-1-alanyl]-S-phenylglycine t-butylester (DAPT), subsequently improves functional outcomes following stroke (Li et al., 2012). Except for differences in animal strain and stroke models, the most plausible explanation for the conflicting results cited above is the spatio-temporal regulation of Notch activity (Zhao et al., 2012); in other words, Notch-1 signaling playing space and time-dependent roles in the sequential process of neurogenesis (Chambers et al., 2001). Moreover, several studies have found that Notch-1 signaling was activated in the acute stage of stroke to promote NSCs proliferation and was attenuated in the subacute stage to promote neuronal differentiation (Oya et al., 2009; Wang L. et al., 2009). Based on this standpoint, the detection of the temporal evolution of Notch1 signaling activation following cerebral ischemia and attempts to timely control its activation are required to augment the neural progenitor pool and promote neural differentiation to attain morphological and functional maturity in the adult brain.

Furthermore, it appears unreasonable and insufficient to define the beneficial or detrimental effects of therapeutic interventions of the Notch1 pathway based on in vitro pathological examinations. Thus, it is important to develop non-invasive methods to monitor modifications of brain tissue and predict long-term motor outcomes, which is essential to promote clinical applications of emerging neurorestorative therapies. Cross-sectional studies have demonstrated that diffusion tensor imaging (DTI) could provide unparalleled insights into the microstructural properties of central nervous system (CNS) tissue (Nucifora et al., 2007; Budde and Frank, 2012). For instance, diffusion parameter changes in the CST have been established as surrogate makers of motor deficit after stroke (Thomalla et al., 2005; Stinear et al., 2007; Lindenberg et al., 2012; Feng et al., 2015).

In this study, firstly, we aimed to detect the temporal evolution of Notch1 signaling activation and NSCs responses after stroke. Based on our results, we then attempted to find the appropriate therapeutic time frame for DAPT treatment. More importantly, for the first time, we measured the comprehensive microstructure changes in the CNS with a set of MR parameters, combined with the post mortem immunohistochemical analysis of neurogenesis and remyelination of the CST, and ultimately demonstrated the neurorestorative effects of DAPT treatment at the subacute stage after stroke.