The circadian clock time tunes axonal regeneration

Clickable, Thermally Responsive Hydrogels Enabled by Recombinant Spider Silk Protein and Spy Chemistry for Sustained Neurotrophin Delivery

The ability to deliver protein therapeutics in a minimally invasive, safe, and sustained manner, without resorting to viral delivery systems, will be crucial for treating a wide range of chronic injuries and diseases. Among these challenges, achieving axon regeneration and functional recovery post-injury or disease in the central nervous system remains elusive to most clinical interventions, constantly calling for innovative solutions. Here, a thermally responsive hydrogel system utilizing recombinant spider silk protein (spidroin) is developed. The protein solution undergoes rapid sol-gel transition at an elevated temperature (37 °C) following brief sonication. This thermally triggered gelation confers injectability to the system. Leveraging SpyTag/SpyCatcher chemistry, the hydrogel, composed of SpyTag-fusion spidroin, can be functionalized with diverse SpyCatcher-fusion bioactive motifs, such as neurotrophic factors (e.g., ciliary neurotrophic factor) and cell-binding ligands (e.g., laminin), rendering it well-suited for neuronal culturing. More importantly, the intravitreous injection of the protein materials decorated with SpyCatcher-fusion CNTF into the vitreous body after optic nerve injury leads to prolonged JAK/STAT3 signaling, increased neuronal survival, and enhanced axon regeneration. This study illustrates a generalizable material system for injectable and sustained delivery of protein therapeutics for neuroprotection and regeneration, with the potential for extension to other chronic diseases and injuries.

Influencing factors and repair advancements in rodent models of peripheral nerve regeneration

Peripheral nerve injuries lead to severe functional impairments, with rodent models essential for studying regeneration. This review examines key factors affecting outcomes. Age-related declines, like reduced nerve fiber density and impaired axonal transport of vesicles, hinder recovery. Hormonal differences influence regeneration, with BDNF/trkB critical for testosterone and nerve growth factor for estrogen signaling pathways. Species and strain selection impact outcomes, with C57BL/6 mice and Sprague-Dawley rats exhibiting varying regenerative capacities. Injury models - crush for early regeneration, chronic constriction for neuropathic pain, stretch for traumatic elongation and transection for severe lacerations - provide insights into clinically relevant scenarios. Repair techniques, such as nerve grafts and conduits, show that autografts are the gold standard for gaps over 3 cm, with success influenced by graft type and diameter. Time course analysis highlights crucial early degeneration and regeneration phases within the first month, with functional recovery stabilizing by three to six months. Early intervention optimizes regeneration by reducing scar tissue formation, while later interventions focus on remyelination. Understanding these factors is vital for designing robust preclinical studies and translating research into effective clinical treatments for peripheral nerve injuries.

Three-dimensional chromatin mapping of sensory neurons reveals that promoter-enhancer looping is required for axonal regeneration

The in vivo three-dimensional genomic architecture of adult mature neurons at homeostasis and after medically relevant perturbations such as axonal injury remains elusive. Here, we address this knowledge gap by mapping the three-dimensional chromatin architecture and gene expression program at homeostasis and after sciatic nerve injury in wild-type and cohesin-deficient mouse sensory dorsal root ganglia neurons via combinatorial Hi-C, promoter-capture Hi-C, CUT&Tag for H3K27ac and RNA-seq. We find that genes involved in axonal regeneration form long-range, complex chromatin loops, and that cohesin is required for the full induction of the regenerative transcriptional program. Importantly, loss of cohesin results in disruption of chromatin architecture and severely impaired nerve regeneration. Complex enhancer-promoter loops are also enriched in the human fetal cortical plate, where the axonal growth potential is highest, and are lost in mature adult neurons. Together, these data provide an original three-dimensional chromatin map of adult sensory neurons in vivo and demonstrate a role for cohesin-dependent long-range promoter interactions in nerve regeneration.

Three-dimensional chromatin mapping of sensory neurons reveals that cohesin-dependent genomic domains are required for axonal regeneration

The in vivo three-dimensional genomic architecture of adult mature neurons at homeostasis and after medically relevant perturbations such as axonal injury remains elusive. Here we address this knowledge gap by mapping the three-dimensional chromatin architecture and gene expression programme at homeostasis and after sciatic nerve injury in wild-type and cohesin-deficient mouse sensory dorsal root ganglia neurons via combinatorial Hi-C and RNA-seq. We find that cohesin is required for the full induction of the regenerative transcriptional program, by organising 3D genomic domains required for the activation of regenerative genes. Importantly, loss of cohesin results in disruption of chromatin architecture at regenerative genes and severely impaired nerve regeneration. Together, these data provide an original three-dimensional chromatin map of adult sensory neurons in vivo and demonstrate a role for cohesin-dependent chromatin interactions in neuronal regeneration.

Stroke in the Time of Circadian Medicine

Time-of-day significantly influences the severity and incidence of stroke. Evidence has emerged not only for circadian governance over stroke risk factors, but also for important determinants of clinical outcome. In this review, we provide a comprehensive overview of the interplay between chronobiology and cerebrovascular disease. We discuss circadian regulation of pathophysiological mechanisms underlying stroke onset or tolerance as well as in vascular dementia. This includes cell death mechanisms, metabolism, mitochondrial function, and inflammation/immunity. Furthermore, we present clinical evidence supporting the link between disrupted circadian rhythms and increased susceptibility to stroke and dementia. We propose that circadian regulation of biochemical and physiological pathways in the brain increase susceptibility to damage after stroke in sleep and attenuate treatment effectiveness during the active phase. This review underscores the importance of considering circadian biology for understanding the pathology and treatment choice for stroke and vascular dementia and speculates that considering a patient's chronotype may be an important factor in developing precision treatment following stroke.

Circadian Biology and the Neurovascular Unit

Mammalian physiology and cellular function are subject to significant oscillations over the course of every 24-hour day. It is likely that these daily rhythms will affect function as well as mechanisms of disease in the central nervous system. In this review, we attempt to survey and synthesize emerging studies that investigate how circadian biology may influence the neurovascular unit. We examine how circadian clocks may operate in neural, glial, and vascular compartments, review how circadian mechanisms regulate cell-cell signaling, assess interactions with aging and vascular comorbidities, and finally ask whether and how circadian effects and disruptions in rhythms may influence the risk and progression of pathophysiology in cerebrovascular disease. Overcoming identified challenges and leveraging opportunities for future research might support the development of novel circadian-based treatments for stroke.