Environmental Circadian Disruption Worsens Neurologic Impairment and Inhibits Hippocampal Neurogenesis in Adult Rats After Traumatic Brain Injury

Targeting Circadian Protein Rev-erbα to Alleviate Inflammation, Oxidative Stress, and Enhance Functional Recovery Following Brain Trauma

Traumatic brain injury (TBI) is a significant cause of morbidity and mortality worldwide, and its pathophysiology is characterized by oxidative stress and inflammation. Despite extensive research, effective treatments for TBI remain elusive. Recent studies highlighted the critical interplay between TBI and circadian rhythms, but the detailed regulation remains largely unknown. Motivated by the observed sustained decrease in Rev-erbα after TBI, we aimed to understand the critical role of Rev-erbα in the pathophysiology of TBI and determine its feasibility as a therapeutic target. Using a mouse model of TBI, we observed that TBI significantly downregulates Rev-erbα levels, exacerbating inflammatory and oxidative stress pathways. The regulation of Rev-erbα with either the pharmacological activator or inhibitor bidirectionally modulated inflammatory and oxidative events, which in turn influenced neurobehavioral outcomes, highlighting the protein's protective role. Mechanistically, Rev-erbα influences the expression of key oxidative stress and inflammatory regulatory genes. A reduction in Rev-erbα following TBI likely contributes to increased oxidative damage and inflammation, creating a detrimental environment for neuronal survival and recovery which could be reversed via the pharmacological activation of Rev-erbα. Our findings highlight the therapeutic potential of targeting Rev-erbα to mitigate TBI-induced damage and improve outcomes, especially in TBI-susceptible populations with disrupted circadian regulation.

Chitosan revokes controlled-cortical impact generated neurological aberrations in circadian disrupted mice via TLR4-NLRP3 axis

The severity of inevitable neurological deficits and long-term psychiatric disorders in the aftermath of traumatic brain injury is influenced by pre-injury biological factors. Herein, we investigated the therapeutic effect of chitosan lactate on neurological and psychiatric aberrations inflicted by circadian disruption (CD) and controlled-cortical impact (CCI) injury in mice. Firstly, CD was developed in mice by altering sporadic day-night cycles for 2 weeks. Then, CCI surgery was performed using a stereotaxic ImpactOne device. Mice subjected to CCI displayed a significant disruption of motor coordination at 1-, 3- and 5-days post-injury (DPI) in the rotarod test. These animals showed anxiety- and depression-like behaviors in the elevated plus maze and forced-swim test at 14 and 15 DPI, respectively. Notably, mice subjected to CD + CCI exhibited severe cognitive impairment in Y-maze and novel object recognition tasks. The compromised neurological, psychiatric, and cognitive functions were mitigated in chitosan-treated mice (1 and 3 mg/mL). Immunohistochemistry and real-time PCR assay results revealed the magnified responses of prima facie biomarkers like glial-fibrillary acidic protein and ionized calcium-binding adaptor molecule 1 in the pericontusional brain region of the CD + CCI group, indicating aggravated inflammation. We also noted the depleted levels of brain-derived neurotrophic factor and augmented expression of toll-like receptor 4 (TLR4)-leucine-rich-containing family pyrin domain-containing 3 (NLRP3) signaling [apoptosis-associated-speck-like protein (ASC), caspase-1, and interleukin 1-β] in the pericontusional area of CD + CCI group. CCI-induced changes in the astrocyte-glia and aggravated immune responses were ameliorated in chitosan-treated mice. These results suggest that the neuroprotective effect of chitosan in CCI-induced brain injury may be mediated by inhibition of the TLR4-NLRP3 axis.

Evaluating the daily modulation of FADD and related molecular markers in different brain regions in male rats

Fas-Associated protein with Death Domain (FADD), a key molecule controlling cell fate by balancing apoptotic versus non-apoptotic functions, is dysregulated in post-mortem brains of subjects with psychopathologies, in animal models capturing certain aspects of these disorders, and by several pharmacological agents. Since persistent disruptions in normal functioning of daily rhythms are linked with these conditions, oscillations over time of key biomarkers, such as FADD, could play a crucial role in balancing the clinical outcome. Therefore, we characterized the 24-h regulation of FADD (and linked molecular partners: p-ERK/t-ERK ratio, Cdk-5, p35/p25, cell proliferation) in key brain regions for FADD regulation (prefrontal cortex, striatum, hippocampus). Samples were collected during Zeitgeber time (ZT) 2, ZT5, ZT8, ZT11, ZT14, ZT17, ZT20, and ZT23 (ZT0, lights-on or inactive period; ZT12, lights-off or active period). FADD showed similar daily fluctuations in all regions analyzed, with higher values during lights off, and opposite to p-ERK/t-ERK ratios regulation. Both Cdk-5 and p35 remained stable and did not change across ZT. However, p25 increased during lights off, but exclusively in striatum. Finally, no 24-h modulation was observed for hippocampal cell proliferation, although higher values were present during lights off. These results demonstrated a clear daily modulation of FADD in several key brain regions, with a more prominent regulation during the active time of rats, and suggested a key role for FADD, and molecular partners, in the normal physiological functioning of the brain's daily rhythmicity, which if disrupted might participate in the development of certain pathologies.

Olfactory Ensheathing Cell Ameliorate Neuroinflammation Following Spinal Cord Injury Through Upregulating REV-ERBα in Microglia

Circadian dysregulation involved in the pathophysiology of spinal cord injury (SCI). Modulation of circadian rhythms hold promise for the SCI treatment. Here, we aim to investigated the mechanism of olfactory ensheathing cells (OEC) in alleviating neuroinflammation via modulating clock gene expression in microglia. In this study, SCI rats were randomly divided into OEC group and vehicle group. At 1 day after the surgery, OECs were intravenously transplanted into OEC group SCI rat, while the rats in vehicle group received culture medium. After 7 days post of OEC transplantation, tissues were collected from the brain (prefrontal cortex, hypothalamus, spinal cord) for PCR, western blotting and immunohistochemistry (IHC) assay at zeitgeber time (ZT) 6, ZT 12, ZT 18, and ZT 24. The roles of OEC in modulating REV-ERBα in microglia were studied by experimental inhibition of gene expression and the co-culture experiment. In the vehicle group, IHC showed a significant increase of Iba-1 expression in the cerebral white matter and spinal cord compared with control group (P < 0.0001 for all comparisons). The expression of Iba-1 was significantly decreased (P < 0.0001 for all comparisons). In the OEC group, the expression of PER 1, PER 2, CLOCK, and REV-ERBα was in a rhythmical manner in both spinal cord and brain regions. SCI disrupted their typical rhythms. And OECs transplantation could modulate those dysregulations by upregulating REV-ERBα. In vitro study showed that OECs couldn't reduce the activation of REV-ERBα inhibited microglia. The intravenous transplantation of OECs can mediate cerebral and spinal microglia activation through upregulation REV-ERBα after SCI.

Development of circadian neurovascular function and its implications

The neurovascular system forms the interface between the tissue of the central nervous system (CNS) and circulating blood. It plays a critical role in regulating movement of ions, small molecules, and cellular regulators into and out of brain tissue and in sustaining brain health. The neurovascular unit (NVU), the cells that form the structural and functional link between cells of the brain and the vasculature, maintains the blood-brain interface (BBI), controls cerebral blood flow, and surveils for injury. The neurovascular system is dynamic; it undergoes tight regulation of biochemical and cellular interactions to balance and support brain function. Development of an intrinsic circadian clock enables the NVU to anticipate rhythmic changes in brain activity and body physiology that occur over the day-night cycle. The development of circadian neurovascular function involves multiple cell types. We address the functional aspects of the circadian clock in the components of the NVU and their effects in regulating neurovascular physiology, including BBI permeability, cerebral blood flow, and inflammation. Disrupting the circadian clock impairs a number of physiological processes associated with the NVU, many of which are correlated with an increased risk of dysfunction and disease. Consequently, understanding the cell biology and physiology of the NVU is critical to diminishing consequences of impaired neurovascular function, including cerebral bleeding and neurodegeneration.

Circadian Rhythmicity of Vital Signs at Intensive Care Unit Discharge and Outcome of Traumatic Brain Injury

BACKGROUND

Physiological functions with circadian rhythmicity are often disrupted during illness.

OBJECTIVE

To assess the utility of circadian rhythmicity of vital signs in predicting outcome of traumatic brain injury (TBI).

METHODS

A retrospective single-center cohort study of adult intensive care unit (ICU) patients with largely isolated TBI to explore the relationship between the circadian rhythmicity of vital signs during the last 24 hours before ICU discharge and clinical markers of TBI severity and score on the Glasgow Outcome Scale 6 months after injury (GOS-6).

RESULTS

The 130 study participants had a median age of 39.0 years (IQR, 23.0-59.0 years), a median Glasgow Coma Scale score at the scene of 8.0 (IQR, 3.0-13.0), and a median Rotterdam score on computed tomography of the head of 3 (IQR, 3-3), with 105 patients (80.8%) surviving to hospital discharge. Rhythmicity was present for heart rate (30.8% of patients), systolic blood pressure (26.2%), diastolic blood pressure (20.0%), and body temperature (26.9%). Independent predictors of a dichotomized GOS-6 ≥4 were the Rotterdam score (odds ratio [OR], 0.38 [95% CI, 0.18-0.81]; P = .01), Glasgow Coma Scale score at the scene (OR, 1.22 [95% CI, 1.05-1.41]; P = .008), age (OR, 0.95 [95% CI, 0.92-0.98]; P = .003), oxygen saturation <90% in the first 24 hours (OR, 0.19 [95% CI, 0.05-0.73]; P = .02), serum sodium level <130 mmol/L (OR, 0.20 [95% CI, 0.05-0.70]; P = .01), and active intracranial pressure management (OR, 0.16 [95% CI, 0.04-0.62]; P = .008), but not rhythmicity of any vital sign.

CONCLUSION

Circadian rhythmicity of vital signs at ICU discharge is not predictive of GOS-6 in patients with TBI.

Chronic altered light-dark cycle differentially affects hippocampal CA1 and DG neuronal arborization in diurnal and nocturnal rodents

The hippocampus, an extension of the temporal part of the cerebral cortex, plays a crucial role in learning and memory. Structural and functional complexity within the hippocampus is greatly affected by a variety of external environmental stimuli including alteration in the light-dark (LD) cycle. The effect of altered LD cycle in learning and memory associated cognitive impairment has been reported in rodents. However, a comparative study of underlying neuronal changes between nocturnal and diurnal species is not well explored. The objective of the present study was to explore the morphological changes in hippocampal CA1 and DG neurons in response to prolonged constant condition viz. constant light (LL) and constant darkness (DD) in diurnal squirrels and nocturnal mice. Animals (n = 5/group) were placed in chronocubicle under 12:12 h LD, LL and DD. After four weeks, brain tissues were collected and processed for Golgi-Cox staining to analyze morphological changes in CA1 and DG neurons. The total and basal dendritic length, basal dendrite number, branch end, the diameter of apical dendrite and spine density were analyzed. The results showed a significant reduction in structural complexity of CA1 and DG neurons of squirrels exposed to prolonged constant darkness, whereas mice showed a significant increase as compared to LD. However, a significantly reduced neuronal complexity was observed in both squirrels and mice exposed to prolonged constant light. The results obtained were further confirmed by Sholl analysis of CA1 and DG neurons. The present study suggests that prolonged constant light may cause adverse effects on the neuronal complexity of both diurnal and nocturnal animals, but constant darkness may cause adverse effects mainly to the diurnal animals.

Circadian Rhythmicity in Cerebral Microvascular Tone Influences Subarachnoid Hemorrhage-Induced Injury

Supplemental Digital Content is available in the text.

Circadian rhythms influence the extent of brain injury following subarachnoid hemorrhage (SAH), but the mechanism is unknown. We hypothesized that cerebrovascular myogenic reactivity is rhythmic and explains the circadian variation in SAH-induced injury.

Persistent CO2 reactivity deficits are associated with neurological dysfunction up to one year after repetitive mild closed head injury in adolescent mice

Cerebrovascular reactivity (CVR) deficits in adolescents with concussion may persist after resolution of neurological symptoms. Whether or not CVR deficits predict long term neurological function is unknown. We used adolescent mice closed head injury (CHI) models (54 g, 107 cm or 117 cm drop height), followed by blood oxygenation level dependent (BOLD)-functional MRI with CO₂ challenge to assess CVR and brain connectivity. At one week, 3HD 107 cm mice showed delayed BOLD responses (p = 0.0074), normal striatal connectivity_, and an impaired respiratory rate response to CO₂ challenge (p = 0.0061 in ΔRmax). The 107 cm group developed rotarod deficits at 6 months (p = 0.02) and altered post-CO₂ brain connectivity (3-fold increase in striatum to motor cortex correlation coefficient) by one year, but resolved their CVR and respiratory rate impairments, and did not develop cognitive or circadian activity deficits. In contrast, the 117 cm group had persistent CVR (delay time: p = 0.016; washout time: p = 0.039) and circadian activity deficits (free-running period: 23.7 hr in sham vs 23.9 hr in 3HD; amplitude: 0.15 in sham vs 0.2 in 3HD; peak activity: 18 in sham vs 21 in 3HD) at one year. Persistent CVR deficits after concussion may portend long-term neurological dysfunction. Further studies are warranted to determine the utility of CVR to predict chronic neurological outcome after mild traumatic brain injury.

Potential Role of Adult Hippocampal Neurogenesis in Traumatic Brain Injury

Traumatic brain injury (TBI) is a serious cause of disability and death among young and adult individuals, displaying complex pathophysiology including cellular and molecular mechanisms that are not fully elucidated. Many experimental and clinical studies investigated the potential relationship between TBI and the process by which neurons are formed in the brain, known as neurogenesis. Currently, there are no available treatments for TBI's long-term consequences being the search for novel therapeutic targets, a goal of highest scientific and clinical priority. Some studies evaluated the benefits of treatments aimed at improving neurogenesis in TBI. In this scenario, herein, we reviewed current pre-clinical studies that evaluated different approaches to improving neurogenesis after TBI while achieving better cognitive outcomes, which may consist in interesting approaches for future treatments.

Artificial Light at Night Increases Recruitment of New Neurons and Differentially Affects Various Brain Regions in Female Zebra Finches

Despite growing evidence that demonstrate adverse effects of artificial light at night (ALAN) on many species, relatively little is known regarding its effects on brain plasticity in birds. We recently showed that although ALAN increases cell proliferation in brains of birds, neuronal densities in two brain regions decreased, indicating neuronal death, which might be due to mortality of newly produced neurons or of existing ones. Therefore, in the present study we studied the effect of long-term ALAN on the recruitment of newborn neurons into their target regions in the brain. Accordingly, we exposed zebra finches (Taeniopygia guttata) to 5 lux ALAN, and analysed new neuronal recruitment and total neuronal densities in several brain regions. We found that ALAN increased neuronal recruitment, possibly as a compensatory response to ALAN-induced neuronal death, and/or due to increased nocturnal locomotor activity caused by sleep disruption. Moreover, ALAN also had a differential temporal effect on neuronal densities, because hippocampus was more sensitive to ALAN and its neuronal densities were more affected than in other brain regions. Nocturnal melatonin levels under ALAN were significantly lower compared to controls, indicating that very low ALAN intensities suppress melatonin not only in nocturnal, but also in diurnal species.

Melatonin receptor activation provides cerebral protection after traumatic brain injury by mitigating oxidative stress and inflammation via the Nrf2 signaling pathway

Traumatic brain injury (TBI) is a principal cause of death and disability worldwide. Melatonin, a hormone made by the pineal gland, is known to have anti-inflammatory and antioxidant properties. In this study, using a weight-drop model of TBI, we investigated the protective effects of ramelteon, a melatonin MT1/MT2 receptor agonist, and its underlying mechanisms of action. Administration of ramelteon (10 mg/kg) daily at 10:00 a.m. alleviated TBI-induced early brain damage on day 3 and long-term neurobehavioral deficits on day 28 in C57BL/6 mice. Ramelteon also increased the protein levels of interleukin (IL)-10, IL-4, superoxide dismutase (SOD), glutathione, and glutathione peroxidase and reduced the protein levels of IL-1β, tumor necrosis factor, and malondialdehyde in brain tissue and serum on days 1, 3, and 7 post-TBI. Similarly, ramelteon attenuated microglial and astrocyte activation in the perilesional cortex on day 3. Furthermore, ramelteon decreased Keap 1 expression, promoted nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear accumulation, and increased levels of downstream proteins, including SOD-1, heme oxygenase-1, and NQO1 on day 3 post-TBI. However, in Nrf2 knockout mice with TBI, ramelteon did not decrease the lesion volume, neuronal degeneration, or myelin loss on day 3; nor did it mitigate depression-like behavior or most motor behavior deficits on day 28. Thus, timed ramelteon treatment appears to prevent inflammation and oxidative stress via the Nrf2-antioxidant response element pathway and might represent a potential chronotherapeutic strategy for treating TBI.

Spinal Cord Injury in Rats Disrupts the Circadian System

Spinal cord injury (SCI) perturbs many physiological systems. The circadian system helps maintain homeostasis throughout the body by synchronizing physiological and behavioral functions to predictable daily events. Whether disruption of these coordinated daily rhythms contributes to SCI-associated pathology remains understudied. Here, we hypothesized that SCI in rats would dysregulate several prominent circadian outputs including glucocorticoids, core temperature, activity, neuroinflammation, and circadian gene networks. Female and male Sprague Dawley rats were subjected to clinically relevant thoracic 9 moderate contusion SCI (or laminectomy sham surgery). Diurnal measures-including rhythms of plasma corticosterone (CORT), body temperature, and activity (using small implanted transmitters), and intraspinal circadian and inflammatory gene expression-were studied prior to and after surgery. SCI caused overall increases and disrupted rhythms of the major rodent glucocorticoid, CORT. Presurgery and sham rats displayed expected rhythms in body temperature and activity, whereas rats with SCI had blunted daily rhythms in body temperature and activity. In parallel, SCI disrupted intraspinal rhythms of circadian clock gene expression. Circadian clock genes can act as transcriptional regulators of inflammatory pathways. Indeed, SCI rats also showed dysregulated rhythms in inflammatory gene expression in both the epicenter and distal spinal cord. Our data show that moderate SCI in rats causes wide-ranging diurnal rhythm dysfunction, which is severe at acute time points and gradually recovers over time. Normalizing post-SCI diurnal rhythms could enhance the recovery of homeostasis and quality of life.

HDAC1 Silence Promotes Neuroprotective Effects of Human Umbilical Cord-Derived Mesenchymal Stem Cells in a Mouse Model of Traumatic Brain Injury via PI3K/AKT Pathway

Stem cell transplantation is a promising therapy for traumatic brain injury (TBI), but low efficiency of survival and differentiation of transplanted stem cells limits its clinical application. Histone deacetylase 1 (HDAC1) plays important roles in self-renewal of stem cells as well as the recovery of brain disorders. However, little is known about the effects of HDAC1 on the survival and efficacy of human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) in vivo. In this study, our results showed that HDAC1 silence promoted hUC-MSCs engraftment in the hippocampus and increased the neuroprotective effects of hUC-MSCs in TBI mouse model, which was accompanied by improved neurological function, enhanced neurogenesis, decreased neural apoptosis, and reduced oxidative stress in the hippocampus. Further mechanistic studies revealed that the expressions of phosphorylated PTEN (p-PTEN), phosphorylated Akt (p-Akt), and phosphorylated GSK-3β (p-GSK-3β) were upregulated. Intriguingly, the neuroprotective effects of hUC-MSCs with HDAC1 silence on behavioral performance of TBI mice was markedly attenuated by LY294002, an inhibitor of the PI3K/AKT pathway. Taken together, our findings suggest that hUC-MSCs transplantation with HDAC1 silence may provide a potential strategy for treating TBI in the future.

Effects of crenolanib, a nonselective inhibitor of PDGFR, in a mouse model of transient middle cerebral artery occlusion

Neurogenesis in the subventricular zone (SVZ) plays a vital role in neurologic recovery after stroke. However, only a small fraction of newly generated neuroblasts from the SVZ will survive long-term. Successful migration and survival of neuroblasts requires angiogenesis, lesion-derived chemo-attractants, and appropriate local microenvironments, which are partly regulated by the platelet-derived growth factor receptor (PDGFR) signaling pathway. In this study, we investigated the effects of PDGFR inhibition in a mouse model of transient middle cerebral artery occlusion (MCAO). We blocked the pathway using a nonselective PDGFR inhibitor, crenolanib, during the acute post-MCAO phase (days 1-3) or during the sub-acute phase (days 7-9). Downregulating the PDGFR signaling pathway with crenolanib from day 1 to day 3 after MCAO significantly decreased the migration of neuroblasts from the SVZ to the peri-infarct region, decreased angiogenesis, and lowered expression of vascular endothelial growth factor, stromal cell-derived factor-1, and monocyte chemotactic protein-1. Downregulation of the PDGFR signaling pathway on days 7-9 with crenolanib significantly increased apoptosis of the neuroblasts that had migrated to the peri-infarct region, increased the number of activated microglia, and decreased the expression of brain-derived neurotrophic factor, neurotrophin-3, and interleukin-10. Crenolanib treatment increased the apoptosis of pericytes and decreased the pericyte/vascular coverage, but had no effects on apoptosis of astrocytes. We conclude that the PDGFR signaling pathway plays a vital role in the SVZ neurogenesis after stroke. It can also affect angiogenesis, lesion-derived chemo-attractants, and the local microenvironment, which are all important to stroke-induced neurogenesis.

Topical application of the hematostatic agent Surgiflo® could attenuate brain injury in experimental TBI mice

OBJECT

The pathologies resulting from traumatic brain injury (TBI) have been thoroughly studied, but rarely have the effects of bleeding and coagulation in the early stage of TBI been considered. In this study, we investigated the effects of topical Surgiflo^® application on brain injury in experimental TBI mice using S100β, MAP-2 and mNSS scores.

METHODS

TBI was induced by modified weight drop injury in male C57BL/6 mice. The mice were then randomly divided into (i) the sham group, (ii) TBI mice applied with saline (vehicle), and (iii) TBI mice applied with Surgiflo^® in the same volume. Modified neurological severity scores (mNSS) were measured on days 0 (before surgery), 1, 3, 7, and 28 to evaluate neurologic functional deficits. At day 28, the mice were sacrificed, and the forebrains were sliced. The effects of Surgiflo^® on microtubule-associated protein 2 and serum S100β protein were examined by immunohistochemistry and electro-chemiluminescence immunoassay.

RESULTS

Serum S100β protein levels were significantly elevated at different time points (24 h, 3 days, 7 days) in the TBI groups (p  <  0.01) compared to normal control groups. Surgiflo^® induced a lower concentration of serum S100β protein levels at day 3 (p < 0.05) and day 7 (p < 0.05) compared to the TBI group applied with saline. H&E staining showed that Surgiflo^® treatment led to a 45% decrease in cortical brain lesion volume and in subcortical white matter 28 days after TBI. Compared with the saline-treated group, the number of MAP2-positive cells was significantly increased in the perilesional area of the Surgiflo^®-treated group. The Surgiflo^®-treated group exhibited lower mNSS scores on days 7 and 28 than did the saline-treated group.

DISCUSSION

Surgiflo^® treatment produced a significant decrease in serum S100β protein levels in TBI mouse models, which may lead to an improvement in the recovery of TBI models.