Adrenalectomy further suppresses the NT-3 mRNA response to traumatic brain injury but this effect is not reversed with corticosterone

Potential Neuroprotective Role of Neurotrophin in Traumatic Brain Injury

Traumatic brain injury (TBI) is a major global health issue that affects millions of people every year. It is caused by any form of external force, resulting in temporary or permanent impairments in the brain. The pathophysiological process following TBI usually involves excitotoxicity, mitochondrial dysfunction, oxidative stress, inflammation, ischemia, and apoptotic cell death. It is challenging to find treatment for TBI due to its heterogeneous nature, and no therapeutic interventions have been approved thus far. Neurotrophins may represent an alternative approach for TBI treatment because they influence various functional activities in the brain. The present review highlights recent studies on neurotrophins shown to possess neuroprotective roles in TBI. Neurotrophins, specifically brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) have demonstrated reduced neuronal death, alleviated neuroinflammatory responses and improved neurological functions following TBI via their immunomodulatory, anti-inflammatory and antioxidant properties. Further studies are required to ensure the efficacy and safety of neurotrophins to be used as TBI treatment in clinical settings.

Brain Trauma, Glucocorticoids and Neuroinflammation: Dangerous Liaisons for the Hippocampus

Glucocorticoid-dependent mechanisms of inflammation-mediated distant hippocampal damage are discussed with a focus on the consequences of traumatic brain injury. The effects of glucocorticoids on specific neuronal populations in the hippocampus depend on their concentration, duration of exposure and cell type. Previous stress and elevated level of glucocorticoids prior to pro-inflammatory impact, as well as long-term though moderate elevation of glucocorticoids, may inflate pro-inflammatory effects. Glucocorticoid-mediated long-lasting neuronal circuit changes in the hippocampus after brain trauma are involved in late post-traumatic pathology development, such as epilepsy, depression and cognitive impairment. Complex and diverse actions of the hypothalamic–pituitary–adrenal axis on neuroinflammation may be essential for late post-traumatic pathology. These mechanisms are applicable to remote hippocampal damage occurring after other types of focal brain damage (stroke, epilepsy) or central nervous system diseases without obvious focal injury. Thus, the liaisons of excessive glucocorticoids/dysfunctional hypothalamic–pituitary–adrenal axis with neuroinflammation, dangerous to the hippocampus, may be crucial to distant hippocampal damage in many brain diseases. Taking into account that the hippocampus controls both the cognitive functions and the emotional state, further research on potential links between glucocorticoid signaling and inflammatory processes in the brain and respective mechanisms is vital.

The Roles of Neurotrophins in Traumatic Brain Injury

Neurotrophins are a collection of structurally and functionally related proteins. They play important roles in many aspects of neural development, survival, and plasticity. Traumatic brain injury (TBI) leads to different levels of central nervous tissue destruction and cellular repair through various compensatory mechanisms promoted by the injured brain. Many studies have shown that neurotrophins are key modulators of neuroinflammation, apoptosis, blood–brain barrier permeability, memory capacity, and neurite regeneration. The expression of neurotrophins following TBI is affected by the severity of injury, genetic polymorphism, and different post-traumatic time points. Emerging research is focused on the potential therapeutic applications of neurotrophins in managing TBI. We conducted a comprehensive review by organizing the studies that demonstrate the role of neurotrophins in the management of TBI.

Intranasal delivery of exosomes from human adipose derived stem cells at forty-eight hours post injury reduces motor and cognitive impairments following traumatic brain injury

The neuroprotective role of human adipose-derived stems cells (hASCs) has raised great interest in regenerative medicine due to their ability to modulate their surrounding environment. Our group has demonstrated that exosomes derived from hASC (hASCexo) are a cell-free regenerative approach to long term recovery following traumatic brain injury (TBI). Previously, we demonstrated the efficacy of exosome treatment with intravenous delivery at 3 h post TBI in rats. Here, we show efficacy of exosomes through intranasal delivery at 48 h post TBI in mice lengthening the therapeutic window of treatment and therefore increasing possible translation to clinical studies. Our findings demonstrate significant recovery of motor impairment assessed by an elevated body swing test in mice treated with exosomes containing MALAT1 compared to both TBI mice without exosomes and exosomes depleted of MALAT1. Significant cognitive improvement was seen in the reversal trial of 8 arm radial arm water maze in mice treated with exosomes containing MALAT1. Furthermore, cortical damage was significantly reduced in mice treated with exosomes containing MALAT1 as well as decreased MHCII+ staining of microglial cells. Mice without exosomes or treated with exosomes depleted of MALAT1 did not show similar recovery. Results demonstrate both inflammation related genes and NRTK3 (TrkC) are target genes modulated by hASC exosomes and further that MALAT1 in hASC exosomes regulates expression of full length TrkC thereby activating the MAPK pathway and promoting recovery. Exosomes are a promising therapeutic approach following TBI with a therapeutic window of at least 48 h and contain long noncoding RNA's, specifically MALAT1 that play a vital role in the mechanism of action.

Temporal control of glucocorticoid neurodynamics and its relevance for brain homeostasis, neuropathology and glucocorticoid-based therapeutics

Glucocorticoids mediate plethora of actions throughout the human body. Within the brain, they modulate aspects of immune system and neuroinflammatory processes, interfere with cellular metabolism and viability, interact with systems of neurotransmission and regulate neural rhythms. The influence of glucocorticoids on memory and emotional behaviour is well known and there is increasing evidence for their involvement in many neuropsychiatric pathologies. These effects, which at times can be in opposing directions, depend not only on the concentration of glucocorticoids but also the duration of their presence, the temporal relationship between their fluctuations, the co-influence of other stimuli, and the overall state of brain activity. Moreover, they are region- and cell type-specific. The molecular basis of such diversity of effects lies on the orchestration of the spatiotemporal interplay between glucocorticoid- and mineralocorticoid receptors, and is achieved through complex dynamics, mainly mediated via the circadian and ultradian pattern of glucocorticoid secretion. More sophisticated methodologies are therefore required to better approach the study of these hormones and improve the effectiveness of glucocorticoid-based therapeutics.

Small molecule activators of the Trk receptors for neuroprotection

The neurotrophin signaling network is critical to the development and survival of many neuronal populations. Especially sensitive to imbalances in the neurotrophin system, cholinergic neurons in the basal forebrain are progressively lost in Alzheimer's disease. Therapeutic use of neurotrophins to prevent this loss is hampered, however, by a number of pharmacological challenges. These include a lack of transport across the blood-brain barrier, rapid degradation in the circulation, and difficulty in production. In this review we discuss the evidence supporting the neurotrophin system's role in preventing neurodegeneration and survey some of the pharmacological strategies being pursued to develop effective therapeutics targeting neurotrophin function.

Human scalp skin and hair follicles express neurotrophin-3 and its high-affinity receptor tyrosine kinase C, and show hair cycle-dependent alterations in expression

BACKGROUND

Neurotrophin (NT)-3 and its high-affinity receptor tyrosine kinase C (Trk C) are essential for nervous system development. These members of the NT family are also involved in murine hair morphogenesis and cycling. However, their role in human hair follicle (HF) biology remains to be elucidated.

OBJECTIVES

To explore the role of NTs in human skin and HF biology.

METHODS

The immunoreactivity (IR) of NT-3 and Trk C was studied in human scalp skin and HFs by immunofluorescent and light microscopic immunohistology. Skin biopsies were obtained from normal human scalp containing mainly anagen VI HFs from women (age 53-57 years) undergoing elective plastic surgery.

RESULTS

Both NT-3 and Trk C showed prominent, yet distinct, IR patterns in human scalp anagen HFs (anagen VI), whereas they were weakly expressed in catagen and increased again in telogen HFs. Within HF compartments, NT-3 IR was prominent in the outer root sheath, inner root sheath, dermal papilla and connective tissue sheath. Trk C IR was prominent in all HF epithelial and mesenchymal compartments. Outside the HF, both NT-3 and Trk C showed prominent IR in the epidermis, sebaceous glands and sweat glands.

CONCLUSIONS

These observations provide the first indication that NT-3 and Trk C are expressed in human scalp skin and HFs, and suggest that Trk C-mediated signalling is involved not only in murine but also in human HF biology. They may be useful in determining therapeutic strategies for the treatment of hair cycle and skin-related disorders.

Dexamethasone enhances NT-3 expression in rat hippocampus after traumatic brain injury

The cellular events in traumatic brain injury (TBI) are complicated, and the factors mediating neurotrophins to protect and repair the injured brain cells are only beginning to be identified. This study examined the effect of dexamethasone (DEX) on neurotrophin-3 (NT-3) expression following TBI. Levels of NT-3 mRNA and protein in rat hippocampus were measured using in situ hybridization and immunohistochemistry, respectively. After TBI, the NT-3 mRNA expression was down-regulated during the first 24 h. DEX reversed the post-traumatic reduction of NT-3 mRNA expression at 2, 4, 6, and 12 h in the hippocampus, and also decreased the cell death in hippocampal hilum and supraventricular cerebral cortex after 7 days. The NT-3 protein levels generally corresponded to the mRNA levels in the hippocampal region. DEX enhanced the NT-3 expression after TBI, indicating that post-traumatic neuroprotection in the hippocampus is at least partially mediated by NT-3 and thus can be modulated by DEX treatment.