The voluminous axon as an organizing principle for traumatic brain injury therapeutics: novel molecular, metabolic, and circuit strategies No abstract available

Wallerian degeneration as a therapeutic target in traumatic brain injury Purpose of review Diffuse or traumatic axonal injury is one of the principal pathologies encountered in traumatic brain injury (TBI) and the resulting axonal loss, disconnection, and brain atrophy contribute significantly to clinical morbidity and disability. The seminal discovery of the slow Wallerian degeneration mice (Wlds) in which transected axons do not degenerate but survive and function independently for weeks has transformed concepts on axonal biology and raised hopes that axonopathies may be amenable to specific therapeutic interventions. Here we review mechanisms of axonal degeneration and also describe how these mechanisms may inform biological therapies of traumatic axonopathy in the context of TBI. Recent findings In the last decade, SARM1 [sterile a and Toll/interleukin-1 receptor (TIR) motif containing 1] and the DLK (dual leucine zipper bearing kinase) and LZK (leucine zipper kinase) MAPK (mitogen-activated protein kinases) cascade have been established as the key drivers of Wallerian degeneration, a complex program of axonal self-destruction which is activated by a wide range of injurious insults, including insults that may otherwise leave axons structurally robust and potentially salvageable. Detailed studies on animal models and postmortem human brains indicate that this type of partial disruption is the main initial pathology in traumatic axonopathy. At the same time, the molecular dissection of Wallerian degeneration has revealed that the decision that commits axons to degeneration is temporally separated from the time of injury, a window that allows potentially effective pharmacological interventions. Summary Molecular signals initiating and triggering Wallerian degeneration appear to be playing an important role in traumatic axonopathy and recent advances in understanding their nature and significance is opening up new therapeutic opportunities for TBI.

Transglutaminases, neuronal cell death and neural repair: implications for traumatic brain injury and therapeutics Purpose of review Traumatic brain injury (TBI) is one of the leading causes of death in the developed world. Despite advances at the bedside, pharmacological interventions have yet to be successful likely because of the need for a better understanding of disease mechanisms as potential targets for intervention. Recent evidence implicates a family of enzymes, namely transglutaminases, in the pathological mechanisms of TBI. Recent findings Transglutaminases are multifunctional, calcium-dependent enzymes that are significantly upregulated in TBI. They are known for their transamidase activity that consists of the covalent crosslinking of glutamines and lysines. Recent data support their ability to aminylate proteins with primary amines such as polyamines or monoamines like serotonin and histamine and to regulate gene transcription. Summary In this review, we will discuss data that support a role for transglutaminases, in particular transglutaminase 2, in mitochondrial damage, excitotoxicity and inflammation and their relationship to the pathobiology of TBI. We will review past evidence and outline the need for new experiments that could clarify the role of these enzymes in cell injury and death associated with traumatic brain injury.

Autonomic dysfunction following mild traumatic brain injury Purpose of review Between 1.6 and 3.6 million concussions, or mild traumatic brain injuries (mTBI), occur each year, nearly half of which go unreported and untreated. Despite the high incidence, practitioners currently lack both objective gold-standard diagnostic tools and evidence-based treatments to enable optimal care of concussed individuals. Recent findings This article aims to review recent research on the topic, emphasizing the role of the autonomic nervous system (ANS) in concussion. Current data suggests that ANS dysfunction is often evident following mTBI and accounts for many of the symptoms commonly seen in concussed patients. This link suggests several objective biomarkers that could be used to diagnose and monitor recovery following mTBI. Contrary to conventional wisdom, symptoms and biomarkers of ANS function improve when individuals are exposed to a program of graded exercise as treatment within the first week following concussion. Summary ANS dysfunction contributes to concussion symptomatology, an effect likely mediated through diffuse axonal injury, including brainstem structures and pathways mediating normal cerebrovascular autoregulation. Exercise, which enhances ANS function, is a well tolerated and effective method of treatment for both acute concussion patients and those suffering from postconcussion syndrome (PCS). The relationship between the ANS, exercise, and concussion creates an opportunity for the identification of objective biomarkers that can facilitate the diagnosis and treatment of mTBI.

Exercise factors as potential mediators of cognitive rehabilitation following traumatic brain injury Purpose of review To summarize what is known about how exercise mediates cognitive rehabilitation post traumatic brain injury (TBI). Recent findings TBI is a devastating condition that leads to cognitive, motor and social deficits with significant social and economic burdens. Physical exercise has been shown to mediate cognitive rehabilitation post-TBI. The therapeutic effects of exercise are related in part to its ability to increase brain-derived neurotrophic factor (Bdnf) expression in the hippocampus. However, we have only recently begun to understand how exercise induces Bdnf expression in the brain through the identification of peripheral exercise factors. In this review, we will discuss the literature describing the various known exercise factors and we will assess their potential role in TBI. Summary The reviewed literature makes a strong case that exercise has important protective roles post-TBI. It also highlights the relevance and role of peripheral exercise factors, such as lactate and beta-hydroxybutyrate in mediating beneficial effects of exercise on cognition. Studying exercise factors in the context of injury will likely contribute to better therapeutic strategies for TBI.

Sugar as a therapeutic target for the cognitive restoration following traumatic brain injury Purpose of review This review aims to discuss examples of changes in glucose (sugar) metabolism after traumatic brain injury (TBI). It will attempt to provide an understanding of what changes in glucose metabolism mean for the injured brain. It will further identify potential therapeutic target(s) emanating from our growing understanding of glucose pathways and their roles in TBI. Recent findings Although a significant fraction of glucose is utilized for the energy production in the brain, a small fraction is utilized in other, often ignored pathways. Recent studies have unraveled unexpected biological effects of glucose through these pathways, including redox regulation, genetic and epigenetic regulation, glycation of proteins, nucleotide synthesis and amino acid synthesis. Summary A number of regulatory players in minor glucose metabolic pathways, such as folate and chondroitin sulfate proteoglycans, have recently been identified as potential targets to restore cognitive functions. Targeting of these players should be combined with the supplementation of alternative energy substrates to achieve the maximal cognitive restoration after TBI. This multimodal therapeutic strategy deserves testing in various models of TBI. Video abstract: Supplemental digital video content 1: Video that demonstrates an effective therapeutic strategy for the cognitive restoration after TBI. http://links.lww.com/CONR/A46.

Novel synaptic plasticity enhancer drug to augment functional recovery with rehabilitation Purpose of review Stroke is a devastating illness which severely attenuates quality of life because of paralysis. Despite recent advances in therapies during acute phase such as thrombolytic therapy, clinical option to intervene the process of rehabilitation is limited. No pharmacological intervention that could enhance the effect of rehabilitation has not been established. Recent articles, which are summarized in the review article, reported novel small compound which accelerates training-dependent motor function recovery after brain damage. Recent findings A novel small compound, edonerpic maleate, binds to collapsin response mediator protein 2 (CRMP2) and enhance synaptic plasticity leading to the acceleration of rehabilitative training-dependent functional recovery after brain damage in rodent and nonhuman primate. The clinical trial to test this effect in human is now ongoing. Future preclinical and clinical studies will delineate the potentials of this compound. Summary A novel CRMP2-binding small compound, edonerpic maleate, accelerates motor function recovery after brain damage in rodent and nonhuman primate.

Enhancing rehabilitation and functional recovery after brain and spinal cord trauma with electrical neuromodulation Purpose of review This review discusses recent advances in the rehabilitation of motor deficits after traumatic brain injury (TBI) and spinal cord injury (SCI) using neuromodulatory techniques. Recent findings Neurorehabilitation is currently the only treatment option for long-term improvement of motor functions that can be offered to patients with TBI or SCI. Major advances have been made in recent years in both preclinical and clinical rehabilitation. Activity-dependent plasticity of neuronal connections and circuits is considered key for successful recovery of motor functions, and great therapeutic potential is attributed to the combination of high-intensity training with electrical neuromodulation. First clinical case reports have demonstrated that repetitive training enabled or enhanced by electrical spinal cord stimulation can yield substantial improvements in motor function. Described achievements include regaining of overground walking capacity, independent standing and stepping, and improved pinch strength that recovered even years after injury. Summary Promising treatment options have emerged from research in recent years using neurostimulation to enable or enhance intense training. However, characterizing long-term benefits and side-effects in clinical trials and identifying patient subsets who can benefit are crucial. Regaining lost motor function remains challenging.

Alternative routes for recovery of hand functions after corticospinal tract injury in primates and rodents Purpose of review Recent studies on various corticospinal tract (CST) lesions have shown the plastic changes at a variety of motor systems after the lesion. This review provides the alternative routes associated with the motor functional recovery after the CST lesions at various levels in nonhuman primates and rodents. Recent findings In the case of the motor cortical lesions, the perilesional area compensates for the lesion. In contrast, sprouting of the corticoreticular tracts was observed after the lesions involving sensorimotor cortical areas. After the internal capsule lesion, sprouting in the cortico-rubral pathway contributes to the recovery. In case of the pyramidal lesion, rubrospinal and reticulospinal tracts play a role of the functional recovery. After the dorsolateral funiculus (DLF) lesion at C4/C5, the indirect pathway via propriospinal tract contributes to the recovery. In case of the hemisection at lower cervical cord, the CST fibers sprouted from the bilateral motor cortex and descended to the contralesional DLF and crossed below the lesion area. Summary The central pathways can change their structure and activity dynamically depending on the lesion sites and size. Revealing the difference of the alternative pathways should be crucial to understand the whole recovery mechanism and develop the further neurorehabilitative treatment.