Cholesterol Biosynthesis Supports Myelin Gene Expression and Axon Ensheathment through Modulation of P13K/Akt/mTor Signaling.

UNLABELLED: Myelin, which ensheaths and insulates axons, is a specialized membrane highly enriched with cholesterol. During myelin formation, cholesterol influences membrane fluidity, associates with myelin proteins such as myelin proteolipid protein, and assembles lipid-rich microdomains within membranes. Surprisingly, cholesterol also is required by oligodendrocytes, glial cells that make myelin, to express myelin genes and wrap axons. How cholesterol mediates these distinct features of oligodendrocyte development is not known. One possibility is that cholesterol promotes myelination by facilitating signal transduction within the cell, because lipid-rich microdomains function as assembly points for signaling molecules. Signaling cascades that localize to cholesterol-rich regions of the plasma membrane include the PI3K/Akt pathway, which acts upstream of mechanistic target of rapamycin (mTOR), a major driver of myelination. Through manipulation of cholesterol levels and PI3K/Akt/mTOR signaling in zebrafish, we discovered that mTOR kinase activity in oligodendrocytes requires cholesterol. Drawing on a combination of pharmacological and rescue experiments, we provide evidence that mTOR kinase activity is required for cholesterol-mediated myelin gene expression. On the other hand, cholesterol-dependent axon ensheathment is mediated by Akt signaling, independent of mTOR kinase activity. Our data reveal that cholesterol-dependent myelin gene expression and axon ensheathment are facilitated by distinct signaling cascades downstream of Akt. Because mTOR promotes cholesterol synthesis, our data raise the possibility that cholesterol synthesis and mTOR signaling engage in positive feedback to promote the formation of myelin membrane. SIGNIFICANCE STATEMENT: The speed of electrical impulse movement through axons is increased by myelin, a specialized, cholesterol-rich glial cell membrane that tightly wraps axons. During development, myelin membrane grows dramatically, suggesting a significant demand on mechanisms that produce and assemble myelin components, while it spirally wraps axons. Our studies indicate that cholesterol is necessary for both myelin growth and axon wrapping. Specifically, we found that cholesterol facilitates signaling mediated by the PI3K/Akt/mTOR pathway, a powerful driver of myelination. Because mTOR promotes the expression of genes necessary for cholesterol synthesis, cholesterol formation and PI3K/Akt/mTOR signaling might function as a feedforward mechanism to produce the large amounts of myelin membrane necessary for axon ensheathment.

Mutation of 3-hydroxy-3-methylglutaryl CoA synthase I reveals requirements for isoprenoid and cholesterol synthesis in oligodendrocyte migration arrest, axon wrapping, and myelin gene expression.

Myelin membrane, which ensheaths axons, has an unusually high amount of cholesterol. Cholesterol influences membrane fluidity and assembles lipid-rich microdomains within membranes, and some studies have shown that cholesterol is important for myelination. How cholesterol influences the development and differentiation of oligodendrocytes, glial cells that make myelin, is not known nor is clear whether isoprenoids, which also are products of the cholesterol biosynthetic pathway, contribute to myelination. Through a forward genetic screen in zebrafish we discovered that mutation of hmgcs1, which encodes an enzyme necessary for isoprenoid and cholesterol synthesis, causes oligodendrocyte progenitor cells (OPCs) to migrate past their target axons and to fail to express myelin genes. Drawing on a combination of pharmacological inhibitor and rescue experiments, we provide evidence that isoprenoids and protein prenylation, but not cholesterol, are required in OPCs to halt their migration at target axons. On the other hand, cholesterol, but not isoprenoids, is necessary both for axon ensheathment and myelin gene expression. Our data reveal that different products of the cholesterol biosynthetic pathway have distinct roles in oligodendrocyte development and that they together help to coordinate directed migration, axon wrapping, and gene expression.

Lost in transition: Perspectives from women and their families living in rural Australia on relocation for specialist maternal and neonatal care.

PROBLEM: Families living in rural communities need to relocate, be transferred or travel long distances to access specialist maternal and neonatal care, leading to isolation from their support networks. BACKGROUND: High-risk maternal and neonatal complexities in rural maternity units results in more transfers and retrievals to metropolitan services. There is limited understanding of the physical and psychological impacts for women and their families when they are transferred or displaced from their rural communities during pregnancy. AIM: To investigate the lived experience of relocation for specialist pregnancy, birthing, postnatal and neonatal care on women and families. METHODS: Women (n=5) and partners (n=4) from rural South Australia, participated in semi-structured interviews on their experiences of transfer from local maternity providers. Couples interviewed together, interactions were recorded, transcribed verbatim and thematically analysed to identify overarching and sub-themes. FINDINGS: The overarching theme was 'mismatched expectations', with three identified sub-themes: 'communication', 'compassion' and 'safety'. Discrepancies between expectations and realities during relocation left participants feeling isolated, alone and needing to self-advocate during this vulnerable period. Despite receiving specialist care, women and partners encountered unique hardships when separated from their rural community. Their social needs were poorly understood and seldom addressed in specialist units, resulting in poor experiences. DISCUSSION: Consideration regarding the impact of attending specialist maternity services for women and partners from rural areas is required. The 'one size fits all' approach for maternity care is unrealistic and research is needed to improve the experiences for those uprooted from rural communities for higher levels of care.

Protein Prenylation and Hsp40 in Thermotolerance of Plasmodium falciparum Malaria Parasites.

During its complex life cycle, the malaria parasite survives dramatic environmental stresses, including large temperature shifts. Protein prenylation is required during asexual replication of Plasmodium falciparum, and the canonical heat shock protein 40 protein (HSP40; PF3D7_1437900) is posttranslationally modified with a 15-carbon farnesyl isoprenyl group. In other organisms, farnesylation of Hsp40 orthologs controls their localization and function in resisting environmental stress. In this work, we find that plastidial isopentenyl pyrophosphate (IPP) synthesis and protein farnesylation are required for malaria parasite survival after cold and heat shock. Furthermore, loss of HSP40 farnesylation alters its membrane attachment and interaction with proteins in essential pathways in the parasite. Together, this work reveals that farnesylation is essential for parasite survival during temperature stress. Farnesylation of HSP40 may promote thermotolerance by guiding distinct chaperone-client protein interactions.

Crosstalk between nitric oxide and zinc pathways to neuronal cell death involving mitochondrial dysfunction and p38-activated K+ channels.

Nitric oxide (NO) and zinc (Zn2+) are implicated in the pathogenesis of cerebral ischemia and neurodegenerative diseases. However, their relationship and the molecular mechanism of their neurotoxic effects remain unclear. Here we show that addition of exogenous NO or NMDA (to increase endogenous NO) leads to peroxynitrite (ONOO-) formation and consequent Zn2+ release from intracellular stores in cerebrocortical neurons. Free Zn2+ in turn induces respiratory block, mitochondrial permeability transition (mPT), cytochrome c release, generation of reactive oxygen species (ROS), and p38 MAP kinase activation. This pathway leads to caspase-independent K+ efflux with cell volume loss and apoptotic-like death. Moreover, Zn2+ chelators, ROS scavengers, Bcl-xL, dominant-interfering p38, or K+ channel blockers all attenuate NO-induced K+ efflux, cell volume loss, and neuronal apoptosis. Thus, these data establish a new form of crosstalk between NO and Zn2+ apoptotic signal transduction pathways that may contribute to neurodegeneration.

Epigenetic modulation of seizure-induced neurogenesis and cognitive decline.

The conceptual understanding of hippocampal function has been challenged recently by the finding that new granule cells are born throughout life in the mammalian dentate gyrus (DG). The number of newborn neurons is dynamically regulated by a variety of factors. Kainic acid-induced seizures, a rodent model of human temporal lobe epilepsy, strongly induce the proliferation of DG neurogenic progenitor cells and are also associated with long-term cognitive impairment. We show here that the antiepileptic drug valproic acid (VPA) potently blocked seizure-induced neurogenesis, an effect that appeared to be mainly mediated by inhibiting histone deacetylases (HDAC) and normalizing HDAC-dependent gene expression within the epileptic dentate area. Strikingly, the inhibition of aberrant neurogenesis protected the animals from seizure-induced cognitive impairment in a hippocampus-dependent learning task. We propose that seizure-generated granule cells have the potential to interfere with hippocampal function and contribute to cognitive impairment caused by epileptic activity within the hippocampal circuitry. Furthermore, our data indicate that the effectiveness of VPA as an antiepileptic drug may be partially explained by the HDAC-dependent inhibition of aberrant neurogenesis induced by seizure activity within the adult hippocampus.

Prevalence of overweight and obesity in collegiate American football players, by position.

OBJECTIVE: The authors' purpose in this study was to determine overweight and obesity prevalence in a collegiate football team. PARTICIPANTS: Eighty-five National Collegiate Athletic Association (NCAA) Division I football players volunteered to participate. METHODS: The authors measured height, weight, and waist circumference (WC), and estimated body fat percentage (% BF) from bioelectrical impedance. RESULTS: Body mass index (BMI), WC, and % BF were all positively correlated (p < .01), but BMI overestimated the prevalence of overweight and obesity in 50.6% of the cases. Fourteen players (16%) qualified as obese under all 3 methods. Offensive linemen had significantly higher % BF (p < .01) than most other positions, and on average this group exceeded the at-risk criteria for BMI (> 30 kg/m2), WC (> 102 cm), and % BF (> 25%). CONCLUSIONS: BMI alone is not a valid indicator of overweight and obesity in a strength-trained athletic population. However, some collegiate football players, especially linemen, meet multiple criteria for obesity.

Tackling resistance: emerging antimalarials and new parasite targets in the era of elimination.

Malaria remains a significant contributor to global human mortality, and roughly half the world's population is at risk for infection with Plasmodium spp. parasites. Aggressive control measures have reduced the global prevalence of malaria significantly over the past decade. However, resistance to available antimalarials continues to spread, including resistance to the widely used artemisinin-based combination therapies. Novel antimalarial compounds and therapeutic targets are greatly needed. This review will briefly discuss several promising current antimalarial development projects, including artefenomel, ferroquine, cipargamin, SJ733, KAF156, MMV048, and tafenoquine. In addition, we describe recent large-scale genetic and resistance screens that have been instrumental in target discovery. Finally, we highlight new antimalarial targets, which include essential transporters and proteases. These emerging antimalarial compounds and therapeutic targets have the potential to overcome multi-drug resistance in ongoing efforts toward malaria elimination.

Evaluation of pediatric ATD biofidelity as compared to child volunteers in low-speed far-side oblique and lateral impacts.

OBJECTIVE: Motor vehicle crashes are a leading cause of injury and mortality for children. Mitigation of these injuries requires biofidelic anthropomorphic test devices (ATDs) to design and evaluate automotive safety systems. Effective countermeasures exist for frontal and near-side impacts but are limited for far-side impacts. Consequently, far-side impacts represent increased injury and mortality rates compared to frontal impacts. Thus, the objective of this study was to evaluate the biofidelity of the Hybrid III and Q-series pediatric ATDs in low-speed far-side impacts, with and without shoulder belt pretightening. METHODS: Low-speed (2 g) far-side oblique (60°) and lateral (90°) sled tests were conducted using the Hybrid III and Q-series 6- and 10-year-old ATDs. ATDs were restrained by a lap and shoulder belt equipped with a precrash belt pretightener. Photoreflective targets were attached to the head, spine, shoulders, and sternum. ATDs were exposed to 8 low-speed sled tests: 2 oblique nontightened, 2 oblique pretightened, 2 lateral nontightened, 2 lateral pretightened. ATDs were compared with previously collected 9- to 11-year-old (n=10) volunteer data and newly collected 6- to 8-year-old volunteer data (n=7) tested with similar methods. Kinematic data were collected from a 3D target tracking system. Metrics of comparison included excursion, seat belt and seat pan reaction loads, belt-to-torso angle, and shoulder belt slip-out. RESULTS: The ATDs exhibited increased lateral excursion of the head top, C4, and T1 as well as increased downward excursion of the head top compared to the volunteers. Volunteers exhibited greater forward excursion than the ATDs in oblique nontightened impacts. These kinematics correspond to increased shoulder belt slip-out for the ATDs in oblique tests (ATDs=90%; volunteers=36%). Contrarily, similar shoulder belt slip-out was observed between ATDs and volunteers in lateral impacts (ATDs=80%; volunteers=78%). In pretightened impacts, the ATDs exhibited reduced lateral excursion and torso roll-out angle compared to the volunteers. CONCLUSIONS: In general, the ATDs overestimated lateral excursion in both impact directions, while underestimating forward excursion of the head and neck in oblique impacts compared to the pediatric volunteers. This was primarily due to pendulum-like lateral bending of the entire ATD torso compared to translation of the thorax relative to the abdomen prior to the lateral bending of the upper torso in the volunteers, likely due to the multisegmented spinal column in the volunteers. Additionally, the effect of belt pretightening on occupant kinematics was greater for the ATDs than the volunteers.

Functional magnetic resonance imaging as experienced by stroke survivors.

Functional magnetic resonance imaging (fMRI), a noninvasive technique that measures brain activation, has been increasingly used in the past decade, particularly among older adults. Use of fMRI in research with stroke survivors in recent years has substantially contributed to researchers' understanding of the pathophysiology of stroke sequelae. However, despite the increasing popularity and use of fMRI, little is known about the patient experience of fMRI under research circumstances. The current research brief reports the findings of a pilot study undertaken to understand stroke survivors' experiences with fMRI under research circumstances. Nine ischemic stroke patients underwent two MRI sessions, each of which lasted 1.5 hours and included several fMRI tasks. Patients were asked about their experiences and to share any advice. All participants reported that they did not feel claustrophobic; in addition, the importance of educating participants about fMRI was a universal theme that emerged. Knowledge of participant experiences may help with enrollment strategies for fMRI studies and improve research outcomes related to the fMRI experience.

Electromyography responses of pediatric and young adult volunteers in low-speed frontal impacts.

No electromyography (EMG) responses data exist of children exposed to dynamic impacts similar to automotive crashes, thereby, limiting active musculature representation in computational occupant biomechanics models. This study measured the surface EMG responses of three neck, one torso and one lower extremity muscles during low-speed frontal impact sled tests (average maximum acceleration: 3.8g; rise time: 58.2ms) performed on seated, restrained pediatric (n=11, 8-14years) and young adult (n=9, 18-30years) male subjects. The timing and magnitude of the EMG responses were compared between the two age groups. Two normalization techniques were separately implemented and evaluated: maximum voluntary EMG (MVE) and neck cross-sectional area (CSA). The MVE-normalized EMG data indicated a positive correlation with age in the rectus femoris for EMG latency; there was no correlation with age for peak EMG amplitudes for the evaluated muscles. The cervical paraspinous exhibited shorter latencies compared with the other muscles (2-143ms). Overall, the erector spinae and rectus femoris peak amplitudes were relatively small. Neck CSA-normalized peak EMG amplitudes negatively correlated with age for the cervical paraspinous and sternocleidomastoid. These data can be useful to incorporate active musculature in computational models, though it may not need to be age-specific in low-speed loading environments.

Evaluation of the hybrid III and Q-series pediatric ATD upper neck loads as compared to pediatric volunteers in low-speed frontal crashes.

Debate exists in the automotive community regarding the validity of the pediatric ATD neck response and corresponding neck loads. Previous research has shown that the pediatric ATDs exhibit hyper-flexion and chin-to-chest contact resulting in overestimations of neck loads and neck injury criteria. Our previous work comparing the kinematics of the Hybrid III and Q-series 6 and 10-year-old ATDs to pediatric volunteers in low-speed frontal sled tests revealed decreased ATD cervical and thoracic spine excursions. These kinematic differences may contribute to the overestimation of upper neck loads by the ATD. The current study compared upper neck loads of the Hybrid III and Q-series 6 and 10-year-old ATDs against size-matched male pediatric volunteers in low-speed frontal sled tests. A 3-D near-infrared target tracking system quantified the position of markers on the ATD and pediatric volunteers (head top, nasion, bilateral external auditory meatus). Shear force (F x ), axial force (F z ), bending moment (M y ), and head angular acceleration ([Formula: see text]) were calculated about the upper neck using standard equations of motion. In general, the ATDs underestimated axial force and overestimated bending moment compared to the human volunteers. The Hybrid III 6, Q6, and Q10 exhibited reduced head angular acceleration and modest increases in upper neck shear compared to the pediatric volunteers. The reduction in axial force and bending moment has important implications for neck injury predictions as both are used when calculating N ij . These analyses provide insight into the biofidelity of the pediatric ATD upper neck loads in low-speed crash environments.

The effect of pretensioning and age on torso rollout in restrained human volunteers in far-side lateral and oblique loading.

Far-side side impact loading of a seat belt restrained occupant has been shown to lead to torso slip out of the shoulder belt. A pretensioned seat belt may provide an effective countermeasure to torso rollout; however the effectiveness may vary with age due to increased flexibility of the pediatric spine compared to adults. To explore this effect, low-speed lateral (90°) and oblique (60°) sled tests were conducted using male human volunteers (20 subjects: 9-14 years old, 10 subjects: 18-30 years old), in which the crash pulse safety envelope was defined from an amusement park bumper-car impact. Each subject was restrained by a lap and shoulder belt system equipped with an electromechanical motorized seat belt retractor (EMSR) and photo- reflective targets were attached to a tight-fitting headpiece or adhered to the skin overlying key skeletal landmarks. Each subject was randomly assigned to either the 60° or 90° direction and was exposed to 4 test conditions - arms up (with hands on their knees) with EMSR on, arms down (with hands low on the hips) with EMSR on, arms up with EMSR off, arms down with EMSR off. The effect of age and pretensioning on the following outcomes was quantified: 1) lateral and forward displacement of the torso, 2) torso rollout angle projected onto three orthogonal planes, and 3) resultant belt-sternal distance. The effect of pretensioning on torso containment within the shoulder belt was strong in both impact directions across all metrics evaluated. EMSR activation significantly reduced lateral displacement of the suprasternal notch (~100 mm, p<0.0001), coronal projection of the torso rollout angle (~15°, p<0.0001), and belt sternal distance when the arms were down (~50 mm, p<0.05). The benefit of pretensioning was achieved by early engagement of the torso by the shoulder belt. An added benefit of pretensioning was the ability to make similar the torso kinematics across a range of anthropometries as assessed within and across age groups. These results can serve as a data set for validating the responses of restrained ATDs and computational human models to low severity far side collisions, in particular the interaction between the torso and the shoulder belt.

Kinematic Comparison of the Hybrid III and Q-Series Pediatric ATDs to Pediatric Volunteers in Low-Speed Frontal Crashes.

Previous research has suggested that the rigid pediatric ATD spine may not adequately represent the relatively mobile, multi-segmented spine of the child and thus may lead to important differences in the head trajectory of the ATD relative to a human. Recently we compared the responses of size-matched child volunteers to the Hybrid III 6-year-old ATD in low-speed frontal sled tests, illustrating differences in head, spinal, and pelvic kinematics as well as seating environment reaction loads. This paper expands this line of work to include comparisons between size-matched restrained child volunteers to the Hybrid III 10-year-old and the Q-series 6 and 10-year-old ATDs tested in the same low speed frontal environment. A 3-D near-infrared video target tracking system quantified the position of markers on the ATDs and volunteers(head top, nasion, external auditory meatus, C4, T1, and pelvis). Angular velocity of the head, seat belt forces, and reaction loads on the seat pan and foot rest were also measured. The Hybrid III 6 and Q6 exhibited significantly greater belt reaction loads compared to the pediatric volunteers, which exhibited greater seat pan shear. Compared to children, the Hybrid III 6 exhibited increased head rotation and similar head top and pelvic excursion, whereas the Q6 exhibited reductions in all three metrics. The Hybrid III 10 and Q10 ATDs exhibited reaction loads similar to the volunteers; however, excursions and head rotation were significantly reduced compared to volunteers. All pediatric ATDs exhibited significant reductions in C4 and T1excursions compared to the volunteers, likely due to the rigidity of the ATD thoracic spine. These analyses provide insight into aspects of ATD biofidelity in low-speed crash environments and illustrate differences in responses of the Hybrid III and Q-series pediatric ATDs.

A fatal case of heparin-induced thrombocytopenia and thrombosis.

Heparin induced thrombocytopenia (HIT) is a significant, potentially life-threatening immune-mediated adverse event that occurs several days after commencement of therapy with unfractionated or low-molecular weight heparin. We present a 51-year-old female treated with unfractionated heparin for acute deep venous thrombosis (DVT) and pulmonary embolism (PE). She developed extension of her thrombosis and was promptly diagnosed with heparin-induced thrombocytopenia and thrombosis (HITT). She did not, however, develop thrombocytopenia until 5 days after the extension of her thrombosis. The possible diagnosis of HITT is important for clinicians to keep in mind for all patients that are receiving any form of heparin, not only those patients who present with thrombocytopenia but also those with otherwise unexplainable thrombosis regardless of the platelet count.

A distinctive layering pattern of mouse dentate granule cells is generated by developmental and adult neurogenesis.

New neurons are continuously added throughout life to the dentate gyrus of the mammalian hippocampus. During embryonic and early postnatal development, the dentate gyrus is formed in an outside-in layering pattern that may extend through adulthood. In this work, we sought to quantify systematically the relative position of dentate granule cells generated at different ages. We used 5'-bromo-2'-deoxyuridine (BrdU) and retroviral methodologies to birth date cells born in the embryonic, early postnatal, and adult hippocampus and assessed their final position in the adult mouse granule cell layer. We also quantified both developmental and adult-born cohorts of neural progenitor cells that contribute to the pool of adult progenitor cells. Our data confirm that the outside-in layering of the dentate gyrus continues through adulthood and that early-born cells constitute most of the adult dentate gyrus. We also found that substantial numbers of the dividing cells in the adult dentate gyrus were derived from early-dividing cells and retained BrdU, suggesting that a subpopulation of hippocampal progenitors divides infrequently from early development onward.

Liver involvement with acute myeloid leukemia.

Liver involvement with acute myeloid leukemia (AML) is rarely reported. The majority of published cases suggest a cholestatic picture and obstructive jaundice at presentation. On the contrary, our patient presented with transaminitis without cholestasis. Elevated liver function tests persisted in our patient despite cholecystectomy; however, they normalized with chemotherapy administration, suggesting that AML was the causative effect of the hepatitis-like picture. Our review of the literature revealed that most reported cases of AML with liver involvement had short-lived remissions and an overall ominous prognosis. In our opinion, patients who have liver involvement with AML should be offered alternative investigational therapies with a low hepatic toxicity profile.

Dominant-interfering forms of MEF2 generated by caspase cleavage contribute to NMDA-induced neuronal apoptosis.

Myocyte enhancer factor-2 (MEF2) transcription factors are activated by p38 mitogen-activated protein kinase during neuronal and myogenic differentiation. Recent work has shown that stimulation of this pathway is antiapoptotic during development but proapoptotic in mature neurons exposed to excitotoxic or other stress. We now report that excitotoxic (N-methyl-D-aspartate) insults to mature cerebrocortical neurons activate caspase-3, -7, in turn cleaving MEF2A, C, and D isoforms. MEF2 cleavage fragments containing a truncated transactivation domain but preserved DNA-binding domain block MEF2 transcriptional activity via dominant interference. Transfection of constitutively active MEF2 (MEF2C-CA) rescues MEF2 transcriptional activity after N-methyl-D-aspartate insult and prevents neuronal apoptosis. Conversely, dominant-interfering MEF2 abrogates neuroprotection by MEF2C-CA. These results define a pathway to excitotoxic neuronal stress/apoptosis via caspase-catalyzed cleavage of MEF2. Additionally, we show that similar MEF2 cleavage fragments are generated in vivo during focal stroke damage. Hence, this pathway appears to have pathophysiological relevance in vivo.