A5 A MOUSE MODEL TO UNRAVEL THE PATHOPHYSIOLOGICAL LINK BETWEEN CROHN’S DISEASE AND TYPE-2 DIABETES-ASSOCIATED METABOLIC DISORDERS

Background

Crohn’s disease (CD), an idiopathic inflammatory bowel disease (IBD), has been recently shown to increase the risk of developing type 2 diabetes (T2D). Moreover, treatment with anti-diabetic drugs has a protective role in preventing the severity and course of CD progression. However, the pathophysiological basis of T2D development in CD remains unclear. Findings have highlighted the contribution of adipose tissue (AT) to the development of chronic inflammatory diseases and have identified parallels between T2D and CD that may provide hints to common mechanisms of disease pathogenesis. Typically, microbial dysbiosis, hyperpermeable intestinal barrier, and intra-abdominal AT accumulation are the common features of both diseases, yet how the interplay of these factors contribute to pathogenesis is not known. Therefore, common pathogenic paradigms underlying both T2D and CD have led us to hypothesize that chronic intestinal inflammation serves as an initiator of AT dysfunction in CD, predisposing individuals to T2D. Further, the lack of appropriate animal models of CD with chronic intestinal inflammation that manifests accumulation of intra-abdominal AT, and extra-intestinal metabolic disorder as observed in CD and T2D patients has been a limitation.

Purpose

To develop a genetic mouse model to investigate if gut inflammation-mediated microbial dysbiosis and metabolic dysregulation of AT are at the nexus that cause T2D in CD.

Method

We developed a CD-mouse model, where we challenged Nod2-deficient mice (NOD2 being the strongest genetic risk factor contributing to CD) with a chronic inflammatory insult regime, using dextran sulfate sodium (cDSS) for 3 cycles. Subsequently, intraperitoneal insulin and oral glucose tolerance tests, metabolic caging, and MRI imaging of mice were performed. Changes in AT metabolism and microbial infiltration into AT were analyzed by quantitative real-time PCR (qRT-PCR) and/or immunohistochemistry (IHC).

Result(s)

Our new CD-mouse model revealed increased gut inflammation (TNF and type-I IFN) in Nod2-deficient mice compared to wild-type control mice post-cDSS. Surprisingly, Nod2-deficient mice gained body weight, which was at least in part accounted for by an increased intra-abdominal AT accumulation along with decreased AT fatty-acid metabolism (Cpt1a, Fabp4 expression) and AT browning (Ucp1, Cidea expression, and UCP-1 staining), reduced intestinal goblet cell numbers, increased gut bacterial infiltration within the fat, more insulin resistance and energy expenditure.

Conclusion(s)

This experimental mouse model mimicking CD-associated T2D will provide insights into how the microbiome-AT axis fuel chronic inflammation-mediated extra-intestinal metabolic disorder and immune dysregulation. Understanding these connections will be transformative, as it will help us devise novel therapeutic strategies to prevent T2D development in progressive CD patients.

Disclosure of Interest

None Declared

Simulating human sleep spindle MEG and EEG from ion channel and circuit level dynamics

BACKGROUND

Although they form a unitary phenomenon, the relationship between extracranial M/EEG and transmembrane ion flows is understood only as a general principle rather than as a well-articulated and quantified causal chain.

METHOD

We present an integrated multiscale model, consisting of a neural simulation of thalamus and cortex during stage N2 sleep and a biophysical model projecting cortical current densities to M/EEG fields. Sleep spindles were generated through the interactions of local and distant network connections and intrinsic currents within thalamocortical circuits. 32,652 cortical neurons were mapped onto the cortical surface reconstructed from subjects' MRI, interconnected based on geodesic distances, and scaled-up to current dipole densities based on laminar recordings in humans. MRIs were used to generate a quasi-static electromagnetic model enabling simulated cortical activity to be projected to the M/EEG sensors.

RESULTS

The simulated M/EEG spindles were similar in amplitude and topography to empirical examples in the same subjects. Simulated spindles with more core-dominant activity were more MEG weighted.

COMPARISON WITH EXISTING METHODS

Previous models lacked either spindle-generating thalamic neural dynamics or whole head biophysical modeling; the framework presented here is the first to simultaneously capture these disparate scales.

CONCLUSIONS

This multiscale model provides a platform for the principled quantitative integration of existing information relevant to the generation of sleep spindles, and allows the implications of future findings to be explored. It provides a proof of principle for a methodological framework allowing large-scale integrative brain oscillations to be understood in terms of their underlying channels and synapses.

Pseudosyndactyly and Musculoskeletal Contractures in Inherited Epidermolysis Bullosa: Experience of the National Epidermolysis Bullosa Registry, 1986–2002

Mitten deformities of the hands and feet occur in nearly every patient with the most severe subtype (Hallopeau-Siemens) of recessive dystrophic epidermolysis bullosa, and in at least 40–50% of all other recessive dystrophic epidermolysis bullosa patients. Smaller numbers of patients with dominant dystrophic, junctional, and simplex types of epidermolysis bullosa are also at risk of this complication. Surgical intervention is commonly performed to correct these deformities, but recurrence and the need for repeated surgery are common. Higher numbers of epidermolysis bullosa patients also develop musculoskeletal contractures in other anatomic sites, further impairing overall function. Lifetable analyses not only better project the cumulative risk of mitten deformities and other contractures but also emphasize the need for early surveillance and intervention, since both of these musculoskeletal complications may occur within the first year of life.

IFPA meeting 2015 workshop report IV: placenta and obesity; stem cells of the feto-maternal interface; placental immunobiology and infection

Workshops are an important part of the IFPA annual meeting as they allow for discussion of specialised topics. At the 2015 IFPA annual meeting there were 12 themed workshops, three of which are summarized in this report. These workshops related to various aspects of placental biology and collectively covered areas of obesity and the placenta, stem cells of the feto-maternal interface, and placental immunobiology and infection.

Linear summation of excitatory inputs by CA1 pyramidal neurons

A fundamental problem in neurobiology is understanding the arithmetic that dendrites use to integrate inputs. The impact of dendritic morphology and active conductances on input summation is still unknown. To study this, we use glutamate iontophoresis and synaptic stimulation to position pairs of excitatory inputs throughout the apical, oblique, and basal dendrites of CA1 pyramidal neurons in rat hippocampal slices. Under a variety of stimulation regimes, we find a linear summation of most input combinations that is implemented by a surprising balance of boosting and shunting mechanisms. Active conductances in dendrites paradoxically serve to make summation linear. This "active linearity" can reconcile predictions from cable theory with the observed linear summation in vivo and suggests that a simple arithmetic is used by apparently complex dendritic trees.

Input summation by cultured pyramidal neurons is linear and position-independent

The role of dendritic morphology in integration and processing of neuronal inputs is still unknown. Models based on passive cable theory suggest that dendrites serve to isolate synapses from one another. Because of decreases in driving force or resistance, two inputs onto the same dendrite would diminish their joint effect, resulting in sublinear summation. When on different dendrites, however, inputs would not interact and therefore would sum linearly. These predictions have not been rigorously tested experimentally. In addition, recent results indicate that dendrites have voltage-sensitive conductances and are not passive cables. To investigate input integration, we characterized the effects of dendritic morphology on the summation of subthreshold excitatory inputs on cultured hippocampal neurons with pyramidal morphologies. We used microiontophoresis of glutamate to systematically position inputs throughout the dendritic tree and tested the summation of two inputs by measuring their individual and joint effects. We find that summation was surprisingly linear regardless of input position. For small inputs, this linearity arose because no significant shunts or changes in driving force occurred and no voltage-dependent channels were opened. Larger inputs also added linearly, but this linearity was caused by balanced action of NMDA and IA potassium conductances. Therefore, active conductances can maintain, paradoxically, a linear input arithmetic. Furthermore, dendritic morphology does not interfere with this linearity, which may be essential for particular neuronal computations.

Spread of synaptic depression mediated by presynaptic cytoplasmic signaling

Postsynaptic activity may modulate presynaptic functions by transsynaptic retrograde signals. At developing neuromuscular synapses in Xenopus nerve-muscle cultures, a brief increase in the cytosolic calcium ion (Ca2+) concentration in postsynaptic myocytes induced persistent depression of presynaptic transmitter secretion. This depression spread to distant synapses formed by the same neuron. Clearance of extracellular fluid did not prevent the spread of depression, and depression could not be induced by increasing the Ca2+ concentration in a nearby myocyte not in contact with the presynaptic neuron. Thus, the spread of depression is mediated by signaling in the presynaptic cytoplasm, rather than by a retrograde factor in the extracellular space.

Postsynaptic elevation of calcium induces persistent depression of developing neuromuscular synapses

Synaptic activity is known to modulate neuronal connectivity in the nervous system. At developing Xenopus neuromuscular synapses in culture, repetitive postsynaptic application of ACh near the synapse leads to immediate and persistent synaptic depression, which was shown to be caused by reduction of presynaptic evoked transmitter release. However, little depression was found when ACh was applied to the muscle 20 microns or further from the synapse. Fluorescence imaging of cytosolic Ca2+ ([Ca2+]i) showed that each ACh pulse induced a transient elevation of myocyte [Ca2+]i that spread approximately 20 microns. Local photoactivated release of Ca2+ from the caged Ca2+ chelators nitr-5 or nitrophen in the postsynaptic cell was sufficient to induce persistent synaptic depression. These results support a model in which localized Ca2+ influx into the postsynaptic myocyte initiates transsynaptic retrograde modulation of presynaptic secretion mechanisms.

Role change after traumatic brain injury in adults

OBJECTIVES

The purpose of this study was to gather information regarding changes in adult life roles following severe traumatic brain injury.

METHOD

The Role Checklist and a semistructured interview were administered to 28 adults with traumatic brain injury who had been in the community for at least 8 months prior to the study. All 28 subjects reported role changes in their lives.

RESULTS

The majority of the role changes were losses (71%). More than 64% percent of the subjects reported three or four role losses. The losses were in major organizing roles such as worker, hobbyist, and friend. Most role gains were seen in the roles of home maintainer, family member, and religious participant. Almost 40% of all roles were reported as changed (loss or gain), while more than 60% of roles were reported as unchanged (continuous or absent). The participants' subjective impressions concerning the role changes and why they occurred were elicited.

CONCLUSION

With a better understanding of possible role change after traumatic brain injury, rehabilitation professionals can target the development of specific skills necessary for the continuation of valued roles.

Cellular mechanisms governing synaptic development in Drosophila melanogaster

The neuromuscular connections of Drosophila are ideally suited for studying synaptic function and development. Hypotheses about cell recognition can be tested in a simple array of pre- and postsynaptic elements. Drosophila muscle fibers are multiply innervated by individually identifiable motoneurons. The neurons express several synaptic cotransmitters, including glutamate, proctolin, and octopamine, and are specialized by their synaptic morphology, neurotransmitters, and connectivity. During larval development the initial motoneuron endings grow extensively over the surface of the muscle fibers, and differentiate synaptic boutons of characteristic morphology. While considerable growth occurs postembryonically, the initial wiring of motoneurons to muscle fibers is accomplished during mid-to-late embryogenesis (stages 15-17). Efferent growth cones sample multiple muscle fibers with rapidly moving filopodia. Upon reaching their target muscle fibers, the growth cones rapidly differentiate into synaptic contacts whose morphology prefigures that of the larval junction. Mismatch experiments show that growth cones recognize specific muscle fibers, and can do so when the surrounding musculature is radically altered. However, when denied their normal targets, motoneurons can establish functional synapses on alternate muscle fibers. Blocking synaptic activity with either injected toxins or ion channel mutants does not derange synaptogenesis, but may influence the number of motor ending processes. The molecular mechanisms governing cellular recognition during synaptogenesis remain to be identified. However, several cell surface glycoproteins known to mediate cellular adhesion events in vitro are expressed by the developing synapses. Furthermore, enhancer detector lines have identified genes with expression restricted to small subsets of muscle fibers and/or motoneurons during the period of synaptogenesis. These observations suggest that in Drosophila a mechanism of target chemoaffinity may be involved in the genesis of stereotypic synaptic wiring.

Growth cone choices of Drosophila motoneurons in response to muscle fiber mismatch

In Drosophila embryos, each motoneuron is accurately matched to one or more singly identifiable muscle fibers. In this article we altered the number and pattern of the embryonic muscle fibers using genetic, heat shock, and laser ablation methods to test whether motoneuron growth cones are able to recognize specific targets. The choices made by two motoneurons were assayed using both intracellular dye fills and immunocytochemistry. The motoneurons RP1 and RP3 have nearly identical central and peripheral axonal trajectories. However, RP3 innervates the two most ventral longitudinal muscle fibers, 7 and 6, while RP1 grows past these fibers to innervate only muscle fiber 13. In rhomboid mutants muscle fiber 7 does not develop. Despite the loss of one of its targets, RP3 faithfully innervated the remaining muscle fiber 6 in over 80% of the observed cases. Furthermore, neuron RP1 accurately innervated muscle fiber 13, although it traversed one fiber fewer to reach it. Laser ablation of muscle fiber 7 confirmed the target choices shown by the motoneurons. In numb mutants, multiple muscle fibers, including 7, 13, and 12, fail to develop. This allowed us to test whether fibers distal to the target are involved in muscle fiber recognition, possibly by halting the growth cone advance. In mutant embryos, RP3 innervated muscle fiber 6 at the same frequency regardless of the absence of the distal muscle fiber 13. By contrast, RP1, which had lost its target entirely, frequently failed to innervate any muscle fiber during the period examined. Finally, muscle fiber 13 can be duplicated in wild-type embryos by means of a brief heat pulse during myogenesis. Presented with two targets, RP1 innervated both fibers in each case examined, while RP3 synapsed with muscle fibers 7 and 6 normally. Neuron-specific antibodies revealed that the embryonic growth cone choices were not transient, but persisted into the larval neuromuscular projections. These results indicate that each motoneuron growth cone has a primary target preference, which is retained even when the numbers of the muscle fibers, and therefore their relative positions, are altered. We therefore suggest that synaptic recognition by Drosophila motoneuron growth cones relies on unique features of the individual muscle fibers.

Alternate neuromuscular target selection following the loss of single muscle fibers in Drosophila

The Drosophila embryonic and larval body wall consists of a simple array of segmental muscle fibers, innervated in a precise manner by identified neurons. During development motoneurons were forced to find alternate targets following the selective deletion of a single muscle fiber, the pleural internal oblique #5. We used backfills, intracellular dyefills, and immunocytochemistry in embryos and larvae to characterize the normal motoneurons to the fiber. Deleting the fiber using either a genetic or laser lesioning method yielded essentially the same result. In nearly half the cases examined, an ectopically placed neuromuscular projection was found on either of two neighboring muscle fibers, with one favored eight times more than the other. The ectopic projection derived from the nerve branch that normally supplied the deleted muscle fiber 5. Motoneuronal endings on undeleted muscle fibers elsewhere in the body wall had normal morphology. The ectopically placed motor terminals accumulated glutamate in normally sized synaptic boutons, beneath which transmitter sensitivity was localized. The number of boutons and branches at the ectopic endings did not differ significantly from those on intact muscle fiber 5s. Also, the native motoneurons did not alter their arborization sizes in response to a supernumerary ectopically placed contact. While the orientation of the individual ectopically placed branches was variable, the ectopic endings occupied a predictable site on the surrogate muscle fibers. The results suggest that Drosophila motoneurons can project to body wall destinations in the absence of their muscle fiber targets, and that alternate muscle fibers are selected by their proximity. The muscle fibers will support apparently stable and functional supernumerary motor endings on ectopic sites, and these inputs do not significantly influence the behavior of the native motoneurons. The data suggest that Drosophila motoneurons may behave autonomously when making synapses, and that competition does not play a major role in the matching of motoneuron to muscle fiber.