BackgroundThe fetal brain is particularly vulnerable to intrauterine growth restriction (IUGR) conditions evidenced by neuronal and white matter abnormalities and altered neurodevelopment in the IUGR infant. To further our understanding of neurodevelopment in the newborn IUGR brain, clinically relevant models of IUGR are required. This information is critical for the design and implementation of successful therapeutic interventions to reduce aberrant brain development in the IUGR newborn. We utilise the piglet as a model of IUGR as growth restriction occurs spontaneously in the pig as a result of placental insufficiency, making it a highly relevant model of human IUGR. The purpose of this study was to characterise neuropathology and neuroinflammation in the neonatal IUGR piglet brain.MethodsNewborn IUGR (< 5th centile) and normally grown (NG) piglets were euthanased on postnatal day 1 (P1; < 18 h) or P4. Immunohistochemistry was utilised to examine neuronal, white matter and inflammatory responses, and PCR for cytokine analysis in parietal cortex of IUGR and NG piglets.ResultsThe IUGR piglet brain displayed less NeuN-positive cells and reduced myelination at both P1 and P4 in the parietal cortex, indicating neuronal and white matter disruption. A concurrent decrease in Ki67-positive proliferative cells and increase in cell death (caspase-3) in the IUGR piglet brain was also apparent on P4. We observed significant increases in the number of both Iba-1-positive microglia and GFAP-positive astrocytes in the white matter in IUGR piglet brain on both P1 and P4 compared with NG piglets. These increases were associated with a change in activation state, as noted by altered glial morphology. This inflammatory state was further evident with increased expression levels of proinflammatory cytokines (interleukin-1β, tumour necrosis factor-α) and decreased levels of anti-inflammatory cytokines (interleukin-4 and -10) observed in the IUGR piglet brains.ConclusionsThese findings suggest that the piglet model of IUGR displays the characteristic neuropathological outcomes of neuronal and white matter impairment similar to those reported in the IUGR human brain. The activated glial morphology and elevated proinflammatory cytokines is indicative of an inflammatory response that may be associated with neuronal damage and white matter disruption. These findings support the use of the piglet as a pre-clinical model for studying mechanisms of altered neurodevelopment in the IUGR newborn.
Key pointsr Neuromuscular junctions from β2-laminin-deficient mice exhibit lower levels of calcium sensitivity.r Loss of β2-laminin leads to a failure in switching from N-to P/Q-type voltage-gated calcium channel (VGCC)-mediated transmitter release that normally occurs with neuromuscular junction maturation.r The motor nerve terminals from β2-laminin-deficient mice fail to up-regulate the expression of P/Q-type VGCCs clusters and down-regulate N-type VGCCs clusters, as they mature.r There is decreased co-localisation of presynaptic specialisations in β2-laminin-deficient neuromuscular junctions as a consequence of lesser P/Q-type VGCC expression.r These findings support the idea that β2-laminin is critical in the organisation and maintenance of active zones at the neuromuscular junction via its interaction with P/Q-type VGCCs, which aid in stabilisation of the synapse.Abstract β2-laminin is a key mediator in the differentiation and formation of the skeletal neuromuscular junction. Loss of β2-laminin results in significant structural and functional aberrations such as decreased number of active zones and reduced spontaneous release of transmitter. In vitro β2-laminin has been shown to bind directly to the pore forming subunit of P/Q-type voltage-gated calcium channels (VGCCs). Neurotransmission is initially mediated by N-type VGCCs, but by postnatal day 18 switches to P/Q-type VGCC dominance. The present study investigated the changes in neurotransmission during the switch from N-to P/Q-type VGCC-mediated transmitter release at β2-laminin-deficient junctions. Analysis of the relationship between quantal content and extracellular calcium concentrations demonstrated a decrease in the calcium sensitivity, but no change in calcium dependence at β2-laminin-deficient junctions. Electrophysiological studies on VGCC sub-types involved in transmitter release indicate N-type VGCCs remain the primary mediator of transmitter release at matured β2-laminin-deficient junctions. Immunohistochemical analyses displayed irregularly shaped and immature β2-laminin-deficient neuromuscular junctions when compared to matured wild-type junctions. β2-laminin-deficient junctions also maintained the presence of N-type VGCC clustering within the presynaptic membrane, which supported the functional findings of the present study. We conclude that β2-laminin is a key regulator in development of the NMJ, with its loss resulting in reduced transmitter release due to decreased calcium sensitivity stemming from a failure to switch from N-to P/Q-type VGCC-mediated synaptic transmission. N. A. Lavidis and P. G. Noakes contributed equally to this work.
BackgroundThe terminal pathway of the innate immune complement system is implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). Terminal complement activation leads to generation of C5a, which through its receptor, C5aR1, drives immune cell recruitment and activation. Importantly, genetic or pharmacological blockage of C5aR1 improves motor performance and reduces disease pathology in hSOD1G93A rodent models of ALS. In this study, we aimed to explore the potential mechanisms of C5aR1-mediated pathology in hSOD1G93A mice by examining their skeletal muscles.ResultsWe found elevated levels of C1qB, C4, fB, C3, C5a, and C5aR1 in tibialis anterior muscles of hSOD1G93A mice, which increased with disease progression. Macrophage cell numbers also progressively increased in hSOD1G93A muscles in line with disease progression. Immuno-localisation demonstrated that C5aR1 was expressed predominantly on macrophages within hSOD1G93A skeletal muscles. Notably, hSOD1G93A × C5aR1-/- mice showed markedly decreased numbers of infiltrating macrophages, along with reduced neuromuscular denervation and improved grip strength in hind limb skeletal muscles, when compared to hSOD1G93A mice.ConclusionThese results indicate that terminal complement activation and C5a production occur in skeletal muscle tissue of hSOD1G93A mice, and that C5a-C5aR1 signalling contributes to the recruitment of macrophages that may accelerate muscle denervation in these ALS mice.
Intrauterine growth restriction (IUGR) is a condition where the fetus does not achieve optimal growth, commonly caused by placental insufficiency. The chronic decrease in blood flow restricts oxygen and nutrient supply to the fetus, which can damage numerous organ systems, with the fetal brain being particularly vulnerable. Although white matter and neuronal injury are evident in IUGR infants, the specific mechanisms underlying these changes are poorly understood. Inflammation is considered to be a main driver in exacerbating brain injury. Using a spontaneous piglet model of IUGR, we aim to determine whether administration of the anti-inflammatory drug ibuprofen will decrease inflammation at postnatal day 4 (P4). The treatment group received ibuprofen (20 mg/kg/day on day 1 and 10 mg/kg/day on days 2 and 3) in piglet formula during the morning feed each day and brains examined on P4. Markers of inflammation, apoptosis, cell proliferation, neuronal injury, and white matter injury were examined. Ibuprofen treatment ameliorated the increase in numbers of microglia and astrocytes in the parietal cortex and white matter tracts of the IUGR piglet brain on P4 as well as decreasing proinflammatory cytokines. Ibuprofen treatment prevented the reduction in apoptosis, neuronal cell counts, and myelin index in the IUGR piglets. Our findings demonstrate ibuprofen reduces the inflammatory response in the IUGR neonatal brain and concurrently reduces neuronal and white matter impairment.
Transactive response DNA-binding protein-43 (TDP-43) is involved in gene regulation via the control of RNA transcription, splicing, and transport. TDP-43 is a major protein component of ubiquinated inclusions that are found in amyotrophic lateral sclerosis (ALS); however, the function of TDP-43 at the neuromuscular junction (NMJ) and its role in ALS pathogenesis is largely unknown. Here, we show that TDP-43 mutation in mice resulted in impaired neurotransmission by age 3 mo, preceding deficits in motor function and motor neuron loss, which were observed from age 10 mo. These defects were in the effective fusion and release of synaptic vesicles within the motor nerve terminal and manifested in decreased quantal content and reduced probability of quantal release. We observed morphologic alterations that were associated with the TDP-43 mutation, such as aberrant innervation patterns and the distribution of synaptic vesicle-related proteins, which is indicative of a failing NMJ undergoing synaptic remodeling. These findings support a growing acceptance that dysregulation of the NMJ function is a key early event in the pathology of ALS.-Chand, K. K., Lee, K. M., Lee, J. D., Qiu, H., Willis, E. F., Lavidis, N. A., Hilliard, M. A., Noakes, P. G. Defects in synaptic transmission at the neuromuscular junction precede motor deficits in a TDP-43 transgenic mouse model of amyotrophic lateral sclerosis.
Ticks are important vectors of pathogens and secreted neurotoxins with approximately 69 out of 692 tick species having the ability to induce severe toxicoses in their hosts. The Australian paralysis tick (Ixodes holocyclus) is known to be one of the most virulent tick species producing a flaccid paralysis and fatalities caused by a family of neurotoxins known as holocyclotoxins (HTs). The paralysis mechanism of these toxins is temperature dependent and is thought to involve inhibition of acetylcholine levels at the neuromuscular junction. However, the target and mechanism of this inhibition remain uncharacterised. Here, we report that three members of the holocyclotoxin family; HT-1 (GenBank AY766147), HT-3 (GenBank KP096303) and HT-12 (GenBank KP963967) induce muscle paralysis by inhibiting the dependence of transmitter release on extracellular calcium. Previous study was conducted using extracts from tick salivary glands, while the present study is the first to use pure toxins from I. holocyclus. Our findings provide greater insight into the mechanisms by which these toxins act to induce paralysis.
Laminin-α4 is involved in the alignment of active zones to postjunctional folds at the neuromuscular junction (NMJ). Prior study has implicated laminin-α4 in NMJ maintenance, with altered NMJ morphology observed in adult laminin-α4 deficient mice (lama4−/−). The present study further investigated the role of laminin-α4 in NMJ maintenance by functional characterization of transmission properties, morphological investigation of synaptic proteins including synaptic laminin-α4, and neuromotor behavioral testing. Results showed maintained perturbed transmission properties at lama4−/− NMJs from adult (3 months) through to aged (18-22 months). Hind-limb grip force demonstrated similar trends as transmission properties, with maintained weaker grip force across age groups in lama4−/−. Interestingly, both transmission properties and hind-limb grip force in aged wild-types resembled those observed in adult lama4−/−. Most significantly, altered expression of laminin-α4 was noted at the wild-type NMJs prior to the observed decline in transmission properties, suggesting that altered laminin-α4 expression precedes the decline of neurotransmission in aging wild-types. These findings significantly support the role of laminin-α4 in maintenance of the NMJ during aging.
Synaptic basal lamina such as laminin-421 (α4β2γ1) mediate differentiation of the neuromuscular junction (NMJ). Laminins interact with their pre- or postsynaptic receptors to provide stability and alignment of the pre- to postsynaptic specializations. Knockout of the laminin-α4 gene (4) does not alter gross NMJ morphogenesis. However, mice deficient in laminin-α4 (4 mice) display disruptions in the alignment of the active zones and postsynaptic folds at the NMJ, although the physiological consequences of this loss have not been examined. The present study investigated the differences in neurotransmission during the early development and maturation of the NMJ in 4 and wild-type mice. 4 NMJs demonstrated a decrease in miniature end-plate potential (EPP) frequency and increased amplitude of miniature EPPs and evoked EPPs. Binomial parameters analysis of neurotransmitter release revealed a decrease in quantal release, the result of a decrease in the number of active release sites, but not in the probability of transmitter release. 4 NMJs displayed higher levels of synaptic depression under high-frequency stimulation and altered facilitation, suggesting compromised delivery of synaptic vesicles. This idea is supported by our molecular investigations of 4 NMJs, where we see altered distribution of Bassoon, a molecular component of active zones, presumably resulting from perturbed neurotransmission.-Chand, K. K., Lee, K. M., Lavidis, N. A., Noakes, P. G. Loss of laminin-α4 results in pre- and postsynaptic modifications at the neuromuscular junction.
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