Activating Transcription Factor 3 and the Nervous System

Activating transcription factor 3 (ATF3) belongs to the ATF/cyclic AMP responsive element binding family of transcription factors and is often described as an adaptive response gene whose activity is usually regulated by stressful stimuli. Although expressed in a number of splice variants and generally recognized as a transcriptional repressor, ATF3 has the ability to interact with a number of other transcription factors including c-Jun to form complexes which not only repress, but can also activate various genes. ATF3 expression is modulated mainly at the transcriptional level and has markedly different effects in different types of cell. The levels of ATF3 mRNA and protein are normally very low in neurons and glia but their expression is rapidly upregulated in response to injury. ATF3 expression in neurons is closely linked to their survival and the regeneration of their axons following axotomy, and that in peripheral nerves correlates with the generation of a Schwann cell phenotype that is conducive to axonal regeneration. ATF3 is also induced by Toll-like receptor (TLR) ligands but acts as a negative regulator of TLR signaling, suppressing the innate immune response which is involved in immuno-surveillance and can enhance or reduce the survival of injured neurons and promote the regeneration of their axons

CTGF expression during mouse embryonic development

Connective tissue growth factor (CTGF) is a potent fibroblast mitogen and angiogenic factor which plays an important role in wound healing, cancerogenesis and fibrotic and vascular disease. Here we explored the regulation and the cellular site of the mRNA synthesis for this growth factor in the developing mouse embryo by in situ hybridisation. Strong and persistent CTGF gene expression was limited to three types of tissue: the vascular endothelium, particularly the high-pressure part of the cardiovascular system, condensed connective tissue around bone and cartilage, and maturing layer VII neurons in the cerebral cortex. With few exceptions (late tooth bud, neuroepithelium) epithelial tissue was negative. Very transient but strong expression was observed early during formation of cartilage, in late stages during perichondral ossification, on cerebral neuroepithelium, and in several discrete stages of tooth formation, on mesenchymal precursors of odontoblasts condensing on inner dental epithelium, and later on apposing regions of ameloblast and odontoblast epithelium. Altogether, the current study suggests that CTGF performs a dual role: a continuous function in the cardiovascular system, bone and cartilage-associated mesenchyme and maturing layer VII neurons, but also a more transient function associated with the formation of cartilage, bone, tooth and cerebral nerve cells

Absence of alpha 7 integrin in dystrophin-deficient mice causes a myopathy similar to Duchenne muscular dystrophy

Both the dystrophin–glycoprotein complex and α7β1 integrin have critical roles in the maintenance of muscle integrity via the provision of mechanical links between muscle fibres and the basement membrane. Absence of either dystrophin or α7 integrin results in a muscular dystrophy. To clarify the role of α7 integrin and dystrophin in muscle development and function, we generated integrin α7/dystrophin double-mutant knockout (DKO) mice. Surprisingly, DKO mice survived post-natally and were indistinguishable from wild-type, integrin α7-deficient and mdx mice at birth, but died within 24–28 days. Histological analysis revealed a severe muscular dystrophy in DKO mice with endomysial fibrosis and ectopic calcification. Weight loss was correlated with the loss of muscle fibres, indicating that progressive muscle wasting in the double mutant was most likely due to inadequate muscle regeneration. The data further support that premature death of DKO mice is due to cardiac and/or respiratory failure. The integrin α7/dystrophin-deficient mouse model, therefore, resembles the pathological changes seen in Duchenne muscular dystrophy and suggests that the different clinical severity of dystrophin deficiency in human and mouse may be due to a fine-tuned difference in expression of dystrophin and integrin α7 in both species. Together, these findings indicate an essential role for integrin α7 in the maintenance of dystrophin-deficient muscles

α4 integrin is expressed during peripheral nerve regeneration and enhances neurite outgrowth

We have shown previously that repair in the peripheral nervous system is associated with a reversion to an embryonic pattern of alternative splicing of the extracellular matrix molecule fibronectin. One of the consequent changes is a relative increase in the number of fibronectins expressing the binding site for α4 integrins. Here we show that α4 integrins are expressed on dorsal root ganglion neuron cell bodies and growth cones in the sciatic nerve during regeneration and that the interaction of α4 integrin with alternatively spliced isoforms of recombinant fibronectins containing the α4 binding site enhances neurite outgrowth in dorsal root ganglion neurons. The pheochromocytoma (PC12) neuronal cell line, which normally extends neurites poorly on fibronectin, does so efficiently when α4 is expressed in the cells. Experiments using chimeric integrins expressed in PC12 cells show that the α4 cytoplasmic domain is necessary and sufficient for this enhanced neurite outgrowth. In both dorsal root ganglion neurons and PC12 cells the α4 cytoplasmic domain is tightly linked to the intracellular adapter protein paxillin. These experiments suggest an important role for α4 integrin and paxillin in peripheral nerve regeneration and show how alternative splicing of fibronectin may provide a mechanism to enhance repair after injury

Melatonin augments hypothermic neuroprotection in a perinatal asphyxia model

Despite treatment with therapeutic hypothermia, almost 50% of infants with neonatal encephalopathy still have adverse outcomes. Additional treatments are required to maximize neuroprotection. Melatonin is a naturally occurring hormone involved in physiological processes that also has neuroprotective actions against hypoxic-ischaemic brain injury in animal models. The objective of this study was to assess neuroprotective effects of combining melatonin with therapeutic hypothermia after transient hypoxia-ischaemia in a piglet model of perinatal asphyxia using clinically relevant magnetic resonance spectroscopy biomarkers supported by immunohistochemistry. After a quantified global hypoxic-ischaemic insult, 17 newborn piglets were randomized to the following: (i) therapeutic hypothermia (33.5°C from 2 to 26 h after resuscitation, n = 8) and (ii) therapeutic hypothermia plus intravenous melatonin (5 mg/kg/h over 6 h started at 10 min after resuscitation and repeated at 24 h, n = 9). Cortical white matter and deep grey matter voxel proton and whole brain (31)P magnetic resonance spectroscopy were acquired before and during hypoxia-ischaemia, at 24 and 48 h after resuscitation. There was no difference in baseline variables, insult severity or any physiological or biochemical measure, including mean arterial blood pressure and inotrope use during the 48 h after hypoxia-ischaemia. Plasma levels of melatonin were 10 000 times higher in the hypothermia plus melatonin than hypothermia alone group. Melatonin-augmented hypothermia significantly reduced the hypoxic-ischaemic-induced increase in the area under the curve for proton magnetic resonance spectroscopy lactate/N-acetyl aspartate and lactate/total creatine ratios in the deep grey matter. Melatonin-augmented hypothermia increased levels of whole brain (31)P magnetic resonance spectroscopy nucleotide triphosphate/exchangeable phosphate pool. Correlating with improved cerebral energy metabolism, TUNEL-positive nuclei were reduced in the hypothermia plus melatonin group compared with hypothermia alone in the thalamus, internal capsule, putamen and caudate, and there was reduced cleaved caspase 3 in the thalamus. Although total numbers of microglia were not decreased in grey or white matter, expression of the prototypical cytotoxic microglial activation marker CD86 was decreased in the cortex at 48 h after hypoxia-ischaemia. The safety and improved neuroprotection with a combination of melatonin with cooling support phase II clinical trials in infants with moderate and severe neonatal encephalopathy