Developmental and injury-induced expression of alpha1beta1 and alpha6beta1 integrins in the rat spinal cord

Integrin β1 is bound to galectin-1 in human trophoblast

Interaction of sugar binding proteins-galectins, with glycoconjugates is considered relevant for various reproductive processes. Galectin-1 (gal-1) is a molecule involved in trophoblast cell invasion, which is accomplished through interaction with cell surface and/or extracellular matrix glycoproteins. A possibility of interaction of endogenous gal-1 and trophoblast β1 integrins, both previously shown relevant for trophoblast invasion, was investigated. Confocal microscopy showed overlap in gal-1 and β1 integrin localization at the plasma membrane of isolated cytotrophoblast, HTR-8/SVneo extravillous trophoblast cell line and JAr choriocarcinoma cells. Immunoprecipitation confirmed an interaction of gal-1 with integrin β1, but not with α1 or α5 integrin subunits. Nondenaturing electrophoresis and subcellular fractionation suggested association of gal-1 with β1 integrin in intracellular and plasma membrane compartments of HTR-8/SVneo cells. Gal-1/β1 integrin complex was sensitive to chemical and enzyme treatments, indicating carbohydrate dependent interaction. Down-regulation of gal-1 by siRNA, however, had no effect on level or distribution of β1 integrin, as determined by qPCR and flow cytometry. These results suggest complex lectin type interaction of gal-1 with β1 integrin at the trophoblast cell membrane, which could influence trophoblast cell adhesion, migration and invasion.

Dynamic structural remodelling of microglia in health and disease: a review of the models, the signals and the mechanisms

Microglia are unique cells within the central nervous system because of their biophysical independence. As a result of this unusual property the cells must undergo significant structural remodelling in order to engage and connect with other elements within the central nervous system. Efficient remodelling is required for all activities that microglia are involved in ranging from monitoring synaptic information flow through to phagocytosis of tissue debris. Despite the fact that morphological remodelling is a pre-requisite to all microglial activities, relatively little research has been undertaken on the topic. This review examines what is known about how microglia transform themselves during development, under physiological conditions in response to changes in neuronal activity, and under pathological circumstances. Specific attention is given to exploring a variety of models that have been proposed to account for microglial transformation as well as the signals that are known to trigger these transformations.

Vascular Pathology as a Potential Therapeutic Target in SCI

Acute traumatic spinal cord injury (SCI) is characterized by a progressive secondary degeneration which exacerbates the loss of penumbral tissue and neurological function. Here, we first provide an overview of the known pathophysiological mechanisms involving injured microvasculature and molecular regulators that contribute to the loss and dysfunction of existing and new blood vessels. We also highlight the differences between traumatic and ischemic injuries which may yield clues as to the more devastating nature of traumatic injuries, possibly involving toxicity associated with hemorrhage. We also discuss known species differences with implications for choosing models, their relevance and utility to translate new treatments towards the clinic. Throughout this review, we highlight the potential opportunities and proof-of-concept experimental studies for targeting therapies to endothelial cell-specific responses. Lastly, we comment on the need for vascular mechanisms to be included in drug development and non-invasive diagnostics such as serum and cerebrospinal fluid biomarkers and imaging of spinal cord pathology.

Targeting microvasculature for neuroprotection after SCI

Spinal cord injury (SCI) is characterized by secondary degeneration, which leads to tissue loss at the epicenter and subsequent functional deficits. This review provides insight into the pathophysiology of microvascular dysfunction and endothelial cell loss, which are among the earliest responses during the first postinjury day. The enigmatic role of the angiogenic response in the penumbra around the lost tissue, which occurs during the first 2 weeks, is also discussed. The importance of stabilizing and rescuing the injured vasculature is now well-recognized, and several pharmacological and genetic treatments have emerged in the past few years. We conclude with suggestions for future experimental research, including development of vascular-selective treatments and exploitation of genetic models. In summary, vascular dysfunction following SCI is an important contributor to neurological deficits, as proposed long ago. However, there now appears to be new and potentially powerful opportunities for treating acute SCI by targeting the vascular responses.

Effects of extracellular matrix molecules on the growth properties of oligodendrocyte progenitor cells in vitro

The extracellular matrix (ECM) is a component of neural cell niches and regulates multiple functions of diverse cell types. To date, limited information is available concerning its biological effects on the growth properties of oligodendrocyte progenitor cells (OPCs). In the present study, we examined effects of several ECM components, i.e., fibronectin, laminin, and Matrigel, on the survival, proliferation, migration, process extension, and purity of OPCs isolated from embryonic day 15 rat spinal cords. All three ECM components enhanced these biological properties of the OPCs compared with a non-ECM substrate, poly-D-lysine. However, the extents of their effects were somewhat different. Among these ECMs, fibronectin showed the strongest effect on almost all aspects of the growth properties of OPCs, implying that this molecule is a better substrate for the growth of OPCs in vitro. Because of its survival- and growth-promoting effects on OPCs, fibronectin may be considered as a candidate substrate for enhancing OPC-mediated repair under conditions when exogenous delivery or endogenous stimulation of OPCs is applied.

Alpha9 integrin promotes neurite outgrowth on tenascin-C and enhances sensory axon regeneration

Damaged CNS axons are prevented from regenerating by an environment containing many inhibitory factors. They also lack an integrin that interacts with tenascin-C, the main extracellular matrix glycoprotein of the CNS, which is upregulated after injury. The alpha9beta1 integrin heterodimer is a receptor for the nonalternatively spliced region of tenascin-C, but the alpha9 subunit is absent in adult neurons. In this study, we show that PC12 cells and adult rat dorsal root ganglion (DRG) neurons do not extend neurites on tenascin-C. However, after forced expression of alpha9 integrin, extensive neurite outgrowth from PC12 cells and adult rat DRG neurons occurs. Moreover, both DRG neurons and PC12 cells secrete tenascin-C, enabling alpha9-transfected cells to grow axons on tissue culture plastic. Using adeno-associated viruses to express alpha9 integrin in vivo in DRGs, we examined axonal regeneration after cervical dorsal rhizotomy or dorsal column crush in the adult rat. After rhizotomy, significantly more dorsal root axons regrew into the dorsal root entry zone at 6 weeks after injury in alpha9 integrin-expressing animals than in green fluorescent protein (GFP) controls. Similarly, after a dorsal column crush injury, there was significantly more axonal growth into the lesion site compared with GFP controls at 6 weeks after injury. Behavioral analysis after spinal cord injury revealed that both experimental and control groups had an increased withdrawal latency in response to mechanical stimulation when compared with sham controls; however, in response to heat stimulation, normal withdrawal latencies returned after alpha9 integrin treatment but remained elevated in control groups.

ADAM8 is selectively up-regulated in endothelial cells and is associated with angiogenesis after spinal cord injury in adult mice

Endothelial cell (EC) loss and subsequent angiogenesis occur over the first week after spinal cord injury (SCI). To identify molecular mechanisms that could be targeted with intravenous (i.v.) treatments, we determined whether transmembrane "a disintegrin and metalloprotease" (ADAM) proteins are expressed in ECs of the injured spinal cord. ADAMs bind to integrins, which are important for EC survival and angiogenesis. Female adult C57Bl/6 mice with a spinal cord contusion had progressively more ADAM8 (CD156) immunostaining in blood vessels and individual ECs between 1 and 28 days following injury. Uninjured spinal cords had little ADAM8 staining. The increase in ADAM8 mRNA and protein was confirmed in spinal cord lysates, and ADAM8 mRNA was present in FACS-enriched ECs. ADAM8 colocalized extensively and exclusively with the EC marker PECAM and also with i.v.-injected lectins. Intravenous isolectin B4 (IB4) labels a subpopulation of blood vessels at and within the injury epicenter 3-7 days after injury, coincident with angiogenesis. Both ADAM8 and the proliferation marker Ki-67 were present in IB4-positive microvessels. ADAM8-positive proliferating cells were seen at the leading end of IB4-positive blood vessels. Angiogenesis was confirmed by BrdU incorporation, binding of i.v.-injected nucleolin antibodies, and MT1-MMP immunostaining in a subset of blood vessels. These data suggest that ADAM8 is vascular selective and plays a role in proliferation and/or migration of ECs during angiogenesis following SCI.

Comparative analysis of the time-dependent functional and molecular changes in spinal cord degeneration induced by the G93A SOD1 gene mutation and by mechanical compression

BACKGROUND

Mutations of the superoxide dismutase 1 (SOD1) gene are linked to amyotrophic lateral sclerosis (ALS), an invariably fatal neurological condition involving cortico-spinal degeneration. Mechanical injury can also determine spinal cord degeneration and act as a risk factor for the development of ALS.

RESULTS

We have performed a comparative ontological analysis of the gene expression profiles of thoracic cord samples from rats carrying the G93A SOD1 gene mutation and from wild-type littermates subjected to mechanical compression of the spinal cord. Common molecular responses and gene expression changes unique to each experimental paradigm were evaluated against the functional development of each animal model. Gene Ontology categories crucial to protein folding, extracellular matrix and axonal formation underwent early activation in both experimental paradigms, but decreased significantly in the spinal cord from animals recovering from injury after 7 days and from the G93A SOD1 mutant rats at end-stage disease. Functional improvement after compression coincided with a massive up-regulation of growth-promoting gene categories including factors involved in angiogenesis and transcription, overcoming the more transitory surge of pro-apoptotic components and cell-cycle genes. The cord from G93A SOD1 mutants showed persistent over-expression of apoptotic and stress molecules with fewer neurorestorative signals, while functional deterioration was ongoing.

CONCLUSION

this study illustrates how cytoskeletal protein metabolism is central to trauma and genetically-induced spinal cord degeneration and elucidates the main molecular events accompanying functional recovery or decline in two different animal models of spinal cord degeneration.

Integrin signaling is integral to regeneration

The inability of the adult injured mammalian spinal cord to successfully regenerate is not well understood. Studies suggest that both extrinsic and intrinsic factors contribute to regeneration failure. In this review, we focus on intrinsic factors that impact regeneration, in particular integrin receptors and their downstream signaling pathways. We discuss studies that address the impact of integrins and integrin signaling pathways on growth cone guidance and motility and how lessons learned from these studies apply to spinal cord regeneration in vivo.