Expression of integrin alpha2beta1 in axons and receptive endings of neurons in rat, hairy skin

Impact of type-1 collagen hydrogel density on integrin-linked morphogenic response of SH-SY5Y neuronal cells

Cellular metabolism and behaviour is closely linked to cytoskeletal tension and scaffold mechanics. In the developing nervous system functional connectivity is controlled by the interplay between chemical and mechanical cues that initiate programs of cell behaviour. Replication of functional connectivity in neuronal populations in vitro has proven a technical challenge due to the absence of many systems of biomechanical regulation that control directional outgrowth in vivo. Here, a 3D culture system is explored by dilution of a type I collagen hydrogel to produce variation in gel stiffness. Hydrogel scaffold remodelling was found to be linked to gel collagen concentration, with a greater degree of gel contraction occurring at lower concentrations. Gel mechanics were found to evolve over the culture period according to collagen concentration. Less concentrated gels reduced in stiffness, whilst a biphasic pattern of increasing and then decreasing stiffness was observed at higher concentrations. Analysis of these cultures by PCR revealed a program of shifting integrin expression and highly variable activity in key morphogenic signal pathways, such as mitogen-associated protein kinase, indicating genetic impact of biomaterial interactions via mechano-regulation. Gel contraction at lower concentrations was also found to be accompanied by an increase in average collagen fibre diameter. Minor changes in biomaterial mechanics result in significant changes in programmed cell behaviour, resulting in adoption of markedly different cell morphologies and ability to remodel the scaffold. Advanced understanding of cell-biomaterial interactions, over short and long-term culture, is of critical importance in the development of novel tissue engineering strategies for the fabrication of biomimetic 3D neuro-tissue constructs. Simple methods of tailoring the initial mechanical environment presented to SH-SY5Y populations in 3D can lead to significantly different programs of network development over time.

Integrins promote axonal regeneration after injury of the nervous system

Integrins are cell surface receptors that form the link between extracellular matrix molecules of the cell environment and internal cell signalling and the cytoskeleton. They are involved in several processes, e.g. adhesion and migration during development and repair. This review focuses on the role of integrins in axonal regeneration. Integrins participate in spontaneous axonal regeneration in the peripheral nervous system through binding to various ligands that either inhibit or enhance their activation and signalling. Integrin biology is more complex in the central nervous system. Integrins receptors are transported into growing axons during development, but selective polarised transport of integrins limits the regenerative response in adult neurons. Manipulation of integrins and related molecules to control their activation state and localisation within axons is a promising route towards stimulating effective regeneration in the central nervous system.

Multiscale mechanics of the cervical facet capsular ligament, with particular emphasis on anomalous fiber realignment prior to tissue failure

The facet capsular ligaments encapsulate the bilateral spinal facet joints and are common sources of painful injury due to afferent innervation. These ligaments exhibit architectural complexity, which is suspected to contribute to the experimentally observed lack of co-localization between macroscopic strain and microstructural tissue damage. The heterogeneous and multiscale nature of this ligament, combined with challenges in experimentally measuring its microscale mechanics, hinders the ability to understand sensory mechanisms under normal or injurious loading. Therefore, image-based, subject-specific, multiscale finite-element models were constructed to predict the mechanical responses of the human cervical facet capsular ligament under uniaxial tensile stretch. The models precisely simulated the force-displacement responses for all samples ([Formula: see text]) and showed promise in predicting the magnitude and location of peak regional strains at two different displacements. Yet, there was a loss of agreement between the model and experiment in terms of fiber organization at large tissue stretch, possibly due to a lack of accounting for tissue failure. The mean fiber stretch ratio predicted by the models was found to be significantly higher in regions that exhibited anomalous fiber realignment experimentally than in regions with normal realignment ([Formula: see text]). The development of microstructural abnormalities was associated with the predicted fiber-level stretch ([Formula: see text]), but not with the elemental maximum principal stress or maximum principal strain by logistic regression. The multiscale models elucidate a potential mechanical basis for predicting injury-prone tissue domains and for defining the relationships between macroscopic ligament stretch and microscale pathophysiology in the subfailure regime.

A Nociceptive Role for Integrin Signaling in Pain After Mechanical Injury to the Spinal Facet Capsular Ligament

Integrins modulate chemically-induced nociception in a variety of inflammatory and neuropathic pain models. Yet, the role of integrins in mechanically-induced pain remains undefined, despite its well-known involvement in cell adhesion and mechanotransduction. Excessive spinal facet capsular ligament stretch is a common injury that induces morphological and functional changes in its innervating afferent neurons and can lead to pain. However, the local mechanisms underlying the translation from tissue deformation to pain signaling are unclear, impeding effective treatment. Therefore, the involvement of the integrin subunit β1 in pain signaling from facet injury was investigated in complementary in vivo and in vitro studies. An anatomical study in the rat identified expression of the integrin subunit β1 in dorsal root ganglion (DRG) neurons innervating the facet, with greater expression in peptidergic than non-peptidergic DRG neurons. Painful facet capsule stretch in the rat upregulated the integrin subunit β1 in small- and medium-diameter DRG neurons at day 7. Inhibiting the α2β1 integrin in a DRG-collagen culture prior to its stretch injury prevented strain-induced increases in axonal substance P (SP) in a dose-dependent manner. Together, these findings suggest that integrin subunit β1-dependent pathways may contribute to SP-mediated pain from mechanical injury of the facet capsular ligament.

Paclitaxel-induced epithelial damage and ectopic MMP-13 expression promotes neurotoxicity in zebrafish

Paclitaxel is a microtubule-stabilizing chemotherapeutic agent that is widely used in cancer treatment and in a number of curative and palliative regimens. Despite its beneficial effects on cancer, paclitaxel also damages healthy tissues, most prominently the peripheral sensory nervous system. The mechanisms leading to paclitaxel-induced peripheral neuropathy remain elusive, and therapies that prevent or alleviate this condition are not available. We established a zebrafish in vivo model to study the underlying mechanisms and to identify pharmacological agents that may be developed into therapeutics. Both adult and larval zebrafish displayed signs of paclitaxel neurotoxicity, including sensory axon degeneration and the loss of touch response in the distal caudal fin. Intriguingly, studies in zebrafish larvae showed that paclitaxel rapidly promotes epithelial damage and decreased mechanical stress resistance of the skin before induction of axon degeneration. Moreover, injured paclitaxel-treated zebrafish skin and scratch-wounded human keratinocytes (HEK001) display reduced healing capacity. Epithelial damage correlated with rapid accumulation of fluorescein-conjugated paclitaxel in epidermal basal keratinocytes, but not axons, and up-regulation of matrix-metalloproteinase 13 (MMP-13, collagenase 3) in the skin. Pharmacological inhibition of MMP-13, in contrast, largely rescued paclitaxel-induced epithelial damage and neurotoxicity, whereas MMP-13 overexpression in zebrafish embryos rendered the skin vulnerable to injury under mechanical stress conditions. Thus, our studies provide evidence that the epidermis plays a critical role in this condition, and we provide a previously unidentified candidate for therapeutic interventions.

Interaction of transient receptor potential vanilloid 4, integrin, and SRC tyrosine kinase in mechanical hyperalgesia

Although the transient receptor potential vanilloid 4 (TRPV4) has been implicated in the process of osmomechanical transduction, it appears to make little contribution to the normal somatosensory detection of mechanical stimuli. However, evidence suggests that it may play an important role in mechanical hyperalgesia. In the present study, we examined the common requirement for TRPV4 in mechanical hyperalgesia associated with diverse pain models and investigated whether the very close association observed between TRPV4 and mechanical hyperalgesia, regardless of etiology, reflects a close functional connection of TRPV4 with other molecules implicated in mechanical transduction. In models of painful peripheral neuropathy associated with vincristine chemotherapy, alcoholism, diabetes, and human immunodeficiency virus/acquired immune deficiency syndrome therapy, mechanical hyperalgesia was markedly reduced by spinal intrathecal administration of oligodeoxynucleotides antisense to TRPV4. Similarly, mechanical hyperalgesia induced by paclitaxel, vincristine, or diabetes was strongly reduced in TRPV4 knock-out mice. We also show that alpha2beta1 integrin and Src tyrosine kinase, which have been implicated in mechanical transduction, are important for the development of mechanical hyperalgesia, and that their contribution requires TRPV4. Furthermore, we establish a direct interaction between TRPV4, alpha2 integrin, and the Src tyrosine kinase Lyn in sensory neurons. We suggest that TRPV4 plays a role in mechanotransduction, as a component of a molecular complex that functions only in the setting of inflammation or nerve injury.

Neuronal conditioning medium and nerve growth factor induce neuronal differentiation of collagen-adherent progenitors derived from human umbilical cord blood

The aim of the study was to isolate and characterize a population of neuronal progenitors in the human umbilical cord blood (HUCB) mononuclear cell (MNC) fraction, for in vitro manipulation towards neuronal differentiation. Selection of the HUCB neuronal progenitors (HUCBNPs) was based on the neuronal prerequisite for adherence to collagen. Populations of collagen-adherent, nestin-positive (94.8+/-2.9%) progenitors expressing alpha1/2 integrin receptors, as revealed by Western blot and adhesion assay using selective antagonists, were isolated and survived for more than 14 days. In vitro differentiation of the HUCBNPs was achieved by treatment with 10% human SH-SY5Y neuroblastoma cell-conditioning media (CM) supplemented with 10 ng/ml nerve growth factor (NGF). Some 83+/-8.2% of the surviving progenitors acquired a neuronal-like morphology, expressed by cellular outgrowths of different lengths. About 35+/-6% of the HUCBNPs had long outgrowths with a length/cell diameter ratio greater than 2, typical of developing neurons. The majority of these progenitors, analyzed by immunocytochemistry and/or RT-PCR, expressed common neuronal markers such as microtubule-associated protein 2 (MAP-2; 98.5+/-2%), neurotrophin receptor (TrkA; 98.5+/-0.06%), neurofillament-160 (NF-160; 94.2+/-1%), beta-tubulin III (89.8+/-4.2%) and neuron specific enolase (NSE). Combined CM and NGF treatment induced constitutive activation of the mitogen-activated protein kinases ERK2 (36-fold vs control), p38alpha (nine-fold vs control) and p38beta (23-fold vs control), most likely related to survival and/or differentiation. The results point to operationally defined conditions for activating neuronal differentiation of HUCBNPs ex vivo and emphasize the crucial role of neuronal CM and NGF in this process.

Primary afferent second messenger cascades interact with specific integrin subunits in producing inflammatory hyperalgesia

We recently reported that hyperalgesia induced by the inflammatory mediator prostaglandin E(2) (PGE(2)) requires intact alpha1, alpha3 and beta1 integrin subunit function, whereas epinephrine-induced hyperalgesia depends on alpha5 and beta1. PGE(2)-induced hyperalgesia is mediated by protein kinase A (PKA), while epinephrine-induced hyperalgesia is mediated by a combination of PKA, protein kinase Cepsilon (PKCepsilon) and mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK). We hypothesized that inflammatory mediator-induced hyperalgesia involves specific interactions between different subsets of integrin subunits and particular second messenger species. In the present study, function-blocking anti-integrin antibodies and antisense oligodeoxynucleotides were used to elucidate these interactions in rat. Hyperalgesia produced by an activator of adenylate cyclase (forskolin) depended on alpha1, alpha3 and beta1 integrins. However, hyperalgesia induced by activation of the cascade at a point farther downstream (by cAMP analog or PKA catalytic subunit) was independent of any integrins tested. In contrast, hyperalgesia induced by a specific PKCepsilon agonist depended only on alpha5 and beta1 integrins. Hyperalgesia induced by agonism of MAPK/ERK depended on all four integrin subunits tested (alpha1, alpha3, alpha5 and beta1). Finally, disruption of lipid rafts antagonized hyperalgesia induced by PGE(2) and by forskolin, but not that induced by epinephrine. Furthermore, alpha1 integrin, but not alpha5, was present in detergent-resistant membrane fractions (which retain lipid raft components). These observations suggest that integrins play a critical role in inflammatory pain by interacting with components of second messenger cascades that mediate inflammatory hyperalgesia, and that such interaction with the PGE(2)-activated pathway may be organized by lipid rafts.

Unraveling gene-gene interactions regulated by ligands of the aryl hydrocarbon receptor

The co-expression of genes coupled to additive probabilistic relationships was used to identify gene sets predictive of the complex biological interactions regulated by ligands of the aryl hydrocarbon receptor ((Italic)Ahr(/Italic)). To maximize the number of possible gene-gene combinations, data sets from murine embryonic kidney, fetal heart, and vascular smooth muscle cells challenged (Italic)in vitro(/Italic) with ligands of the (Italic)Ahr(/Italic) were used to create predictor/training data sets. Biologically relevant gene predictor sets were calculated for (Italic)Ahr(/Italic), cytochrome P450 1B1, insulin-like growth factor-binding protein-5, lysyl oxidase, and osteopontin. Transcript levels were categorized into ternary expressions and target genes selected from the data set and tested for all possible combinations using three gene sets as predictors of transitional level. The goodness of prediction for each set was quantified using a multivariate nonlinear coefficient of determination. Evidence is presented that predictor gene combinations can be effectively used to resolve gene-gene interactions regulated by (Italic)Ahr(/Italic) ligands. (Italic)Key words:(/Italic) aryl hydrocarbon receptor, bioinformatics, gene networks, genomics. (Italic)Environ Health Perspect (/Italic)112:403-412 (2004). [Online 14 January 2004]

Biomechanics of musculoskeletal pain: dynamics of the neuromatrix

Pain, due to mechanical stimuli, is a normal, indeed healthy, response of animals to potential or actual damage to tissues. Mammals in general, and humans in particular, have evolved a highly sophisticated system of pain perception, which is characterized in humans by complementary but distinct neural processing of the intensity and location of a noxious stimulus, and a motivational/emotional or affective response to the stimulus. The peripheral and central neurons that comprise this system, which has been called the 'neuromatrix', dynamically (temporally) respond and adapt to noxious biomechanical stimuli. However, phenotypic variability of the neuromatrix can be large, which can result in a host of musculoskeletal conditions that are characterized by altered pain perception, which can and often does alter the course of the condition. This neural plasticity has been well recognized in the central nervous system, but it has only more recently become known that peripheral nociceptors also adapt to their altered extracellular matrix environment. This work reviews the biomechanics of pain focusing on the relevant stimulus that initiates responses by nociceptors to the cognitive perception of pain.

Integrin α2β1 affects mechano-transduction in slowly and rapidly adapting cutaneous mechanoreceptors in rat hairy skin

The role of a transmembrane protein, integrin alpha2beta1, to modulate the neural responses of cutaneous mechanoreceptors to mechanical indentation was examined using an isolated skin-nerve preparation in a rat model. Skin and its intact innervation were harvested from the medial thigh of the hindlimb and placed in a dish containing synthetic interstitial fluid. Using a standard teased nerve preparation, the neural responses of single slowly or rapidly adapting mechanoreceptors (SA or RA, respectively) were identified and the afferents categorized according to standard protocols (i.e. response to constant stimuli). The most sensitive spot of a mechanoreceptor's receptive field was identified and then stimulated using controlled compressive stress (constant or dynamic loads between threshold and saturation load for SAs and RAs, respectively). Loads were applied before, during, and after passive diffusion into the skin of a function-blocking anti-integrin alpha2 monoclonal antibody (FBmAb) or one of two types of control antibodies (immunoglobulin G or a FBmAb conjugated with a secondary antibody). The sensitivities of both SA and RA mechanoreceptors were profoundly reduced in the presence of the FBmAb, while not changing the waveforms of their action potentials or their adaptation properties. Both control antibodies had no significant effect on mechanoreceptors' sensitivities. Following removal of the FBmAb, the effects in some neurons were partially reversible. Taken together, the data from this study support the hypothesis that integrin alpha2beta1 plays a significant role in modulating mechanoreceptive response to compressive indentation.

Presence of β-arrestin-1 immunoreactivity in the cutaneous nerve fibers of rat glabrous skin

beta-Arrestin-1 (betaArr1) plays a major role in the desensitization and internalization of G protein-coupled receptors. We previously localized betaArr1 in the sensory neurons of rat lumbar 4 and 5 dorsal root ganglia (DRG) and reported the predominant presence of betaArr1 in the small-diameter DRG neurons that are often implicated with nociception. Because of betaArr1's crucial role in regulating the initiation of cellular signaling, in the current study we evaluated the distribution of betaArr1 in the peripheral sensory terminals where various receptors are present. Western blotting confirmed the presence of betaArr1 immunoreactivity in the rat skin. Sciatic nerve ligation demonstrated that betaArr1 is transported peripherally from the DRG, and immunohistochemistry showed betaArr1 immunoreactivity in the glabrous skin of the rat hindpaw. In the glabrous skin, strong betaArr1 immunoreactivity was detected in nerve fibers in the dermal nerve plexus and dermal papillae. Fine varicose immunoreactive fibers were found in the epidermis. In addition, betaArr1 was observed in specialized sensory receptors such as Meissner corpuscles. Our observations thus indicate that betaArr1 may be involved in modulation of specific tactile stimulation from the skin in addition to nociception.

Encoding of compressive stress during indentation by group III and IV muscle mechano-nociceptors in rat gracilis muscle

The mechanical state encoded by group III and IV muscle afferents, putative mechano-nociceptors, during indentation was examined using an isolated muscle-nerve preparation in a rat model. Gracilis muscle and its intact innervation were surgically removed from the medial thigh of the rat hindlimb and placed in a dish containing rodent synthetic interstitial fluid. The tendons of the muscle were coupled to an apparatus that could stretch and apply compression to the muscle. Using a standard teased-nerve preparation, the neural responses of single mechanically sensitive group III or IV afferents were identified. Afferents were classified as mechano-nociceptors on the basis of their graded response to noxious levels of compressive stress (or strain) as well as, in some cases, their polymodal response to noxious thermal stimuli. Mechano-nociceptors (n = 13) were stimulated using controlled compressive stress (10-30 kPa) or strain (40-80%) while simultaneously measuring displacement and force by compressing the muscle between a flat cylinder and a hard platform. Linear regression was used to evaluate the relationships between neural response and mechanical stress, force, strain, and displacement. The mean neural response (threshold: 1.1 +/- 0.4 kPa; sensitivity: 0.5 +/- 0.1 Hz/kPa; means +/- SE) was significantly and substantially more highly correlated with compressive stress than force, strain, or displacement. The data from this study support the hypothesis that muscle nociceptors stimulated by indentation encode compressive stress rather than force, strain, or displacement.