Neuronal myosin-X is upregulated after peripheral nerve injury and mediates laminin-induced growth of neurites

Transcriptomic Analysis of the Rat Dorsal Root Ganglion After Fracture

In fractures, pain signals are transmitted from the dorsal root ganglion (DRG) to the brain, and the DRG generates efferent signals to the injured bone to participate in the injury response. However, little is known about how this process occurs. We analyzed DRG transcriptome at 3, 7, 14, and 28 days after fracture. We identified the key pathways through KEGG and GO enrichment analysis. We then used IPA analysis to obtain upstream regulators and disease pathways. Finally, we compared the sequencing results with those of nerve injury to identify the unique transcriptome changes in DRG after fracture. We found that the first 14 days after fracture were the main repair response period, the 3rd day was the peak of repair activity, the 14th day was dominated by the stimulus response, and on the 28th day, the repair response had reached a plateau. ECM-receptor interaction, protein digestion and absorption, and the PI3K-Akt signaling pathway were most significantly enriched, which may be involved in repair regeneration, injury response, and pain transmission. Compared with the nerve injury model, DRG after fracture produced specific alterations related to bone repair, and the bone density function was the most widely activated bone-related function. Our results obtained some important genes and pathways in DRG after fracture, and we also summarized the main features of transcriptome function at each time point through functional annotation clustering of GO pathway, which gave us a deeper understanding of the role played by DRG in fracture.

Commonly Overlooked Factors in Biocompatibility Studies of Neural Implants

Biocompatibility of cutting-edge neural implants, surgical tools and techniques, and therapeutic technologies is a challenging concept that can be easily misjudged. For example, neural interfaces are routinely gauged on how effectively they determine active neurons near their recording sites. Tissue integration and toxicity of neural interfaces are frequently assessed histologically in animal models to determine tissue morphological and cellular changes in response to surgical implantation and chronic presence. A disconnect between histological and efficacious biocompatibility exists, however, as neuronal numbers frequently observed near electrodes do not match recorded neuronal spiking activity. The downstream effects of the myriad surgical and experimental factors involved in such studies are rarely examined when deciding whether a technology or surgical process is biocompatible. Such surgical factors as anesthesia, temperature excursions, bleed incidence, mechanical forces generated, and metabolic conditions are known to have strong systemic and thus local cellular and extracellular consequences. Many tissue markers are extremely sensitive to the physiological state of cells and tissues, thus significantly impacting histological accuracy. This review aims to shed light on commonly overlooked factors that can have a strong impact on the assessment of neural biocompatibility and to address the mismatch between results stemming from functional and histological methods.

Tunneling nanotubes: Reshaping connectivity

Tunneling nanotubes (TNTs), open membranous channels between connected cells, represent a novel direct way of communication between distant cells for the diffusion of various cellular material, including survival or death signals, genetic material, organelles, and pathogens. Their discovery prompted us to review our understanding of many physiological and pathological processes involving cellular communication but also allowed us to discover new mechanisms of communication at a distance. While this has enriched the field, it has also generated some confusion, as different TNT-like protrusions have been described, and it is not clear whether they have the same structure-function. Most studies have been based on low-resolution imaging methods, and one of the major problems is the inconsistency in demonstrating the capacity of these various connections to transfer material between cells belonging to different populations. This brief review examines the fundamental properties of TNTs. In adult tissues, TNTs are stimulated by different diseases, stresses, and inflammatory signals. 'Moreover', based on the similarity of the processes of development of synaptic spines and TNT formation, we argue that TNTs in the brain predate synaptic transmission, being instrumental in the orchestration of the immature neuronal circuit.

Retrograde Ret signaling controls sensory pioneer axon outgrowth

The trafficking mechanisms and transcriptional targets downstream of long-range neurotrophic factor ligand/receptor signaling that promote axon growth are incompletely understood. Zebrafish carrying a null mutation in a neurotrophic factor receptor, Ret, displayed defects in peripheral sensory axon growth cone morphology and dynamics. Ret receptor was highly enriched in sensory pioneer neurons and Ret51 isoform was required for pioneer axon outgrowth. Loss-of-function of a cargo adaptor, Jip3, partially phenocopied Ret axonal defects, led to accumulation of activated Ret in pioneer growth cones, and reduced retrograde Ret51 transport. Jip3 and Ret51 were also retrogradely co-transported, ultimately suggesting Jip3 is a retrograde adapter of active Ret51. Finally, loss of Ret reduced transcription and growth cone localization of Myosin-X, an initiator of filopodial formation. These results show a specific role for Ret51 in pioneer axon growth, and suggest a critical role for long-range retrograde Ret signaling in regulating growth cone dynamics through downstream transcriptional changes.

Gelatin promotes rapid restoration of the blood brain barrier after acute brain injury

Gelatin coating of brain implants is known to provide considerable benefits in terms of reduced inflammatory sequalae and long-term neuroprotective effects. However, the mechanisms for gelatin's protective role in brain injury are still unknown. To address this question, cellular and molecular markers were studied with quantitative immunohistochemical microscopy at acute (<2hours, 1, 3days), intermediate (1-2 weeks) and long-term time points (6 weeks) after transient insertion of stainless steel needles into female rat cortex cerebri with or without gelatin coating. Compared to non-coated controls, injuries caused by gelatin coated needles showed a significantly faster resolution of post-stab bleeding/leakage and differential effects on different groups of microglia cells. While similar levels of matrix metalloproteinase (MMP-2 and MMP-9, two gelatinases) was found for coated and noncoated needle stabs during the first week, markedly increased levels of both MMPs was seen for gelatin-coated but not non-coated needle stabs after 2weeks. Neuronal populations and activated astrocytes were largely unaffected. In conclusion, the beneficial effects of gelatin may be the combined results of faster healing of the blood brain barrier curtailing leakage of blood borne molecules/cells into brain parenchyma and to a modulation of the microglial population response favoring restitution of the injured tissue. These findings present an important therapeutic potential for gelatin coatings in various disease, injury and surgical conditions.

STATEMENT OF SIGNIFICANCE

The neural interfaces field holds great promise to enable elucidation of neural information processing and to develop new implantable devices for stimulation based therapy. Currently, this field is struggling to find solutions for reducing tissue reactions to implanted micro and nanotechnology. Prior studies have recently shown that gelatin coatings lower activation of digestive microglia and mitigate the ubiquitous loss of neurons adjacent to implanted probes, both of which impede implant function. The underlying mechanisms remain to be elucidated, however. Our findings demonstrate for the first time that gelatin has a significant effect on the BBB by promoting rapid restoration of integrity after injury. Moreover, gelatin alters microglia phenotypes and modulates gelatinase activity for up to 2weeks favoring anti-inflammation and restoration of the tissue. Given the key importance of the BBB for normal brain functions, we believe our findings have substantial significance and will be highly interesting to researchers in the biomaterial field.

Membrane shaping by actin and myosin during regulated exocytosis

The cortical actin network in neurosecretory cells is a dense mesh of actin filaments underlying the plasma membrane. Interaction of actomyosin with vesicular membranes or the plasma membrane is vital for tethering, retention, transport as well as fusion and fission of exo- and endocytic membrane structures. During regulated exocytosis the cortical actin network undergoes dramatic changes in morphology to accommodate vesicle docking, fusion and replenishment. Most of these processes involve plasma membrane Phosphoinositides (PIP) and investigating the interactions between the actin cortex and secretory structures has become a hotbed for research in recent years. Actin remodelling leads to filopodia outgrowth and the creation of new fusion sites in neurosecretory cells and actin, myosin and dynamin actively shape and maintain the fusion pore of secretory vesicles. Changes in viscoelastic properties of the actin cortex can facilitate vesicular transport and lead to docking and priming of vesicle at the plasma membrane. Small GTPase actin mediators control the state of the cortical actin network and influence vesicular access to their docking and fusion sites. These changes potentially affect membrane properties such as tension and fluidity as well as the mobility of embedded proteins and could influence the processes leading to both exo- and endocytosis. Here we discuss the multitudes of actin and membrane interactions that control successive steps underpinning regulated exocytosis.

Minireview: Syndecans and their crucial roles during tissue regeneration

Syndecans are transmembrane heparan sulfate proteoglycans, with roles in development, tumorigenesis and inflammation, and growing evidence for involvement in tissue regeneration. This is a fast developing field with the prospect of utilizing tissue engineering and biomaterials in novel therapies. Syndecan receptors are not only ubiquitous in mammalian tissues, regulating cell adhesion, migration, proliferation, and differentiation through independent signaling but also working alongside other receptors. Their importance is highlighted by an ability to interact with a diverse array of ligands, including extracellular matrix glycoproteins, growth factors, morphogens, and cytokines that are important regulators of regeneration. We also discuss the potential for syndecans to regulate stem cell properties, and suggest that understanding these proteoglycans is relevant to exploiting cell, tissue, and materials technologies.

Dopamine transporter is enriched in filopodia and induces filopodia formation

Dopamine transporter (DAT, SLC6A3) controls dopamine (DA) neurotransmission by mediating re-uptake of extracellular DA into DA neurons. DA uptake depends on the amount of DAT at the cell surface, and is therefore regulated by DAT subcellular distribution. Hence we used spinning disk confocal microscopy to demonstrate DAT localization in membrane protrusions that contained filamentous actin and myosin X (MyoX), a molecular motor located in filopodia tips, thus confirming that these protrusions are filopodia. DAT was enriched in filopodia. In contrast, R60A and W63A DAT mutants with disrupted outward-facing conformation were not accumulated in filopodia, suggesting that this conformation is necessary for DAT filopodia targeting. Three independent approaches of filopodia counting showed that DAT expression leads to an increase in the number of filopodia per cell, indicating that DAT can induce filopodia formation. Depletion of MyoX by RNA interference resulted in a significant loss of filopodia but did not completely eliminate filopodia, implying that DAT-enriched filopodia can be formed without MyoX. In cultured postnatal DA neurons MyoX was mainly localized to growth cones that displayed highly dynamic DAT-containing filopodia. We hypothesize that the concave shape of the DAT molecule functions as the targeting determinant for DAT accumulation in outward-curved membrane domains, and may also allow high local concentrations of DAT to induce an outward membrane bending. Such targeting and membrane remodeling capacities may be part of the mechanism responsible for DAT enrichment in the filopodia and its targeting to the axonal processes of DA neurons.

Integrin signalling and traffic during axon growth and regeneration

Adult corticospinal tract axons do not regenerate because they have low intrinsic growth ability, and are exposed to inhibitory molecules after injury. PNS axons have a better regenerative capacity, mediated in part by integrins (extracellular matrix receptors). These are subject to complex regulation by signalling and trafficking. Recent studies have found that integrin mediated axon growth relies on signalling via focal adhesion molecules, and that integrins are inactivated by inhibitory molecules in the CNS. Forced activation of integrins can overcome inhibition and increase axon regeneration, however integrins are not transported into some CNS axons. Studies of PNS integrin traffic have identified molecules that can be manipulated to increase axonal integrin expression, suggesting strategies for repairing the injured spinal cord.

High frequency of rare variants with a moderate-to-high predicted biological effect in protocadherin genes of extremely obese

Relatively rare variants with a moderate-to-high biological effect may contribute to the genetic predisposition of common disorders. To investigate this for obesity, we performed exome sequencing for 30 young (mean age: 29.7 years) extremely obese Caucasian subjects (mean body mass index: 51.1 kg/m(2); m/f = 11/29). Rare variants with a moderate-to-high predicted biological effect were assembled and subjected to functional clustering analysis. It showed that the 55 clustered protocadherin genes on chromosome 5q31 have a significantly (P = 0.002) higher frequency of rare variants than a set of 325 reference genes. Since the protocadherin genes are expressed in the hypothalamus, we tested another 167 genes related to the function of the hypothalamus, but in those genes, the frequency of rare variants was not different from that of the reference genes. To verify the relation of variation in the protocadherin genes with extreme obesity, we analyzed data from more than 4,000 European Americans present on the Exome Variant Server, representing a sample of the general population. The significant enrichment of rare variants in the protocadherin genes was only observed with the group of extremely obese individuals but not in the "general population", indicating an association between rare variants in the protocadherin cluster genes and extreme obesity.

The cortical acto-Myosin network: from diffusion barrier to functional gateway in the transport of neurosecretory vesicles to the plasma membrane

Dysregulation of regulated exocytosis is linked to an array of pathological conditions, including neurodegenerative disorders, asthma, and diabetes. Understanding the molecular mechanisms underpinning neuroexocytosis including the processes that allow neurosecretory vesicles to access and fuse with the plasma membrane and to recycle post-fusion, is therefore critical to the design of future therapeutic drugs that will efficiently tackle these diseases. Despite considerable efforts to determine the principles of vesicular fusion, the mechanisms controlling the approach of vesicles to the plasma membrane in order to undergo tethering, docking, priming, and fusion remain poorly understood. All these steps involve the cortical actin network, a dense mesh of actin filaments localized beneath the plasma membrane. Recent work overturned the long-held belief that the cortical actin network only plays a passive constraining role in neuroexocytosis functioning as a physical barrier that partly breaks down upon entry of Ca(2+) to allow secretory vesicles to reach the plasma membrane. A multitude of new roles for the cortical actin network in regulated exocytosis have now emerged and point to highly dynamic novel functions of key myosin molecular motors. Myosins are not only believed to help bring about dynamic changes in the actin cytoskeleton, tethering and guiding vesicles to their fusion sites, but they also regulate the size and duration of the fusion pore, thereby directly contributing to the release of neurotransmitters and hormones. Here we discuss the functions of the cortical actin network, myosins, and their effectors in controlling the processes that lead to tethering, directed transport, docking, and fusion of exocytotic vesicles in regulated exocytosis.

Myo10 is a key regulator of TNT formation in neuronal cells

Cell-to-cell communication is essential in multicellular organisms. Tunneling nanotubes (TNTs) have emerged as a new type of intercellular spreading mechanism allowing the transport of various signals, organelles and pathogens. Here, we study the role of the unconventional molecular motor myosin-X (Myo10) in the formation of functional TNTs within neuronal CAD cells. Myo10 protein expression increases the number of TNTs and the transfer of vesicles between co-cultured cells. We also show that TNT formation requires both the motor and tail domains of the protein, and identify the F2 lobe of the FERM domain within the Myo10 tail as necessary for TNT formation. Taken together, these results indicate that, in neuronal cells, TNTs can arise from a subset of Myo10-driven dorsal filopodia, independent of its binding to integrins and N-cadherins. In addition our data highlight the existence of different mechanisms for the establishment and regulation of TNTs in neuronal cells and other cell types.