Semaphorin III is needed for normal patterning and growth of nerves, bones and heart

Sensory nerve regulation of bone homeostasis: Emerging therapeutic opportunities for bone-related diseases

Understanding the intricate interplay between sensory nerves and bone tissue cells is of paramount significance in the field of bone biology and clinical medicine. The regulatory role of sensory nerves in bone homeostasis offers a novel perspective for the development of targeted therapeutic interventions for a spectrum of bone-related diseases, including osteoarthritis, osteoporosis, and intervertebral disc degeneration. By elucidating the mechanisms through which sensory nerves and their neuropeptides influence the differentiation and function of bone tissue cells, this review aims to shed light on emerging therapeutic targets that harness the neuro-skeletal axis for the treatment and management of debilitating bone disorders. Moreover, a comprehensive understanding of sensory nerve-mediated bone regulation may pave the way for the development of innovative strategies to promote bone health and mitigate the burden of skeletal pathologies in clinical practice.

The role of semaphorin 3A on chondrogenic differentiation

Osteoblast-derived semaphorin3A (Sema3A) has been reported to be involved in bone protection, and Sema3A knockout mice have been reported to exhibit chondrodysplasia. From these reports, Sema3A is considered to be involved in chondrogenic differentiation and skeletal formation, but there are many unclear points about its function and mechanism in chondrogenic differentiation. This study investigated the pharmacological effects of Sema3A in chondrogenic differentiation. The amount of Sema3A secreted into the culture supernatant was measured using an enzyme-linked immunosorbent assay. The expression of chondrogenic differentiation-related factors, such as Type II collagen (COL2A1), Aggrecan (ACAN), hyaluronan synthase 2 (HAS2), SRY-box transcription factor 9 (Sox9), Runt-related transcription factor 2 (Runx2), and Type X collagen (COL10A1) in ATDC5 cells treated with Sema3A (1,10 and 100 ng/mL) was examined using real-time reverse transcription polymerase chain reaction. Further, to assess the deposition of total glycosaminoglycans during chondrogenic differentiation, ATDC5 cells were stained with Alcian Blue. Moreover, the amount of hyaluronan in the culture supernatant was measured by enzyme-linked immunosorbent assay. The addition of Sema3A to cultured ATDC5 cells increased the expression of Sox9, Runx2, COL2A1, ACAN, HAS2, and COL10A1 during chondrogenic differentiation. Moreover, it enhanced total proteoglycan and hyaluronan synthesis. Further, Sema3A was upregulated in the early stages of chondrogenic differentiation, and its secretion decreased later. Sema3A increases extracellular matrix production and promotes chondrogenic differentiation. To the best of our knowledge, this is the first study to demonstrate the role of Sema3A on chondrogenic differentiation.

Semaphorins and the bone marrow microenvironment: New candidates that influence the hematopoietic system

The bone marrow is a haven for hematopoietic and non-hematopoietic cells, creating complex micro-anatomical regions called niches. These distinct niches all participate in an intricate orchestra of cellular interactions that regulates the hematopoietic stem cell and its progenies. In this review, we provide a detailed description of the three most well-known bone marrow niches and their participation in hematopoiesis. We use pre-clinical data, including different in vitro and in vivo studies to discuss how a group of proteins called Semaphorins could potentially modulate both hematopoietic and non-hematopoietic cells, establishing links between the niches, semaphorins, and hematopoietic regulation. Thus, here we provide a deep dive into the inner functioning of the bone marrow and discuss the overarching implications that semaphorins might have on blood formation.

Peripheral nerve-derived Sema3A promotes osteogenic differentiation of mesenchymal stem cells through the Wnt/β-catenin/Nrp1 positive feedback loop

Sensory nerves play a crucial role in maintaining bone homeostasis by releasing Semaphorin 3A (Sema3A). However, the specific mechanism of Sema3A in regulation of bone marrow mesenchymal stem cells (BMMSCs) during bone remodelling remains unclear. The tibial denervation model was used and the denervated tibia exhibited significantly lower mass as compared to sham operated bones. In vitro, BMMSCs cocultured with dorsal root ganglion cells (DRGs) or stimulated by Sema3A could promote osteogenic differentiation through the Wnt/β-catenin/Nrp1 positive feedback loop, and the enhancement of osteogenic activity could be inhibited by SM345431 (Sema3A-specific inhibitor). In addition, Sema3A-stimulated BMMSCs or intravenous injection of Sema3A could promote new bone formation in vivo. To sum up, the coregulation of bone remodelling is due to the ageing of BMMSCs and increased osteoclast activity. Furthermore, the sensory neurotransmitter Sema3A promotes osteogenic differentiation of BMMSCs via Wnt/β-catenin/Nrp1 positive feedback loop, thus promoting osteogenesis in vivo and in vitro.

Expression of semaphorin-3A in the joint and role in osteoarthritis

Osteoarthritis (OA) is characterised by the deterioration of cartilage in the joints and pain. We hypothesise that semaphorin-3A (sema-3A), a chemorepellent for sensory nerves, plays a role in joint degradation and pain. We used the mechanical joint loading (MJL) model of OA to investigate sema-3A expression in the joint and examine its association with the development of OA and pain. We also analyse its effect on chondrocyte differentiation using the ATDC5 cell line. We demonstrate that sema-3A is present in most tissues in the healthy joint and its expression increases in highly innervated tissues, such as cruciate ligaments, synovial lining and subchondral bone, in loaded compared to nonloaded control joints. In contrast, sema-3A expression in cartilage was decreased in the severe OA induced by the application of high loads. There was a significant increase in circulating sema-3A, 6 weeks after MJL compared to the nonloaded mice. mRNA for sema-3A and its receptor Plexin A1 were upregulated in the dorsal root ganglia of mice submitted to MJL. These increases were supressed by zoledronate, an inhibitor of bone pain. Sema-3A was expressed at all stages of Chondrocyte maturation and, when added exogenously, stimulated expression of markers of chondrocyte differentiation. This indicates that sema-3A could affect joint tissues distinctively during the development of OA. In highly innervated joint tissues, sema-3A could control innervation and/or induce pain-associated neuronal changes. In cartilage, sema-3A could favour its degeneration by modifying chondrocyte differentiation.

Transcriptomic and proteomic strategies to reveal the mechanism of Gymnocypris przewalskii scale development

BACKGROUND

Fish scales are typical products of biomineralization and play an important role in the adaptation of fish to their environment. The Gymnocypris przewalskii scales are highly specialized, with scales embedded in only specific parts of the dermis, such as the areas around the anal fin and branchiostegite, making G. przewalskii an ideal material for biomineralization research. In this study, we aimed to unveil genes and pathways controlling scale formation through an integrated analysis of both transcriptome and proteome, of which G. przewalskii tissues of the dorsal skin (no scales) and the rump side skin (with scales) were sequenced. The sequencing results were further combined with cellular experiments to clarify the relationship between genes and signaling pathways.

RESULTS

The results indicated the following: (1) a total of 4,904 differentially expressed genes were screened out, including 3,294 upregulated genes and 1,610 downregulated genes (with a filtering threshold of |log2Fold-Change|> 1 and p-adjust < 0.05). The identified differentially expressed genes contained family members such as FGF, EDAR, Wnt10, and bmp. (2) A total of 535 differentially expressed proteins (DEPs) were filtered out from the proteome, with 204 DEPs downregulated and 331 DEPs upregulated (with a filtering threshold of |Fold-Change|> 1.5 and p < 0.05). (3) Integrated analyses of transcriptome and proteome revealed that emefp1, col1a1, col6a2, col16a1, krt8, and krt18 were important genes contributing to scale development and that PI3K-AKT was the most important signaling pathway involved. (4) With the use of the constructed G. przewalskii fibroblast cell line, emefp1, col1a1, col6a2, col16a1, krt8, and krt18 were confirmed to be positively regulated by the PI3K-AKT signaling pathway.

CONCLUSION

This study provides experimental evidence for PI3K-AKT controlled scale development in G. przewalskii and would benefit further study on stress adaptation, scale biomineralization, and the development of skin appendages.

Treadmill exercise with nanoselenium supplementation affects the expression of Irisin/FNDC5 and semaphorin 3A in rats exposed to cigarette smoke extract

In the current study, we investigated the impacts of 6 weeks of aerobic interval training (AIT) with selenium nanoparticles (SeNPs) on muscle, serum, and lung irisin (FNDC5) and Sema3A in rats exposed to cigarette smoke extract (CSE). To this end, 49 male Wistar rats (8 weeks old) were divided into seven groups: control, SeNPs (2.5 mg/kg b.w by oral gavage, 3 days/week, 6 weeks), AIT (49 min/day, 5 days/week for 6 weeks, interval), SeNPs + AIT, CSE (150 µL by IP injection, 1 day/week for 6 weeks), CSE + AIT, and CSE + SeNPs + AIT. The CSE group showed a significant reduction in irisin and Sema3A serum levels, as well as a decrease in FNDC5 and Sema3A gene expression in lung tissue (p < 0.05). A combined treatment (AIT with SeNPs) significantly increased the serum level and the expression of muscle and lung irisin (FNDC5) and Sema3A in CSE received groups (p < 0.05). There was a positive and significant correlation between muscle FNDC5 and lung FNDC5 in the CSE + SeNPs + AIT group (r = 0.92, p = 0.025). In addition, there was a positive and significant correlation between serum Sema3A and lung Sema3A of CSE + SeNPs + AIT group (r = 0.97, p = 0.004). Seemingly, performing aerobic exercises with the antioxidant and anti-inflammatory supplement nano-selenium in the model of lung damage (similar to COPD) can boost myokine irisin and Sema3A, especially in serum and lung tissue. These results displayed the paracrine/endocrine regulatory function of these myokines on other tissues. In other words, these interventions emphasized the creation of crosstalk between skeletal muscles and damaged lung, focusing on its recovery; however, further research is needed.

RAS‑stimulated release of exosomal miR‑494‑3p promotes the osteolytic bone metastasis of breast cancer cells

RAS activation is a key determinant of breast cancer progression and metastasis. However, the role of the interaction among exosomes, RAS and microRNAs (miRNAs/miRs) in the osteolytic bone metastasis of breast cancer remains unclear. Therefore, the present study aimed to examine the role of activated RAS (KRAS, HRAS and NRAS) in the release of exosome‑mediated osteoclastogenic miRNAs and to elucidate their functional role in bone microenvironment remodeling in vitro and in vivo. Exosomes derived from RAS‑activated breast cancer cells promoted RANKL‑induced osteoclastogenesis; however, RAS inhibition abolished this effect. miR‑494‑3p, miR‑4508 and miR‑6869‑5p were identified as osteoclastogenic miRNAs in the exosomes secreted by RAS‑activated breast cancer cells. The levels of these osteoclastogenic miRNAs in the sera of patients with human epidermal growth factor receptor 2‑positive luminal breast cancer were significantly higher than those in the sera of patients with triple‑negative breast cancer. miR‑494‑3p exhibited both osteoclastogenic and anti‑osteoblastogenic activity. Treatment with a miR‑494‑3p inhibitor abolished the exosome‑mediated increase in RANKL‑induced osteoclastogenesis. Treatment with a miR‑494‑3p mimic enhanced RANKL‑induced osteoclast formation; however, treatment with its inhibitor suppressed this effect by targeting leucine‑rich repeat‑containing G‑protein coupled receptor 4 in osteoclast precursors. Furthermore, miR‑494‑3p inhibited bone morphogenetic protein 2‑induced osteoblast formation by targeting semaphorin 3A. In a mouse model, exosomes derived from breast cancer cells promoted osteolytic bone lesions; however, treatment with a miR‑494‑3p inhibitor significantly suppressed this effect. On the whole, the present study provides a novel mechanism, demonstrating that the RAS activation of breast cancer cells induces osteolytic bone metastasis by stimulating the exosome‑mediated transfer of osteoclastogenic miRNAs, including miR‑494‑3p to bone cells.

Axon Fasciculation, Mediated by Transmembrane Semaphorins, Is Critical for the Establishment of Segmental Specificity of Corticospinal Circuits

Axon fasciculation is thought to be a critical step in neural circuit formation and function. Recent studies have revealed various molecular mechanisms that underlie axon fasciculation; however, the impacts of axon fasciculation, and its corollary, defasciculation, on neural circuit wiring remain unclear. Corticospinal (CS) neurons in the sensorimotor cortex project axons to the spinal cord to control skilled movements. In rodents, the axons remain tightly fasciculated in the brain and traverse the dorsal funiculus of the spinal cord. Here we show that plexinA1 (PlexA1) and plexinA3 (PlexA3) receptors are expressed by CS neurons, whereas their ligands, semaphorin-5A (Sema5A) and semaphorin-5B (Sema5B) are expressed in the medulla at the decussation site of CS axons to inhibit premature defasciculation of these axons. In the absence of Sema5A/5B-PlexA1/A3 signaling, some CS axons are prematurely defasciculated in the medulla of the brainstem, and those defasciculated CS axons aberrantly transverse in the spinal gray matter instead of the spinal dorsal funiculus. In the absence of Sema5A/Sema5B-PlexA1/A3 signaling, CS axons, which would normally innervate the lumbar spinal cord, are unbundled in the spinal gray matter, and prematurely innervate the cervical gray matter with reduced innervation of the lumbar gray matter. In both Sema5A/5B and PlexA1/A3 mutant mice (both sexes), stimulation of the hindlimb motor cortex aberrantly evokes robust forelimb muscle activation. Finally, Sema5A/5B and PlexA1/A3 mutant mice show deficits in skilled movements. These results suggest that proper fasciculation of CS axons is required for appropriate neural circuit wiring and ultimately affect the ability to perform skilled movements.SIGNIFICANCE STATEMENT Axon fasciculation is believed to be essential for neural circuit formation and function. However, whether and how defects in axon fasciculation affect the formation and function of neural circuits remain unclear. Here we examine whether the transmembrane proteins semaphorin-5A (Sema5A) and semaphorin-5B (Sema5B), and their receptors, plexinA1 (PlexA1) and plexinA3 (PlexA3) play roles in the development of corticospinal circuits. We find that Sema5A/Sema5B and PlexA1/A3 are required for proper axon fasciculation of corticospinal neurons. Furthermore, Sema5A/5B and PlexA1/A3 mutant mice show marked deficits in skilled motor behaviors. Therefore, these results strongly suggest that proper corticospinal axon fasciculation is required for the appropriate formation and functioning of corticospinal circuits in mice.

A mysterious triangle of blood, bones, and nerves

The relationship between bone tissue and bone marrow, which is responsible for hematopoiesis, is inseparable. Osteoblasts and osteocytes, which produce and consist of bone tissue, regulate the function of hematopoietic stem cells (HSC), the ancestors of all hematopoietic cells in the bone marrow. The peripheral nervous system finely regulates bone remodeling in bone tissue and modulates HSC function within the bone marrow, either directly or indirectly via modification of the HSC niche function. Peripheral nerve signals also play an important role in the development and progression of malignant tumors (including hematopoietic tumors) and normal tissues, and peripheral nerve control is emerging as a potential new therapeutic target. In this review, we summarize recent findings on the linkage among blood system, bone tissue, and peripheral nerves.

Structure and evolution of neuronal wiring receptors and ligands

One of the fundamental properties of a neuronal circuit is the map of its connections. The cellular and developmental processes that allow for the growth of axons and dendrites, selection of synaptic targets, and formation of functional synapses use neuronal surface receptors and their interactions with other surface receptors, secreted ligands, and matrix molecules. Spatiotemporal regulation of the expression of these receptors and cues allows for specificity in the developmental pathways that wire stereotyped circuits. The families of molecules controlling axon guidance and synapse formation are generally conserved across animals, with some important exceptions, which have consequences for neuronal connectivity. Here, we summarize the distribution of such molecules across multiple taxa, with a focus on model organisms, evolutionary processes that led to the multitude of such molecules, and functional consequences for the diversification or loss of these receptors.

Semaphorin 3A-Neuropilin-1 Signaling Modulates MMP13 Expression in Human Osteoarthritic Chondrocytes

Osteoarthritis (OA) is a complex disorder of diarthrodial joints caused by multiple risk factors and is characterized by articular cartilage destruction as well as changes in other articular tissues. Semaphorin 3A (Sema3A), known to be a chemo-repellent for sensory nerve fibers, has recently been implicated in cartilage OA pathophysiology. We demonstrated that the expression of SEMA3A and its receptor neuropilin-1 (NRP1) are synchronously upregulated in chondrocytes isolated from knee cartilage of OA patients compared to non-OA control chondrocytes. In addition, we observed that during in vitro passaging of OA chondrocytes, the Nrp-1 level increases, whereas the Sema3A level decreases. In this study, we aimed to uncover how Sema3A-Nrp-1 signaling affects metabolism and viability of OA chondrocytes via siRNA-mediated inhibition of Nrp-1 expression. We observed a decreased proliferation rate and an increase in adhesion and senescence after Nrp-1 silencing. Moreover, MMP13 gene expression was reduced by approximately 75% in NRP1 knockdown OA chondrocytes, whereas MMP13 expression was induced by Sema3A treatment in control (nt siRNA) OA chondrocytes, accompanied by an impaired AKT phosphorylation. These findings suggest a potential catabolic function of Sema3A signaling in OA chondrocytes by inducing MMP13 expression and by compromising pro-survival AKT activation. We propose that targeting the Sema3A-Nrp-1 signaling axis might be an opportunity to interfere with OA pathogenesis and progression.

A Review on the Technological Advances and Future Perspectives of Axon Guidance and Regeneration in Peripheral Nerve Repair

Despite a significant advance in the pathophysiological understanding of peripheral nerve damage, the successful treatment of large nerve defects remains an unmet medical need. In this article, axon growth guidance for peripheral nerve regeneration was systematically reviewed and discussed mainly from the engineering perspective. In addition, the common approaches to surgery, bioengineering approaches to emerging technologies such as optogenetic stimulation and magnetic stimulation for functional recovery were discussed, along with their pros and cons. Additionally, clear future perspectives of axon guidance and nerve regeneration were addressed.

Malignant Transformation of Giant Cell Tumour of Bone: A Review of Literature and the Experience of a Referral Centre

Giant cell tumour of bone (GCTB) is a benign, locally aggressive primary bone neoplasm that represents 5% of all bone tumours. The principal treatment approach is surgery. Although generally GCTB is considered only a locally aggressive disease, it can metastasise, and lung metastases occur in 1–9% of patients. To date, only the use of denosumab has been approved as medical treatment for GCTB. Even more rarely, GCTB undergoes sarcomatous transformation into a malignant tumour (4% of all GCTB), but history of this malignant transformation is unclear and unpredictable. Considering the rarity of the event, the data in the literature are few. In this review, we summarise published data of GCTB malignant transformation and we analyse three cases of malignant transformation of GCTB, evaluating histopathology, genetics, and radiological aspects. Despite the rarity of this event, we conclude that a strict follow up is recommended to detect early malignant transformation.

Neuronal Guidance Molecules in Bone Remodeling and Orthodontic Tooth Movement

During orthodontic tooth movement, mechanically induced remodeling occurs in the alveolar bone due to the action of orthodontic forces. The number of factors identified to be involved in mechanically induced bone remodeling is growing steadily. With the uncovering of the functions of neuronal guidance molecules (NGMs) for skeletal development as well as for bone homeostasis, NGMs are now also among the potentially significant factors for the regulation of bone remodeling during orthodontic tooth movement. This narrative review attempts to summarize the functions of NGMs in bone homeostasis and provides insight into the currently sparse literature on the functions of these molecules during orthodontic tooth movement. Presently, four families of NGMs are known: Netrins, Slits, Semaphorins, ephrins and Eph receptors. A search of electronic databases revealed roles in bone homeostasis for representatives from all four NGM families. Functions during orthodontic tooth movement, however, were only identified for Semaphorins, ephrins and Eph receptors. For these, crucial prerequisites for participation in the regulation of orthodontically induced bone remodeling, such as expression in cells of the periodontal ligament and in the alveolar bone, as well as mechanical inducibility, were shown, which suggests that the importance of NGMs in orthodontic tooth movement may be underappreciated to date and further research might be warranted.

Directed mechanisms for apical dendrite development during neuronal polarization

The development of the dendrite and the axon during neuronal polarization underlies the directed flow of information in the brain. Seminal studies on axon development have dominated the mechanistic analysis of neuronal polarization. These studies, many originating from examinations in cultured hippocampal and cortical neurons in vitro, have established a prevalent view that axon formation precedes and is necessary for neuronal polarization. There is also in vivo evidence supporting this view. Nevertheless, the establishment of bipolar polarity and the leading edge, and apical dendrite development in pyramidal neurons in vivo occur when axon formation is prevented. Furthermore, recent mounting evidence suggest that directed mechanisms might mediate bipolar polarity/leading process and subsequent apical dendrite development. In the presence of spatially directed extracellular cues in the developing brain, these events may operate independently of axon forming events. In this perspective we summarize evidence in support of these evolving views in neuronal polarization and highlight recent findings on dedicated mechanisms acting in apical dendrite development.

Sema3A accelerates bone formation during distraction osteogenesis in mice

Distraction osteogenesis (DO) is a bone regeneration technique used to treat maxillofacial disorders, fracture nonunion, and large bone defects. It is well known for its amazing regenerative potential, but an extended consolidation period limits its clinical use. The interaction between the nervous system and bone regeneration has attracted great attention in recent years. Sema3A is a key axonal chemorepellent which has been proved to have bone-protective effects. In this article, we try to improve DO by local administration of Sema3A and explore the possible mechanisms. Forty wildtype, male, adult mice were divided into two groups after tibia osteotomy surgery. Sema3A or Saline was daily injected transcutaneous into the center of the distraction zone during the consolidation period. Micro-CT images were taken at 4, 6,8 and 10 weeks post-surgery; vascular density and biomechanical testing were performed at 10 weeks post-surgery. We also set up in vitro vessel growth assay to evaluate the effect of Sema3A on angiogenesis. Compared with the Saline group, Sema3A treatment significantly accelerated bone regeneration, improved angiogenesis and callus' biomechanical strength. At 10 weeks post-surgery, compared with the Saline group, the BV/TV, BMD, TMD increased by about 23%, 22%, 18% respectively, vascular density increased by about 49% in the Sema3A group. Histological images and western-blot showed decreased expression of VEGF-A and increased expression of Ang-1 at 4 weeks post-surgery in the Sema3A group. In vitro, Sema3A suppressed VEGF-induced angiogenesis but had little effect on Ang-induced angiogenesis. Conclusion: Sema3A could accelerate bone regeneration and improve angiogenesis during DO.

Secondary Malignancy in Giant Cell Tumor: A Single-Center Study

Giant cell tumor of bone (GCTB) undergoes a sarcomatous transformation. Secondary malignancy in giant cell tumor (MGCT) is associated with radiotherapy and has a dismal prognosis. We reviewed medical records to investigate the clinicopathological characteristics and prognosis of MGCT patients. The enrollment criterion was high-grade spindle-cell sarcoma, which developed at the site of prior GCTB treatment. Twelve patients were analyzed: six females and six males. The median age was 42.5 years. Benign recurrence occurred in five GCTB patients not treated with radiotherapy. No pulmonary implants were observed. The median latency to the malignant transformation was 63 months. Nine patients were AJCC stage IIB, and three were stage IVA. The median follow-up period after malignant transformation was 62.5 months. Five patients developed local recurrence, and six had distant metastasis. Five-year overall recurrence and metastasis-free survival rates were 61.9%, 66.7%, and 58.3%, respectively. Initial metastasis was a predictive factor for overall survival. Benign local recurrence of GCTB was also a negative factor for metastasis-free survival of MGCT patients. Differences in overall survival according to benign recurrence also showed a tendency toward significance. In our series, secondary MGCT did not occur after radiotherapy. The prognosis was better than previous findings. Benign recurrence of GCTB could reflect the prognosis of MGCT.

Crosstalk between axon guidance signaling and bone remodeling

The maintenance of skeletal integrity is tightly regulated by two cell types, bone forming osteoblasts and bone resorbing osteoclasts. Although the role of the nervous system in regulating osteoblasts and osteoclasts was identified over a decade ago, the molecular mechanism of skeletal-neural interactions in bone homeostasis has only been studied recently. In particular, the complex roles of axon guidance molecules, such as semaphorins and ephrins, in the bone have been studied extensively. In this review, we highlight the latest advances in determining the functions of semaphorins and ephrins in the establishment and maintenance of the skeletal system, with a focus on the functional interaction between the skeletal and nervous systems.

Semaphorin3A/PlexinA3 association with the Scribble scaffold for cGMP increase is required for apical dendrite development

The development of the apical dendrite from the leading process of the bipolar pyramidal neuron might be directed by spatially organized extrinsic cues acting on localized intrinsic determinants. The extracellular cues regulating apical dendrite polarization remain elusive. We show that leading process and apical dendrite development are directed by class III Semaphorins and mediated by a localized cGMP-synthesizing complex. The scaffolding protein Scribble that associates with the cGMP-synthesizing enzyme soluble guanylate cyclase (sGC) also associates with the Semaphorin3A (Sema3A) co-receptor PlexinA3. Deletion or knockdown of PlexinA3 and Sema3A or disruption of PlexinA3-Scribble association prevents Sema3A-mediated cGMP increase and causes defects in apical dendrite development. These manipulations also impair bipolar polarity and leading process establishment. Local cGMP elevation or sGC expression rescues the effects of PlexinA3 knockdown or PlexinA3-Scribble complex disruption. During neuronal polarization, leading process and apical dendrite development are directed by a scaffold that links Semaphorin cue to cGMP increase.

Szczurkowska et al. show that spatially directed Sema3A may promote development of the leading process and the apical dendrite via the co-receptor PlexinA3 by orchestrating localized cGMP increase on the scaffold protein, Scribble, at the leading edge of developing pyramidal neurons.

Basolateral Amygdala Mediates Central Mechanosensory Feedback of Musculoskeletal System

Musculoskeletal diseases, such as osteoporosis and sarcopenia, are tremendous and growing public health concerns. Considering the intimate functional relationship between muscle and bone throughout development, growth, and aging, muscle provides the primary source of skeletal loading through contraction force. However, significant gaps exist in our knowledge regarding the role of muscle in bone homeostasis and little is known regarding the mechanism through which the central nervous system responds and regulates unloading-induced bone loss. Here, we showed that the basolateral amygdala (BLA) and medial part of the central nucleus (CeM) are anatomically connected with the musculoskeletal system. Unloading-induced bone loss is accompanied by a decrease in serum semaphorin 3A (Sema3A) levels as well as sensory denervation. In vivo fiber photometry recordings indicated that the mechanical signal is integrated by the BLA and CeM within 24 h and subsequently regulates bone remodeling. Moreover, chemogenetic activation of BLA^CaMKII neurons mitigates severe bone loss caused by mechanical unloading via increased serum levels of Sema3A and sensory innervation. These results indicate that the BLA integrates the mechanosensory signals rapidly and mediates the systemic hormonal secretion of Sema3A to maintain bone homeostasis.

Semaphorin 3A attenuates the hypoxia suppression of osteogenesis in periodontal ligament stem cells

OBJECTIVE AND BACKGROUND

The occurrence and development of periodontitis are closely related to hypoxia of the periodontal microenvironment. Periodontal ligament stem cells (PDLSCs) are considered to have potential to regenerate periodontal tissues. Semaphorin 3A (Sema3A) plays an essential role in promoting osteogenesis. However, the effect of Sema3A on osteogenesis of PDLSCs under hypoxia remains unclear. The aim of this study was to investigate the effect of Sema3A on osteogenesis of PDLSCs under hypoxia.

METHODS

Isolated PDLSCs were identified using flow cytometry. Adipogenic differentiation potential was identified by oil red O staining. Osteogenesis was measured using Alizarin Red S staining and ALP staining. Intracellular hypoxia was induced using cobalt chloride (CoCl₂ ). The expression level of hypoxia-inducible factor-1α (HIF-1α) was detected via ELISA. Expression of osteogenic markers and Sema3A was analyzed using western blot and real-time PCR.

RESULTS

The proliferation and osteogenesis of PDLSCs were markedly inhibited with increased concentrations of CoCl₂ . Under the treatment with a low concentration of CoCl₂ , expression of related osteogenic markers and Sema3A decreased in a time-dependent manner. ARS and ALP staining results also showed that osteogenic calcification decreased under hypoxia. Apigenin, an inhibitor of HIF-1α, effectively up-regulated expression of Sema3A and osteogenic markers with CoCl₂ treatment. Moreover, exogenous Sema3A significantly increased the expression of osteogenesis-related markers and mineralization of PDLSCs according to ALP and ARS staining with CoCl₂ treatment.

CONCLUSIONS

Hypoxia markedly inhibited osteogenesis of PDLSCs. Sema3A explicitly attenuated the hypoxia suppression of osteogenesis in PDLSCs.

KCNQ1OT1 inhibition alleviates high glucose-induced podocyte injury by adsorbing miR-23b-3p and regulating Sema3A

BACKGROUND

Diabetic nephropathy (DN), a diabetic complication, is the leading cause of end-stage renal disease. KCNQ1 opposite strand/antisense transcript 1 (KCNQ1OT1), a long non-coding RNA, has been unmasked to participate in the pathogenesis of DN. However, the specific mechanism by which KCNQ1OT1 regulates podocyte injury remains unclear.

METHODS

Relative expression of KCNQ1OT1 was measured with quantitative real-time polymerase chain reaction (qRT-PCR). The levels of inflammatory cytokines were analyzed by enzyme linked immunosorbent assay (ELISA). The viability, proliferation, and apoptosis of high glucose (HG)-treated podocyte were analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), 5-ethynyl-2'-deoxyuridine (EdU), and flow cytometry assays. Protein levels were analyzed by western blotting. The regulatory mechanism of KCNQ1OT1 was surveyed by bioinformatics analysis, dual-luciferase reporter, and RNA immunoprecipitation (RIP) assays.

RESULTS

We observed an apparent upregulation in KCNQ1OT1 expression in serums of DN patients and HG-treated podocytes. Furthermore, KCNQ1OT1 downregulation alleviated HG-induced inflammation, proliferation repression, and apoptosis in podocytes. Notably, KCNQ1OT1 was identified as a miR-23b-3p sponge, and miR-23b-3p directly targeted Semaphorin-3A (Sema3A). Moreover, miR-23b-3p silencing reversed KCNQ1OT1 knockdown-mediated effects on inflammation, proliferation, and apoptosis of HG-induced podocytes. Also, Sema3A overexpression reversed the effects of miR-23b-3p mimic on inflammation, proliferation, and apoptosis of HG-induced podocytes. Importantly, KCNQ1OT1 regulated Sema3A expression by sponging miR-23b-3p.

CONCLUSIONS

HG-induced KCNQ1OT1 promoted inflammation, proliferation repression, and apoptosis of podocytes via increasing Sema3A expression through sponging miR-23b-3p. This study provided evidence to support the involvement of KCNQ1OT1 in the pathogenesis of DN.

Recent Advances in Osteoclast Biological Behavior

With the progress of the aging population, bone-related diseases such as osteoporosis and osteoarthritis have become urgent problems. Recent studies have demonstrated the importance of osteoclasts in bone homeostasis, implying these will be an important mediator in the treatment of bone-related diseases. Up to now, several reviews have been performed on part of osteoclast biological behaviors such as differentiation, function, or apoptosis. However, few reviews have shown the complete osteoclast biology and research advances in recent years. Therefore, in this review, we focus on the origin, differentiation, apoptosis, behavior changes and coupling signals with osteoblasts, providing a simple but comprehensive overview of osteoclasts for subsequent studies.

Neuropilin 1 regulates bone marrow vascular regeneration and hematopoietic reconstitution

Ionizing radiation and chemotherapy deplete hematopoietic stem cells and damage the vascular niche wherein hematopoietic stem cells reside. Hematopoietic stem cell regeneration requires signaling from an intact bone marrow (BM) vascular niche, but the mechanisms that control BM vascular niche regeneration are poorly understood. We report that BM vascular endothelial cells secrete semaphorin 3 A (SEMA3A) in response to myeloablation and SEMA3A induces p53 - mediated apoptosis in BM endothelial cells via signaling through its receptor, Neuropilin 1 (NRP1), and activation of cyclin dependent kinase 5. Endothelial cell - specific deletion of Nrp1 or Sema3a or administration of anti-NRP1 antibody suppresses BM endothelial cell apoptosis, accelerates BM vascular regeneration and concordantly drives hematopoietic reconstitution in irradiated mice. In response to NRP1 inhibition, BM endothelial cells increase expression and secretion of the Wnt signal amplifying protein, R spondin 2. Systemic administration of anti - R spondin 2 blocks HSC regeneration and hematopoietic reconstitution which otherwise occurrs in response to NRP1 inhibition. SEMA3A - NRP1 signaling promotes BM vascular regression following myelosuppression and therapeutic blockade of SEMA3A - NRP1 signaling in BM endothelial cells accelerates vascular and hematopoietic regeneration in vivo.

The role of the odorant receptors in the formation of the sensory map

In the olfactory system, odorant receptors (ORs) expressed at the cell membrane of olfactory sensory neurons detect odorants and direct sensory axons toward precise target locations in the brain, reflected in the presence of olfactory sensory maps. This dual role of ORs is corroborated by their subcellular expression both in cilia, where they bind odorants, and at axon terminals, a location suitable for axon guidance cues. Here, we provide an overview and discuss previous work on the role of ORs in establishing the topographic organization of the olfactory system and recent findings on the mechanisms of activation and function of axonal ORs.

A Multi-Omics Approach Using a Mouse Model of Cardiac Malformations for Prioritization of Human Congenital Heart Disease Contributing Genes

Congenital heart disease (CHD) is the most common type of birth defect, affecting ~1% of all live births. Malformations of the cardiac outflow tract (OFT) account for ~30% of all CHD and include a range of CHDs from bicuspid aortic valve (BAV) to tetralogy of Fallot (TOF). We hypothesized that transcriptomic profiling of a mouse model of CHD would highlight disease-contributing genes implicated in congenital cardiac malformations in humans. To test this hypothesis, we utilized global transcriptional profiling differences from a mouse model of OFT malformations to prioritize damaging, de novo variants identified from exome sequencing datasets from published cohorts of CHD patients. Notch1 +/- ; Nos3 -/- mice display a spectrum of cardiac OFT malformations ranging from BAV, semilunar valve (SLV) stenosis to TOF. Global transcriptional profiling of the E13.5 Notch1 +/- ; Nos3 -/- mutant mouse OFTs and wildtype controls was performed by RNA sequencing (RNA-Seq). Analysis of the RNA-Seq dataset demonstrated genes belonging to the Hif1α, Tgf-β, Hippo, and Wnt signaling pathways were differentially expressed in the mutant OFT. Mouse to human comparative analysis was then performed to determine if patients with TOF and SLV stenosis display an increased burden of damaging, genetic variants in gene homologs that were dysregulated in Notch1 +/- ; Nos3 -/- OFT. We found an enrichment of de novo variants in the TOF population among the 1,352 significantly differentially expressed genes in Notch1 +/- ; Nos3 -/- mouse OFT but not the SLV population. This association was not significant when comparing only highly expressed genes in the murine OFT to de novo variants in the TOF population. These results suggest that transcriptomic datasets generated from the appropriate temporal, anatomic and cellular tissues from murine models of CHD may provide a novel approach for the prioritization of disease-contributing genes in patients with CHD.

A Potential Role of Semaphorin 3A during Orthodontic Tooth Movement

BACKGROUND

Induced tooth movement during orthodontic therapy requires mechano-induced bone remodeling. Besides various cytokines and growth-factors, neuronal guidance molecules gained attention for their roles in bone homeostasis and thus, potential roles during tooth movement. Several neuronal guidance molecules have been implicated in the regulation of bone remodeling. Amongst them, Semaphorin 3A is particular interesting as it concurrently induces osteoblast differentiation and disturbs osteoclast differentiation.

METHODS

Mechano-regulation of Sema3A and its receptors PlexinA1 and Neuropilin (RT-qPCR, WB) was evaluated by applying compressive and tension forces to primary human periodontal fibroblasts (hPDLF) and alveolar bone osteoblasts (hOB). The association of the transcription factor Osterix (SP7) and SEMA3A was studied by RT-qPCR. Mechanisms involved in SEMA3A-mediated osteoblast differentiation were assessed by Rac1GTPase pull-downs, β-catenin expression analyses (RT-qPCR) and nuclear translocation assays (IF). Osteogenic markers were analyzed by RT-qPCR.

RESULTS

SEMA3A, PLXNA1 and NRP1 were differentially regulated by tension or compressive forces in hPDLF. Osterix (SP7) displayed the same pattern of regulation. Recombinant Sema3A induced the activation of Rac1GTPase, the nuclear translocation of β-catenin and the expression of osteogenic marker genes.

CONCLUSION

Sema3A, its receptors and Osterix are regulated by mechanical forces in hPDLF. SEMA3A upregulation was associated with Osterix (SP7) modulation. Sema3A-enhanced osteogenic marker gene expression in hOB might be dependent on a pathway involving Rac1GTPase and β-catenin. Thus, Semaphorin 3A might contribute to bone remodeling during induced tooth movement.

Interactions between semaphorins and plexin-neuropilin receptor complexes in the membranes of live cells

Signaling of semaphorin ligands via their plexin-neuropilin receptors is involved in tissue patterning in the developing embryo. These proteins play roles in cell migration and adhesion but are also important in disease etiology, including in cancer angiogenesis and metastasis. While some structures of the soluble domains of these receptors have been determined, the conformations of the full-length receptor complexes are just beginning to be elucidated, especially within the context of the plasma membrane. Pulsed-interleaved excitation fluorescence cross-correlation spectroscopy allows direct insight into the formation of protein-protein interactions in the membranes of live cells. Here, we investigated the homodimerization of neuropilin-1 (Nrp1), plexin A2, plexin A4, and plexin D1 using pulsed-interleaved excitation fluorescence cross-correlation spectroscopy. Consistent with previous studies, we found that Nrp1, plexin A2, and plexin A4 are present as dimers in the absence of exogenous ligand. Plexin D1, on the other hand, was monomeric under similar conditions, which had not been previously reported. We also found that plexin A2 and A4 assemble into a heteromeric complex. Stimulation with semaphorin 3A or semaphorin 3C neither disrupts nor enhances the dimerization of the receptors when expressed alone, suggesting that activation involves a conformational change rather than a shift in the monomer-dimer equilibrium. However, upon stimulation with semaphorin 3C, plexin D1 and Nrp1 form a heteromeric complex. This analysis of interactions provides a complementary approach to the existing structural and biochemical data that will aid in the development of new therapeutic strategies to target these receptors in cancer.

Vinaxanthone inhibits Semaphorin3A induced axonal growth cone collapse in embryonic neurons but fails to block its growth promoting effects on adult neurons

Semaphorin3A is considered a classical repellent molecule for developing neurons and a potent inhibitor of regeneration after nervous system trauma. Vinaxanthone and other Sema3A inhibitors are currently being tested as possible therapeutics to promote nervous system regeneration from injury. Our previous study on Sema3A demonstrated a switch in Sema3A's function toward induction of nerve regeneration in adult murine corneas and in culture of adult peripheral neurons. The aim of the current study is to determine the direct effects of Vinaxanthone on the Sema3A induced adult neuronal growth. We first demonstrate that Vinaxanthone maintains its anti-Sema3A activity in embryonic dorsal root ganglia neurons by inhibiting Sema3A-induced growth cone collapse. However, at concentrations approximating its IC50 Vinaxanthone treatment does not significantly inhibit neurite formation of adult peripheral neurons induced by Sema3A treatment. Furthermore, Vinaxanthone has off target effects when used at concentrations above its IC50, and inhibits neurite growth of adult neurons treated with either Sema3A or NGF. Our results suggest that Vinaxanthone's pro-regenerative effects seen in multiple in vivo models of neuronal injury in adult animals need further investigation due to the pleiotropic effect of Sema3A on various non-neuronal cell types and the possible effect of Vinaxanthone on other neuroregenerative signals.

Glucocorticoids suppressed osteoblast differentiation by decreasing Sema3A expression via the PIK3/Akt pathway

Glucocorticoids(GCs) are extensively used to treat inflammatory and autoimmune diseases. Excessive prolonged exposure to glucocorticoids is associated with an increased risk of osteoporosis. The inhibition of osteoblast differentiation by GCs is suggested as a major cause for GCs-induced osteoporosis (GIO). However, the precise mechanism underlying the role of GCs in osteoblasts differentiation is not fully elucidated. Semaphorin 3A (Sema3A), a secreted member of the Semaphorin family, enhances bone formation and promotes fracture healing, which is known to increase osteoblastic differentiation and stimulate osteogenesis in bone metabolism. Here, the present study explored the effect of Sema3A in osteoblast differentiation using dexamethasone (Dex) treatment of bone marrow stromal cells (BMSCs). Dex treatment decreased Sema3A expression in BMSCs in a dose-dependent manner. Moreover, Dex stimulation suppressed the differentiation of osteoblasts by reducing alkaline phosphatase (ALP) activity, osteoblastic marker genes expression and mineralization, but all of these effects were ameliorated by exogenous recombinant Sema3A administration. Furthermore, exogenous Sema3A administration reversed the Dex-mediated decrease in nuclear accumulation of β-catenin and β-catenin activity in BMSCs. Meanwhile, Dex was capable of simultaneously suppressing the phosphorylation of protein kinase B(Akt) and the expression level of Sema3A in BMSCs. These changes were significantly abolished by the PI3K/Akt agonist. These results suggest that Dex inhibits osteoblast differentiation by suppressing Sema3A expression via the PI3K/Akt pathway. These data provide new insights into the molecular mechanisms of Dex-induced osteoblast differentiation inhibition.

A Localized Scaffold for cGMP Increase Is Required for Apical Dendrite Development

Studies in cultured neurons have established that axon specification instructs neuronal polarization and is necessary for dendrite development. However, dendrite formation in vivo occurs when axon formation is prevented. The mechanisms promoting dendrite development remain elusive. We find that apical dendrite development is directed by a localized cyclic guanosine monophosphate (cGMP)-synthesizing complex. We show that the scaffolding protein Scribble associates with cGMP-synthesizing enzymes soluble-guanylate-cyclase (sGC) and neuronal nitric oxide synthase (nNOS). The Scribble scaffold is preferentially localized to and mediates cGMP increase in dendrites. These events are regulated by kinesin KifC2. Knockdown of Scribble, sGC-β1, or KifC2 or disrupting their associations prevents cGMP increase in dendrites and causes severe defects in apical dendrite development. Local cGMP elevation or sGC expression rescues the effects of Scribble knockdown on dendrite development, indicating that Scribble is an upstream regulator of cGMP. During neuronal polarization, dendrite development is directed by the Scribble scaffold that might link extracellular cues to localized cGMP increase.

SEMAPHORINS and their receptors: focus on the crosstalk between melanoma and hypoxia

Hypoxia, a condition of oxygen deprivation, is considered a hallmark of tumor microenvironment regulating several pathways and promoting cancer progression and resistance to therapy. Semaphorins, a family of about 20 secreted, transmembrane and GPI-linked glycoproteins, and their cognate receptors (plexins and neuropilins) play a pivotal role in the crosstalk between cancer and stromal cells present in the tumor microenvironment. Many studies reported that some semaphorins are involved in the development of a permissive tumor niche, guiding cell-cell communication and, consequently, the development and progression, as well as the response to therapy, of different cancer histotypes, including melanoma.

In this review we will summarize the state of art of semaphorins regulation by hypoxic condition in cancer with different origin. We will also describe evidence about the ability of semaphorins to affect the expression and activity of transcription factors activated by hypoxia, such as hypoxia-inducible factor-1. Finally, we will focus our attention on findings reporting the role of semaphorins in melanocytes transformation, melanoma progression and response to therapy. Further studies are necessary to understand the mechanisms through which semaphorins induce their effect and to shed light on the possibility to use semaphorins or their cognate receptors as prognostic markers and/or therapeutic targets in melanoma or other malignancies.

Semaphorin3E-PlexinD1 signaling in coronary artery and lymphatic vessel development with clinical implications in myocardial recovery

Blood and lymphatic vessels surrounding the heart develop through orchestrated processes from cells of different origins. In particular, cells around the outflow tract which constitute a primordial transient vasculature, referred to as aortic subepicardial vessels, are crucial for the establishment of coronary artery stems and cardiac lymphatic vessels. Here, we revealed that the epicardium and pericardium-derived Semaphorin 3E (Sema3E) and its receptor, PlexinD1, play a role in the development of the coronary stem, as well as cardiac lymphatic vessels. In vitro analyses demonstrated that Sema3E may demarcate areas to repel PlexinD1-expressing lymphatic endothelial cells, resulting in proper coronary and lymphatic vessel formation. Furthermore, inactivation of Sema3E-PlexinD1 signaling improved the recovery of cardiac function by increasing reactive lymphangiogenesis in an adult mouse model of myocardial infarction. These findings may lead to therapeutic strategies that target Sema3E-PlexinD1 signaling in coronary artery diseases.

Crosstalk between skeletal and neural tissues is critical for skeletal health

Emerging evidence in the literature describes a physical and functional association between the neural and skeletal systems that forms a neuro-osteogenic network. This communication between bone cells and neural tissues within the skeleton is important in facilitating bone skeletal growth, homeostasis and repair. The growth and repair of the skeleton is dependent on correct neural innervation for correct skeletal developmental growth and fracture repair, while pathological conditions such as osteoporosis are accelerated by disruptions to sympathetic innervation. To date, different molecular mechanisms have been reported to mediate communication between bone and neural populations. This review highlights the important role of various cell surface receptors, cytokines and associated ligands as potential regulators of skeletal development, homeostasis, and repair, by mediating interactions between the skeletal and nervous systems. Specifically, this review describes how Bone Morphogenetic Proteins (BMPs), Eph/ephrin, Chemokine CXCL12, Calcitonin Gene-related Peptide (CGRP), Netrins, Neurotrophins (NTs), Slit/Robo and the Semaphorins (Semas) contribute to the cross talk between bone cells and peripheral nerves, and the importance of these interactions in maintaining skeletal health.

Further delineation of a recognizable type of syndromic short stature caused by biallelic SEMA3A loss-of-function variants

The semaphorin protein family is a diverse set of extracellular signaling proteins that perform fundamental roles in the development and operation of numerous biological systems, notably the nervous, musculoskeletal, cardiovascular, endocrine, and reproductive systems. Recently, recessive loss-of-function (LoF) variants in SEMA3A (semaphorin 3A) have been shown to result in a recognizable syndrome characterized by short stature, skeletal abnormalities, congenital heart defects, and variable additional anomalies. Here, we describe the clinical and molecular characterization of a female patient presenting with skeletal dysplasia, hypogonadotropic hypogonadism (HH), and anosmia who harbors a nonsense variant c.1633C>T (p.Arg555*) and a deletion of exons 15, 16, and 17 in SEMA3A in the compound heterozygous state. These variants were identified through next-generation sequencing analysis of a panel of 26 genes known to be associated with HH/Kallmann syndrome. Our findings further substantiate the notion that biallelic LoF SEMA3A variants cause a syndromic form of short stature and expand the phenotypic spectrum associated with this condition to include features of Kallmann syndrome.

Denosumab in Giant Cell Tumor of Bone: Current Status and Pitfalls

Denosumab is a monoclonal antibody against RANK ligand for treatment of giant cell tumor of bone (GCTB). Clinical trials and case series have demonstrated that denosumab is relevant to beneficial tumor response and surgical down-staging in patients of GCTB. However, these trials or case series have limitations with a short follow-up. Recent increasing studies revealed that denosumab probably increased the local recurrence risk in patients treated with curettage. This may be caused by the thicken bone margin of tumor that trapped tumor cells from curettage. The direct bone formation by tumor cells in the margin after denosumab treatment also contributed to the local recurrence. in vitro studies showed denosumab resulted in a cytostatic instead of a true cytotoxic response on neoplastic stromal cells. More importantly, denosumab-treated GCTB exhibited morphologic overlap with malignancy, and a growing number of patients of malignant transformation of GCTB during denosumab treatment have been reported. The optimal duration, long term safety, maintenance dose, and optimum indications remain to be elucidated. With these concerns in mind, this review warns that the denosumab therapy of GCTB should be applied with caution.

Osteoblast-Osteoclast Communication and Bone Homeostasis

Bone remodeling is tightly regulated by a cross-talk between bone-forming osteoblasts and bone-resorbing osteoclasts. Osteoblasts and osteoclasts communicate with each other to regulate cellular behavior, survival and differentiation through direct cell-to-cell contact or through secretory proteins. A direct interaction between osteoblasts and osteoclasts allows bidirectional transduction of activation signals through EFNB2-EPHB4, FASL-FAS or SEMA3A-NRP1, regulating differentiation and survival of osteoblasts or osteoclasts. Alternatively, osteoblasts produce a range of different secretory molecules, including M-CSF, RANKL/OPG, WNT5A, and WNT16, that promote or suppress osteoclast differentiation and development. Osteoclasts also influence osteoblast formation and differentiation through secretion of soluble factors, including S1P, SEMA4D, CTHRC1 and C3. Here we review the current knowledge regarding membrane bound- and soluble factors governing cross-talk between osteoblasts and osteoclasts.

Hypoxia-induced downregulation of Sema3a and CXCL12/CXCR4 regulate the formation of the coronary artery stem at the proper site

BACKGROUND

During the formation of the coronary artery stem, endothelial strands from the endothelial progenitor pool surrounding the conotruncus penetrate into the aortic wall. Vascular endothelial growth factors (VEGFs) as well as CXCL12/CXCR4 signaling are thought to play a role in the formation of the coronary stem. However, the mechanisms regulating how endothelial strands exclusively invade into the aorta remain unknown.

METHODS AND RESULTS

Immunohistochemistry showed that before the formation of endothelial strands, Sema3a was highly expressed in endothelial progenitors surrounding the great arteries. At the onset of/during invasion of endothelial strands into the aorta, Sema3a was downregulated and CXCR4 was upregulated in the endothelial strands. In situ hybridization showed that Cxcl12 was highly expressed in the aortic wall compared with in the pulmonary artery. Using avian embryonic hearts, we established two types of endothelial penetration assay, in which coronary endothelial strands preferentially invaded into the aorta in culture. Sema3a blocking peptide induced an excess number of endothelial strands penetrating into the pulmonary artery, whereas recombinant Sema3a inhibited the formation of endothelial strands. In cultured coronary endothelial progenitors, recombinant VEGF protein induced CXCR4-positive endothelial strands, which were capable of being attracted by CXCL12-impregnated beads. Monoazo rhodamine detected that hypoxia was predominant in aortic/subaortic region in ovo and hypoxic condition downregulated the expression of Sema3a in culture.

CONCLUSION

Results suggested that hypoxia in the aortic region downregulates the expression of Sema3a, thereby enhancing VEGF activity to induce the formation of CXCR4-positive endothelial strands, which are subsequently attracted into the Cxcl12-positive aortic wall to connect the aortic lumen.

Shootin-1 is required for nervous system development in zebrafish

BACKGROUND

Semaphorin6A (Sema6A) and its PlexinA2 (PlxnA2) receptor canonically function as repulsive axon guidance cues. To understand downstream signaling mechanisms, we performed a microarray screen and identified the "clutch molecule" shootin-1 (shtn-1) as a transcriptionally repressed target. Shtn-1 is a key proponent of cell migration and neuronal polarization and must be regulated during nervous system development. The mechanisms of Shtn-1 regulation and the phenotypic consequences of loss of repression are poorly understood.

RESULTS

We demonstrate shtn-1 overexpression results in impaired migration of the optic vesicles, lack of retinal pigmented epithelium, and pathfinding errors of retinotectal projections. We also observed patterning defects in the peripheral nervous system. Importantly, these phenotypes were rescued by overexpressing PlxnA2.

CONCLUSIONS

We demonstrate a functional role for repression of shtn-1 by PlxnA2 in development of the eyes and peripheral nervous system in zebrafish. These results demonstrate that careful regulation of shtn-1 is critical for development of the nervous system.

Premature satellite cell activation before injury accelerates myogenesis and disrupts neuromuscular junction maturation in regenerating muscle

Satellite cell (SC) activation, mediated by nitric oxide (NO), is essential to myogenic repair, whereas myotube function requires innervation. Semaphorin (Sema) 3A, a neuro-chemorepellent, is thought to regulate axon guidance to neuromuscular junctions (NMJs) during myotube differentiation. We tested whether "premature" SC activation (SC activation before injury) by a NO donor (isosorbide dinitrate) would disrupt early myogenesis and/or NMJs. Adult muscle was examined during regeneration in two models of injury: myotoxic cardiotoxin (CTX) and traumatic crush (CR) (n = 4-5/group). Premature SC activation was confirmed by increased DNA synthesis by SCs immediately in pretreated mice after CTX injury. Myotubes grew faster after CTX than after CR; growth was accelerated by pretreatment. NMJ maturation, classified by silver histochemistry (neurites) and acetylcholinesterase (AchE), and α-bungarotoxin staining (Ach receptors, AchRs) were delayed by pretreatment, consistent with a day 6 rise in the denervation marker γ-AchR. With pretreatment, S100B from terminal Schwann cells (TSCs) increased 10- to 20-fold at days 0 and 10 after CTX and doubled 6 days after CR. Premature SC activation disrupted motoneuritogenesis 8-10 days post-CTX, as pretreatment reduced colocalization of pre- and postsynaptic NMJ features and increased Sema3A-65. Premature SC activation before injury both accelerated myogenic repair and disrupted NMJ remodeling and maturation, possibly by reducing Sema3A neuro-repulsion and altering S100B. This interpretation extends the model of Sema3A-mediated motoneuritogenesis during muscle regeneration. Manipulating the timing and type of Sema3A by brief NO effects on SCs suggests an important role for TSCs and Sema3A-65 processing in axon guidance and NMJ restoration during muscle repair.

The neural system regulates bone homeostasis via mesenchymal stem cells: a translational approach

Large bone reconstruction is a major clinical issue associated with several challenges, and autograft is the main method for reconstructing large defects of maxillofacial bone. However, postoperative osteoporosis of the bone graft, even with sufficient vascularization, remains a primary problem. Therefore, better understanding of the mechanisms and clinical translation of bone homeostasis is required. Neuronal innervation of the bone is an emerging research topic, especially with regards to the role of peripheral nerves in regulating bone homeostasis. Moreover, sensory and autonomic nerves regulate this process via different types of neurotransmitters, but the specific mechanism is still elusive. In this review article, the current understanding of the interaction between the peripheral nerve and the skeleton system is summarized, with a particular focus on bone marrow mesenchymal stem cells (BMMSCs), except for osteoblasts and osteoclasts. The novel application of nerve-based bone regeneration via BMMSCs may provide a new strategy in tissue engineering and clinical treatment of osteoporosis and bone disorders.

Roles of axon guidance molecules in neuronal wiring in the developing spinal cord

The spinal cord receives, relays and processes sensory information from the periphery and integrates this information with descending inputs from supraspinal centres to elicit precise and appropriate behavioural responses and orchestrate body movements. Understanding how the spinal cord circuits that achieve this integration are wired during development is the focus of much research interest. Several families of proteins have well-established roles in guiding developing spinal cord axons, and recent findings have identified new axon guidance molecules. Nevertheless, an integrated view of spinal cord network development is lacking, and many current models have neglected the cellular and functional diversity of spinal cord circuits. Recent advances challenge the existing spinal cord axon guidance dogmas and have provided a more complex, but more faithful, picture of the ontogenesis of vertebrate spinal cord circuits.

Semaphorin 5A suppresses the proliferation and migration of lung adenocarcinoma cells

Semaphorin 5A (SEMA5A), a member of the semaphorin family, plays an important role in axonal guidance. Previously, the authors identified another possible role of SEMA5A as a prognostic biomarker for non-smoking women with lung adenocarcinoma in Taiwan, and this phenomenon has been validated in other ethnic groups. However, the functional significance of SEMA5A in lung adenocarcinoma remains unclear. Therefore, we assessed the function of SEMA5A in three lung adenocarcinoma cell lines in this study. Kaplan-Meier Plotter for lung cancer was conducted for survival analyses. Reverse transcription-quantitative PCR (RT-qPCR) and western blot analysis were performed to investigate the expression and post-translational regulation of SEMA5A in lung adenocar-cinoma cell lines. A pre-designed PyroMark CpG assay and 5-aza-2′-deoxycytidine treatment were used to measure the methylation levels of SEMA5A. The biological functions of lung adenocarcinoma cells overexpressing SEMA5A were investigated by microarrays, and validated both in vitro (proliferation, colony formation and migration assays) and in vivo (tumor xenografts) experiments. The results revealed that the hypermethylation of SEMA5A and the cleavage of the extracellular domain of SEMA5A were responsible for the downregulation of the SEMA5A levels in lung adenocarcinoma cells (A549 and H1299) as compared to the normal controls. Functional analysis of SEMA5A-regulated genes revealed that they were involved in cellular growth and proliferation. The overexpression of SEMA5A in A549 and H1299 cells significantly decreased the proliferation (P<0.01), colony formation (P<0.001) and migratory ability (P<0.01) of the cells. The suppressive effects of SEMA5A on the proliferative and migratory ability of the cells were also observed in both in vitro and in vivo experiments using brain metastatic Bm7 lung adenocarcinoma cells. On the whole, the findings of this study suggest a suppressive role for SEMA5A in lung adenocarcinoma involving the inhibition of the proliferation and migration of lung transformed cells.

Retrograde signaling via axonal transport through signaling endosomes

Neurons extend axons far from cell bodies, and retrograde communications from distal axons to cell bodies and/or dendrites play critical roles in the development and maintenance of neuronal circuits. In neurotrophin signaling, the retrograde axonal transport of endosomes containing active ligand-receptor complexes from distal axons to somatodendrite compartments mediates retrograde signaling. However, the generality and specificity of these endosome-based transportations called "signaling endosomes" remain to be elucidated. Here, I summarize the discovery of semaphorin3A signaling endosomes, the first example other than neurotrophins to regulate dendritic development via AMPA receptor GluA2 localization in dendrites. The molecular components of Sema3A and neurotrophin signaling endosomes are distinct, but partially overlap to regulate specific and common cellular events. Because receptors are transported back to the cell bodies, neurons must replenish receptors on the growth cone surface to ensure continued response to the target-derived ligands. Recent findings have demonstrated that retrograde signaling endosomes also induce anterograde delivery of nascent receptors in neurotrophin signaling. The coupling between anterograde and retrograde axonal transport via signaling endosomes therefore plays a critical role in regulating proper neuronal network formation.

Role of angiocrine signals in bone development, homeostasis and disease

Skeletal vasculature plays a central role in the maintenance of microenvironments for osteogenesis and haematopoiesis. In addition to supplying oxygen and nutrients, vasculature provides a number of inductive factors termed as angiocrine signals. Blood vessels drive recruitment of osteoblast precursors and bone formation during development. Angiogenesis is indispensable for bone repair and regeneration. Dysregulation of the angiocrine crosstalk is a hallmark of ageing and pathobiological conditions in the skeletal system. The skeletal vascular bed is complex, heterogeneous and characterized by distinct capillary subtypes (type H and type L), which exhibit differential expression of angiocrine factors. Furthermore, distinct blood vessel subtypes with differential angiocrine profiles differentially regulate osteogenesis and haematopoiesis, and drive disease states in the skeletal system. This review provides an overview of the role of angiocrine signals in bone during homeostasis and disease.

Skilled Movements in Mice Require Inhibition of Corticospinal Axon Collateral Formation in the Spinal Cord by Semaphorin Signaling

Corticospinal (CS) neurons in layer V of the sensorimotor cortex are essential for voluntary motor control. Those neurons project axons to specific segments along the rostro-caudal axis of the spinal cord, and reach their spinal targets by sending collateral branches interstitially along axon bundles. Currently, little is known how CS axon collaterals are formed in the proper spinal cord regions. Here, we show that the semaphorin3A (Sema3A)-neuropilin-1 (Npn-1) signaling pathway is an essential negative regulator of CS axon collateral formation in the spinal cord from mice of either sex. Sema3A is expressed in the ventral spinal cord, whereas CS neurons express Npn-1, suggesting that Sema3A might prevent CS axons from entering the ventral spinal cord. Indeed, the ectopic expression of Sema3A in the spinal cord in vivo inhibits CS axon collateral formation, whereas Sema3A or Npn-1 mutant mice have ectopic CS axon collateral formation within the ventral spinal cord compared with littermate controls. Finally, Npn-1 mutant mice exhibit impaired skilled movements, likely because of aberrantly formed CS connections in the ventral spinal cord. These genetic findings reveal that Sema3A-Npn-1 signaling-mediated inhibition of CS axon collateral formation is critical for proper CS circuit formation and the ability to perform skilled motor behaviors.SIGNIFICANCE STATEMENT CS neurons project axons to the spinal cord to control skilled movements in mammals. Previous studies revealed some of the molecular mechanisms underlying different phases of CS circuit development such as initial axon guidance in the brain, and midline crossing in the brainstem and spinal cord. However, the molecular mechanisms underlying CS axon collateral formation in the spinal gray matter has remained obscure. In this study, using in vivo gain-of- and loss-of-function experiments, we show that Sema3A-Npn-1 signaling functions to inhibit CS axon collateral formation in the ventral spinal cord, allowing for the development of proper skilled movements in mice.

Nerves in Bone: Evolving Concepts in Pain and Anabolism

The innervation of bone has been described for centuries, and our understanding of its function has rapidly evolved over the past several decades to encompass roles of subtype-specific neurons in skeletal homeostasis. Current research has been largely focused on the distribution and function of specific neuronal populations within bone, as well as their cellular and molecular relationships with target cells in the bone microenvironment. This review provides a historical perspective of the field of skeletal neurobiology that highlights the diverse yet interconnected nature of nerves and skeletal health, particularly in the context of bone anabolism and pain. We explore what is known regarding the neuronal subtypes found in the skeleton, their distribution within bone compartments, and their central projection pathways. This neuroskeletal map then serves as a foundation for a comprehensive discussion of the neural control of skeletal development, homeostasis, repair, and bone pain. Active synthesis of this research recently led to the first biotherapeutic success story in the field. Specifically, the ongoing clinical trials of anti-nerve growth factor therapeutics have been optimized to titrated doses that effectively alleviate pain while maintaining bone and joint health. Continued collaborations between neuroscientists and bone biologists are needed to build on this progress, leading to a more complete understanding of neural regulation of the skeleton and development of novel therapeutics. © 2019 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals, Inc.

Nestin in immature embryonic neurons affects axon growth cone morphology and Semaphorin3a sensitivity

Correct wiring in the neocortex requires that responses to an individual guidance cue vary among neurons in the same location, and within the same neuron over time. Nestin is an atypical intermediate filament expressed strongly in neural progenitors and is thus used widely as a progenitor marker. Here we show a subpopulation of embryonic cortical neurons that transiently express nestin in their axons. Nestin expression is thus not restricted to neural progenitors, but persists for 2-3 d at lower levels in newborn neurons. We found that nestin-expressing neurons have smaller growth cones, suggesting that nestin affects cytoskeletal dynamics. Nestin, unlike other intermediate filament subtypes, regulates cdk5 kinase by binding the cdk5 activator p35. Cdk5 activity is induced by the repulsive guidance cue Semaphorin3a (Sema3a), leading to axonal growth cone collapse in vitro. Therefore, we tested whether nestin-expressing neurons showed altered responses to Sema3a. We find that nestin-expressing newborn neurons are more sensitive to Sema3a in a roscovitine-sensitive manner, whereas nestin knockdown results in lowered sensitivity to Sema3a. We propose that nestin functions in immature neurons to modulate cdk5 downstream of the Sema3a response. Thus, the transient expression of nestin could allow temporal and/or spatial modulation of a neuron's response to Sema3a, particularly during early axon guidance.