Project description:Sympathetic tone has long been known as a central signaling axis inhibiting osteogenesis. However, the mechanism of this nerve to bone influence remains elusive, especially regarding the specific cellular targets of sympathetic activity. Recently, a bona fide tissue-resident stem cell giving rise to skeletal cell types, skeletal stem cells (SSCs), have been identified. To explore if and how nerves impact SSCs, we utilized mice with conditional deletion of SLIT2, a classic axonal repellent, finding that neural (Slit2syn1 mice) and sympathetic (Slit2th mice) but not bone stem/progenitor (Slit2prx1 mice) or sensory (Slit2adv mice) deletion of Slit2, led to osteopenia due to impaired bone formation associated with an increase in sympathetic innervation and a decrease in the numbers of SSCs. Consistent with this, pharmacological or surgical sympathectomy caused expansion of the SSC pool. More directly, wild type (WT) SSCs transplanted orthotopically into the bones of Slit2th mice with increased sympathetic innervation displayed impaired osteogenic capability, demonstrating that sympathetic nerves functionally contribute to the SSC niche. In line with these findings, the increased sympathetic innervation in Slit2th mice disrupted bone regeneration and bone fracture healing by reducing SSC expansion. Transcriptomic profiling in sympathetic neurons identified Follistatin-like 1 (FSTL1) as a SLIT2-regulated soluble factor that suppressed SSC self-renewal and osteogenic capacity. Accordingly, ablation of Fstl1 in sympathetic neurons enhanced SSC-driven osteogenesis and attenuated the bone loss seen in Slit2th mice in vivo. Altogether, our study both newly establishes SLIT2 as a regulator of skeletal sympathetic innervation and establishes sympathetic nerves as a key component of the SSC niche, providing new therapeutic opportunities to augment SSC function to treat skeletal disorders.
Project description:Regulation of membrane receptors involves management of endocytosis. At the neuromuscular junction, the synapse between skeletal muscle and motoneuron, proper density of the major receptor, the acetylcholine receptor, is of utmost importance for sustaining life in context of mobility. Recent work has revealed innervation of NMJs by sympathetic neurons and destruction of them had morphological and functional consequences, suggesting influence on endocytosis. To investigate the pathways and proteins that are relevant for acetylcholine receptor turnover and affected by sympathetic signaling, proteomes of mouse hindlimb muscles from sympathectomized and saline-treated control muscles were compared. Using proteomic, Western blot, and immunofluorescence analysis in chemically sympathectomized mouse hindlimb muscles, the cause of these consequences were aimed to analyzed. This revealed extensive regulation of the proteome by the sympathetic nervous system and a possible regulatory function of the endo/lysosomal and autophagic pathway by sympathetic neuronal input. This finding might provide a new explanation to the observed benefit of sympathicomimetic treatment in several congenital myasthenic syndromes.
Project description:Piloerection (goosebump) requires concerted actions of the hair follicle, the arrector pili muscle (APM), and the sympathetic nerve, providing a model to study interactions across epithelium, mesenchyme, and nerves. Here, we show that APMs and sympathetic nerves form a dual component niche to modulate hair follicle stem cell (HFSC) activity. Sympathetic nerves form synapse-like structures with HFSCs and regulate HFSCs through norepinephrine, whereas APMs maintain sympathetic innervation to HFSCs. Without norepinephrine signaling, HFSCs enter a deep quiescence state by down-regulating cell cycle machinery and mitochondria metabolism, while up-regulating quiescence regulators Lhx2, Foxp1, and Fgf18. During development, HFSC progeny secrets Sonic Hedgehog (SHH) to direct the formation of this APM-sympathetic nerve niche, which in turn controls hair follicle regeneration in adults. Our results reveal a reciprocal interdependence between a regenerative tissue and its niche at different stages, and illustrate that nerves can modulate stem cell quiescence through synapses and neurotransmitters.
Project description:Dysregulation of glucagon secretion in type 1 diabetes (T1D) involves hypersecretion during postprandial states, but insufficient secretion during hypoglycemia. The sympathetic nervous system regulates glucagon secretion. To investigate islet sympathetic innervation in T1D, sympathetic tyrosine hydroxylase (TH) axons were analyzed in control non-diabetic organ donors, non-diabetic islet autoantibody-positive individuals (AAb), and age-matched persons with T1D. Islet TH axon numbers and density were significantly decreased in AAb compared to T1D with no significant differences observed in exocrine TH axon volume or lengths between groups. TH axons were in close approximation to islet α-cells in T1D individuals with long-standing diabetes. Islet RNA-sequencing and qRT-PCR analyses identified significant alterations in noradrenalin degradation, α-adrenergic signaling, cardiac b-adrenergic signaling, catecholamine biosynthesis, and additional neuropathology pathways. The close approximation of TH axons at islet α-cells supports a model for sympathetic efferent neurons directly regulating glucagon secretion. Sympathetic islet innervation and intrinsic adrenergic signaling pathways could be novel targets for improving glucagon secretion in T1D.
Project description:The sympathetic nervous system innervates peripheral organs to regulate their function and maintain homeostasis, whereas target cells also produce neurotrophic factors to promote sympathetic innervation1,2. The molecular basis of this bi-directional communication is unknown. Here we use thermogenic adipose tissue from mice as a model system to show that T cells, specifically T cells, have a crucial role in promoting sympathetic innervation, at least in part by driving the expression of TGF1 in parenchymal cells via the IL-17 receptor complex (IL-17RC). Ablation of IL-17RC specifically in adipose tissue reduces expression of TGF1 in adipocytes, impairs local sympathetic innervation and causes obesity and other metabolic phenotypes that are consistent with defective thermogenesis; innervation can be fully rescued by restoring TGF1 expression. Ablating cells and the IL-17RC signalling pathway also impairs sympathetic innervation in salivary glands and the lungs. These findings demonstrate coordination between T cells and parenchymal cells to regulate sympathetic innervation.
Project description:The sympathetic nervous system innervates peripheral organs to regulate their function and maintain homeostasis, whereas target cells also produce neurotrophic factors to promote sympathetic innervation. The molecular basis of this bi-directional communication remains to be fully elucidated. We use thermogenic adipose tissue as a model system to show that T cells, specifically gdT cells, play a critical role in promoting sympathetic innervation, at least in part through driving TGFβ1 expression in parenchymal cells via IL-17 Receptor C. Adipose-specific ablation of IL-17 Receptor C reduces TGFβ1 expression in adipocytes, impairs local sympathetic innervation and causes obesity and other metabolic phenotypes consistent with defective thermogenesis; innervation can be fully rescued by restoring TGFβ1 expression. Ablating gdT cells and the IL-17 Receptor C signaling pathway also impairs sympathetic innervation in salivary glands and the lung. These findings demonstrate T cell/parenchymal cell coordination to regulate sympathetic innervation.
Project description:We performed single-cell RNA-seq (10x Chromium 3' v.3.1) on dissociated single cell suspensions from mouse (C57BL/6) celiac and superior mesenteric sympathetic ganglia to determine transcriptomic cell types. We identified sympathetic neuron types that specifically innervate unique combinations of visceral organs and control physiological functions.
Project description:Rationale: Slit2 is a possible modulator of vascular endothelial growth factor (VEGF) - induced angiogenesis, but its effects have not been tested in large animal models. Objective: We studied the effect of Slit2 on therapeutic angiogenesis induced by VEGF receptor 2 (VEGFR2) ligands Vammin and VEGF-DΔNΔC in vivo in rabbit skeletal muscles. The Slit2 target genes were also studied by RNA sequencing (RNA-Seq) in endothelial cells. Methods and Results: Adenoviral intramuscular gene transfers were performed into rabbit hindlimbs. Confocal and multiphoton microscopy were used for blood vessel imaging. Signaling experiments and gene expression analyses were performed to study mechanisms of Slit2 action. Slit2 decreased VEGFR2-mediated vascular permeability. It also reduced VEGFR2-mediated increase in blood perfusion and capillary enlargement, whereas sprouting of the capillaries was increased. Slit2 gene transfer alone did not have any effects on vascular functions or morphology. VEGFR2 activation was not affected by Slit2, but eNOS phosphorylation was diminished. The transcriptome profiling showed Slit2 downregulating angiogenesis-related genes such as nuclear receptor subfamily 4 group A member 1 (NR4A1) and Stanniocalcin-1 (STC-1) as well as genes related to endothelial cell migration and vascular permeability. Conclusions: Combining Slit2 with VEGFs adjusts VEGFR2-mediated angiogenic effects into a more physiological direction. This possibly allows the use of higher VEGF vector doses to achieve a more widespread vector and VEGF distribution in the target tissues leading to a better therapeutic outcome while reducing excess vascular permeability. HUVEC mRNA profiles after adenoviral vector gene transfers in duplicate.
Project description:Background: Skeletal muscle crucially depends on motor innervation, and, when damaged, on the resident muscle stem cells (MuSCs). However, the role and function of MuSCs in the context of denervation remains poorly understood. Methods: Alterations of MuSCs and their myofiber niche after denervation were investigated in a surgery-based mouse model of unilateral sciatic nerve transection. FACS-isolated MuSCs were subjected to RNA-sequencing and mass spectrometry for the analysis of intrinsic changes after denervation and in vivo assays, such as Cardiotoxin-induced muscle injury or MuSC transplantation, were performed to assess MuSC functions after denervation. Bioinformatic and histological analyses were conducted to further examine MuSCs and their myofiber niche after denervation. Results: Muscle cross section analysis revealed a significant increase in Pax7 (p-value= 0.0441), Pax7/Ki67 (p-value= 0.0023), MyoD (p-value= 0.0016) and Myog (p-value= 0.0057) positive cells after denervation, illustrating a break of quiescence and commitment to the myogenic lineage. An Omics approach showed profound intrinsic alterations on the mRNA (2613 differentially expressed genes, p-value <0.05) and protein (1096 differentially abundant proteins, q-value <0.05) level of MuSCs 21 days after denervation. Skeletal muscle injury together with denervation surgery caused deregulated regeneration, indicated by the reduced number of proliferating MuSCs and sustained high levels of developmental myosin heavy chain (Sham: 1 % vs DEN: 40 % of all myofibers), at 21 days post-surgery. In a transplantation assay, MuSCs from a denervated host were still able to engraft and fuse to form new myofibers, irrespective of the innervation status of the recipient muscle. Analysis of myofibers revealed not only massive changes in the expression profile (10492 differentially expressed genes, p-value <0.05) after denervation, but it was also shown that secretion of Opn and Tgfb1 from denervated myofibers was increased 30-fold and 6000-fold, respectively. Bioinformatic analyses indicated strong upregulation of gene expression of the transcription factor Junb in MuSCs from denervated muscles (log2 fold change = 3.27). Of interest, Tgfb1 recombinant protein was able to induce Junb gene expression in vitro, demonstrating that myofiber-secreted ligands can induce gene expression changes in MuSCs, which might result in the phenotypes observed after denervation. Conclusion: Skeletal muscle denervation is altering myofiber secretion, causing MuSC activation and profound intrinsic changes, leading to reduced regenerative capacity. As MuSCs possess a remarkable regenerative potential, they might represent a promising target for novel treatment options for neuromuscular disorders and peripheral nerve injuries.