Neuronal TRPV1-CGRP axis regulates bone defect repair through Hippo signaling pathway

A bilayer hydrogel mimicking the periosteum-bone structure for innervated bone regeneration

In bone tissue, nerves are primarily located in the periosteum and play an indispensable role in bone defect repair. However, most bone tissue engineering approaches ignored the reconstruction of the nerve network. Herein, we aimed to develop a bilayer hydrogel simulating periosteum-bone structure to induce innervated bone regeneration. The bottom "bone" layer consisted of gelatin methacryloyl (GelMA), poly(ethylene glycol) diacrylate (PEGDA), and nano-hydroxyapatite (nHA), whereas the upper "periosteum" layer consisted of GelMA, sodium alginate (SA) and MgCl2. The mechanical properties of the upper and bottom hydrogels were designed to be suitable for neurogenesis and osteogenesis, respectively. Besides, Mg2+ from the "periosteum" layer released at the early stage (within 7 d), which aligned with the optimal time window for nerve regeneration and osteogenic related neuropeptide release. Simultaneously, the prevention of long-term Mg2+ release (after 7 d) could avoid osteogenic inhibition caused by prolonged Mg2+ exposure. Additionally, the incorporation of nHA in the bottom "bone" layer supported the long-term osteogenesis due to its osteoconductivity and slow degradation. In vitro biological experiments revealed that the bilayer hydrogel (GS@Mg/GP@nHA) promoted neurite growth and calcitonin gene-related peptide (CGRP) expression in rat dorsal root ganglion (DRG) neurons, as well as the osteogenesis of rat bone-derived mesenchymal stem cells (BMSCs). Moreover, the in vivo experiments demonstrated that the GS@Mg/GP@nHA hydrogel efficiently promoted nerve network reconstruction and bone regeneration of rat calvarial bone defects. Altogether, the bilayer hydrogel GS@Mg/GP@nHA could promote innervated bone regeneration, providing new insights for biomaterial design for bone tissue engineering.

Effects of Capsaicin on Migration and Alkaline Phosphatase Activity of Dental Pulp Cells

OBJECTIVES

 Dental pulp, a specialized mesenchymal tissue within teeth, is pivotal in dental health and tissue repair. Capsaicin, the primary pungent component of chili peppers, is known for its diverse pharmacological properties. While capsaicin's effects on various cell types have been studied, its impact on dental pulp cells remains relatively unexplored. This study investigated the influence of pure capsaicin extract on dental pulp cell behavior, focusing on cell viability, proliferation, migration, and alkaline phosphatase (ALP) activity.

MATERIALS AND METHODS

 Capsaicin solution was prepared and diluted to various concentrations (1 nM, 0.01 µM, 0.1 µM, 1 µM, 10 µM, and 100 µM), then was tested on rat dental pulp cells (RPC-C2A). Cell viability and proliferation were assessed using the MTT assay. Boyden chamber tests and wound healing were used for evaluating cell migration. The activity of ALP was determined to show cell function during dental pulp repair.

STATISTICAL ANALYSIS

 The data were analyzed using a one-way analysis of variance or an independent-sample Kruskal-Wallis, followed by multiple comparison tests.

RESULTS

 Capsaicin of 100 µM exhibited cytotoxicity, whereas those with lower concentrations stimulated cell proliferation. Wound healing assays revealed increased cell migration, particularly when cultured with 1 nM capsaicin (p = 0.002). Boyden chamber assays demonstrated enhanced cell invasion without statistical significance. ALP activity of dental pulp cells increased significantly at 1 nM (p < 0.001) and 1 µM (p = 0.021) capsaicin concentrations, indicating potential dentinogenesis and pulp repair.

CONCLUSION

 Capsaicin of lower concentrations, less than 10 µM, is likely to promote proliferation, migration, and ALP activity of dental pulp cells. Our findings offer potential applications for capsaicin as a medication for dental pulp repair.

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.

Capsaicin attenuates Porphyromonas gingivalis-suppressed osteogenesis of periodontal ligament stem cells via regulating mitochondrial function and activating PI3K/AKT/mTOR pathway

BACKGROUND AND OBJECTIVE

Prevention of periodontal bone resorption triggered by Porphyromonas gingivalis (P. gingivalis) is crucial for dental stability. Capsaicin, known as the pungent ingredient of chili peppers, can activate key signaling molecules involved in osteogenic process. However, the effect of capsaicin on osteogenesis of periodontal ligament stem cells (PDLSCs) under inflammation remains elusive.

METHODS

P. gingivalis culture suspension was added to mimic the inflammatory status after capsaicin pretreatment. The effects of capsaicin on the osteogenesis of PDLSCs, as well as mitochondrial morphology, Ca2+ level, reactive oxygen species (ROS), mitochondrial membrane potential (MMP), and osteogenesis-regulated protein expression levels were analyzed. Furthermore, a mouse experimental periodontitis model was established to evaluate the effect of capsaicin on alveolar bone resorption and the expression of osteogenesis-related proteins.

RESULTS

Under P. gingivalis stimulation, capsaicin increased osteogenesis of PDLSCs. Not surprisingly, capsaicin rescued the damage to mitochondrial morphology, decreased the concentration of intracellular Ca2+ and ROS, enhanced MMP and activated phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway. The in vivo results showed that capsaicin significantly attenuated alveolar bone loss and augmented the expression of bone associated proteins.

CONCLUSION

Capsaicin increases osteogenesis of PDLSCs under inflammation and reduces alveolar bone resorption in mouse experimental periodontitis.

Nociceptive adenosine A2A receptor on trigeminal nerves orchestrates CGRP release to regulate the progression of oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) associated pain commonly predicts adverse events among patients. This clinical feature indicates the engagement of nociceptors on sensory neurons during the development of malignancy. However, it is yet to be determined if targeting oncometabolite-associated nociception processes can hinder OSCC progression. In this study, we reported that nociceptive endings infiltrating both clinical samples and mouse tumor xenografts were associated with poorer clinical outcomes and drove tumor progression in vivo, as evidenced by clinical tissue microarray analysis and murine lingual denervation. We observed that the OSCC microenvironment was characteristic of excessive adenosine due to CD73 upregulation which negatively predicted clinical outcomes in the TCGA-HNSC patient cohort. Notably, such adenosine concentrative OSCC niche was associated with the stimulation of adenosine A2A receptor (A2AR) on trigeminal ganglia. Antagonism of trigeminal A2AR with a selective A2AR inhibitor SCH58261 resulted in impeded OSCC growth in vivo. We showed that trigeminal A2AR overstimulation in OSCC xenograft did not entail any changes in the transcription level of CGRP in trigeminal ganglia but significantly triggered the release of CGRP, an effect counteracted by SCH58261. We further demonstrated the pro-tumor effect of CGRP by feeding mice with the clinically approved CGRP receptor antagonist rimegepant which inhibited the activation of ERK and YAP. Finally, we diminished the impact of CGRP on OSCC with istradefylline, a clinically available drug that targets neuronal A2AR. Therefore, we established trigeminal A2AR-mediated CGRP release as a promising druggable circuit in OSCC treatment.

Sensory neuron transient receptor potential vanilloid-1 channel regulates angiogenesis through CGRP in vivo

Angiogenesis plays a key role in bone regeneration. The role of neurons of peripheral nerves involved in angiogenesis of bone defects needs to be explored. The transient receptor potential vanilloid 1 (TRPV1), a nociceptor of noxious stimuli, is expressed on sensory neurons. Apart from nociception, little is known about the role of sensory innervation in angiogenesis. Calcitonin gene-related peptide (CGRP), a neuropeptide secreted by sensory nerve terminals, has been associated with vascular regeneration. We characterized the reinnervation of vessels in bone repair and assessed the impact of TRPV1-CGRP signaling on early vascularization. We investigated the pro-angiogenic effect of neuronal TRPV1 in the mouse model of femur defect. Micro-CT analysis with Microfil® reagent perfusion demonstrated neuronal TRPV1 activation enhanced angiogenesis by increasing vessel volume, number, and thickness. Meanwhile, TRPV1 activation upregulated the mRNA and protein expression of vascular endothelial growth factor A (VEGF-A), cell adhesion molecule-1 (CD31), and CGRP. Immunostaining revealed the co-localization of TRPV1 and CGRP in dorsal root ganglia (DRG) sensory neurons. By affecting neuronal TRPV1 channels, the release of neuronal and local CGRP was controlled. We demonstrated that TRPV1 influenced on blood vessel development by promoting CGRP release from sensory nerve terminals. Our results showed that neuronal TRPV1 played a crucial role in regulating angiogenesis during bone repair and provided important clinical implications for the development of novel therapeutic approaches for angiogenesis.

Activation of Transient Receptor Potential Vanilloid 1 Is Involved in Both Pain and Tumor Growth in a Mouse Model of Cancer Pain

Activation of calcitonin gene-related peptide (CGRP)-positive sensory neurons in the tumor microenvironment has been shown to be involved in tumor growth. However, how CGRP-positive sensory neurons are activated requires elucidation. In this study, we focused on transient receptor potential vanilloid 1 (TRPV1) and examined the contribution of TRPV1 to tumor growth and cancer pain in a mouse cancer model in which Lewis lung carcinoma was subcutaneously inoculated in the left plantar region. Tumor inoculation gradually increased the volumes of the hind paws of wild type (WT) mice over time, but those of both αCGRP knockout mice and TRPV1 knockout mice were significantly smaller than those of WT mice after tumor inoculation. Both TRPV1 and CGRP are therefore suggested to be involved in tumor growth. In an immunohistochemical study, the percentage of phosphorylated cyclic adenosine monophosphate response element-binding protein (p-CREB)-positive profiles in CGRP-positive dorsal root ganglion (DRG) neurons in WT mice was significantly increased after tumor inoculation. The percentage of p-CREB-positive profiles in CGRP-positive DRG neurons in TRPV1 knockout mice was also increased after tumor inoculation, but was significantly lower than that in WT mice, indicating the contribution of TRPV1 to activation of CGRP-positive DRG neurons. Cancer pain in TRPV1 knockout mice was significantly lower than that in WT mice. In conclusion, TRPV1 is involved in both tumor growth and cancer pain, potentially leading to a novel strategy for the treatment of cancer pain and cancer development. Cancer pain is also suggested to facilitate tumor growth.

Neuro-bone tissue engineering: emerging mechanisms, potential strategies, and current challenges

The skeleton is a highly innervated organ in which nerve fibers interact with various skeletal cells. Peripheral nerve endings release neurogenic factors and sense skeletal signals, which mediate bone metabolism and skeletal pain. In recent years, bone tissue engineering has increasingly focused on the effects of the nervous system on bone regeneration. Simultaneous regeneration of bone and nerves through the use of materials or by the enhancement of endogenous neurogenic repair signals has been proven to promote functional bone regeneration. Additionally, emerging information on the mechanisms of skeletal interoception and the central nervous system regulation of bone homeostasis provide an opportunity for advancing biomaterials. However, comprehensive reviews of this topic are lacking. Therefore, this review provides an overview of the relationship between nerves and bone regeneration, focusing on tissue engineering applications. We discuss novel regulatory mechanisms and explore innovative approaches based on nerve-bone interactions for bone regeneration. Finally, the challenges and future prospects of this field are briefly discussed.

Hippo pathway in intestinal diseases: focusing on ferroptosis

The incidence of intestinal diseases, such as inflammatory bowel disease, gastric cancer, and colorectal cancer, has steadily increased over the past decades. The Hippo pathway is involved in cell proliferation, tissue and organ damage, energy metabolism, tumor formation, and other physiologic processes. Ferroptosis is a form of programmed cell death characterized by the accumulation of iron and lipid peroxides. The Hippo pathway and ferroptosis are associated with various intestinal diseases; however, the crosstalk between them is unclear. This review elaborates on the current research on the Hippo pathway and ferroptosis in the context of intestinal diseases. We summarized the connection between the Hippo pathway and ferroptosis to elucidate the underlying mechanism by which these pathways influence intestinal diseases. We speculate that a mutual regulatory mechanism exists between the Hippo pathway and ferroptosis and these two pathways interact in several ways to regulate intestinal diseases.

Calcitonin Gene-Related Peptide Systemic Effects: Embracing the Complexity of Its Biological Roles-A Narrative Review

The calcitonin gene-related peptide (CGRP) is a neuropeptide widely distributed throughout the human body. While primarily recognized as a nociceptive mediator, CGRP antagonists are currently utilized for migraine treatment. However, its role extends far beyond this, acting as a regulator of numerous biological processes. Indeed, CGRP plays a crucial role in vasodilation, inflammation, intestinal motility, and apoptosis. In this review, we explore the non-nociceptive effects of CGRP in various body systems, revealing actions that can be contradictory at times. In the cardiovascular system, it functions as a potent vasodilator, yet its antagonists do not induce arterial hypertension, suggesting concurrent modulation by other molecules. As an immunomodulator, CGRP exhibits intriguing complexity, displaying both anti-inflammatory and pro-inflammatory effects. Furthermore, CGRP appears to be involved in obesity development while paradoxically reducing appetite. A thorough investigation of CGRP's biological effects is crucial for anticipating potential side effects associated with its antagonists' use and for developing novel therapies in other medical fields. In summary, CGRP represents a neuropeptide with a complex systemic impact, extending well beyond nociception, thus offering new perspectives in medical research and therapeutics.