Sensory nerve niche regulates mesenchymal stem cell homeostasis via FGF/mTOR/autophagy axis

Application of autophagy in mesenchymal stem cells

In this editorial, we have taken an in-depth look at the article published by Wan et al. The study showed that preconditioning mesenchymal stem cells (MSCs) protected them against programmed cell death, and increased their survival rate and therapeutic potential. Autophagy, a type of programmed cell death, is a major intracellular degradation and recycling pathway that is crucial for maintaining cellular homeostasis, self-renewal, and pluripotency. We have explored the relationship between autophagy and MSCs to determine the role of autophagy in the therapeutic applications of MSCs.

Glutamine-αKG axis affects dentin regeneration and regulates osteo/odontogenic differentiation of mesenchymal adult stem cells via IGF2 m6A modification

BACKGROUND

Multi-lineage differentiation of mesenchymal adult stem cells (m-ASCs) is crucial for tissue regeneration and accompanied with metabolism reprogramming, among which dental-pulp-derived m-ASCs has obvious advantage of easy accessibility. Stem cell fate determination and differentiation are closely related to metabolism status in cell microenvironment, which could actively interact with epigenetic modification. In recent years, glutamine-α-ketoglutarate (αKG) axis was proved to be related to aging, tumorigenesis, osteogenesis etc., while its role in m-ASCs still lack adequate research evidence.

METHODS

We employed metabolomic analysis to explore the change pattern of metabolites during dental-pulp-derived m-ASCs differentiation. A murine incisor clipping model was established to investigate the influence of αKG on dental tissue repairment. shRNA technique was used to knockdown the expression of related key enzyme-dehydrogenase 1(GLUD1). RNA-seq, m6A evaluation and MeRIP-qPCR were used to dig into the underlying epigenetic mechanism.

RESULTS

Here we found that the glutamine-αKG axis displayed an increased tendency along with the osteo/odontogenic differentiation of dental-pulp-derived m-ASCs, same as expression pattern of GLUD1. Further, the key metabolite αKG was found able to accelerate the repairment of clipped mice incisor and promote dentin formation. Exogenous DM-αKG was proved able to promote osteo/odontogenic differentiation of dental-pulp-derived m-ASCs, while the inhibition of glutamine-derived αKG level via GLUD1 knockdown had the opposite effect. Under the circumstance of GLUD1 knockdown, extracellular matrix (ECM) function and PI3k-Akt signaling pathway was screened out to be widely involved in the process with insulin-like growth factor 2 (IGF2) participation via RNA-seq. Inhibition of glutamine-αKG axis may affect IGF2 translation efficiency via m6A methylation and can be significantly rescued by αKG supplementation.

CONCLUSION

Our findings indicate that glutamine-αKG axis may epigenetically promote osteo/odontogenic differentiation of dental-pulp-derived m-ASCs and dentin regeneration, which provide a new research vision of potential dental tissue repairment therapy method or metabolite-based drug research.

Stem Cell-Associated Proteins and Extracellular Matrix Composition of the Human Atrioventricular Junction

The human heart regenerates slowly through life, but how new cells are generated is mostly unknown. The atrioventricular junction (AVj) has been indicated as a potential stem cell niche region. Little is known about the protein composition of the human AVj. To map the extracellular matrix (ECM) and expression of stem cell-related biomarkers, this study compares protein and gene expression patterns in AVj and Left Ventricular (LV) tissues. Biopsies were collected from 15 human hearts. Global quantitative proteomics and mRNA sequencing were used to identify differentially expressed proteins and altered genes. Of the total 4904 identified proteins, 1138 were differently expressed between the AVj and LV. While the top proteins in LV were involved in cardiac motor function and energy regulation, the AVj displayed proteins associated with early cardiomyocyte development, differentiation, proliferation, migration, and hypoxia. Furthermore, several developmental signalling pathways, including TGF-β, TNF, WNT, Notch, and FGF, were represented. RNA-seq data verified that the expressed genes were involved with differentiation, cell growth, proliferation, or ECM organization. Immunohistochemistry confirmed the expression of the stem cell-related biomarkers NPPA and POSTN in the AVj, further strengthening the hypothesis of the AVj as a specialized microenvironment conducive to stem cell niche activity.

An Acellular, Self-Healed Trilayer Cryogel for Osteochondral Regeneration in Rabbits

Osteochondral regeneration remains formidable challenges despite significant advances in microsurgery. Herein, an acellular trilayer cryogel (TC) with injectability, tunable pore sizes (80-200 µm), and appropriate compressive modulus (10.8 kPa) is manufactured from self-healable hydrogel under different gelling times through Schiff reaction between chitosan and difunctionalized polyurethane (DFPU). Bioactive molecules (Y27632 and dexamethasone) are respectively loaded in the top and bottom layers to form the Y27632/dexamethasone-loaded trilayer cryogel (Y/DEX-TC). Mesenchymal stem cells (MSCs) seeded in Y/DEX-TC proliferated ≈350% in vitro and underwent chondrogenesis or osteogenesis in response to the respective release of Y or DEX in 14 days. Acupuncture is administered to animals in an attempt to modulate the innate regulatory system and mobilize endogenous MSCs for osteochondral defect regeneration. In vivo rabbit experiments using Y/DEX-TC combined with acupuncture successfully regulate SDF-1 and TGF-β1 levels, which possibly cause MSC migration toward Y/DEX-TC. The synergistic effect of cryogel and acupuncture on immunomodulation is verified with a ≈7.3-fold enhancement of the M2-/M1-macrophage population ratio by treatment of Y/DEX-TC combining acupuncture, significantly greater than ≈1.5-fold increase by acupuncture or ≈2.2-fold increase by Y/DEX-TC alone. This novel strategy using acellular drug-loaded cryogel and accessible acupuncture shows promise in treating osteochondral defects of joint damage.

The sensory nerve regulates stem cell homeostasis through Wnt5a signaling

Increasing evidence indicates that nerves play a significant role in regulating stem cell homeostasis and developmental processes. To explore the impact of nerves on epithelial stem cell homeostasis during tooth development, the regulation of sensory nerves on stem cell homeostasis was investigated using a rat model of incisor development. Impaired mineralization, decreased enamel thickness, and fractured enamel rods of the incisor were observed after denervation. qPCR and histological staining revealed that the expression of enamel-related factors ameloblastin (AMBN), kallikrein-4, amelogenin (Amelx), collagen type XVII (col17a), and enamelin were decreased in the incisor enamel of rats with sensory nerve injure. The decreased expression of Wnt5a in ameloblasts was coupled with the downregulation of calcium ion-related calmodulin kinase II. These results implicate that the sensory nerves are essential in stem cell homeostasis for enamel mineralization and development.

TNFα prevents FGF4-mediated rescue of astrocyte dysfunction and reactivity in human ALS models

Astrocytes play a crucial role in the onset and progression of amyotrophic lateral sclerosis (ALS), a fatal disorder marked by the degeneration of motor neurons (MNs) in the central nervous system. Although astrocytes in ALS are known to be toxic to MNs, the pathological changes leading to their neurotoxic phenotype remain poorly understood. In this study, we generated human astrocytes from induced pluripotent stem cells (iPSCs) carrying the ALS-associated A4V mutation in superoxide dismutase 1 (SOD1) to examine early cellular pathways and network changes. Proteomic analysis revealed that ALS astrocytes are both dysfunctional and reactive compared to control astrocytes. We identified significant alterations in the levels of proteins linked to ALS pathology and the innate immune cGAS-STING pathway. Furthermore, we found that ALS astrocyte reactivity differs from that of control astrocytes treated with tumor necrosis factor alpha (TNFα), a key cytokine in inflammatory reactions. We then evaluated the potential of fibroblast growth factor (FGF) 2, 4, 16, and 18 to reverse ALS astrocyte phenotype. Among these, FGF4 successfully reversed ALS astrocyte dysfunction and reactivity in vitro. When delivered to the spinal cord of the SOD1G93A mouse model of ALS, FGF4 lowered astrocyte reactivity. However, this was not sufficient to protect MNs from cell death. Further analysis indicated that TNFα abrogated the reactivity reduction achieved by FGF4, suggesting that complete rescue of the ALS phenotype by FGF4 is hindered by ongoing complex neuroinflammatory processes in vivo. In summary, our data demonstrate that astrocytes generated from ALS iPSCs are inherently dysfunctional and exhibit an immune reactive phenotype. Effectively targeting astrocyte dysfunction and reactivity in vivo may help mitigate ALS and prevent MN death.

Sensory nerves drive migration of dental pulp stem cells via the CGRP-Ramp1 axis in pulp repair

Dental pulp stem cells (DPSCs) are responsible for maintaining pulp structure and function after pulp injury. DPSCs migrate directionally to the injury site before differentiating into odontoblast-like cells, which is a prerequisite and a determinant in pulp repair. Increasing evidence suggests that sensory neuron-stem cell crosstalk is critical for maintaining normal physiological functions, and sensory nerves influence stem cells mainly by neuropeptides. However, the role of sensory nerves on DPSC behaviors after pulp injury is largely unexplored. Here, we find that sensory nerves released significant amounts of calcitonin gene-related peptide (CGRP) near the injury site, acting directly on DPSCs via receptor activity modifying protein 1 (RAMP1) to promote collective migration of DPSCs to the injury site, and ultimately promoting pulp repair. Specifically, sensory denervation leads to poor pulp repair and ectopic mineralization, in parallel with that DPSCs failed to be recruited to the injury site. Furthermore, in vitro evidence shows that sensory nerve-deficient microenvironment suppressed DPSC migration prominently among all related behaviors. Mechanistically, the CGRP-Ramp1 axis between sensory neurons and DPSCs was screened by single-cell RNA-seq analysis and immunohistochemical studies confirmed that the expression of CGRP rather than Ramp1 increases substantially near the damaged site. We further demonstrated that CGRP released by sensory nerves binds the receptor Ramp1 on DPSCs to facilitate cell collective migration by an indirect co-culture system using conditioned medium from trigeminal neurons, CGRP recombinant protein and antagonists BIBN4096. The treatment with exogenous CGRP promoted the recruitment of DPSCs, and ultimately enhanced the quality of pulp repair. Targeting the sensory nerve could therefore provide a new strategy for stem cell-based pulp repair and regeneration.

Recent Advances in Nanomaterials for Modulation of Stem Cell Differentiation and Its Therapeutic Applications

Challenges in directed differentiation and survival limit the clinical use of stem cells despite their promising therapeutic potential in regenerative medicine. Nanotechnology has emerged as a powerful tool to address these challenges and enable precise control over stem cell fate. In particular, nanomaterials can mimic an extracellular matrix and provide specific cues to guide stem cell differentiation and proliferation in the field of nanotechnology. For instance, recent studies have demonstrated that nanostructured surfaces and scaffolds can enhance stem cell lineage commitment modulated by intracellular regulation and external stimulation, such as reactive oxygen species (ROS) scavenging, autophagy, or electrical stimulation. Furthermore, nanoframework-based and upconversion nanoparticles can be used to deliver bioactive molecules, growth factors, and genetic materials to facilitate stem cell differentiation and tissue regeneration. The increasing use of nanostructures in stem cell research has led to the development of new therapeutic approaches. Therefore, this review provides an overview of recent advances in nanomaterials for modulating stem cell differentiation, including metal-, carbon-, and peptide-based strategies. In addition, we highlight the potential of these nano-enabled technologies for clinical applications of stem cell therapy by focusing on improving the differentiation efficiency and therapeutics. We believe that this review will inspire researchers to intensify their efforts and deepen their understanding, thereby accelerating the development of stem cell differentiation modulation, therapeutic applications in the pharmaceutical industry, and stem cell therapeutics.

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.

Progranulin inhibits autophagy to facilitate intracellular colonization of Helicobacter pylori through the PGRN/mTOR/DCN axis in gastric epithelial cells

Helicobacter pylori (H. pylori) infection is the primary risk factor for the progress of gastric diseases. The persistent stomach colonization of H. pylori is closely associated with the development of gastritis and malignancies. Although the involvement of progranulin (PGRN) in various cancer types has been well-documented, its functional role and underlying mechanisms in gastric cancer (GC) associated with H. pylori infection remain largely unknown. This report demonstrated that PGRN was up-regulated in GC and associated with poor prognosis, as determined through local and public database analysis. Additionally, H. pylori induced the up-regulation of PGRN in gastric epithelial cells both in vitro and in vivo. Functional studies have shown that PGRN promoted the intracellular colonization of H. pylori. Mechanistically, H. pylori infection induced autophagy, while PGRN inhibited autophagy to promote the intracellular colonization of H. pylori. Furthermore, PGRN suppressed H. pylori-induced autophagy by down-regulating decorin (DCN) through the mTOR pathway. In general, PGRN inhibited autophagy to facilitate intracellular colonization of H. pylori via the PGRN/mTOR/DCN axis. This study provides new insights into the molecular mechanisms underlying the progression of gastric diseases, suggesting PGRN as a potential therapeutic target and prognostic predictor for these disorders.

Neural regulation of mesenchymal stem cells in craniofacial bone: development, homeostasis and repair

Mesenchymal stem cells endow various functions, including proliferation, multipotency, migration, etc. Craniofacial bones originate from the cranial neural crest and are developed mainly through intramembranous ossification, which are different from long bones. There are varied mesenchymal stem cells existing in the craniofacial bone, including Gli1 + cells, Axin2 + cells, Prx1 + cells, etc. Nerves distributed in craniofacial area are also derived from the neural crest, and the trigeminal nerve is the major sensory nerve in craniofacial area. The nerves and the skeleton are tightly linked spatially, and the skeleton is broadly innervated by sensory and sympathetic nerves, which also participate in bone development, homeostasis and healing process. In this review, we summarize mesenchymal stem cells located in craniofacial bone or, to be more specific, in jaws, temporomandibular joint and cranial sutures. Then we discuss the research advance concerning neural regulation of mesenchymal stem cells in craniofacial bone, mainly focused on development, homeostasis and repair. Discovery of neural regulation of mesenchymal stem cells may assist in treatment in the craniofacial bone diseases or injuries.

FGF signaling modulates mechanotransduction/WNT signaling in progenitors during tooth root development

Stem/progenitor cells differentiate into different cell lineages during organ development and morphogenesis. Signaling pathway networks and mechanotransduction are important factors to guide the lineage commitment of stem/progenitor cells during craniofacial tissue morphogenesis. Here, we used tooth root development as a model to explore the roles of FGF signaling and mechanotransduction as well as their interaction in regulating the progenitor cell fate decision. We show that Fgfr1 is expressed in the mesenchymal progenitor cells and their progeny during tooth root development. Loss of Fgfr1 in Gli1+ progenitors leads to hyperproliferation and differentiation, which causes narrowed periodontal ligament (PDL) space with abnormal cementum/bone formation leading to ankylosis. We further show that aberrant activation of WNT signaling and mechanosensitive channel Piezo2 occurs after loss of FGF signaling in Gli1-CreER;Fgfr1fl/fl mice. Overexpression of Piezo2 leads to increased osteoblastic differentiation and decreased Piezo2 leads to downregulation of WNT signaling. Mechanistically, an FGF/PIEZO2/WNT signaling cascade plays a crucial role in modulating the fate of progenitors during root morphogenesis. Downregulation of WNT signaling rescues tooth ankylosis in Fgfr1 mutant mice. Collectively, our findings uncover the mechanism by which FGF signaling regulates the fate decisions of stem/progenitor cells, and the interactions among signaling pathways and mechanotransduction during tooth root development, providing insights for future tooth root regeneration.

Harmonized cross-species cell atlases of trigeminal and dorsal root ganglia

Sensory neurons in the dorsal root ganglion (DRG) and trigeminal ganglion (TG) are specialized to detect and transduce diverse environmental stimuli to the central nervous system. Single-cell RNA sequencing has provided insights into the diversity of sensory ganglia cell types in rodents, nonhuman primates, and humans, but it remains difficult to compare cell types across studies and species. We thus constructed harmonized atlases of the DRG and TG that describe and facilitate comparison of 18 neuronal and 11 non-neuronal cell types across six species and 31 datasets. We then performed single-cell/nucleus RNA sequencing of DRG from both human and the highly regenerative axolotl and found that the harmonized atlas also improves cell type annotation, particularly of sparse neuronal subtypes. We observed that the transcriptomes of sensory neuron subtypes are broadly similar across vertebrates, but the expression of functionally important neuropeptides and channels can vary notably. The resources presented here can guide future studies in comparative transcriptomics, simplify cell-type nomenclature differences across studies, and help prioritize targets for future analgesic development.

Mapping Somatosensory Afferent Circuitry to Bone Identifies Neurotrophic Signals Required for Fracture Healing

The profound pain accompanying bone fracture is mediated by somatosensory neurons, which also appear to be required to initiate bone regeneration following fracture. Surprisingly, the precise neuroanatomical circuitry mediating skeletal nociception and regeneration remains incompletely understood. Here, we characterized somatosensory dorsal root ganglia (DRG) afferent neurons innervating murine long bones before and after experimental long bone fracture in mice. Retrograde labeling of DRG neurons by an adeno-associated virus with peripheral nerve tropism showed AAV-tdT signal. Single cell transcriptomic profiling of 6,648 DRG neurons showed highest labeling across CGRP+ neuron clusters (6.9-17.2%) belonging to unmyelinated C fibers, thinly myelinated Aδ fibers and Aβ-Field LTMR (9.2%). Gene expression profiles of retrograde labeled DRG neurons over multiple timepoints following experimental stress fracture revealed dynamic changes in gene expression corresponding to the acute inflammatory ( S100a8 , S100a9 ) and mechanical force ( Piezo2 ). Reparative phase after fracture included morphogens such as Tgfb1, Fgf9 and Fgf18 . Two methods to surgically or genetically denervate fractured bones were used in combination with scRNA-seq to implicate defective mesenchymal cell proliferation and osteodifferentiation as underlying the poor bone repair capacity in the presence of attenuated innervation. Finally, multi-tissue scRNA-seq and interactome analyses implicated neuron-derived FGF9 as a potent regulator of fracture repair, a finding compatible with in vitro assessments of neuron-to-skeletal mesenchyme interactions.

Vascular architecture regulates mesenchymal stromal cell heterogeneity via P53-PDGF signaling in the mouse incisor

Mesenchymal stem cells (MSCs) reside in niches to maintain tissue homeostasis and contribute to repair and regeneration. Although the physiological functions of blood and lymphatic vasculature are well studied, their regulation of MSCs as niche components remains largely unknown. Using adult mouse incisors as a model, we uncover the role of Trp53 in regulating vascular composition through THBS2 to maintain mesenchymal tissue homeostasis. Loss of Trp53 in GLI1+ progeny increases arteries and decreases other vessel types. Platelet-derived growth factors from arteries deposit in the MSC region and interact with PDGFRA and PDGFRB. Significantly, PDGFRA+ and PDGFRB+ cells differentially contribute to defined cell lineages in the adult mouse incisor. Collectively, our results highlight Trp53's importance in regulating the vascular niche for MSCs. They also shed light on how different arterial cells provide unique cues to regulate MSC subpopulations and maintain their heterogeneity. Furthermore, they provide mechanistic insight into MSC-vasculature crosstalk.

Systemic and local regulation of hematopoietic homeostasis in health and disease

Hematopoietic stem cells (HSCs) generate all blood cell lineages responsible for tissue oxygenation, life-long hematopoietic homeostasis and immune protection. In adulthood, HSCs primarily reside in the bone marrow (BM) microenvironment, consisting of diverse cell types that constitute the stem cell 'niche'. The adaptability of the hematopoietic system is required to respond to the needs of the host, whether to maintain normal physiology or during periods of physical, psychosocial or environmental stress. Hematopoietic homeostasis is achieved by intricate coordination of systemic and local factors that orchestrate the function of HSCs throughout life. However, homeostasis is not a static process; it modulates HSC and progenitor activity in response to circadian rhythms coordinated by the central and peripheral nervous systems, inflammatory cues, metabolites and pathologic conditions. Here, we review local and systemic factors that impact hematopoiesis, focusing on the implications of aging, stress and cardiovascular disease.

ARID1B maintains mesenchymal stem cell quiescence via inhibition of BCL11B-mediated non-canonical Activin signaling

ARID1B haploinsufficiency in humans causes Coffin-Siris syndrome, associated with developmental delay, facial dysmorphism, and intellectual disability. The role of ARID1B has been widely studied in neuronal development, but whether it also regulates stem cells remains unknown. Here, we employ scRNA-seq and scATAC-seq to dissect the regulatory functions and mechanisms of ARID1B within mesenchymal stem cells (MSCs) using the mouse incisor model. We reveal that loss of Arid1b in the GLI1+ MSC lineage disturbs MSCs' quiescence and leads to their proliferation due to the ectopic activation of non-canonical Activin signaling via p-ERK. Furthermore, loss of Arid1b upregulates Bcl11b, which encodes a BAF complex subunit that modulates non-canonical Activin signaling by directly regulating the expression of activin A subunit, Inhba. Reduction of Bcl11b or non-canonical Activin signaling restores the MSC population in Arid1b mutant mice. Notably, we have identified that ARID1B suppresses Bcl11b expression via specific binding to its third intron, unveiling the direct inter-regulatory interactions among BAF subunits in MSCs. Our results demonstrate the vital role of ARID1B as an epigenetic modifier in maintaining MSC homeostasis and reveal its intricate mechanistic regulatory network in vivo, providing novel insights into the linkage between chromatin remodeling and stem cell fate determination.

Effect of chitin-architected spatiotemporal three-dimensional culture microenvironments on human umbilical cord-derived mesenchymal stem cells

Mesenchymal stem cell (MSC) transplantation has been explored for the clinical treatment of various diseases. However, the current two-dimensional (2D) culture method lacks a natural spatial microenvironment in vitro. This limitation restricts the stable establishment and adaptive maintenance of MSC stemness. Using natural polymers with biocompatibility for constructing stereoscopic MSC microenvironments may have significant application potential. This study used chitin-based nanoscaffolds to establish a novel MSC three-dimensional (3D) culture. We compared 2D and 3D cultured human umbilical cord-derived MSCs (UCMSCs), including differentiation assays, cell markers, proliferation, and angiogenesis. When UCMSCs are in 3D culture, they can differentiate into bone, cartilage, and fat. In 3D culture condition, cell proliferation is enhanced, accompanied by an elevation in the secretion of paracrine factors, including vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), Interleukin-6 (IL-6), and Interleukin-8 (IL-8) by UCMSCs. Additionally, a 3D culture environment promotes angiogenesis and duct formation with HUVECs (Human Umbilical Vein Endothelial Cells), showing greater luminal area, total length, and branching points of tubule formation than a 2D culture. MSCs cultured in a 3D environment exhibit enhanced undifferentiated, as well as higher cell activity, making them a promising candidate for regenerative medicine and therapeutic applications.

The Role of Sensory Nerves in Dental Pulp Homeostasis: Histological Changes and Cellular Consequences after Sensory Denervation

Homeostatic maintenance is essential for pulp function. Disrupting pulp homeostasis may lead to pulp degeneration, such as fibrosis and calcifications. Sensory nerves constitute a crucial component of the dental pulp. However, the precise involvement of sensory nerves in pulp homeostasis remains uncertain. In this study, we observed the short-term and long-term histological changes in the dental pulp after inferior alveolar nerve transection. Additionally, we cultured primary dental pulp cells (DPCs) from the innervated and denervated groups and compared indicators of cellular senescence and cellular function. The results revealed that pulp fibrosis occurred at 2 w after the operation. Furthermore, the pulp area, as well as the height and width of the pulp cavity, showed accelerated reductions after sensory denervation. Notably, the pulp area at 16 w after the operation was comparable to that of 56 w old rats. Sensory denervation induced excessive extracellular matrix (ECM) deposition and increased predisposition to mineralization. Furthermore, sensory denervation promoted the senescence of DPCs. Denervated DPCs exhibited decelerated cell proliferation, arrest in the G2/M phase of the cell cycle, imbalance in the synthesis and degradation of ECM, and enhanced mineralization. These findings indicate that sensory nerves play an essential role in pulp homeostasis maintenance and dental pulp cell fate decisions, which may provide novel insights into the prevention of pulp degeneration.

Sensory nerve regulates progenitor cells via FGF-SHH axis in tooth root morphogenesis

Nerves play important roles in organ development and tissue homeostasis. Stem/progenitor cells differentiate into different cell lineages responsible for building the craniofacial organs. The mechanism by which nerves regulate stem/progenitor cell behavior in organ morphogenesis has not yet been comprehensively explored. Here, we use tooth root development in mouse as a model to investigate how sensory nerves regulate organogenesis. We show that sensory nerve fibers are enriched in the dental papilla at the initiation of tooth root development. Through single cell RNA-sequencing analysis of the trigeminal ganglion and developing molar, we reveal several signaling pathways that connect the sensory nerve with the developing molar, of which FGF signaling appears to be one of the important regulators. Fgfr2 is expressed in the progenitor cells during tooth root development. Loss of FGF signaling leads to shortened roots with compromised proliferation and differentiation of progenitor cells. Furthermore, Hh signaling is impaired in Gli1-CreER;Fgfr2fl/fl mice. Modulation of Hh signaling rescues the tooth root defects in these mice. Collectively, our findings elucidate the nerve-progenitor crosstalk and reveal the molecular mechanism of the FGF-SHH signaling cascade during tooth root morphogenesis.

Cellular microenvironment: a key for tuning mesenchymal stem cell senescence

Mesenchymal stem cells (MSCs) possess the ability to self-renew and differentiate into multiple cell types, making them highly suitable for use as seed cells in tissue engineering. These can be derived from various sources and have been found to play crucial roles in several physiological processes, such as tissue repair, immune regulation, and intercellular communication. However, the limited capacity for cell proliferation and the secretion of senescence-associated secreted phenotypes (SASPs) pose challenges for the clinical application of MSCs. In this review, we provide a comprehensive summary of the senescence characteristics of MSCs and examine the different features of cellular microenvironments studied thus far. Additionally, we discuss the mechanisms by which cellular microenvironments regulate the senescence process of MSCs, offering insights into preserving their functionality and enhancing their effectiveness.

Lepr-Expressing PDLSCs Contribute to Periodontal Homeostasis and Respond to Mechanical Force by Piezo1

Periodontium supports teeth in a mechanically stimulated tissue environment, where heterogenous stem/progenitor populations contribute to periodontal homeostasis. In this study, Leptin receptor+ (Lepr+) cells are identified as a distinct periodontal ligament stem cell (PDLSC) population by single-cell RNA sequencing and lineage tracing. These Lepr+ PDLSCs are located in the peri-vascular niche, possessing multilineage potential and contributing to tissue repair in response to injury. Ablation of Lepr+ PDLSCs disrupts periodontal homeostasis. Hyper-loading and unloading of occlusal forces modulate Lepr+ PDLSCs activation. Piezo1 is demonstrated that mediates the mechanosensing of Lepr+ PDLSCs by conditional Piezo1-deficient mice. Meanwhile, Yoda1, a selective activator of Piezo1, significantly accelerates periodontal tissue growth via the induction of Lepr+ cells. In summary, Lepr marks a unique multipotent PDLSC population in vivo, to contribute toward periodontal homeostasis via Piezo1-mediated mechanosensing.

Unlocking the potential of Mesenchymal stem cells in liver Fibrosis: Insights into the impact of autophagy and aging

Liver fibrosis is a chronic liver disease characterized by extracellular matrix protein accumulation, potentially leading to cirrhosis or hepatocellular carcinoma. Liver cell damage, inflammatory responses, and apoptosis due to various reasons induce liver fibrosis. Although several treatments, such as antiviral drugs and immunosuppressive therapies, are available for liver fibrosis, they only provide limited efficacy. Mesenchymal stem cells (MSCs) have become a promising therapeutic option for liver fibrosis, because they can modulate the immune response, promote liver regeneration, and inhibit the activation of hepatic stellate cells that contribute to disease development. Recent studies have suggested that the mechanisms through which MSCs gain their antifibrotic properties involve autophagy and senescence. Autophagy, a vital cellular self-degradation process, is critical for maintaining homeostasis and protecting against nutritional, metabolic, and infection-mediated stress. The therapeutic effects of MSCs depend on appropriate autophagy levels, which can improve the fibrotic process. Nonetheless, aging-related autophagic damage is associated with a decline in MSC number and function, which play a crucial role in liver fibrosis development. This review summarizes the recent advancements in the understanding of autophagy and senescence in MSC-based liver fibrosis treatment, presenting the key findings from relevant studies.