Single-cell transcriptome analysis reveals cellular heterogeneity in mouse intra- and extra articular ligaments

Comparative Single-Cell Analysis Reveals Tendon Progenitor Dysfunction by Age-Associated Oxidative Stress and Its Restoration by Antioxidant Treatments

Impaired healing of adult tendons with fibrosis remains clinical challenges while neonatal tendons have full functional restoration. However, age-associated cellular and molecular changes in tendon cells and tendon stem/progenitor cells (TSPCs) remain unknown. Here, comparative single cell transcriptomics of early postnatal (2 weeks old) and adult (20 weeks old) mouse tendons revealed that adult tendons have reduced number of TSPCs, decreased gene expression in tendon and cartilage development, and a greater population of fibro-tenogenic cells. Notably, adult TSPCs and tenocytes exhibit increased expression of immune-response and oxidative-stress genes with higher EGFR but decreased IGF signaling. Adult tendon cells show increased levels of intracellular reactive oxygen species (ROS) in vivo. In contrast, antioxidant treatment of adult tendons significantly reduces intracellular ROS of TSPCs and improves tendon strength in vivo. Hence, these findings suggest that increased inflammation and ROS during tendon aging deteriorates tendon function and regeneration that can be mitigated by antioxidant treatment.

Single-cell transcriptomic profiling of lung fibroblasts in a bleomycin-induced systemic sclerosis mouse model

Systemic sclerosis (SSc) is a complex autoimmune disease characterized by fibrosis, vascular abnormalities, and immune dysfunction, with no definitive cure. Patients with progressive pulmonary fibrosis face a high mortality risk, underscoring the urgent need for effective treatments. Although fibroblasts are recognized as key drivers of fibrosis, the precise molecular mechanisms remain poorly understood. In this study, we employ single-cell RNA sequencing to explore the role of fibroblasts in pulmonary fibrosis. Using a mouse model induced by subcutaneous bleomycin administration, we identify two distinct fibroblast subpopulations: nephronectin-positive (NPNT) and peptidase inhibitor 16-positive cells(PI16). NPNT-positive fibroblasts, located around the alveoli, exhibit increased extracellular matrix expression following bleomycin treatment. To further understand pulmonary fibrosis, subcutaneous and intratracheal bleomycin-induced mouse models are compared. A comparative gene expression analysis reveals shared and unique features between the models, highlighting the complexity of the fibrotic process. These findings offer valuable insights into the molecular mechanisms of SSc-associated pulmonary fibrosis and may inform the development of therapies targeting specific fibroblast subpopulations or pathways.

High-mobility group box 1 fragment ameliorates chronic pancreatitis induced by caerulein in mice

BACKGROUND

Chronic pancreatitis (CP) is a progressive disease characterized by pancreatic fibrosis for which effective treatment options are lacking. Mesenchymal stem cells (MSCs) have shown potential for fibrosis treatment but face limitations in clinical application. The high-mobility group box 1 (HMGB1) fragment mobilizes MSCs from bone marrow into the blood and has emerged as a promising therapeutic agent for tissue regeneration in various pathological conditions. The aim of this study was to investigate the potential therapeutic effects of systemic administration of the HMGB1 fragment in a mouse model of CP.

METHODS

A caerulein-induced CP mouse model was used, and the HMGB1 fragment was administered by tail vein injection. Parameters such as body weight, pancreatic tissue damage, fibrosis, inflammatory cytokine expression, and collagen-related gene expression were evaluated using various assays, including immunohistochemistry, real-time PCR, serum analysis, and single-cell transcriptome analysis. And the migration of MSCs to the pancreas was evaluated using the parabiosis model.

RESULTS

Administration of the HMGB1 fragment was associated with significant improvements in pancreatic tissue damage and fibrosis. It suppressed the expression of inflammatory cytokines and activated platelet-derived growth factor receptor-α+ MSCs, leading to their accumulation in the pancreas. The HMGB1 fragment also shifted gene expression patterns associated with pancreatic fibrosis toward those of the normal pancreas. Systemic administration of the HMGB1 fragment demonstrated therapeutic efficacy in attenuating pancreatic tissue damage and fibrosis in a CP mouse model.

CONCLUSION

These findings highlight the potential of the HMGB1 fragment as a therapeutic target for the treatment of CP.

Single-nucleus RNA and multiomics in situ pairwise sequencing reveals cellular heterogeneity of the abnormal ligamentum teres in patients with developmental dysplasia of the hip

Developmental dysplasia of the hip (DDH) is the most common hip deformity in pediatric orthopedics. One of the common pathological changes in DDH is the thickening and hypertrophy of the ligamentum teres. However, the underlying pathogenic mechanism responsible for these changes remains unclear. This study represents the first time that the heterogeneity of cell subsets in the abnormal ligamentum teres of patients with DDH has been resolved at the single-cell and spatial levels by snRNA-Seq and MiP-Seq. Through gene set enrichment and intercellular communication network analyses, we found that receptor-like cells and ligament stem cells may play an essential role in the pathological changes resulting in ligamentum teres thickening and hypertrophy. Eight ligand-receptor pairs related to the ECM-receptor pathway were observed to be closely associated with DDH. Further, using the Monocle R package, we predicted a differentiation trajectory of pericytes into two branches, leading to junctional ligament stem cells or fibroblasts. The expression of extracellular matrix-related genes along pseudotemporal trajectories was also investigated. Using MiP-Seq, we determined the expression distribution of marker genes specific to different cell types within the ligamentum teres, as well as differentially expressed DDH-associated genes at the spatial level.

Identification of anterior cruciate ligament fibroblasts and their contribution to knee osteoarthritis progression using single-cell analyses

The mechanical properties of the anterior cruciate ligament (ACL) in the knee have been highlighted, but its role in the regulation of the joint microenvironment remains unclear, especially in the progression of Knee Osteoarthritis (KOA). Here, single-cell RNA sequencing (scRNA-seq) and single-cell assay for transposase-accessible chromatin sequencing (scATAC-seq) data were integrated to reveal the transcriptional and epigenomic landscape of ACL in normal and OA states. We identified a novel subpopulation of fibroblasts in ACL, which provides new insights into the role of the ACL in knee homeostasis and disease. Degeneration of the ACL during OA mechanically alters the knee joint homeostasis and influences the microenvironment by regulating inflammatory- and osteogenic-related factors, thereby contributing to the progression of KOA. Additionally, the specific mechanism by which these Inflammation-associated Fibroblasts (IAFs) regulate KOA progression was uncovered, providing new foundation for the development of targeted treatments for KOA.

Decoding the transcriptomic expression and genomic methylation patterns in the tendon proper and its peritenon region in the aging horse

OBJECTIVES

Equine tendinopathies are challenging because of the poor healing capacity of tendons commonly resulting in high re-injury rates. Within the tendon, different regions - tendon proper (TP) and peritenon (PERI) - contribute to the tendon matrix in differing capacities during injury and aging. Aged tendons have decreased repair potential; the underlying transcriptional and epigenetic changes that occur in the TP and PERI regions are not well understood. The objective of this study was to assess TP and PERI regional differences in adolescent, midlife, and geriatric horses using RNA sequencing and DNA methylation techniques.

RESULTS

Differences existed between TP and PERI regions of equine superficial digital flexor tendons by age as evidenced by RNASeq and DNA methylation. Cluster analysis indicated that regional distinctions existed regardless of age. Genes such as DCN, COMP, FN1, and LOX maintained elevated TP expression while genes such as GSN and AHNAK were abundant in PERI. Increased gene activity was present in adolescent and geriatric populations but decreased during midlife. Regional differences in DNA methylation were also noted. Notably, when evaluating all ages of TP against PERI, five genes (HAND2, CHD9, RASL11B, ADGRD1, and COL14A1) had regions of differential methylation as well as differential gene expression.

Tendon cell and tissue culture: Perspectives and recommendations

The wide variety of cell and tissue culture systems used to study and engineer tendons can make it difficult to choose the best approach and "optimal" culture conditions to test a given hypothesis. Therefore, a breakout session was organized at the 2022 ORS Tendon Section Meeting that focused on establishing a set of guidelines for conducting cell and tissue culture studies of tendon. This paper summarizes the outcomes of that discussion and presents recommendations for future studies. In the case of studying tendon cell behavior, cell and tissue culture systems are reductionist models in which the culture conditions should be strictly defined to approximate the in vivo condition as closely as possible. In contrast, for tissue engineering tendon replacements, the culture conditions do not need to replicate native tendon, but the outcome measures for success should be narrowly defined for the specific clinical application. Common recommendations for both applications are that researchers should perform a baseline phenotypic characterization of the cells that are ultimately used for experimentation. For models of tendon cell behavior, culture conditions should be well justified by existing literature and meticulously reported, tissue explant viability should be assessed, and comparisons to in vivo conditions should be made to determine baseline physiological relevance. For tissue engineering applications, the functional/structural/compositional outcome targets should be defined by the specific tendons they seek to replace, with key biologic and material properties prioritized for construct assessment. Lastly, when engineering tendon replacements, researchers should utilize clinically approved cGMP materials to facilitate clinical translation.