Cellular apoptosis and proliferation in the middle and late intrasynovial tendon healing periods

Single-Cell Integration Analysis of Heterotopic Ossification and Fibrocartilage Developmental Lineage: Endoplasmic Reticulum Stress Effector Xbp1 Transcriptionally Regulates the Notch Signaling Pathway to Mediate Fibrocartilage Differentiation

INTRODUCTION

Regeneration of fibrochondrocytes is essential for the healing of the tendon-bone interface (TBI), which is similar to the formation of neurogenic heterotopic ossification (HO). Through single-cell integrative analysis, this study explored the homogeneity of HO cells and fibrochondrocytes.

METHODS

This study integrated six datasets, namely, GSE94683, GSE144306, GSE168153, GSE138515, GSE102929, and GSE110993. The differentiation trajectory and key transcription factors (TFs) for HO occurrence were systematically analyzed by integrating single-cell RNA (scRNA) sequencing, bulk RNA sequencing, and assay of transposase accessible chromatin seq. The differential expression and enrichment pathways of TFs in heterotopically ossified tissues were identified.

RESULTS

HO that mimicked pathological cells was classified into HO1 and HO2 cell subsets. Results of the pseudo-temporal sequence analysis suggested that HO2 is a differentiated precursor cell of HO1. The analysis of integrated scRNA data revealed that ectopically ossified cells have similar transcriptional characteristics to cells in the fibrocartilaginous zone of tendons. The modified SCENIC method was used to identify specific transcriptional regulators associated with ectopic ossification. Xbp1 was defined as a common key transcriptional regulator of ectopically ossified tissues and the fibrocartilaginous zone of tendons. Subsequently, the CellPhoneDB database was completed for the cellular ligand-receptor analysis. With further pathway screening, this study is the first to propose that Xbp1 may upregulate the Notch signaling pathway through Jag1 transcription. Twenty-four microRNAs were screened and were found to be potentially associated with upregulation of XBP1 expression after acute ischemic stroke.

CONCLUSION

A systematic analysis of the differentiation landscape and cellular homogeneity facilitated a molecular understanding of the phenotypic similarities between cells in the fibrocartilaginous region of tendon and HO cells. Furthermore, by identifying Xbp1 as a hub regulator and by conducting a ligand-receptor analysis, we propose a potential Xbp1/Jag1/Notch signaling pathway.

Fine tuning of the side-to-side tenorrhaphy: A biomechanical study assessing different side-to-side suture techniques in a porcine tendon model

Recent studies conclude that a new technique for tendon transfers, the side-to-side tenorrhaphy by Fridén (FR) provides higher biomechanical stability than the established standard first described by Pulvertaft (PT). The aim of this study was to optimize side-to-side tenorrhaphies. We compared PT and FR tenorrhaphies as well as a potential improvement, termed Woven-Fridén tenorrhaphy (WF), with regard to biomechanical stability. Our results demonstrate superior biomechanical stability and lower bulk of FR and, in particular, WF over PT tenorrhaphies. The WF and FR technnique therefore seem to be a notable alternative to the established standard tenorrhaphy as they display lower bulk and higher stability, permitting successful immediate active mobilization after surgery.

Characterization of a purified exosome product and its effects on canine flexor tenocyte biology

Flexor tendon injuries and tendinopathy are very common but remain challenging in clinical treatment. Exosomes-based cell-free therapy appears to be a promising strategy for tendon healing, while limited studies have evaluated its impacts on tenocyte biology. The objective of this study was to characterize a novel purified exosome product (PEP) derived from plasma, as well as to explore its cellular effects on canine tenocyte biology. The transmission electron microscope revealed that exosomes of PEP present cup-shaped structures with the diameters ranged from 80 to 141 nm, and the NanoSight report presented that their size mainly concentrated around 100 nm. The enzyme-linked immunosorbent assay kits analysis showed that PEP was positive for CD63 and AChE expression, and the cellular uptake of exosomes internalized into tenocyte cytoplasm was observed. The cell growth assays displayed that tenocyte proliferation ability was enhanced by PEP solution in a dose-dependent manner. Tenogenic phenotype was preserved as is evident by that tendon-related genes expression (SCX, COL1A, COL3A1, TNMD, DCN, and MKX) were expressed insistently in a high level, while tenocytes were treated with 5% PEP solution. Furthermore, migration capability was maintained and total collagen deposition was increased. More interesting, dexamethasone-induced cellular apoptosis was attenuated during the incubation of tenocytes with a 5% PEP solution. These findings will provide the basic understandings about the PEP, and support the potential use of this biological strategy for tendon healing.

Intra-articular treatment with corticosteroids increases apoptosis in human rotator cuff tears

PURPOSE

The aim of this study is to evaluate in vivo the level of apoptosis in human rotator cuff tears and the relationship it might have with tendon degeneration.

METHODS

Rotator cuff biopsies from 19 male and female patients, ages between 38 and 68 years, with and without previous corticosteroid infiltrations were collected via arthroscopy. Biopsies from seven patients with healthy rotator cuffs were used as a control group. An in situ terminal deoxynucleotidyl transferase dUTP nick end labeling assay was performed to detect the level of apoptosis, which was expressed as a percentage of apoptotic cells (PAC).

RESULTS

PAC in patients with corticosteroid infiltrations was 76.97 ± 16.99 in all tendon rupture zones, in non-infiltrated patients was 35.89 ± 22.96, whereas in control patients was 14.48 ± 8.15. Likewise, the tendency of PAC reveals that apoptosis in control and non-infiltrated groups was different and dispersed in all tear zones; while in corticosteroid treated patients, the tendency was similar in all rupture sites.

CONCLUSIONS

This investigation leads us to conclude that the administration of corticosteroid is associated with a higher amount of apoptosis at the insertion site of the rotator cuff (rupture edge).

The effect of mesenchymal stromal cell sheets on the inflammatory stage of flexor tendon healing

Background

The clinical outcomes following intrasynovial flexor tendon repair are highly variable. Excessive inflammation is a principal factor underlying the formation of adhesions at the repair surface and affecting matrix regeneration at the repair center that limit tendon excursion and impair tendon healing. A previous in-vitro study revealed that adipose-derived mesenchymal stromal cells (ASCs) modulate tendon fibroblast response to macrophage-induced inflammation. The goal of the current study was therefore to explore the effectiveness of autologous ASCs on the inflammatory stage of intrasynovial tendon healing in vivo using a clinically relevant animal model.

Methods

Zone II flexor tendon transections and suture repairs were performed in a canine model. Autologous ASC sheets were delivered to the surface of repaired tendons. Seven days after repair, the effects of ASCs on tendon healing, with a focus on the inflammatory response, were evaluated using gene expression assays, immunostaining, and histological assessments.

Results

ASCs delivered via the cell sheet infiltrated the host tendon, including the repair surface and the space between the tendon ends, as viewed histologically by tracking GFP-expressing ASCs. Gene expression results demonstrated that ASCs promoted a regenerative/anti-inflammatory M2 macrophage phenotype and regulated tendon matrix remodeling. Specifically, there were significant increases in M2-stimulator (IL-4), marker (CD163 and MRC1), and effector (VEGF) gene expression in ASC-sheet treated tendons compared with nontreated tendons. When examining changes in extracellular matrix expression, tendon injury caused a significant increase in scar-associated COL3A1 expression and reductions in COL2A1 and ACAN expression. The ASC treatment effectively counteracted these changes, returning the expression levels of these genes closer to normal. Immunostaining further confirmed that ASC treatment increased CD163⁺ M2 cells in the repaired tendons and suppressed cell apoptosis at the repair site.

Conclusions

This study provides a novel approach for delivering ASCs with outcomes indicating potential for substantial modulation of the inflammatory environment and enhancement of tendon healing after flexor tendon repair.

Thermographic and histological analysis of rabbit different tenorrhaphies techniques (4 and 6 strands) after early active mobilization

Introduction This research is based on the results of the surgeries of tenorraphy, which have been improved due to the association between strong and not voluminous sutures and physiotherapic protocols, which preconize the early active motion to the postoperative period. Objective To evaluate the healing process in vivo in different types of tenorraphies. Methods Thirty-six rabbits that underwent early active motion after tenorraphy. The sample was constituted of 3 groups of 12, in accordance with the 3 different types of suture (Brasil, Indiana and Tsai). Results On the 15th and 30th days after the surgery, thermographic and histological analyses revealed similar results that all groups showed similar behaviors in the same time of surgical repair, just differentiating between the periods. On the 30th day analysis were observed that collagen fibers being more exuberant thickening, thus being able to offer higher tensile strength to the tendon. Conclusion That suggests early active motion may be increased gradually to around the 30th day taking this as clinical relevance.

Regulatory effects of introduction of an exogenous FGF2 gene on other growth factor genes in a healing tendon

In this study of a tendon injury model, we investigated how injection of a vector incorporating one growth factor gene changes expression levels of multiple growth factor genes in the healing process. The flexor tendon of chicken toes was completely cut and repaired surgically. The tendons in the experimental arm were injected with an adeno-associated virus-2 vector incorporating basic fibroblast growth-factor gene, whereas the tendons in the control arm were not injected or injected with sham vectors. Using real-time polymerase chain reaction, we found that, within the tendon healing period, a set of growth factor genes-transforming growth factor-β1, vascular endothelial growth factor, and connective tissue growth factor-were significantly up-regulated. Expression of the platelet-derived growth factor-B gene was not changed, and the insulin-like growth factor was down-regulated. A tendon marker gene, scleraxis, was significantly up-regulated in the period. Our study revealed an intriguing finding that introduction of one growth factor gene in the healing tendon modulated expression of multiple growth factor genes. We believe this study may have significant implications in determining the approach of gene therapy, and the findings substantiate that gene therapy using a single growth factor could affect multiple growth factors.

Rotator cuff tear degeneration and cell apoptosis in smokers versus nonsmokers

PURPOSE

The purpose of this study was to assess the effect of smoking on supraspinatus tendon degeneration, including cellular alterations, proliferation, and apoptosis of tendon cells.

METHODS

Supraspinatus tendon samples of 10 smokers and 15 nonsmokers with full-thickness tears were compared, focusing on the severity of tendon histopathology including apoptosis (programmed cell death), cellularity, and proliferation. Immunohistochemistry was used to assess the density of apoptotic cells and proliferation. The extent of tendon degeneration was classified according to a revised version of the Bonar tendon histopathology score.

RESULTS

The smokers were younger (P = .01). The symptom duration among smokers was longer (P < .05). The supraspinatus tendons from the smokers presented significantly more advanced degenerative changes (Bonar score, 13.5 [interquartile range, 1.4] v 9 [interquartile range, 3]; P < .001). The smokers' tendons showed increased density of apoptotic cells (0.108 [SE, 0.038] v 0.0107 [SE, 0.007]; P = .024) accompanied by reduced tenocyte density (P = .019) and upregulation of proliferative activity (P < .0001).

CONCLUSIONS

Smoking is associated with worsened supraspinatus tendon histopathology and increased apoptosis.

CLINICAL RELEVANCE

Pronounced degenerative changes, reduced tendon cellularity, and increased apoptosis may indicate reduced tendon healing capacity in smokers.

The comparison of macroscopic and histologic healing of side-to-side (SS) tenorrhaphy technique and primer tendon repair in a rabbit model

INTRODUCTION

The side-to-side (SS) tenorrhaphy technique has been used in tendon transfer surgery. The mechanical properties of SS tendon suture have been studied previously. However, the histo-pathological healing of the SS tenorrhaphy of the tendons is unknown. The aim of this study was to assess the gross and histological effects of SS tenorrhaphy in a rabbit model.

MATERIALS AND METHODS

Twenty New Zealand rabbits were used. The extensor hallucis longus and tibialis anterior tendon were sewed SS at the level distal to the ankle joint. The patellar tendon (PT) at the same side was used as control group. A unilateral midline incision was made and repaired with a single suture. The animals were killed at the 12th week postoperatively. The histological sections were obtained from the side of surgery from each group. Each sample was stained with hematoxylene and eosin (H&E). Gross and microscopic healing was compared between the two groups.

RESULTS

Gross examination of the control group showed complete healing with a thin peri-tendinous sheath formation around the suture site, whereas in the study group, a thick peri-tendinous sheath was formed around the area of the tendon-tendon anastomosis. In the control group, at the 12th week after surgery, the healing was almost completed in all samples. In the study group, a thick fibro vascular sheath has formed around the side of anastomosis. In all specimens few inter-digitations were observed between the tendons;however, the trough was still present.

CONCLUSION

The result of the current study showed that histological healing and union of SS tenorrhaphy differ from that in primary tendon injury and healing. Further studies are required to clarify the healing stages at the tenorrhaphy site.

Increased levels of apoptosis and p53 in partial-thickness supraspinatus tendon tears

PURPOSE

The role of apoptosis in the progression of rotator cuff tendinopathy remains poorly understood. In particular, the extent of apoptosis in the partially torn supraspinatus tendon has not been well examined.

METHODS

Biopsies were obtained from nine partially torn supraspinatus tendons, from the matched intact subscapularis tendons, and from 10 reference subscapularis tendons. Immunohistochemistry was used to assess the density of apoptotic cells (activated caspase-3; Asp175), proliferation (Ki67), and p53 (M7001), a key protein involved in regulating cell death. The Bonar scale was used to evaluate tendon degeneration.

RESULTS

The density of apoptotic tendon cells and the density of cells expressing p53 were significantly increased in both the partially torn supraspinatus tendons and in the matched subscapularis tendons, compared with uninjured reference tendons. The Bonar score revealed significant tendon degeneration in the partially torn supraspinatus tendons compared with both matched and reference subscapularis tendons. Tendon cell proliferation was significantly increased in the partially torn supraspinatus tendons compared with reference subscapularis tendons.

CONCLUSIONS

Partial-thickness tears of the supraspinatus tendon demonstrated an increased density of apoptotic, p53+ tendon cells. The fact that apoptosis was accompanied by increased tendon cell proliferation suggests that apoptosis may be related to an ongoing injury-repair process. Increased tenocyte apoptosis may be a relatively early feature in rotator cuff tendinopathy and could represent a possible target for therapeutic intervention.

Apoptosis in adhesions and the adhesion-tendon gliding interface: relationship to adhesion-tendon gliding mechanics

PURPOSE

Adhesion formation is closely related to tendon-gliding function. We aimed to investigate apoptosis (programmed cell death) in adhesions and tendons and study its relationship to the mechanics of adhesions and healing tendons.

METHODS

The flexor digitorum profundus tendons of 30 long toes in 15 chickens were completely transected and repaired surgically. At postoperative weeks 4, 6, and 8, tendon-gliding excursions were tested and adhesion scores were recorded. Tendons and surrounding adhesions were then harvested for analysis of apoptosis using in situ terminal deoxynucleotidyl transferase dUTP (deoxyuridine triphosphate) nick end labeling assay. Three-dimensional image reconstruction was used to provide an overall view of cellular distribution in tendons and adhesions. Finally, we analyzed the correlation between the apoptotic index measured at the adhesions and the gliding excursions. Ten uninjured tendons served as normal controls.

RESULTS

Apoptosis was found to be a dominant cellular event in the adhesion tissues at both the adhesion-tendon gliding interface and the adhesion core. The apoptotic index in the adhesions was generally above 20% to 50%. The apoptotic index was significantly higher in the adhesions than in the junction region of the cut tendon ends at weeks 4, 6, and 8. A higher apoptotic index in the adhesions significantly correlated to lower tendon excursions at week 6.

CONCLUSIONS

Apoptosis in adhesions and at the adhesion-tendon interface is a prominent event in the tendon-healing process. The tendons exhibiting a lower tendon-gliding amplitude, meaning more severe adhesions, tended to have a greater apoptotic index in their adhesions during a certain period of the tendon-remodeling process.

CLINICAL RELEVANCE

Apoptosis in the adhesions and at the adhesion-tendon interface may contribute remarkably to the fate of adhesions and the restoration of the tendon gliding surface, which may be closely related to the tendon function.

Tendon healing, edema, and resistance to flexor tendon gliding: clinical implications

Early flexor tendon healing is characterized by peak cellular apoptosis of both inflammatory and tendon cells in the first week, followed by progressively greater tenocyte proliferation in the second and third weeks. Tenocyte apoptosis is a predominant event, but proliferation of tenocytes is minimal in the middle and late healing periods. Edematous subcutaneous tissues, edema of the tendon, the intact annular pulleys, and extensor tendons all greatly contribute to the resistance. Careful consideration of the contributing factors and dynamics offers insight into strategies to reduce repair rupture and maximize tendon gliding through surgery and postoperative motion protocols.

Allograft tendon for second-stage tendon reconstruction

Tendons are made of compact dense collagen fibers with only sparse cellularity and naturally low immunogenicity. Allogenic tendons may be preserved through deep freezing methods and retain excellent mechanical properties after revitalization. Allogenic tendons were used in 22 patients (30 tendons) for second-stage tendon reconstruction in the hand. Preliminary results indicate no observable adverse tissue reactions, and functional recovery after tendon grafting does not seem different from reconstruction using tendon autografts. This type of allogenic graft does not seem to produce serious concern as a foreign tissue in the body, at least in the short term.