Effect of TGF-beta inducible early gene deficiency on flexor tendon healing

Stem Cell‐Based Therapies and Tissue Engineering Innovations for Tendinopathy: A Comprehensive Review of Current Strategies and Future Directions

Tendon diseases commonly lead to physical disability, exerting a profound impact on the routine of affected patients. These conditions respond poorly to existing treatments, presenting a substantial challenge for orthopedic scientists. Research into clinical translational therapy has yet to yield highly versatile interventions capable of effectively addressing tendon diseases, including tendinopathy. Stem cell‐based therapies have emerged as a promising avenue for modifying the biological milieu through the secretion of regenerative and immunomodulatory factors. The current review provides an overview of the intricate tendon microenvironment, encompassing various tendon stem progenitor cells within distinct tendon sublocations, gene regulation, and pathways pertinent to tendon development, and the pathology of tendon diseases. Subsequently, the advantages of stem cell‐based therapies are discussed that utilize distinct types of autologous and allogeneic stem cells for tendon regeneration at the translational level. Moreover, this review outlines the challenges, gaps, and future innovations to propose a consolidated stem cell‐based therapy to treat tendinopathy. Finally, regenerative soluble therapies, insoluble bio‐active therapies, along with insoluble bio‐active therapies, and implantable 3D scaffolds for tendon tissue engineering are discussed, thereby presenting a pathway toward enhanced tissue regeneration and engineering.

From fetal tendon regeneration to adult therapeutic modalities: TGF-β3 in scarless healing

Tendon injuries are common disorders that can significantly impact people's lives. Unfortunately, the limited regenerative ability of tendons results in tissue healing in a scar-mediated manner. The current therapeutic strategies fail to fully recover the functions of the injured tendons, and as such, the conception of 'scarless healing' has gained prominent attention in the field of regenerative medicine. Interestingly, injured fetal tendons possess the capability to heal through regeneration, which builds an ideal blueprint for adult tendon regeneration. Studies have shown that fetal biochemical cues have the potential to improve adult tendon healing. Here we review the biological factors that contribute to fetal tendon regeneration and how manipulation of these biochemical cues in the adult tendon healing process could achieve regeneration.

The tendon unit: biochemical, biomechanical, hormonal influences

The current literature has mainly focused on the biology of tendons and on the characterization of the biological properties of tenocytes and tenoblasts. It is still not understood how these cells can work together in homeostatic equilibrium. We put forward the concept of the "tendon unit" as a morpho-functional unit that can be influenced by a variety of external stimuli such as mechanical stimuli, hormonal influence, or pathological states. We describe how this unit can modify itself to respond to such stimuli. We evidence the capability of the tendon unit of healing itself through the production of collagen following different mechanical stimuli and hypothesize that restoration of the homeostatic balance of the tendon unit should be a therapeutic target.

A Simplified Murine Model to Imitate Flexor Tendon Adhesion Formation without Suture

Peritendinous adhesion (PA) around tendons are daunting challenges for hand surgeons. Tenotomy with various sutures are considered classical tendon repair models (TRM) of tendon adhesion as well as tendon healing. However, potential biomimetic therapies such as anti-adhesion barriers and artificial tendon sheaths to avoid recurrence of PA are sometimes tested in these models without considering tendon healing. Thus, our aim is to create a simplified model without sutures in this study by using three 6 mm longitudinal and parallel incisions called the longitudinal incision model (LCM) in the murine flexor tendon. We found that the adhesion score of LCM has no significant difference to that in TRM. The range of motion (ROM) reveals similar adhesion formation in both TRM and LCM groups. Moreover, mRNA expression levels of collagen I and III in LCM shows no significant difference to that in TRM. The breaking force and stiffness of LCM were significantly higher than that of TRM. Therefore, LCM can imitate flexor tendon adhesion formation without sutures compared to TRM, without significant side effects on biomechanics with an easy operation.

Serum and Soleus Metabolomics Signature of Klf10 Knockout Mice to Identify Potential Biomarkers

The transcription factor Krüppel-like factor 10 (Klf10), also known as Tieg1 for TGFβ (Inducible Early Gene-1) is known to control numerous genes in many cell types that are involved in various key biological processes (differentiation, proliferation, apoptosis, inflammation), including cell metabolism and human disease. In skeletal muscle, particularly in the soleus, deletion of the Klf10 gene (Klf10 KO) resulted in ultrastructure fiber disorganization and mitochondrial metabolism deficiencies, characterized by muscular hypertrophy. To determine the metabolic profile related to loss of Klf10 expression, we analyzed blood and soleus tissue using UHPLC-Mass Spectrometry. Metabolomics analyses on both serum and soleus revealed profound differences between wild-type (WT) and KO animals. Klf10 deficient mice exhibited alterations in metabolites associated with energetic metabolism. Additionally, chemical classes of aromatic and amino-acid compounds were disrupted, together with Krebs cycle intermediates, lipids and phospholipids. From variable importance in projection (VIP) analyses, the Warburg effect, citric acid cycle, gluconeogenesis and transfer of acetyl groups into mitochondria appeared to be possible pathways involved in the metabolic alterations observed in Klf10 KO mice. These studies have revealed essential roles for Klf10 in regulating multiple metabolic pathways whose alterations may underlie the observed skeletal muscle defects as well as other diseases.

Single-cell transcriptomic profiling reveals distinct mechanical responses between normal and diseased tendon progenitor cells

Regenerative medicine approaches utilizing stem cells offer a promising strategy to address tendinopathy, a class of common tendon disorders associated with pain and impaired function. Tendon progenitor cells (TPCs) are important in healing and maintaining tendon tissues. Here we provide a comprehensive single cell transcriptomic profiling of TPCs from three normal and three clinically classified tendinopathy samples in response to mechanical stimuli. Analysis reveals seven distinct TPC subpopulations including subsets that are responsive to the mechanical stress, highly clonogenic, and specialized in cytokine or growth factor expression. The single cell transcriptomic profiling of TPCs and their subsets serves as a foundation for further investigation into the pathology and molecular hallmarks of tendinopathy in mechanical stimulation conditions.

Talipes Equinus Deformity Caused by Fibrous Gastrocnemius Muscle Contracture After Direct Contusion in Football Players: Report of Two Cases

Two main causes of gastrocnemius contracture have been considered: 1) congenital deformities in pediatric patients, such as limb-length discrepancy, cerebral palsy, flatfoot, and clubfoot; and 2) secondary conditions such as immobilization for trauma or a nonfunctional limb. Talipes equinus deformity caused by fibrous gastrocnemius contracture after a direct muscle contusion is extremely rare. We describe 2 cases of talipes equinus deformity caused by fibrous gastrocnemius muscle contracture after a direct contusion in football players. Both of the players had a talipes equinus deformity with a severe restriction of ankle dorsiflexion, and a cord-like structure was observed at the proximal part of the lateral gastrocnemius head. Both patients' histological examinations revealed fibrous tendon-like tissue within the structure. After discission of the cord-like structures, the restriction of ankle dorsiflexion was completely resolved, and the patients were able to fully return to playing football without any discomfort in their calves.

Thermal pretreatment promotes the protective effect of HSP70 against tendon adhesion in tendon healing by increasing HSP70 expression

Tendon adhesion is a substantial challenge for tendon repair. Thermal pretreatment (TP) may decrease inflammation by upregulating heat shock proteins (HSPs). The present study intends to identify the function that TP serves when combined with HSP70 overexpression in tendon healing and adhesion in rats. Sprague‑Dawley male rats were used to establish a surgically ablative tendon postoperative suture model, and the positive expression of the HSP70 protein was measured using immunohistochemistry. Changes to the blood vessels and collagenous fiber, in addition to the maximum tensile strength and the tendon sliding distance, were detected under a microscope. Finally, HSP70, tumor growth factor β (TGF‑β), and insulin‑like growth factor 1 (IGF‑1) mRNA and protein levels were all determined by employing reverse transcription‑quantitative polymerase chain reaction and western blot analysis methods. The positive expression of the HSP70 protein increased following TP. Furthermore, TP reduced the infiltration of inflammatory cells and improved the collagenous arrangement, accompanied by an increased maximum tensile force and tendon gliding distance following surgery. In addition, TP increased the mRNA and protein expression levels of HSP70, TGF‑β and IGF‑1. Altogether, TP increases HSP70 expression, thereby reducing postoperative traumatic inflammation and establishing tendon adhesion and promoting tendon healing. Thus, TP may be a potential strategy for the treatment of tendon adhesion.

Role of a combination dietary supplement containing mucopolysaccharides, vitamin C, and collagen on tendon healing in rats

Objective

The aim of this study was to investigate the effect of mucopolysaccharide, vitamin C, and collagen supplementation on the healing of Achilles tendon in rats.

Methods

Sixteen rats were separated into 2 groups. Both Achilles tendons of all rats were transected 5 mm above the insertion and repaired using a Kessler suture. After the surgical repair, the study group received the daily recommended amount of the supplement by gastric gavage, while the control group received a placebo. At the end of the third week, the animals were sacrificed. The biomechanical properties of the groups were compared with ultimate tensile strength and stiffness tests. The biological properties of the 2 groups were assessed with a histomorphometric comparison to determine the amount of collagen type I (COL1), proliferating cell nuclear antigen (PCNA), and transforming growth factor β1 (TGF-β1) expression in 3 different tissue subgroups (collagen matrix, tenocytes, and endotenon fibroblasts).

Results

Analysis of histomorphometric results revealed that the rats receiving dietary supplements demonstrated a significant increase in PCNA (mean value of 86 in the control group and 168.85 in the trial group; p < 0.05) and TGF-β1 (mean value of 87.57 in the control group and 161.85 in the trial group; p < 0.05) in the endotenon fibroblasts of the repair site. However, there was no difference between the groups in PCNA or TGF-β1 when the collagen matrix and the tenocytes of the repair site were examined. Furthermore, no significant difference could be found between groups in COL1 in any of the 3 tissue subgroups (collagen matrix, tenocytes, and endotenon fibroblasts). The statistical analysis also indicated that the rats receiving supplements did not demonstrate a significant increase in the ultimate tendon tensile strength or stiffness.

Conclusion

The results of this study revealed no advantage to the oral administration of the trial supplement in collagen synthesis or biomechanical properties in rats after 3 weeks using the presented study design. However, the increased expression of PCNA and TGFβ1 seen in the endotenon fibroblasts of the repair site might play a role in the continuum of tendon healing.

KLF10 as a Tumor Suppressor Gene and Its TGF-β Signaling

Krüppel-like factor 10 (KLF10), originally named TGF-β (Transforming growth factor beta) inducible early gene 1 (TIEG1), is a DNA-binding transcriptional regulator containing a triple C2H2 zinc finger domain. By binding to Sp1 (specificity protein 1) sites on the DNA and interactions with other regulatory transcription factors, KLF10 encourages and suppresses the expression of multiple genes in many cell types. Many studies have investigated its signaling cascade, but other than the TGF-β/Smad signaling pathway, these are still not clear. KLF10 plays a role in proliferation, differentiation as well as apoptosis, just like other members of the SP (specificity proteins)/KLF (Krüppel-like Factors). Recently, several studies reported that KLF10 KO (Knock out) is associated with defects in cell and organs such as osteopenia, abnormal tendon or cardiac hypertrophy. Since KLF10 was first discovered, several studies have defined its role in cancer as a tumor suppressor. KLF10 demonstrate anti-proliferative effects and induce apoptosis in various carcinoma cells including pancreatic cancer, leukemia, and osteoporosis. Collectively, these data indicate that KLF10 plays a significant role in various biological processes and diseases, but its role in cancer is still unclear. Therefore, this review was conducted to describe and discuss the role and function of KLF10 in diseases, including cancer, with a special emphasis on its signaling with TGF-β.

Knockout of krüppel-like factor 10 suppresses hepatic cell proliferation in a partially hepatectomized mouse model

The liver has marked regenerative capabilities, and numerous signaling pathways are involved in liver regeneration. The transforming growth factor-β (TGF-β)/Smad pathway, which is also involved in liver regeneration, regulates numerous biological processes. Krüppel-like factor 10 (KLF10) has been reported to activate the TGF-β/Smad signaling pathway; however, the exact functions of KLF10 under various pathophysiological conditions remain unclear. In the present study, the role of KLF10 in liver regeneration following partial hepatectomy (PH) was investigated using KLF10-knockout (KO) mice. KLF10-KO mice exhibited lower liver/body weight ratios and 5-bromo-2-deoxy-uridine labeling indices compared with wild-type (WT) mice, and significant differences (P=0.028) were obtained at 72 h after PH. To understand the causes of the gross and histopathological findings, the expression levels of the components of the TGF-β/Smad pathway were examined using reverse transcription-quantitative polymerase chain reaction and western blot analysis. The mRNA and protein levels of Smad3, p15, TGF-β1 and TGF-β receptor 1 were significantly increased, while those of cMyc and cyclin D1 (proliferation-associated genes) were significantly lower in the liver tissues of the KLF10-KO mice compared with those of the WT mice at 72 h post-PH. These results indicated that KLF10-KO may exhibit antiproliferative effects on liver regeneration following PH, through strengthening the TGF-β/Smad signaling pathway in a delayed manner.

The effects of substance P and acetylcholine on human tenocyte proliferation converge mechanistically via TGF-β1

Previous in vitro studies on human tendon cells (tenocytes) have demonstrated that the exogenous administration of substance P (SP) and acetylcholine (ACh) independently result in tenocyte proliferation, which is a prominent feature of tendinosis. Interestingly, the possible link between SP and ACh has not yet been explored in human tenocytes. Recent studies in other cell types demonstrate that both SP and ACh independently upregulate TGF-β1 expression via their respective receptors, the neurokinin 1 receptor (NK-1R) and muscarinic ACh receptors (mAChRs). Furthermore, TGF-β1 has been shown to downregulate NK-1R expression in human keratocytes. The aim of this study was to examine if TGF-β1 is the intermediary player involved in mediating the proliferative pathway shared by SP and ACh in human tenocytes. The results showed that exogenous administration of SP and ACh both caused significant upregulation of TGF-β1 at the mRNA and protein levels. Exposing cells to TGF-β1 resulted in increased cell viability of tenocytes, which was blocked in the presence of the TGFβRI/II kinase inhibitor. In addition, the proliferative effects of SP and ACh on tenocytes were reduced by the TGFβRI/II kinase inhibitor; this supports the hypothesis that the proliferative effects of these signal substances are mediated via the TGF-β axis. Furthermore, exogenous TGF-β1 downregulated NK-1R and mAChRs expression at both the mRNA and protein levels, and these effects were negated by simultaneous exposure to the TGFβRI/II kinase inhibitor, suggesting a negative feedback loop. In conclusion, the results indicate that TGF-β1 is the intermediary player through which the proliferative actions of both SP and ACh converge mechanistically.

Murine Flexor Tendon Injury and Repair Surgery

Tendon connects skeletal muscle and bone, facilitating movement of nearly the entire body. In the hand, flexor tendons (FTs) enable flexion of the fingers and general hand function. Injuries to the FTs are common, and satisfactory healing is often impaired due to excess scar tissue and adhesions between the tendon and surrounding tissue. However, little is known about the molecular and cellular components of FT repair. To that end, a murine model of FT repair that recapitulates many aspects of healing in humans, including impaired range of motion and decreased mechanical properties, has been developed and previously described. Here an in-depth demonstration of this surgical procedure is provided, involving transection and subsequent repair of the flexor digitorum longus (FDL) tendon in the murine hind paw. This technique can be used to conduct lineage analysis of different cell types, assess the effects of gene gain or loss-of-function, and to test the efficacy of pharmacological interventions in the healing process. However, there are two primary limitations to this model: i) the FDL tendon in the mid-portion of the murine hind paw, where the transection and repair occur, is not surrounded by a synovial sheath. Therefore this model does not account for the potential contribution of the sheath to the scar formation process. ii) To protect the integrity of the repair site, the FT is released at the myotendinous junction, decreasing the mechanical forces of the tendon, likely contributing to increased scar formation. Isolation of sufficient cells from the granulation tissue of the FT during the healing process for flow cytometric analysis has proved challenging; cytology centrifugation to concentrate these cells is an alternate method used, and allows for generation of cell preparations on which immunofluorescent labeling can be performed. With this method, quantification of cells or proteins of interest during FT healing becomes possible.

PRP Treatment Efficacy for Tendinopathy: A Review of Basic Science Studies

Platelet-Rich Plasma (PRP) has been widely used in orthopaedic surgery and sport medicine to treat tendon injuries. However, the efficacy of PRP treatment for tendinopathy is controversial. This paper focuses on reviewing the basic science studies on PRP performed under well-controlled conditions. Both in vitro and in vivo studies describe PRP's anabolic and anti-inflammatory effects on tendons. While some clinical trials support these findings, others refute them. In this review, we discuss the effectiveness of PRP to treat tendon injuries with evidence presented in basic science studies and the potential reasons for the controversial results in clinical trials. Finally, we comment on the approaches that may be required to improve the efficacy of PRP treatment for tendinopathy.

Biological Augmentation of Flexor Tendon Repair: A Challenging Cellular Landscape

Advances in surgical technique and rehabilitation have transformed zone II flexor tendon injuries from an inoperable no-man's land to a standard surgical procedure. Despite these advances, many patients develop substantial range of motion-limiting adhesions after primary flexor tendon repair. These suboptimal outcomes may benefit from biologic augmentation or intervention during the flexor tendon healing process. However, there is no consensus biological approach to promote satisfactory flexor tendon healing; we propose that insufficient understanding of the complex cellular milieu in the healing tendon has hindered the development of successful therapies. This article reviews recent advances in our understanding of the cellular components of flexor tendon healing and adhesion formation, including resident tendon cells, synovial sheath, macrophages, and bone marrow-derived cells. In addition, it examines molecular approaches that have been used in translational animal models to improve flexor tendon healing and gliding function, with a specific focus on progress made using murine models of healing. This information highlights the importance of understanding and potentially exploiting the heterogeneity of the cellular environment during flexor tendon healing, to define rational therapeutic approaches to improve healing outcomes.

Recent Scientific Advances Towards the Development of Tendon Healing Strategies

There exists a range of surgical and non-surgical approaches to the treatment of both acute and chronic tendon injuries. Despite surgical advances in the management of acute tears and increasing treatment options for tendinopathies, strategies frequently are unsuccessful, due to impaired mechanical properties of the treated tendon and/or a deficiency in progenitor cell activities. Hence, there is an urgent need for effective therapeutic strategies to augment intrinsic and/or surgical repair. Such approaches can benefit both tendinopathies and tendon tears which, due to their severity, appear to be irreversible or irreparable. Biologic therapies include the utilization of scaffolds as well as gene, growth factor, and cell delivery. These treatment modalities aim to provide mechanical durability or augment the biologic healing potential of the repaired tissue. Here, we review the emerging concepts and scientific evidence which provide a rationale for tissue engineering and regeneration strategies as well as discuss the clinical translation of recent innovations.

Progression of diet induced nonalcoholic steatohepatitis is accompanied by increased expression of Kruppel-like-factor 10 in mice

BACKGROUND

Kruppel-like-factor (KLF) 10 is identified as transforming growth factor (TGF) β inducible early gene and is reported to suppress lipogenic genes. Although previous studies report that TGFβ plays an important role in progression of nonalcoholic steatohepatitis (NASH) by regulating liver fibrosis, the association of KLF10 and NASH has never been explored. Thus we evaluated expressions and changes of KLF10 in diet induced NASH and in NASH which was alleviated by ursodeoxycholic acid (UDCA). We also assessed KLF10 in quiescent and activated hepatic stellate cells (HSCs).

METHODS

C57BL/6 mice were given high fat, sucrose diet (HFSD) at least for 12 weeks up to 48 weeks and sacrificed at 12, 24 and 48 weeks thereafter. In other groups, either standard diet (SD) or HFSD was given for 24 weeks at which point mice fed with HFSD were divided into two groups, and were given either UDCA in combination with HFSD or vehicle with HFSD. Mice under SD were given vehicle. HSCs were isolated from C57BL/6 mice in order to evaluated KLF10 expression in activated HSCs.

RESULTS

The mice were found to acquire liver steatosis and inflammation starting from week 12 of HFSD feeding, although significant liver fibrosis was noticed by week 24. Increased TGFβ and collagen α1(I) (Col1α(I)) expression was also apparent from week 24. However, expression of KLF10 mRNA started to increase from week 12, earlier than TGFβ gene. Up-regulation of KLF10 was accompanied by suppressed carbohydrate response element-binding protein (ChREBP) that is known to be protective against insulin resistance. The mice fed with HFSD and UDCA had decreased Colα(I) mRNA that was coincided with reduced TGFβ and KLF10 expression. Expression of ChREBP was also recovered by UDCA administration. Enhanced KLF10 was noticed in activated HSCs when quiescent cell showed minimal expression.

CONCLUSIONS

Our study demonstrated that KLF10 expression was significantly increased in diet induced NASH and collagen producing activated HSCs. We also noticed that this up-regulation of KLF10 was accompanied by increased TGFβ signaling genes and suppressed ChREBP expression. These observations suggest possible association of KLF10 and NASH progression.

Smad3 binds Scleraxis and Mohawk and regulates tendon matrix organization

TGFβ plays a critical role in tendon formation and healing. While its downstream effector Smad3 has been implicated in the healing process, little is known about the role of Smad3 in normal tendon development or tenocyte gene expression. Using mice deficient in Smad3 (Smad3(-/-) ), we show that Smad3 ablation disrupts tendon architecture and has a dramatic impact on normal gene and protein expression during development as well as in mature tendon. In developing and adult tendon, loss of Smad3 results in reduced protein expression of the matrix components Collagen 1 and Tenascin-C. Additionally, when compared to wild type, tendon from adult Smad3(-/-) mice shows a down regulation of key tendon marker genes. Finally, we have established that Smad3 has the ability to physically interact with the critical transcriptional regulators Scleraxis and Mohawk. Together these results indicate a central role for Smad3 in normal tendon formation and in the maintenance of mature tendon.

Cellular and molecular factors in flexor tendon repair and adhesions: a histological and gene expression analysis

Flexor tendon healing is mediated by cell proliferation, migration, and extracellular matrix synthesis that contribute to the formation of scar tissue and adhesion. The biological mechanisms of flexor tendon adhesion formation have been linked to transforming growth factor β (TGF-β). To elucidate the cellular and molecular events in this pathology, we implanted live flexor digitorum longus grafts from the reporter mouse Rosa26(LacZ/+) in wild-type recipients, and used histological β-galactosidase (β-gal) staining to evaluate the intrinsic versus extrinsic cellular origins of scar, and reverse transcription-polymerase chain reaction to measure gene expression of TGF-β and its receptors, extracellular matrix proteins, and matrix metalloproteinases (MMPs) and their regulators. Over the course of healing, graft cellularity and β-gal activity progressively increased, and β-gal-positive cells migrated out of the Rosa26(LacZ/+) graft. In addition, there was an evidence of influx of host cells (β-gal-negative) into the gliding space and the graft, suggesting that both graft and host cells contribute to adhesions. Interestingly, we observed a biphasic pattern in which Tgfb1 expression was the highest in the early phases of healing and gradually decreased thereafter, whereas Tgfb3 increased and remained upregulated later. The expression of TGF-β receptors was also upregulated throughout the healing phases. In addition, type III collagen and fibronectin were upregulated during the proliferative phase of healing, confirming that murine flexor tendon heals by scar tissue. Furthermore, gene expression of MMPs showed a differential pattern in which inflammatory MMPs were the highest early and matrix MMPs increased over time. These findings offer important insights into the complex cellular and molecular factors during flexor tendon healing.

Impaired cutaneous wound healing in transforming growth factor-β inducible early gene1 knockout mice

Transforming growth factor-β inducible early gene (TIEG) is induced by transforming growth factor-β (TGF-β) and acts as the primary response gene in the TGF-β/Smad pathway. TGF-β is a multifunctional growth factor that affects dermal wound healing; however, the mechanism of how TGF-β affects wound healing is still not well understood because of the complexity of its function and signaling pathways. We hypothesize that TIEG may play a role in dermal wound healing, with involvement in wound closure, contraction, and reepithelialization. In this study, we have shown that TIEG1 knockout (TIEG1-/-) mice have a delay in wound closure related to an impairment in wound contraction, granulation tissue formation, collagen synthesis, and reepithelialization. We also found that Smad7 was increased in the wounds and appeared to play a role in this wound healing model in TIEG1-/- mice.

Role of growth factors in rotator cuff healing

The histologic lesion underlying overuse rotator cuff tendinopathy is a failed healing response, with haphazard proliferation of tenocytes, disruption of tendon cells and collagen fibers, and increased noncollagenous extracellular matrix. Recent attention has focused on the biological pathways by which tendons heal, leading to the identification of several growth factors (GFs) involved in this process. No studies have been published on the time course of the various GFs during rotator cuff healing process in vivo, in humans. We review what is known about these GFs and their role in rotator cuff healing.

TIEG1/KLF10 modulates Runx2 expression and activity in osteoblasts

Deletion of TIEG1/KLF10 in mice results in a gender specific osteopenic skeletal phenotype with significant defects in both cortical and trabecular bone, which are observed only in female animals. Calvarial osteoblasts isolated from TIEG1 knockout (KO) mice display reduced expression levels of multiple bone related genes, including Runx2, and exhibit significant delays in their mineralization rates relative to wildtype controls. These data suggest that TIEG1 plays an important role in regulating Runx2 expression in bone and that decreased Runx2 expression in TIEG1 KO mice is in part responsible for the observed osteopenic phenotype. In this manuscript, data is presented demonstrating that over-expression of TIEG1 results in increased expression of Runx2 while repression of TIEG1 results in suppression of Runx2. Transient transfection and chromatin immunoprecipitation assays reveal that TIEG1 directly binds to and activates the Runx2 promoter. The zinc finger containing domain of TIEG1 is necessary for this regulation supporting that activation occurs through direct DNA binding. A role for the ubiquitin/proteasome pathway in fine tuning the regulation of Runx2 expression by TIEG1 is also implicated in this study. Additionally, the regulation of Runx2 expression by cytokines such as TGFβ1 and BMP2 is shown to be inhibited in the absence of TIEG1. Co-immunoprecipitation and co-localization assays indicate that TIEG1 protein associates with Runx2 protein resulting in co-activation of Runx2 transcriptional activity. Lastly, Runx2 adenoviral infection of TIEG1 KO calvarial osteoblasts leads to increased expression of Runx2 and enhancement of their ability to differentiate and mineralize in culture. Taken together, these data implicate an important role for TIEG1 in regulating the expression and activity of Runx2 in osteoblasts and suggest that decreased expression of Runx2 in TIEG1 KO mice contributes to the observed osteopenic bone phenotype.

The process of tendon regeneration in an achilles tendon resection rat model as a model for hamstring regeneration after harvesting for anterior cruciate ligament reconstruction

PURPOSE

The purpose of this study was to clarify the mechanism of tendon regeneration by investigating macroscopically, histologically, and biomechanically.

METHODS

Fifty, adult, female Sprague-Dawley rats were used. The Achilles tendon in the left hind limb was removed totally by use of the tendon-stripping device. Rats were killed at 2, 7, 30, 90, and 180 days after surgery, and the regenerate tendons were dissected. Contralateral Achilles tendons were used as normal controls. Gross anatomic changes, microscopic remodeling, and recovery of biomechanical properties of regenerate tendons were investigated. The expressions of type I collagen, type III collagen, and transforming growth factor β1 were also investigated by immunohistochemistry.

RESULTS

The regenerate tendons formed in all specimens. In the early phase, hematoma and soft granulation tissue were observed at the harvest defect. These gradually matured with time, and the microscopic structure became quite similar to normal at 180 days after surgery. These findings occurred uniformly along the entire length of the regenerate tendon. However, the biomechanical properties were significantly inferior to the normal tendons (P < .05). Transforming growth factor β1 was well co-localized with inflammatory cells and fibroblasts in the regenerate tendons. The type I-type III collagen ratio in the regenerate tendon was significantly decreased in the early phase (P < .05) but gradually increased with time.

CONCLUSIONS

Tendon regeneration and maturation occurred uniformly along the length of regenerate tendons. The hematoma that initially occupies the harvest defect acted as a scaffold for fibroblast precursor cells from the surrounding peritendinous tissue and tendon sheath. The mechanical properties of regenerate tendon were significantly inferior to contralateral control even at 180 days after surgery, and the alteration of the collagen composition would have an influence on mechanical properties of regenerate tendon.

CLINICAL RELEVANCE

Clinicians should be cautious about using reharvested hamstring tendons for ligament reconstruction surgery.

Inhibition effect of mannose-6-phosphate on expression of transforming growth factor Beta receptor in flexor tendon cells

Transforming growth factor beta (TGF-β) has an important role in tendon healing and adhesion formation. Inhibiting TGF-β and its receptor expression may prevent adhesions after tendon open. The goal of this study was to examine the effects of mannose-6-phosphate, a natural inhibitor of TGF-β, on TGF-β and its receptor production in tendon sheath fibroblasts, epitenon tenocytes, and endotenon tenocytes of rabbit flexor tendons. Tendon sheath fibroblasts, epitenon tenocytes, and endotenon tenocytes were isolated from rabbit flexor tendons and cultured separately. The cells were divided into 2 groups at random: an experiment group supplemented with mannose-6-phosphate and a control group without mannose-6-phosphate. The expression of TGF-β and TGF-β receptor was quantified with enzyme-linked immunosorbent assay. The luciferase assay measured TGF-β bioactivity. Transforming growth factor beta expression in the experimental group was not decreased compared with the control group, with no significant difference (P>.05) Transforming growth factor beta receptor expression in the experiment group was significantly lower than that in control group (P<.05). Mannose-6-phosphate significantly decreased the expression of TGF-β receptor and TGF-β bioactivity. Modulation of mannose-6-phosphate levels may provide a means of modulating the effects of TGF-β on adhesion formation in flexor tendon wound healing.

Tendon healing in vivo and in vitro: neutralizing antibody to TGF-β improves range of motion after flexor tendon repair

Adhesion formation between the flexor tendon and its surrounding fibro-osseous sheath results in a decreased postoperative range of motion (ROM) in the hand. Transforming growth factor-beta (TGF-β) is a key cytokine in the pathogenesis of tissue fibrosis. In this study, the effects of TGF-β1 neutralizing antibody were investigated in vitro and in vivo. In the in vitro investigation, primary cell cultures from rabbit flexor tendon sheath, epitenon, and endotenon were established and each was supplemented with TGF-β along with increasing doses of TGF-β1 neutralizing antibody. Collagen I production was measured with enzyme-linked immunosorbent assay. In the in vivo study, rabbit zone-II flexor tendons were transected and then immediately repaired. Transforming growth factor-β1 neutralizing antibody or phosphate-buffered saline solution (control) was added to the repair sites, and the forepaws were tested for ROM and repair strength at 8 weeks postoperatively. Transforming growth factor-β1 neutralizing antibody reduced TGF-β upregulated collagen production. Intraoperative application of TGF-β1 neutralizing antibody significantly improved the ROM of the operatively treated digits. The effect on breaking strength of the tendon repair was inconclusive.

Functional role of KLF10 in multiple disease processes

Since the discovery by this laboratory of the zinc finger transcription factor, KLF10, a member of the Krüppel-like family of transcription factors, there have been multiple publications regarding its functions and its immediate family members, in numerous cell types. KLF10 has been shown to be rapidly induced by TGFbeta1, 2, 3, E(2), epidermal growth factor, and bone morphogenetic protein-2. TGFbeta inducible early gene-1 activates the TGFbeta-Smad signaling pathway via repression of Smad 7 expression and activation of Smad 2 expression and activity. Overall, KLF10 has been implicated in cell differentiation, as a target gene for a variety of signaling pathways, and in serving as a potential marker for human diseases such as breast cancer, cardiac hypertrophy, and osteoporosis. Like other KLF members, KLF10 is expressed in specific cell types in numerous tissues and is known to be involved in repressing cell proliferation and inflammation as well as inducing apoptosis similar to that of TGFbeta. KLF10 binds to Sp-1-GC rich DNA sequences and can activate or repress the transcription of a number of genes. Overall, KLF10 has been shown to play a major role in the TGFbeta inhibition of cell proliferation and inflammation and induction of apoptosis, and its overexpression in human osteoblasts and pancreatic carcinoma cells mimics the actions of TGFbeta.

Remodeling of murine intrasynovial tendon adhesions following injury: MMP and neotendon gene expression

Tendon injury frequently results in the formation of adhesions that reduce joint range of motion. To study the cellular, molecular, and biomechanical events involved in intrasynovial tendon healing and adhesion formation, we developed a murine flexor tendon healing model in which the flexor digitorum longus (FDL) tendon of C57BL/6 mice was transected and repaired using suture. This model was used to test the hypothesis that murine flexor tendons heal with differential expression of matrix metalloproteases (MMPs), resulting in the formation of scar tissue as well as the subsequent remodeling of scar and adhesions. Healing tendons were evaluated by histology, gene expression via real-time RT-PCR, and in situ hybridization, as well as biomechanical testing to assess the metatarsophalangeal (MTP) joint flexion range of motion (ROM) and the tensile failure properties. Tendons healed with a highly disorganized fibroblastic tissue response that was progressively remodeled through day 35 resulting in a more organized pattern of collagen fibers. Initial repair involved elevated levels of Mmp-9 at day 7, which is associated with catabolism of damaged collagen fibers. High levels of Col3 are consistent with scar tissue, and gradually transition to the expression of Col1. Scleraxis expression peaked at day 7, but the expression was limited to the original tendon adjacent to the injury site, and no expression was present in granulation tissue involved in the repair response. The MTP joint ROM with standardized force on the tendon was decreased on days 14 and 21 compared to day 0, indicating the presence of adhesions. Peak expressions of Mmp-2 and Mmp-14 were observed at day 21, associated with tendon remodeling. At day 28, two genes associated with neotendon formation, Smad8 and Gdf-5, were elevated and an improvement in MTP ROM occurred. Tensile strength of the tendon progressively increased, but by 63 days the repaired tendons had not reached the tensile strength of normal tendon. The murine model of primary tendon repair, described here, provides a novel mechanism to study the tendon healing process, and further enhances the understanding of this process at the molecular, cellular, and biomechanical level.

Effect of transosseous application of low-intensity ultrasound at the tendon graft-bone interface healing: gene expression and histological analysis in rabbits

The present study investigates the effect of transosseous low-intensity pulsed ultrasound (LiUS) on the healing at tendon graft-bone interface, in molecular and histological level. The anterior cruciate ligament (ACL) in both knees of 52 New Zealand White rabbits was excised and replaced with the long digital extensor. A custom-made ultrasound transducer was implanted onto the medial tibial condyle, adjacent to the surface of the bone tunnel at both knees of the rabbits. The LiUS-treated right knees received 200-mus bursts of 1 MHz sine waves at a pulse repetition rate of 1 kHz and with 30 mW/cm(2) spatial-average temporal-average intensity for 20 min daily (study group), while the left knee received no LiUS (control group). Thirty-six rabbits were used to perform semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis from both study and control groups for transforming growth factor-beta1 (TGF-beta1), biglycan and collagen I. RT-PCR products showed statistically significant upregulation of biglycan and collagen I gene expression in the study group, while TGF-beta1 gene expression exhibited a bimodal profile. Histological examination performed in 16 rabbits from both groups supported the findings of the molecular analysis, indicating a faster healing rate and a more efficient ligamentization process after ultrasound treatment. These findings suggest that transosseous application of LiUS enhances the healing rate of the tendon graft-bone interface, possibly by affecting the expression levels of genes significant for the tendon to bone healing process.

In vitro flexor tendon cell response to TGF-beta1: a gene expression study

PURPOSE

Adhesion formation around zone II flexor tendon repairs remains an important clinical challenge. Tendon healing is complex, and when uncontrolled it may lead to adhesion formation. Transforming growth factor-beta1 (TGF-beta1) is a multipotent growth factor known to be involved in wound healing and scar formation. It has also been shown to have a role in both tendon healing and adhesion formation.

METHODS

Uninjured rabbit flexor tendons were divided into endotenon, epitenon, and sheath cells and cultured separately. The in vitro effect of TGF-beta1 gene expression was determined on quiescent tendon cells using real-time polymerase chain reaction for collagen type 1, collagen type 3, fibronectin, plasminogen activator inhibitor-1 (PAI-1), and tissue plasminogen activator (t-PA).

RESULTS

Endotenon-derived cells showed a statistically significant down-regulation of collagen type I gene expression in response to TGF-beta1 compared with untreated endotenon cells and with both epitenon and sheath cells at a number of time points. However, endotenon cells showed an increase in collagen type 3 gene expression compared with untreated cells and epitenon cells. All cells showed a statistically significant increase in fibronectin in the later time points compared with the untreated cells. Endotenon-derived cells showed an early increase in PAI-1, whereas sheath cells showed a later increase.

CONCLUSIONS

We have shown that cells cultured from 3 separate parts of the flexor tendon-sheath complex respond in different ways when stimulated with TGF-beta1. The down-regulation of collagen types 1 and 3 in endotenon cells may give further insight into the effects of TGF-beta1 in tendon healing. Also, the upregulation of fibronectin and PAI-1, combined with a down-regulation of tissue plasminogen activator, could explain the association of TGF-beta1 with tendon adhesion formation. Treatments aimed at improving tendon healing and the prevention of adhesions may arise from modification of the effects of TGF-beta1.

Effects of leptin deficiency on postnatal lung development in mice

Leptin modulates energy metabolism and lung development. We hypothesize that the effects of leptin on postnatal lung development are volume dependent from 2 to 10 wk of age and are independent of hypometabolism associated with leptin deficiency. To test the hypotheses, effects of leptin deficiency on lung maturation were characterized in age groups of C57BL/6J mice with varying Lep(ob) genotypes. Quasi-static pressure-volume curves and respiratory impedance measurements were performed to profile differences in respiratory system mechanics. Morphometric analysis was conducted to estimate alveolar size and number. Oxygen consumption was measured to assess metabolic rate. Lung volume at 40-cmH(2)O airway pressure (V(40)) increased with age in each genotypic group, and V(40) was significantly (P < 0.05) lower in leptin-deficient (ob/ob) mice beginning at 2 wk. Differences were amplified through 7 wk of age relative to wild-type (+/+) mice. Morphometric analysis showed that alveolar surface area was lower in ob/ob compared with +/+ and heterozygote (ob/+) mice beginning at 2 wk. Unlike the other genotypic groups, alveolar size did not increase with age in ob/ob mice. In another experiment, ob/ob at 4 wk received leptin replacement (5 microg.g(-1) x day(-1)) for 8 days, and expression levels of the Col1a1, Col3a1, Col6a3, Mmp2, Tieg1, and Stat1 genes were significantly increased concomitantly with elevated V(40). Leptin-induced increases in V(40) corresponded with enlarged alveolar size and surface area. Gene expression suggested a remodeling event of lung parenchyma after exogenous leptin replacement. These data support the hypothesis that leptin is critical to postnatal lung remodeling, particularly related to increased V(40) and enlarged alveolar surface area.

Role of TIEG1 in biological processes and disease states

A novel TGFbeta Inducible Early Gene-1 (TIEG1) was discovered in human osteoblast (OB) cells by our laboratory. Over the past decade, a handful of laboratories have revealed a multitude of organismic, cellular, and molecular functions of this gene. TIEG1 is now classified as a member of the 3 zinc finger family of Krüppel-like transcription factors (KLF10). Other closely related factors [TIEG2 (KLF11) and TIEG3/TIEG2b] have been reported and are briefly compared. As described in this review, TIEG1 is shown to play a role in regulating estrogen and TGFbeta actions, the latter through the Smad signaling pathway. In both cases, TIEG1 acts as an inducer or repressor of gene transcription to enhance the TGFbeta/Smad pathway, as well at other signaling pathways, to regulate cell proliferation, differentiation, and apoptosis. This review outlines TIEG1's molecular functions and roles in skeletal disease (osteopenia/osteoporosis), heart disease (hypertrophic cardiomyopathy), and cancer (breast and prostate).

Tendon: biology, biomechanics, repair, growth factors, and evolving treatment options

Surgical treatment of tendon ruptures and lacerations is currently the most common therapeutic modality. Tendon repair in the hand involves a slow repair process, which results in inferior repair tissue and often a failure to obtain full active range of motion. The initial stages of repair include the formation of functionally weak tissue that is not capable of supporting tensile forces that allow early active range of motion. Immobilization of the digit or limb will promote faster healing but inevitably results in the formation of adhesions between the tendon and tendon sheath, which leads to friction and reduced gliding. Loading during the healing phase is critical to avoid these adhesions but involves increased risk of rupture of the repaired tendon. Understanding the biology and organization of the native tendon and the process of morphogenesis of tendon tissue is necessary to improve current treatment modalities. Screening the genes expressed during tendon morphogenesis and determining the growth factors most crucial for tendon development will likely lead to treatment options that result in superior repair tissue and ultimately improved functional outcomes.

Kruppel-like Factors (KLFs) in muscle biology

The Kruppel-like Factor (KLF) family of zinc-finger transcription factors are critical regulators of cell differentiation, phenotypic modulation and physiologic function. An emerging body of evidence implicates an important role for these factors in cardiovascular biology, however, the role of KLFs in muscle biology is only beginning to be understood. This article reviews the published data describing the role of KLFs in the heart, smooth muscle, and skeletal muscle and highlights the importance of these factors in cardiovascular development, physiology and disease pathobiology.

Identification and analysis of cabut orthologs in invertebrates and vertebrates

Cabut (cbt) is a Drosophila melanogaster gene involved in epidermal dorsal closure (DC). Its expression is dependent on the Jun N-terminal kinase (JNK) cascade, and it functions downstream of Jun regulating dpp expression in the leading edge cells. The Cbt protein contains three C(2)H(2)-type zinc fingers and a serine-rich domain, suggesting that it functions as a transcription factor. We have identified single cbt orthologs in other Drosophila species, as well as in other insects and invertebrate organisms like ascidians and echinoderms, but not in nematodes. Gene structure and protein sequence are highly conserved among Drosophilidae, but are more diverged in the other species of invertebrates analyzed. According to this, we demonstrate that cbt expression is detected in the embryonic lateral epidermis in several Drosophila species, as it occurs in D. melanogaster, thus suggesting that the cbt orthologs may have a conserved role in these species during DC. We have also analyzed the genomes of several vertebrate species, finding that the cbt orthologous genes in these organisms encode proteins that belong to the TIEG family of Sp1-like/Krüppel-like transcription factors. Phylogenetic analysis of the invertebrate and vertebrate proteins identified indicates that they mainly follow the expected phylogeny of the species, and that the cbt gene was duplicated during vertebrate evolution. Because we were not able to identify cbt orthologous genes neither in yeast nor in plants, our results suggest that this gene has been probably conserved throughout metazoans and that it may play a fundamental role in animal biology.