Modulating the mesenchymal stromal cell microenvironment alters exosome RNA content and ligament healing capacity.

Although mesenchymal stromal cell (MSC) based therapies hold promise in regenerative medicine, their clinical application remains challenging due to issues such as immunocompatibility. MSC-derived exosomes are a promising off-the-shelf therapy for promoting wound healing in a cell-free manner. However, the potential to customize the content of MSC-exosomes, and understanding how such modifications influence exosome effects on tissue regeneration remain underexplored. In this study, we used an in vitro system to compare the priming of human MSCs by 2 inflammatory inducers TNF-α and CRX-527 (a highly potent synthetic TLR4 agonist that can be used as a vaccine adjuvant or to induce anti-tumor immunity) on exosome molecular cargo, as well as on an in vivo rat ligament injury model to validate exosome potency. Different microenvironmental stimuli used to prime MSCs in vitro affected their exosomal microRNAs and mRNAs, influencing ligament healing. Exosomes derived from untreated MSCs significantly enhance the mechanical properties of healing ligaments, in contrast to those obtained from MSCs primed with inflammation-inducers, which not only fail to provide any improvement but also potentially deteriorate the mechanical properties. Additionally, a link was identified between altered exosomal microRNA levels and expression changes in microRNA targets in ligaments. These findings elucidate the nuanced interplay between MSCs, their exosomes, and tissue regeneration.

SIRT1 as a potential therapeutic target in pelvic organ prolapse due to protective effects against oxidative stress and cellular senescence in human uterosacral ligament fibroblasts.

INTRODUCTION: The pathogenesis of pelvic organ prolapse (POP), an age-related disease, has not been fully elucidated. Therapeutic targets of POP are limited. Silencing information regulator 2 related enzyme 1 (SIRT1), a gene considered capable of regulating oxidative stress and cellular senescence, has been widely demonstrated involved in aging and age-related diseases. The present study aimed to explore the role of SIRT1 in POP in vivo and in vitro. METHODS: Expression levels of SIRT1 in uterosacral ligament (USL) tissues from patients with or without POP were measured using immunohistochemical assays. SRT1720, a SIRT1 agonist, was used to upregulate SIRT1, and hydrogen peroxide (H2O2) was used to establish an oxidative stress model in human uterosacral ligament fibroblasts (hUSLFs). The effects of SIRT1 on cell viability, apoptosis, senescence, and reactive oxygen species (ROS) levels were detected, respectively. Western blot assays were used to examine expression levels of apoptosis- and senescence-associated biomarkers. Unpaired Student's t test, Mann-Whitney U test, χ2 test, and one-way ANOVA were performed for determining statistically significant differences. RESULTS: Compared to the control group, expression levels of SIRT1 were downregulated in USL tissues and hUSLFs from patients with POP, and associated with stage (p < 0.05). hUSLFs of patients with POP had lower growth rates (p < 0.0001) than those of the control group, which were improved by upregulating SIRT1 (p < 0.05). The senescent proportion was higher in the POP group than the control group (43.63 ± 10.62% vs. 4.84 ± 5.32%, p < 0.0001), which could be reduced by upregulating SIRT1 (p < 0.0001). High ROS levels in the POP group were also alleviated by SRT1720. H2O2 exposure increased ROS levels, inhibited proliferation, and triggered apoptosis and senescence in hUSLFs of patients without POP in a concentration-dependent manner. Further, these damages were alleviated by pretreatment with SRT1720. CONCLUSIONS: SIRT1 is downregulated in patients with POP, and the development of SIRT1 activators or agonists may have applications in the treatment and prevention of POP through antioxidative stress and antisenescence effects.

Effect of Vaginal Microecological Alterations on Female Pelvic Organ Prolapse.

INTRODUCTION AND HYPOTHESIS: The objective was to investigate the correlation between endogenous vaginal microecological alterations and female pelvic organ prolapse (POP). METHODS: Patients who underwent vaginal hysterectomy were retrospectively analyzed as the POP group (n = 30) and the non-POP group (n = 30). The vaginal microbial metabolites and enzyme levels were tested using the dry chemoenzymatic method. The mRNA and protein expression were tested using real-time quantitative PCR and immunohistochemistry. SPSS version 25.0 and GraphPad Prism 8.0 were performed for statistical analysis. RESULTS: Compared with the non-POP group, the vaginal pH, H2O2 positivity and leukocyte esterase positivity were higher in patients with POP (all p < 0.05). Further analysis showed that patients with pelvic organ prolapse quantification (POP-Q) stage IV had higher rates of vaginal pH, H2O2 positivity and leukocyte esterase positivity than those with POP-Q stage III. Additionally, the mRNA expression of decorin (DCN), transforming growth factor beta 1 (TGF-ß1), and matrix metalloproteinase-3 (MMP-3) in uterosacral ligament tissues were higher, whereas collagen I and III were lower. Similarly, the positive expression of MMP-3 in uterosacral ligament tissue was significantly upregulated in the POP group compared with the non-POP group (p = 0.035), whereas collagen I (p = 0.004) and collagen III (p = 0.019) in uterosacral ligament tissue were significantly downregulated in the POP group. Correlation analysis revealed that there was a significant correlation between vaginal microecology and collagen metabolism. In addition, MMP-3 correlated negatively with collagen I and collagen III (p = 0.002, r = -0.533; p = 0.002, r = -0.534 respectively), whereas collagen I correlated positively with collagen III (p = 0.001, r = 0.578). CONCLUSIONS: Vaginal microecological dysbiosis affects the occurrence of female POP, which could be considered a novel therapeutic option.

Synthesis of lysinonorleucine and mass spectrometric analysis of lysinonorleucine and merodesmosine in bovine ligament and eggshell membrane.

Elastin is an important extracellular matrix protein that contributes to the elasticity of cells, tissues, and organs. Although crosslinking amino acids such as desmosine and isodesmosine have been identified in elastin, details regarding the structure remain unclear. In this study, an elastin crosslinker, lysinonorleucine, was chemically synthesized and detected in hydrolyzed bovine ligament and eggshell membrane samples utilizing tandem mass spectrometry. Merodesmosine, another crosslinker of elastin, was also measured in the same samples using the same analytical method. The resulting data should aid in the elucidating the crosslinking structure of elastin and eggshell membranes.

Bone morphology is regulated modularly by global and regional genetic programs.

Bone protrusions provide stable anchoring sites for ligaments and tendons and define the unique morphology of each long bone. Despite their importance, the mechanism by which superstructures are patterned is unknown. Here, we identify components of the genetic program that control the patterning of Sox9+/Scx+ superstructure progenitors in mouse and show that this program includes both global and regional regulatory modules. Using light-sheet fluorescence microscopy combined with genetic lineage labeling, we mapped the broad contribution of the Sox9+/Scx+ progenitors to the formation of bone superstructures. Then, by combining literature-based evidence, comparative transcriptomic analysis and genetic mouse models, we identified Gli3 as a global regulator of superstructure patterning, whereas Pbx1, Pbx2, Hoxa11 and Hoxd11 act as proximal and distal regulators, respectively. Moreover, by demonstrating a dose-dependent pattern regulation in Gli3 and Pbx1 compound mutations, we show that the global and regional regulatory modules work in a coordinated manner. Collectively, our results provide strong evidence for genetic regulation of superstructure patterning, which further supports the notion that long bone development is a modular process.This article has an associated 'The people behind the papers' interview.

Mechanical stress influences the morphology and function of human uterosacral ligament fibroblasts and activates the p38 MAPK pathway.

INTRODUCTION AND HYPOTHESIS: Pelvic organ prolapse (POP) is a common condition in older women that affects quality of life. Mechanical injury of the pelvic floor support system contributes to POP development. In our study, we aimed to examine the mechanical damage to human uterosacral ligament fibroblasts (hUSLFs) to preliminarily explore the mechanism of mechanical transduction in POP. METHODS: hUSLFs were derived from POP and non-POP patients. Mechanical stress was induced by the FX-5000 T-cell stress loading system. Student's t-test was used for comparisons between different groups. RESULTS: We found that hUSLFs from POP patients were larger and longer than those from non-POP patients and exhibited cytoskeleton F-actin rearrangement. Collagen I and III expression levels were lower and matrix metalloproteinase 1 (MMP1) levels were higher in POP patients than in non-POP patients. Additionally, the apoptosis rate was significantly increased in POP patients compared to non-POP patients. After mechanical stretching, hUSLFs underwent a POP-like transformation. Cells became longer, and the cytoskeleton became thicker and rearranged. The extracellular matrix (ECM) was remodelled because of the upregulation of collagen I and III expression and downregulation of MMP1 expression. Mechanical stress also induced hUSLF apoptosis. Notably, we found that the p38 MAPK pathway was activated by mechanical stretching. CONCLUSIONS: Mechanical stress induced morphological changes in ligament fibroblasts, leading to cytoskeleton and ECM remodelling and cell apoptosis. p38 MAPK might be involved in this process, providing novel insights into the mechanical biology of and possible therapies for this disease.

Collagens in primary frozen shoulder: expression of collagen mRNA isoforms in the different phases of the disease.

OBJECTIVES: Primary frozen shoulder (pFS) has three phases that differ in clinical presentation. It is characterized by contracture of the joint capsule. We hypothesized that there is a general upregulation of collagens in pFS, and that this is highest in the first phase of the disease. The aims of this study were to investigate the expression of various collagens and degradation of collagens in patients with primary pFS and relate this to the three phases of the condition. METHODS: From twenty-six patients with pFS and eight control patients with subacromial impingement, biopsies were obtained during shoulder arthroscopy from the middle glenohumeral ligament and the anterior capsule, and mRNA levels for collagens, MMP-2 and -14 and TGF-ß1, - ß2 and -ß3 in the tissue were analysed using real-time PCR. RESULTS: Genes for collagens type I, III, IV, V, VI and XIV, were activated in pFS, and the total mRNA for all collagens was increased (P < 0.05). This upregulation was independent of disease phases in pFS. In addition, MMP-2, MMP-14, TGF-ß1 and TGF-ß3 were upregulated in all phases of the disease. CONCLUSION: There is a general upregulation and an increased degradation of collagens in pFS in all three phases of the disease. This indicates a constantly increased turnover of the fibrotic tissue in the capsule from pFS. The difference in clinical presentation of pFS observed in the three phases of the disease is not primarily a result of variations in collagen production.

Transforming Growth Factor Beta 1 and p44/42 Expression in Cardinal Ligament Tissues of Patients with Pelvic Organ Prolapse.

BACKGROUND Pelvic organ prolapse (POP) is a disease associated with collagen loss and decreased fibroblast proliferation. Transforming growth factor beta 1 (TGF-ß1) controls collagen synthesis and degradation in pelvic connective tissue. Although the p44/42 MAPK pathway has been implicated in collagen production and extracellular matrix disorders, its expression in POP remains unknown. This study aimed to investigate TGF-ß1 and p44/42 expression in cardinal ligament tissues in patients with POP. MATERIAL AND METHODS Cardinal ligament tissues were obtained from 30 patients with POP (POP group) and 30 patients with benign gynecological disorders who had undergone total hysterectomy (control group). The clinical characteristics of the 2 groups were summarized. Immunohistochemical staining and western blotting analysis were performed to measure the expression of TGF-ß1, p44/42, phospho-p44/42, MMP9, TIMP1, caspase 3, collagen I, and collagen III in the cardinal ligament tissues. RESULTS Patients with POP had significantly lower TGF-ß1 and phospho-p44/42 levels than did control patients (P<0.05). The expression of TIMP1, collagen I, and collagen III was significantly lower, and the expression of MMP9 and caspase 3 was significantly higher in the POP group than in the control group (P<0.05). Moreover, the expression of phospho-p44/42 was positively correlated with the expression of TGF-ß1, collagen I, and collagen III. CONCLUSIONS The expression levels of phospho-p44/42 and TGF-ß1 were decreased in patients with POP and were positively correlated with collagen expression. Low levels of TGF-ß1 and phospho-p44/42 expression in patients with POP may be associated with the occurrence of POP.

Heterotopic ossification of tendon and ligament.

Much of the similarities of the tissue characteristics, pathologies and mechanisms of heterotopic ossification (HO) formation are shared between HO of tendon and ligament (HOTL). Unmet need and no effective treatment has been developed for HOTL, primarily attributable to poor understanding of cellular and molecular mechanisms. HOTL forms via endochondral ossification, a common process of most kinds of HO. HOTL is a dynamic pathologic process that includes trauma/injury, inflammation, mesenchymal stromal cell (MSC) recruitment, chondrogenic differentiation and, finally, ossification. A variety of signal pathways involve HOTL with multiple roles in different stages of HO formation, and here in this review, we summarize the progress and provide an up-to-date understanding of HOTL.

Unique molecular networks: Formation and role of elastin cross-links.

Elastic fibers are essential assemblies of vertebrates and confer elasticity and resilience to various organs including blood vessels, lungs, skin, and ligaments. Mature fibers, which comprise a dense and insoluble elastin core and a microfibrillar mantle, are extremely resistant toward intrinsic and extrinsic influences and maintain elastic function over the human lifespan in healthy conditions. The oxidative deamination of peptidyl lysine to peptidyl allysine in elastin's precursor tropoelastin is a crucial posttranslational step in their formation. The modification is catalyzed by members of the family of lysyl oxidases and the starting point for subsequent manifold condensation reactions that eventually lead to the highly cross-linked elastomer. This review summarizes the current understanding of the formation of cross-links within and between the monomer molecules, the molecular sites, and cross-link types involved and the pathological consequences of abnormalities in the cross-linking process.

The role of tenascin-X in the uterosacral ligaments of postmenopausal women with pelvic organ prolapse: an immunohistochemical study.

INTRODUCTION AND HYPOTHESIS: Abnormalities of connective tissue structure or its repair mechanism may predispose women to pelvic organ prolapse (POP). We hypothesized that the expression of tenascin-X in the uterosacral ligament of postmenopausal women with symptomatic POP is increased compared with postmenopausal women without POP. Furthermore, we identified clinical risk factors associated with POP in our study population. METHODS: We conducted a retrospective case-control study in which 33 postmenopausal women with symptomatic POP ≥ pelvic organ prolapse quantification system (POP-Q) stage II were matched with 33 postmenopausal women without POP. Studied tissue specimens were taken from hysterectomy specimens, and tenascin-X expression was investigated by immunohistochemistry. The immunohistochemical profile of the uterosacral connective tissue of cases and controls was compared. RESULTS: Tenascin-X was expressed in 94% of POP cases and in 91% of controls. Our study failed to show any statistically significant differences in tenascin-X expression between women with and without POP (p = 0.64). However, tenascin-X was significantly more expressed in cases with severe prolapse (POP-Q stage IV) compared with moderate prolapse stages (POP-Q stage II and III) (p = 0.001). Advanced patient age as well as early menopausal age remained independent risk factors associated with POP in multiple logistic regression analysis (p = 0.001). CONCLUSION: No difference could be demonstrated between tenascin-X expression in patients with or without POP. Tenascin-X does not seem to play a major role in the pathogenesis of POP in postmenopausal women.

Estrogen Enhances Osteogenic Differentiation of Human Periodontal Ligament Stem Cells by Activating the Wnt/ß-Catenin Signaling Pathway.

OBJECTIVES: This study was designed to investigate the role of the Wnt/ß-catenin signaling pathway in estrogen-enhanced osteogenic differentiation of human peridontal ligament stem cells (hPLSCs). METHODS: The limiting dilution technique was used for cloning and purification of hPLSCs. Flow cytometric analysis of STRO-1, CD146, and CD45 was conducted to identify hPLSCs. The P3 hPDLSCs were divided into 4 groups: Control, 10M E2, 10M E2+100 ng/mL Wnt3a, 10M E2+5 × 10M Xav939. After 7 days of osteogenic induction, qRT-PCR was used to detect the mRNA expression of ß-catenin, CyclinD1, alkaline phosphatase, Runx2, and OCN; Western blot was used to detect the protein expression of ß-catenin, GSK3ß, P-GSK3ß, CyclinD1, Runx2, and OCN; After 1, 3, 5, 7 days of osteogenic induction, the activity of alkaline phosphatase was detected. RESULTS: The authors' results showed that E2 was able to enhance the osteogenic differentiation of hPDLSCs and Wnt/ß-catenin signaling pathway was involved. Wnt3a activated the signaling pathway of Wnt/ß-catenin and further enhanced the osteogenesis of hPDLSCs. Xav939 inhibited the Wnt/ß-catenin signaling pathway in estrogen-mediated environment, but did not obviously inhibit the osteogenic differentiation of hPDLSCs. CONCLUSIONS: E2 enhanced osteogenic differentiation of hPDLSCs through the activation of the Wnt/ß-catenin signaling pathway.

Facilitation of Chemotaxis Activity of Mesenchymal Stem Cells via Stromal Cell-Derived Factor-1 and Its Receptor May Promote Ectopic Ossification of Human Spinal Ligaments.

Mesenchymal stem cells (MSCs) have been used to elucidate the pathogenesis of numerous diseases. Our recent study showed that MSCs may conduce to the ossification of spinal ligaments. Stromal cell-derived factor-1 (SDF-1) and CXC chemokine receptor 4 (CXCR4) regulate MSC migration. Moreover, their expression is elevated in sites of damage and remodeling in pathologic states. We explored the possible role of the SDF-1/CXCR4 axis in the chemotactic behavior of MSCs in the ossification of spinal ligaments. Specimens of thoracic vertebra ossified ligamentum flavum (OLF) and non-OLF plaques were received from patients in whom we had performed spine surgery. Paraffin-embedded tissue sections were prepared for immunohistochemical staining. Cultured MSCs from the ligamentum flavum were prepared for in vitro analyses. We observed SDF-1 and CXCR4 localization immunohistochemically in the perivascular area and collagenous matrix of ligaments and in chondrocytes near the ossification front of OLF. And then, immunohistochemical staining showed a close relationship between MSCs and the SDF-1/CXCR4 axis. In the in vitro analyses, expression of the SDF-1/CXCR4 and the migratory capacity of MSCs in OLF were remarkably higher compared with non-OLF MSCs. Furthermore, the migration of MSCs was upregulated by SDF-1 and downregulated by treatment with AMD3100 (C28H54N88HCl), a specific antagonist for CXCR4. All in vitro test data showed a significant difference in MSCs from OLF compared with non-OLF MSCs. Our results reveal that the SDF-1/CXCR4 axis may contribute to an MSC-mediated increase in the ossification process, indicating that the SDF-1/CXCR4 axis may become a potential target for a novel therapeutic strategy for ossification of spinal ligaments.

Selective ablation of ligament of Marshall inhibits ventricular arrhythmias during acute myocardial infarction: Possible mechanisms.

INTRODUCTION: Our recent study found that selective ablation of the distal part of the ligament of Marshall (LOMLSPV ) could suppress ventricular arrhythmias (VAs) during acute myocardial infarction (AMI). This study was to investigate the possible underlying mechanisms. METHODS: Dogs were randomly divided into the sham-operated group (SO; n = 6), AMI group (AMI; n = 8) and the group undergoing LOMLSPV ablation ahead of AMI (LOMD+AMI; n = 8). Incidence of VAs, serum levels of malondialdehyde (MDA) and superoxide dismutase (SOD), expression of connexin (Cx43), Bcl-2, Bax, caspase-3, tumor necrosis factor (TNF)-α, interleukin-6 (IL-6), and high mobility group box (HMGB)1 were compared. Anatomic and immunostaining examinations of LOM LSPV were performed. RESULTS: Compared with the AMI group, incidence of VAs was reduced in the LOMD+AMI group. Compared with the SO group, Cx43, SOD, and Bcl-2 were decreased, MDA, Bax, caspase-3, TNF-α, IL-6, and HMGB1 were increased in the MI group, and all the alterations were significantly restrained in the LOMD+AMI group. A visual nerve fiber communication between the left stellate ganglion (LSG) and LOM and abundant sympathetic nerve bundles distribution in LOMLSPV were revealed. CONCLUSIONS: LOMLSPV ablation could suppress VAs during AMI. The possible mechanism may be associated with disconnection of the sympathetic conduit from LSG to the ventricles. Preservation of Cx43, inhibition of cardiac oxidative stress, apoptosis, and inflammation may be involved.

Ultrasound-Mediated Gene Delivery Enhances Tendon Allograft Integration in Mini-Pig Ligament Reconstruction.

Ligament injuries occur frequently, substantially hindering routine daily activities and sports participation in patients. Surgical reconstruction using autogenous or allogeneic tissues is the gold standard treatment for ligament injuries. Although surgeons routinely perform ligament reconstructions, the integrity of these reconstructions largely depends on adequate biological healing of the interface between the ligament graft and the bone. We hypothesized that localized ultrasound-mediated, microbubble-enhanced therapeutic gene delivery to endogenous stem cells would lead to significantly improved ligament graft integration. To test this hypothesis, an anterior cruciate ligament reconstruction procedure was performed in Yucatan mini-pigs. A collagen scaffold was implanted in the reconstruction sites to facilitate recruitment of endogenous mesenchymal stem cells. Ultrasound-mediated reporter gene delivery successfully transfected 40% of cells recruited to the reconstruction sites. When BMP-6 encoding DNA was delivered, BMP-6 expression in the reconstruction sites was significantly enhanced. Micro-computed tomography and biomechanical analyses showed that ultrasound-mediated BMP-6 gene delivery led to significantly enhanced osteointegration in all animals 8 weeks after surgery. Collectively, these findings demonstrate that ultrasound-mediated gene delivery to endogenous mesenchymal progenitor cells can effectively improve ligament reconstruction in large animals, thereby addressing a major unmet orthopedic need and offering new possibilities for translation to the clinical setting.

Differential gene expression of extracellular-matrix-related proteins in the vaginal apical compartment of women with pelvic organ prolapse.

INTRODUCTION AND HYPOTHESIS: Pelvic organ prolapse (POP) is a multifactorial disorder that impairs the quality of life (QoL) of older women in particular. The purpose of this study was to elucidate the pathogenesis of POP by focusing on the extracellular matrix (ECM). METHODS: Patients were classified into two groups-with or without cervical elongation-using the POP quantification system. Specimens were obtained from 29 women with POP during hysterectomy. The expression of fibulin-5, elastin, integrin ß1 (ITGß1), lysyl oxidase-like protein-1 (LOXL1) and collagen in the vagina, uterosacral ligament, and uterine cervix was investigated by quantitative real-time polymerase chain reaction (RT-PCR) and correlation between gene levels and severity of POP examined. The location of proteins was analyzed using immunohistochemical staining and expression of fibulin-5 protein analyzed by Western blotting. RESULTS: Fibulin-5 and elastin were mainly expressed in lamina propria and fibromuscular layers of the vagina and uterosacral ligament. Gene levels of fibulin-5 and ITGß1 in uterosacral ligaments increased with severity of POP in women with cervical elongation, while no correlation was observed in women with a normal cervix. In women with uterine cervical elongation, each ECM-related gene significantly increased with POP staging. Furthermore, fibulin-5 protein also increased in the uterosacral ligament and uterine cervix. CONCLUSIONS: The severity of POP and gene expression of ECM-related proteins were inversely correlated in vaginal tissue in a normal and elongated cervix. These results suggested that the differing progression of the two types of POP have a relationship with ECM-related protein.

RNA-seq in Skeletal Biology.

PURPOSE OF REVIEW: The goal of this paper is to review state-of-the-art transcriptome profiling methods and their recent applications in the field of skeletal biology. RECENT FINDINGS: Next-generation sequencing of mRNA (RNA-seq) methods have been established and routinely used in skeletal biology research. RNA-seq has led to the identification of novel genes and transcription factors involved in skeletal development and disease, through its application in small and large animal models, as well as human tissue and cells. With the availability of advanced techniques such as single-cell RNA-seq, novel cell types in skeletal tissues are being identified. As the sequencing technologies are rapidly evolving, the exciting discoveries supported by transcriptomics will continue to emerge and improve our understanding of the biology of the skeleton.

Variations in internal structure, composition and protein distribution between intra- and extra-articular knee ligaments and tendons.

Tendons and ligaments play key roles in the musculoskeletal system in both man and animals. Both tissues can undergo traumatic injury, age-related degeneration and chronic disease, causing discomfort, pain and increased susceptibility to wider degenerative joint disease. To date, tendon and ligament ultrastructural biology is relatively under-studied in healthy, non-diseased tissues. This information is essential to understand the pathology of these tissues with regard to function-related injury and to assist with the future development of tissue-engineered tendon and ligament structures. This study investigated the morphological, compositional and extracellular matrix protein distribution differences between tendons and ligaments around the non-diseased canine stifle joint. The morphological, structural characteristics of different regions of the periarticular tendons and ligaments (the intra-articular anterior cruciate ligament, the extra-articular medial collateral ligament, the positional long digital extensor tendon and energy-storing superficial digital flexor tendons) were identified using a novel semi-objective histological scoring analysis and by determining their biochemical composition. Protein distribution of extracellular matrix collagens, proteoglycans and elastic fibre proteins in anterior cruciate ligament and long digital extensor tendon were also determined using immunostaining techniques. The anterior cruciate ligament was found to have significant morphological differences in comparison with the other three tissues, including less compact collagen architecture, differences in cell nuclei phenotype and increased glycosaminoglycan and elastin content. Intra- and interobserver differences of histology scoring resulted in an average score 0.7, indicative of good agreement between observers. Statistically significant differences were also found in the extracellular matrix composition in terms of glycosaminoglycan and elastin content, being more prominent in the anterior cruciate ligament than in the other three tissues. A different distribution of several extracellular matrix proteins was also found between long digital extensor tendon and anterior cruciate ligament, with a significantly increased immunostaining of aggrecan and versican in the anterior cruciate ligament. These findings directly relate to the different functions of tendon and ligament and indicate that the intra-articular anterior cruciate ligament is subjected to more compressive forces, reflecting an adaptive response to normal or increased loads and resulting in different extracellular matrix composition and arrangement to protect the tissue from damage.

Myo/Nog cells are present in the ciliary processes, on the zonule of Zinn and posterior capsule of the lens following cataract surgery.

Myo/Nog cells, named for their expression of MyoD and noggin, enter the eye during early stages of embryonic development. Their release of noggin is critical for normal morphogenesis of the lens and retina. Myo/Nog cells are also present in adult eyes. Single nucleated skeletal muscle cells designated as myofibroblasts arise from Myo/Nog cells in cultures of lens tissue. In this report we document the presence of Myo/Nog cells in the lens, ciliary body and on the zonule of Zinn in mice, rabbits and humans. Myo/Nog cells were rare in all three structures. Their prevalence increased in the lens and ciliary body of rabbits 24 h following cataract surgery. Rabbits developed posterior capsule opacification (PCO) within one month of surgery. The number of Myo/Nog cells continued to be elevated in the lens and ciliary body. Myo/Nog cells containing alpha smooth muscle actin and striated muscle myosin were present on the posterior capsule and overlaid deformations in the capsule. Myo/Nog cells also were present on the zonule fibers and external surface of the posterior capsule. These findings suggest that Myo/Nog contribute to PCO and may use the zonule fibers to migrate between the ciliary processes and lens.

Slow viscoelastic response of resilin.

The high importance of resilin in invertebrate biomechanics is widely known. It is generally assumed to be an almost perfect elastomer in different tissues. Whereas mechanical properties of resilin were previously determined mainly in tension, here we aimed at studying its mechanical properties in compression. Microindentation of resilin from the wing hinge of Locusta migratoria revealed the clear viscoelastic response of resilin: about a quarter of the mechanical response was assigned to a viscous component in our experiments. Mechanical properties were characterized using a generalized Maxwell model with two characteristic time constants, poroelasticity theory, and alternatively using a 1D model with just one characteristic time constant. Slow viscous responses with 1.7 and 16 s characteristic times were observed during indentation. These results demonstrate that the locust flight system is adapted to both fast and slow mechanical processes. The fast highly elastic process is related to the flight function and the slow viscoelastic process may be related to the wing folding.