Hypoxic culture conditions induce increased metabolic rate and collagen gene expression in ACL-derived cells

Platelet-rich plasma pretreatment protects anterior cruciate ligament fibroblasts correlated with PI3K-Akt-mTOR pathway under hypoxia condition

Background

/Objective: Biological factors such as platelet-rich plasma (PRP) combined with anterior cruciate ligament (ACL) primary repair technology are used to treat ACL injury. However, the protective mechanism of PRP for ACL fibroblasts under hypoxia condition is still unknown. The aim of this study was to investigate the protective effect of PRP on ACL fibroblasts under hypoxia condition and illustrate the mechanism of PRP regulating the ACL fibroblasts under hypoxia condition.

Methods

The cells were divided into three groups: control group, hypoxia group and PRP pretreatment group. Lethal dose (LD) 50 for hypoxia induction time and the maximum efficacy of PRP concentration were confirmed by CCK-8 assay. The ability of cell apoptosis, cell proliferation, and cell migration were tested by flow cytometry, scratch assay and transwell assay, respectively. Extracellular matrix (ECM) synthesis and hypoxia-inducible factor 1α (HIF-1α) were identified by immunofluorescence staining, Masson's staining and transmission electron microscope analysis. Inflammatory cell infiltration was assessed by hematoxylin and eosin staining as well as immunofluorescence staining. Western blot analysis and real-time PCR were performed to assess the associated gene and protein expression, respectively. The ratio of phosphorylated/total PI3K, Akt and mTOR were also assessed by western blot analysis.

Results

① LD 50 of hypoxia was 48 ​h and the maximum efficacy of PRP concentration was 600 ​× ​10⁹/L. ② ANNEXIN V-FITC/PI flow cytometry showed that the hypoxia condition significantly increased the apoptosis of cells (P ​< ​0.001) whereas PRP pretreatment significantly decreased the apoptosis of cells under hypoxia (P ​< ​0.001). The expressions of gene and protein of Bax, Bcl-2, cleaved-caspase 3 were consistent with the results of flow cytometric analysis. ③ Cell cycle analysis for flow cytometry showed the inhibitory effect of hypoxia and promotive effect of PRP pretreatment. ④ Immunofluorescence staining (HIF-1α, collagen I and III) showed the positive effect of hypoxia and negative effect of PRP on these parameters. Real-time PCR showed that type I and III collagen were 2.1 folds and 2.5 folds higher after 48 ​h hypoxia induction compared to the control group. PRP pretreatment significantly reduced the type I and III collagen mRNA expression of the hypoxia induced ACL fibroblasts to 78.5% and 77.7% at 48 ​h compared to hypoxia group (P ​< ​0.001), respectively.⑤ Cell migration assay showed that hypoxia condition significantly restrained cell migration compared with the control group. PRP could alleviate the inhibitory effect of hypoxia on fibroblasts. ⑥ Western blot analysis showed the ratio of phosphorylated/total PI3K, Akt and mTOR in hypoxia group increased to 31%, 20% and 44/% compared to control group, respectively. ⑦ The results of in vivo analysis was in accordance with the results of in vitro analysis.

Conclusion

PRP can protect ACL fibroblasts via decreasing apoptosis and increasing cell viability, cell migration and cell proliferation under hypoxia condition. And such PRP protective effect was correlated with PI3K/Akt/mTOR pathway.

The translational potential of this article

PRP can be used to treat patients with ACL tear by injection under arthroscopy or ultrasound guiding.

Ligament/Tendon Culture under Hypoxic Conditions: A Systematic Review

The hypoxic environment is a substantial factor in maintenance, proliferation, and differentiation of the cell cultures. Low oxygen is known as a potent chondrogenesis stimulus in stem cells that is important for clinical application and engineering of functional cartilage. Hypoxia can potentially induce angiogenesis process by secretion of cytokines. This systematic review goal is to discover the effect of hypoxic condition on tendon/ ligament culture and the best oxygen level of hypoxia for in vitro and in vivo studies. We included 21 articles. A comprehensive review of this database confirms that the hypoxic condition is a substantial factor in the maintenance, proliferation, and differentiation of ligament/tendon cultures. Cell proliferation in the severe hypoxic (oxygen concentration of 1%) group at 24 h postcultivation was considered significant, but cell proliferation was markedly inhibited in the severe hypoxic group after 48 h.

A Review of Biomechanics Analysis of the Umbilical-Placenta System With Regards to Diseases

Placenta is an important organ that is crucial for both fetal and maternal health. Abnormalities of the placenta, such as during intrauterine growth restriction (IUGR) and pre-eclampsia (PE) are common, and an improved understanding of these diseases is needed to improve medical care. Biomechanics analysis of the placenta is an under-explored area of investigation, which has demonstrated usefulness in contributing to our understanding of the placenta physiology. In this review, we introduce fundamental biomechanics concepts and discuss the findings of biomechanical analysis of the placenta and umbilical cord, including both tissue biomechanics and biofluid mechanics. The biomechanics of placenta ultrasound elastography and its potential in improving clinical detection of placenta diseases are also discussed. Finally, potential future work is listed.

Hypoxia-Induced Mesenchymal Stem Cells Exhibit Stronger Tenogenic Differentiation Capacities and Promote Patellar Tendon Repair in Rabbits

Tendon injury is a common but tough medical problem. Unsatisfactory clinical results have been reported in tendon repair using mesenchymal stem cell (MSC) therapy, creating a need for a better strategy to induce MSCs to tenogenic differentiation. This study was designed to examine the effect of hypoxia on the tenogenic differentiation of different MSCs and their tenogenic differentiation capacities under hypoxia condition in vitro and to investigate the in vivo inductility of hypoxia in tenogenesis. Adipose tissue-derived MSCs (AMSCs) and bone marrow-derived MSCs (BMSCs) were isolated and characterized. The expression of hypoxia-induced factor-1 alpha (Hif-1α) was examined to confirm the establishment of hypoxia condition. qRT-PCR, western blot, and immunofluorescence staining were used to evaluate the expression of tendon-associated marker Col-1a1, Col-3a1, Dcn, and Tnmd in AMSCs and BMSCs under hypoxia condition, compared with Tgf-β1 induction. In vivo, a patellar tendon injury model was established. Normoxic and hypoxic BMSCs were cultured and implanted. Histological, biomechanical, and transmission electron microscopy analyses were performed to assess the improved healing effect of hypoxic BMSCs on tendon injury. Our in vitro results showed that hypoxia remarkably increased the expression of Hif-1α and that hypoxia not only promoted a significant increase in tenogenic markers in both AMSCs and BMSCs compared with the normoxia group but also showed higher inductility compared with Tgf-β1. In addition, hypoxic BMSCs exhibited higher potential of tenogenic differentiation than hypoxic AMSCs. Our in vivo results demonstrated that hypoxic BMSCs possessed better histological and biomechanical properties than normoxic BMSCs, as evidenced by histological scores, patellar tendon biomechanical parameters, and the range and average of collagen fibril diameters. These findings suggested that hypoxia may be a practical and reliable strategy to induce tenogenic differentiation of BMSCs for tendon repair and could enhance the effectiveness of MSCs therapy in treating tendon injury.

Enhancement of in vitro proliferation and bioactivity of human anterior cruciate ligament fibroblasts using an in situ tissue isolation method and basic fibroblast growth factor culture conditions: A pilot analysis

BACKGROUND

Previous studies have reported poor proliferation and bioactivity of human anterior cruciate ligament fibroblasts (hACLFs) after injury. As hACLFs are one of the most significant and indispensable source of seed cells in constructing tissue-engineered ligament, enhancing hACLF proliferation would offer favorable cellular-biological ability and induce the extracellular matrix secretion of hACLFs after loading on multiple types of scaffolds. Enhancing the bioactivity of hACLFs would improve tissue repair and functional recovery after tissue-engineered ligament transplantation. This study compared cells prepared by collagenase digestion and the in situ culture of tissue pieces and investigated the effect of basic fibroblast growth factor (bFGF) on hACLFs.

METHODS

Six adult patients participated in this study. Of these patients, tissues from three were compared after culture establishment through collagenase digestion or in situ tissue isolation. hACLF phenotypic characteristics were assessed, and the effect of bFGF on hACLF cultures was observed. hACLFs cultured with and without bFGF served as the experimental and control groups, respectively. Cell Counting Kit-8 was used to detect proliferation. The expression of ligament-related genes and proteins was evaluated by immunofluorescence staining, real-time polymerase chain reaction (PCR) assays, and Western blot assays.

RESULTS

The morphology of hACLFs isolated using the two methods differed after the 2nd passage. The proliferation of cells obtained by in situ culture was higher than that of cells obtained by collagenase digestion. hACLFs cultured with bFGF after the 3rd passage exhibited a higher proliferation rate than the controls. Immunofluorescence staining, real-time PCR, and Western blot analysis showed a significant increase in ligament-related gene and protein expression in the hACLFs cultured with bFGF.

CONCLUSIONS

The in situ isolation of tissue pieces enhanced hACLF proliferation in vitro, and the hACLFs exhibited phenotypic characteristics of fibroblasts. hACLFs cultured with bFGF exhibited increased hACLF bioactivity.

Mesenchymal Stem Cells Isolated from the Anterior Cruciate Ligament: Characterization and Comparison of Cells from Young and Old Donors

Purpose

Mesenchymal stem cells (MSCs) isolated from the anterior cruciate ligament (ACL) share multiple characteristics of bone marrow-derived mesenchymal stem cells (BMSCs), allowing their use for regenerative therapies. Injuries to the ACL can affect people of all ages. This study assesses whether the regenerative potential of ACL-derived MSCs (ACL-MSCs) from old donors is as high as the potential of ACL-MSCs from young donors.

Materials and Methods

ACL-MSCs were isolated from ACL tissues obtained from young and old donors at the time of ACL reconstruction or arthroplasty. Proliferative capacity, multilineage differentiation potential (chondrogenic, osteogenic, and adipogenic lineages), and transcriptome-wide gene expression were assessed and compared between young and old donors. BMSCs of middle-aged donors served as an additional comparator.

Results

No substantial differences between ACL-MSCs from young and old donors were observed in their proliferative capacity and multilineage differentiation potential. The latter did not substantially differ between both ACL-MSC groups and BMSCs. Differential expression of genes related to the cytoskeleton and to protein dephosphorylation amongst other pathways was detected between ACL-MSCs from young and old donors.

Conclusions

Regenerative potential of ACL-MSCs from old donors was not substantially lower than that from young donors, suggesting that regenerative therapies of ACL tears are feasible in both age groups. In vivo studies of the effect of age on the efficacy of such therapies are needed.

Differentiation of Human Amniotic Mesenchymal Stem Cells into Human Anterior Cruciate Ligament Fibroblast Cells by In Vitro Coculture

Anterior cruciate ligament injuries are common in humans, though cellular components of the knee have little regenerative or proliferation potential. This study investigated the differentiation of human amnion-derived mesenchymal stem cells (hAMSCs) into human anterior cruciate ligament fibroblasts (hACLFs) in vitro through induction with bFGF and TGF-β1 with coculture systems. Groups A and B comprised hAMSCs at the 3rd passage cultured with and without bFGF and TGF-β1, respectively; Groups C and D consisted of hAMSCs and hACLFs in monolayer coculture with and without bFGF and TGF-β1, respectively; Groups E and F were composed of hAMSCs and hACLFs in Transwell coculture with and without bFGF and TGF-β1, respectively. Cell morphology and proliferation were recorded. Protein expression and relative mRNA expression were evaluated in each group. Cell proliferation was significantly higher in the induced groups than in the noninduced groups. Protein expression increased over time with the highest expression observed in Group E. mRNA levels were significantly higher in Group E than in other groups. This study is the first to demonstrate the use of the Transwell coculture system for this purpose, and hAMSCs were successfully differentiated into hACLFs. Thus, hAMSCs may be a superior choice for hACLF differentiation via Transwell coculture.

Ligament-Derived Stem Cells: Identification, Characterisation, and Therapeutic Application

Ligament is prone to injury and degeneration and has poor healing potential and, with currently ineffective treatment strategies, stem cell therapies may provide an exciting new treatment option. Ligament-derived stem cell (LDSC) populations have been isolated from a number of different ligament types with the majority of studies focussing on periodontal ligament. To date, only a few studies have investigated LDSC populations in other types of ligament, for example, intra-articular ligaments; however, this now appears to be a developing field. This literature review aims to summarise the current information on nondental LDSCs including in vitro characteristics of LDSCs and their therapeutic potential. The stem cell niche has been shown to be vital for stem cell survival and function in a number of different physiological systems; therefore, the LDSC niche may have an impact on LDSC phenotype. The role of the LDSC niche on LDSC viability and function will be discussed as well as the therapeutic potential of LDSC niche modulation.

Clinical results of anterior cruciate ligament reconstruction with ligament remnant tissue preservation: A systematic review

PURPOSE

To clarify the effects of ACL remnant tissue preservation on the clinical outcome of ACL reconstruction.

METHODS

This is a systematic review.

RESULTS

The majority of the reviewed articles suggested that remnant preservation significantly improved knee stability after ACL reconstruction, although there was some controversy. In addition, it was suggested that the degree of initial graft coverage significantly affected postoperative knee stability. Remnant preservation did not increase the occurrence rate of cyclops lesion.

CONCLUSION

Sufficient coverage of the graft with remnant tissue improves postoperative knee stability without any detrimental effects on the subjective and functional results.