Comparative Analysis of Tenogenic Gene Expression in Tenocyte-Derived Induced Pluripotent Stem Cells and Bone Marrow-Derived Mesenchymal Stem Cells in Response to Biochemical and Biomechanical Stimuli

A human embryonic limb cell atlas resolved in space and time

Human limbs emerge during the fourth post-conception week as mesenchymal buds, which develop into fully formed limbs over the subsequent months1. This process is orchestrated by numerous temporally and spatially restricted gene expression programmes, making congenital alterations in phenotype common2. Decades of work with model organisms have defined the fundamental mechanisms underlying vertebrate limb development, but an in-depth characterization of this process in humans has yet to be performed. Here we detail human embryonic limb development across space and time using single-cell and spatial transcriptomics. We demonstrate extensive diversification of cells from a few multipotent progenitors to myriad differentiated cell states, including several novel cell populations. We uncover two waves of human muscle development, each characterized by different cell states regulated by separate gene expression programmes, and identify musculin (MSC) as a key transcriptional repressor maintaining muscle stem cell identity. Through assembly of multiple anatomically continuous spatial transcriptomic samples using VisiumStitcher, we map cells across a sagittal section of a whole fetal hindlimb. We reveal a clear anatomical segregation between genes linked to brachydactyly and polysyndactyly, and uncover transcriptionally and spatially distinct populations of the mesenchyme in the autopod. Finally, we perform single-cell RNA sequencing on mouse embryonic limbs to facilitate cross-species developmental comparison, finding substantial homology between the two species.

Fabricating oxygen self-supplying 3D printed bioactive hydrogel scaffold for augmented vascularized bone regeneration

Limited cells and factors, inadequate mechanical properties, and necrosis of defects center have hindered the wide clinical application of bone-tissue engineering scaffolds. Herein, we construct a self-oxygenated 3D printed bioactive hydrogel scaffold by integrating oxygen-generating nanoparticles and hybrid double network hydrogel structure. The hydrogel scaffold possesses the characteristics of extracellular matrix; Meanwhile, the fabricated hybrid double network structure by polyacrylamide and CaCl2-crosslinked sodium carboxymethylcellulose endows the hydrogel favorable compressive strength and 3D printability. Furthermore, the O2 generated by CaO2 nanoparticles encapsulated in ZIF-8 releases steadily and sustainably because of the well-developed microporous structure of ZIF-8, which can significantly promote cell viability and proliferation in vitro, as well as angiogenesis and osteogenic differentiation with the assistance of Zn2+. More significantly, the synergy of O2 and 3D printed pore structure can prevent necrosis of defects center and facilitate cell infiltration by providing cells the nutrients and space they need, which can further induce vascular network ingrowth and accelerate bone regeneration in all areas of the defect in vivo. Overall, this work provides a new avenue for preparing cell/factor-free bone-tissue engineered scaffolds that possess great potential for tissue regeneration and clinical alternative.

A systematic investigation of the effects of TGF-β3 and mechanical stimulation on tenogenic differentiation of mesenchymal stromal cells in a poly(ethylene glycol)/gelatin-based hydrogel

Background

High post-surgical failure rates following tendon injury generate high medical costs and poor patient recovery. Cell-based tendon tissue engineering has the potential to produce fully functional replacement tissue and provide new strategies to restore tendon function and healing. In this endeavour, the application of mesenchymal stromal cells (MSCs) encapsulated in biomaterial scaffolds has shown great promise. However, a consensus on optimal promotion of tenogenic differentiation of MSCs has yet to be reached, although growth factors and mechanical cues are generally acknowledged as important factors.

Methods

In this study, we prepared a hydrogel cell culture system consisting of methacrylated poly(d,l-lactic acid-ethylene glycol-d,l-lactic acid) (P(LA-EG-LA)) and gelatin methacrylate (GelMA) to encapsulate human bone marrow-derived MSCs (hBMSCs). We further systematically investigated the influence of static and intermittent cyclic uniaxial strain mechanical stimulation, in combination with transforming growth factor-β3 (TGF-β3) supplementation, on tenogenic differentiation of hBMSCs.

Results

Increased TGF-β3 concentration upregulated the tenogenic genes Scleraxis (SCX) and collagen type I (COL1A1) but showed no effects on tenascin-c (TNC) and collagen type III (COL3A1) expression. Mechanical stimulation had no observable effect on gene expression, but intermittent cyclic uniaxial strain stimulation improved matrix deposition. Together, these data provide new insights into how TGF-β3 and mechanical stimulation regulate MSC tenogenesis, with TGF-β3 promoting the expression of key tenogenic genes whilst mechanical stimulation aided matrix deposition in the engineered tissue. Furthermore, intermittent cyclic uniaxial strain at 3% elongation and 0.33 ​Hz for 1 ​h/day showed improved matrix effects compared to static strain.

Conclusion

Together, the most promising result for tenogenic differentiation of hBMSCs was identified as treatment with 5 ​ng/ml TGF-β3 under intermittent cyclic uniaxial strain (3% strain; 0.33 ​Hz; 1 ​h/day). This knowledge is of importance for the development of an improved protocol for tenogenic differentiation of MSCs and thereby for tendon tissue engineering.

The translational potential of this article

Tissue-engineered strategies for tendon repair require a consensus on the differentiation of mesenchymal stromal cells to tenocytes, which is currently lacking. This article provides a systematic investigation of two main tenogenic differentiation conditions to further development of a tenogenic differentiation protocol.

Biomimetic Scaffolds for Tendon Tissue Regeneration

Tendon tissue connects muscle to bone and plays crucial roles in stress transfer. Tendon injury remains a significant clinical challenge due to its complicated biological structure and poor self-healing capacity. The treatments for tendon injury have advanced significantly with the development of technology, including the use of sophisticated biomaterials, bioactive growth factors, and numerous stem cells. Among these, biomaterials that the mimic extracellular matrix (ECM) of tendon tissue would provide a resembling microenvironment to improve efficacy in tendon repair and regeneration. In this review, we will begin with a description of the constituents and structural features of tendon tissue, followed by a focus on the available biomimetic scaffolds of natural or synthetic origin for tendon tissue engineering. Finally, we will discuss novel strategies and present challenges in tendon regeneration and repair.

MKX-AS1 Gene Expression Associated with Variation in Drug Response to Oxaliplatin and Clinical Outcomes in Colorectal Cancer Patients

Oxaliplatin (OXAL) is a commonly used chemotherapy for treating colorectal cancer (CRC). A recent genome wide association study (GWAS) showed that a genetic variant (rs11006706) in the lncRNA gene MKX-AS1 and partnered sense gene MKX could impact the response of genetically varied cell lines to OXAL treatment. This study found that the expression levels of MKX-AS1 and MKX in lymphocytes (LCLs) and CRC cell lines differed between the rs11006706 genotypes, indicating that this gene pair could play a role in OXAL response. Further analysis of patient survival data from the Cancer Genome Atlas (TCGA) and other sources showed that patients with high MKX-AS1 expression status had significantly worse overall survival (HR = 3.2; 95%CI = (1.17-9); p = 0.024) compared to cases with low MKX-AS1 expression status. Alternatively, high MKX expression status had significantly better overall survival (HR = 0.22; 95%CI = (0.07-0.7); p = 0.01) compared to cases with low MKX expression status. These results suggest an association between MKX-AS1 and MKX expression status that could be useful as a prognostic marker of response to OXAL and potential patient outcomes in CRC.

Induced pluripotent stem cells in companion animals: how can we move the field forward?

Following a one medicine approach, the development of regenerative therapies for human patients leads to innovative treatments for animals, while pre-clinical studies on animals provide knowledge to advance human medicine. Among many different biological products under investigation, stem cells are among the most prominent. Mesenchymal stromal cells (MSCs) are extensively investigated, but they present challenges such as senescence and limited differentiation ability. Embryonic stem cells (ESCs) are pluripotent cells with a virtually unlimited capacity for self-renewal and differentiation, but the use of embryos carries ethical concerns. Induced pluripotent stem cells (iPSCs) can overcome all of these limitations, as they closely resemble ESCs but are derived from adult cells by reprogramming in the laboratory using pluripotency-associated transcription factors. iPSCs hold great potential for applications in therapy, disease modeling, drug screening, and even species preservation strategies. However, iPSC technology is less developed in veterinary species compared to human. This review attempts to address the specific challenges associated with generating and applying iPSCs from companion animals. Firstly, we discuss strategies for the preparation of iPSCs in veterinary species and secondly, we address the potential for different applications of iPSCs in companion animals. Our aim is to provide an overview on the state of the art of iPSCs in companion animals, focusing on equine, canine, and feline species, as well as to identify which aspects need further optimization and, where possible, to provide guidance on future advancements. Following a "step-by-step" approach, we cover the generation of iPSCs in companion animals from the selection of somatic cells and the reprogramming strategies, to the expansion and characterization of iPSCs. Subsequently, we revise the current applications of iPSCs in companion animals, identify the main hurdles, and propose future paths to move the field forward. Transferring the knowledge gained from human iPSCs can increase our understanding in the biology of pluripotent cells in animals, but it is critical to further investigate the differences among species to develop specific approaches for animal iPSCs. This is key for significantly advancing iPSC application in veterinary medicine, which at the same time will also allow gaining pre-clinical knowledge transferable to human medicine.

Dynamic Superior Capsular Reconstruction for Irreparable Massive Rotator Cuff Tears: Histologic Analysis in a Rat Model and Short-term Clinical Evaluation

BACKGROUND

Superior capsular reconstruction (SCR) has been demonstrated to be a valuable treatment for patients with irreparable massive rotator cuff tears (IMRCTs). However, the torn medial supraspinatus (SSP) tendons, which acted as dynamic stabilizers, were left untreated in conventional SCR, and the dynamic force from the SSP tendon was not restored.

PURPOSE

To evaluate the effect of dynamic SCR (dSCR) on fascia-to-bone healing in a rat model, and to compare the short-term clinical effectiveness of dSCR and SCR using autologous fascia lata (FL) in patients with IMRCTs.

STUDY DESIGN

Controlled laboratory study and cohort study; Level of evidence, 3.

METHODS

A total of 50 rats were divided randomly into 2 groups: the dSCR group and the SCR group (25 rats per group). First, chronic IMRCTs were created, and then the torn tendons in both groups were subjected to SCR using autologous thoracolumbar fascial (TLF) grafts. The remnant of the SSP tendon was sutured to the medial part of the TLF graft in the dSCR group but not in the SCR group. Histologic sections were assessed at 1, 2, 4, 8, and 16 weeks postoperatively. In the clinical study, 22 patients (9 SCR, 13 dSCR) were analyzed. The recovery of shoulder function, including the active range of motion (ROM), visual analog scale (VAS), American Shoulder and Elbow Surgeons score, Constant score, and University of California Los Angeles score, acromiohumeral distance (AHD), and fatty infiltration, was evaluated before surgery and at the last follow-up.

RESULTS

Histologic analysis of the fascia-to-bone junction in the rat model showed that the TLF gradually migrated into tendon-like tissue over the rotator cuff defects in both groups, and the modified tendon maturation score of the fascia-to-bone interface in the dSCR group was higher than that in the SCR group at 4 weeks (12.20 ± 1.30 vs 14.60 ± 1.52; P = .004), 8 weeks (19.60 ± 1.14 vs 22.20 ± 1.10; P = .019), and 16 weeks (23.80 ± 0.84 vs 26.20 ± 0.84 P = .024). The dSCR group showed earlier fibrocartilage cell formation and angiogenesis. In the clinical study, all 22 patients completed a minimum of 12 months of follow-up after surgery, and the mean follow-up duration was 22.89 ± 7.59 months in the SCR group and 25.62 ± 7.32 months in the dSCR group. The patients in both groups showed significant improvements in terms of ROM, shoulder function scores, and AHD. At the last follow-up, abduction (56.67°± 27.39° vs 86.54°± 30.37°; P = .029), external rotation (25.00°± 9.35° vs 33.08°± 8.55°; P = .049), internal rotation cone rank (-2.78 ± 2.44 vs -4.38 ± 1.12; P = .049), VAS (-3.00 ± 0.87 vs -3.92 ± 0.95; P = .031) and Constant (47.89 ± 15.39 vs 59.15 ± 9.74; P = .048) scores, and the AHD improvement degree (3.06 ± 1.41 mm vs 4.38 ± 1.35 mm; P = .039) in the dSCR group were significantly improved compared with those in the SCR group. The results of fatty infiltration at the last follow-up showed that there was significant improvement compared with the preoperative results in both the conventional SCR (P = .036) and the dSCR (P = .001) groups. However, there were no significant differences between the 2 groups (P = .511).

CONCLUSION

dSCR can promote faster fascia-to-bone healing in a rat model, and the dSCR technique could provide a preferable treatment option for patients with IMRCTs.

CLINICAL RELEVANCE

dSCR might restore the dynamic of SSP in some sense and then improve the fatty infiltration in the SSP.

Melatonin and the Programming of Stem Cells

Melatonin interacts with various types of stem cells, in multiple ways that comprise stimulation of proliferation, maintenance of stemness and self-renewal, protection of survival, and programming toward functionally different cell lineages. These various properties are frequently intertwined but may not be always jointly present. Melatonin typically stimulates proliferation and transition to the mature cell type. For all sufficiently studied stem or progenitor cells, melatonin’s signaling pathways leading to expression of respective morphogenetic factors are discussed. The focus of this article will be laid on the aspect of programming, particularly in pluripotent cells. This is especially but not exclusively the case in neural stem cells (NSCs) and mesenchymal stem cells (MSCs). Concerning developmental bifurcations, decisions are not exclusively made by melatonin alone. In MSCs, melatonin promotes adipogenesis in a Wnt (Wingless-Integration-1)-independent mode, but chondrogenesis and osteogenesis Wnt-dependently. Melatonin upregulates Wnt, but not in the adipogenic lineage. This decision seems to depend on microenvironment and epigenetic memory. The decision for chondrogenesis instead of osteogenesis, both being Wnt-dependent, seems to involve fibroblast growth factor receptor 3. Stem cell-specific differences in melatonin and Wnt receptors, and contributions of transcription factors and noncoding RNAs are outlined, as well as possibilities and the medical importance of re-programming for transdifferentiation.

Differentiation of human adipose-derived mesenchymal stem cells toward tenocyte by platelet-derived growth factor-BB and growth differentiation factor-6

Mesenchymal Stem Cells (MSCs) are important in regenerative medicine and tissue engineering and will be a very sensible choice for repair and regeneration of tendon. New biological practices, such as cellular therapy using stem cells, are promising for facilitating or expediting tendon therapy. Before using these cells clinically, it is best to check and confirm the optimal conditions for differentiation of these cells in the laboratory. Hence, in the present study, the impacts of PDGF-BB and GDF-6 supplementation on adipose-derived MSCs (ASCs) culture were studied. The frozen ASC were recovered and expanded in basic culture medium (DMEM with 10%FBS). The cells after passage five (P5) were treated with basic medium containing L-Prolin, Ascorbic Acid and only PDGF-BB or GDF-6 (20 ng/ml) or both of them (mix) as 3 groups for 14 days to investigate efficiency of ASCs differentiation towards tenocytes. The cells culturing in basic medium were used as control group. To validate tenogenic differentiation, H&E and Sirius Red staining were used to assess cell morphology and collagen production, respectively. In addition, mRNA levels of collagen I and III, Scleraxis and Tenomodulin as tenogenic markers were analyzed using qPCR. In all test groups, cells appeared slenderer, elongated cytoplasmic attributes compared to the control cells. The intensity of Sirius Red staining was significantly higher in GDF-6, PDGF-BB alone, than in group without supplements. The optical density was higher in the GDF-6 than PDGF-BB and mix-group. QPCR results showed that Col I and III gene expression was increased in all groups compared to the control. SCX expression was significantly increased only in the PDGF-BB group. TNMD mRNA expression was not significant among groups. In this study, we have corroborated that human ASCs are reactionary to tenogenic induction by GDF-6 and PDGF-BB alone or in combination. These outcomes will help greater insight into GDF-6 and PDGF-BB driven tenogenesis of ASCs and new directions of discovery in the design of ASC-based treatments for tendon healing.