Secretome from In Vitro Mechanically Loaded Myoblasts Induces Tenocyte Migration, Transition to a Fibroblastic Phenotype and Suppression of Collagen Production

Effects of Late-Passage Small Umbilical Cord-Derived Fast Proliferating Cells on Tenocytes from Degenerative Rotator Cuff Tears under an Interleukin 1β-Induced Tendinopathic Environment

BACKGROUND

Tendinopathy is a chronic tendon disease. Mesenchymal stem cells (MSCs), known for their anti-inflammatory properties, may lose effectiveness with extensive culturing. Previous research introduced "small umbilical cord-derived fast proliferating cells" (smumf cells), isolated using a novel minimal cube explant method. These cells maintained their MSC characteristics through long-term culture. Thus, the purpose of the present study was to assess the anti-inflammatory effects of late-passage smumf cells at P10 on tenocytes derived from degenerative rotator cuff tears in a tendinopathic environment.

METHODS

The mRNA expression with respect to aging of MSCs and secretion of growth factors (GFs) by smumf cells at P10 were measured. mRNA and protein synthesis in tenocytes with respect to the tenocyte phenotype, inflammatory cytokines, and matrix- degradation enzymes were measured. The inflammatory signal pathways involving nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) in tenocytes were also investigated. The proliferative response of degenerative tenocytes to co-culture with smumf cells over 7 days in varying IL-1β induced tendinopathic environments was investigated.

RESULTS

smumf cells at P10 showed no signs of aging compared to those at P3. smumf cells at P10, secreting 2,043 pg/ml of hepatocyte growth factor (HGF), showed a 1.88-fold (p = .002) increase in HGF secretion in a tendinopathic environment. Degenerative tenocytes co-cultured with smumf cells showed significantly increased protein expression levels of collagen type I (Col I) and the Col I/III ratio by 1.46-fold (p < .001) and 1.66-fold (p < .001), respectively. The smumf cells at P10 reduced both mRNA and protein expression levels of matrix metalloproteinases-1, -2, -3, -8, -9, and -13 in tenocytes and attenuated NF-κB (phosphorylated IκBα/IκBα and phosphorylated p65/p65) and MAPK (phosphorylated p38/p38 and phosphorylated JNK/JNK) pathways activated by IL-1β. Removal of IL-1β from the co-culture accelerated the growth of tenocytes by 1.42-fold (p < .001). Removal of IL-1β accelerated tenocyte growth in co-cultures.

CONCULSION

Late-passage smumf cells exert anti-inflammatory effects on tenocytes derived from degenerative rotator cuff tears under a tendinopathic environment, primarily through the secretion of growth factors (GFs).

Mechanical Loading Modulates AMPK and mTOR Signaling in Muscle Cells

Skeletal muscle adaptation to exercise involves various phenotypic changes that enhance the metabolic and contractile functions. One key regulator of these adaptive responses is the activation of AMPK, which is influenced by exercise intensity. However, the mechanistic understanding of AMPK activation during exercise remains incomplete. In this study, we utilized an in vitro model to investigate the effects of mechanical loading on AMPK activation and its interaction with the mTOR signaling pathway. Proteomic analysis of muscle cells subjected to static loading (SL) revealed distinct quantitative protein alterations associated with RNA metabolism, with 10% SL inducing the most pronounced response compared to lower intensities of 5% and 2% as well as the control. Additionally, 10% SL suppressed RNA and protein synthesis while activating AMPK and inhibiting the mTOR pathway. We also found that SRSF2, necessary for pre-mRNA splicing, is regulated by AMPK and mTOR signaling, which, in turn, is regulated in an intensity-dependent manner by SL with the highest expression in 2% SL. Further examination showed that the ADP/ATP ratio was increased after 10% SL compared to the control and that SL induced changes in mitochondrial biogenesis. Furthermore, Seahorse assay results indicate that 10% SL enhances mitochondrial respiration. These findings provide novel insights into the cellular responses to mechanical loading and shed light on the intricate AMPK-mTOR regulatory network in muscle cells.

Effect of tetrahedral framework nucleic acids on the reconstruction of tendon-to-bone injuries after rotator cuff tears

Clinicians and researchers have always faced challenges in performing surgery for rotator cuff tears (RCT) due to the intricate nature of the tendon-bone gradient and the limited long-term effectiveness. At the same time, the occurrence of an inflammatory microenvironment further aggravates tissue damage, which has a negative impact on the regeneration process of mesenchymal stem cells (MSCs) and eventually leads to the production of scar tissue. Tetrahedral framework nucleic acids (tFNAs), novel nanomaterials, have shown great potential in biomedicine due to their strong biocompatibility, excellent cellular internalisation ability, and unparalleled programmability. The objective of this research was to examine if tFNAs have a positive effect on regeneration after RCTs. Experiments conducted in a controlled environment demonstrated that tFNAs hindered the assembly of inflammasomes in macrophages, resulting in a decrease in the release of inflammatory factors. Next, tFNAs were shown to exert a protective effect on the osteogenic and chondrogenic differentiation of bone marrow MSCs under inflammatory conditions. The in vitro results also demonstrated the regulatory effect of tFNAs on tendon-related protein expression levels in tenocytes after inflammatory stimulation. Finally, intra-articular injection of tFNAs into a rat RCT model showed that tFNAs improved tendon-to-bone healing, suggesting that tFNAs may be promising tendon-to-bone protective agents for the treatment of RCTs.

Secretome from myoblasts statically loaded at low intensity promotes tenocyte proliferation via the IGF-1 receptor pathway

Exercise is widely recognized as beneficial for tendon healing. Recently, it has been described that muscle-derived molecules secreted in response to static exercise influence tendon healing. In this study, the optimal static loading intensity for tendon healing and the composition of secretome released by myoblasts in response to different intensities of static strain were investigated. In an in vitro coculture model, myoblasts were mechanically loaded using a Flexcell Tension System. Tenocytes were seeded on transwell inserts that allowed communication between the tenocytes and myoblasts without direct contact. Proliferation and migration assays, together with RNA sequencing, were used to determine potential cellular signaling pathways. The secretome from myoblasts exposed to 2% static loading increased the proliferation and migration of the cocultured tenocytes. RNA-seq analysis revealed that this loading condition upregulated the expression of numerous genes encoding secretory proteins, including insulin-like growth factor-1 (IGF-1). Confirmation of IGF-1 expression and secretion was carried out using qPCR and enzyme-linked immunosorbt assay (ELISA), revealing a statistically significant upregulation in response to 2% static loading in comparison to both control conditions and higher loading intensities of 5% and 10%. Addition of an inhibitor of the IGF-1 receptor (PQ401) to the tenocytes significantly reduced myoblast secretome-induced tenocyte proliferation. In conclusion, IGF-1 may be an important molecule in the statically loaded myoblast secretome, which is responsible for influencing tenocytes during exercise-induced healing.

Healing of Ligaments and Tendons: Tissue Engineering and Models

The aim of this Special Issue is to summarize the latest developments in tendon/ligament research and tissue engineering (TE), providing helpful approaches for future tendon/ligament reconstruction (Figure 1) [...].