SS-31 as a Mitochondrial Protectant in the Treatment of Tendinopathy: Evaluation in a Murine Supraspinatus Tendinopathy Model

Peptide therapy: new promising therapeutics for acute kidney injury

Acute kidney injury (AKI) is a common fatal condition among hospitalized patients. AKI may be induced by a variety of complicating factors such as sepsis, ischemia-reperfusion injury, nephrotoxic substances, and rhabdomyolysis. At present, symptomatic treatment is mainly used, and there are no US Food and Drug Administration (FDA)-approved drugs for the prevention or treatment of AKI. Peptides have become a promising area of research in AKI treatment because of their high efficiency and low toxicity. In this paper, we systematically review the experimental advancements of peptide therapy for AKI, analyze the mechanism of peptide action in different pathological models, discuss the challenges facing peptide therapy, and provide a scientific basis for further clinical research.

The mitochondrial protectant SS31 optimized decellularized Wharton's jelly scaffold improves allogeneic chondrocyte implantation-mediated articular cartilage repair

Background

The process of allogeneic chondrocyte implantation entails obtaining donor chondrocytes, culturing them in a medium enriched with growth factors, and then introducing them-either individually or in conjunction with biocompatible scaffolds-into areas of cartilage damage. While promising, this approach is hindered by mitochondrial dysfunction in the implanted chondrocytes.

Methods

This research introduced an innovative approach by creating a new type of scaffold derived from Decellularized Umbilical Cord Wharton's Jelly (DUCWJ) extracted from human umbilical cords. The scaffold was manufactured using procedures involving decellularization and lyophilization. The resulting scaffold demonstrated superior characteristics, including high porosity, hydrophilic properties, and excellent biocompatibility. To enhance its function, SS31 peptides, known for their mitochondrial-protective properties, were chemically bonded to the scaffold surface, creating an SS31@DUCWJ system. This system aims to protect chondrocytes and regulate the mitochondrial respiratory chain (MRC), thereby improving cartilage repair mediated by allogeneic chondrocyte implantation.

Results

In vitro studies have shown that SS31 effectively attenuates metabolic dysfunction, extracellular matrix degradation, oxidative stress, inflammation, and mitochondrial damage induced by serial cell passages. Complementary in vivo experiments showed that the SS31@DUCWJ scaffold promoted regeneration of healthy articular cartilage in femoral condylar defects in rabbits.

Conclusions

This SS31-modified porous decellularized scaffold represents an innovative biomaterial with anti-inflammatory properties and targeted mitochondrial regulation. It offers a promising new approach for treating articular cartilage injuries.

The translational potential of this article

Our study was the first to successfully load the mitochondrial protectant SS31 onto a DUCWJ hydrogel scaffold for localized drug delivery. This method is highly efficacious in repairing cartilage defects and offers a promising new avenue for the treatment of such conditions.

The P2X7R/NLRP3 inflammasome axis suppresses enthesis regeneration through inflammatory and metabolic macrophage-stem cell cross-talk

The regeneration of the enthesis remains a formidable challenge in regenerative medicine. However, key regulators underlying unsatisfactory regeneration remain poorly understood. This study reveals that the purinergic receptor P2X7 (P2X7R)/Nod-like receptor family protein 3 (NLRP3) inflammasome axis suppresses enthesis regeneration by amplifying IL-1β-mediated inflammatory cross-talk and suppressing docosatrienoic acid (DTA) metabolic cross-talk. NLRP3 inflammasomes were activated in macrophages following enthesis injury, thereby impairing the histological and functional recovery of the injured enthesis. Single-cell RNA sequencing (scRNA-seq) indicated that Nlrp3 knockout attenuated pathological inflammation and ameliorated the detrimental effects of IL-1β signaling cross-talk. Furthermore, NLRP3 inflammasomes suppressed the secretion of anti-inflammatory cytokines (IL-10 and IL-13) and DTA. The NLRP3 inflammasome-mediated secretome reduced differentiation and migration of stem cells. Neutralizing IL-1β or replenishing docosatrienoic acid accelerated enthesis regeneration. Moreover, conditional knockout of P2rx7 in myeloid cells attenuated NLRP3 inflammasome activation and facilitated enthesis regeneration. This study demonstrates that the P2X7R/NLRP3 inflammasome axis represents a promising therapeutic target for enthesis repair.

Muscle-Derived Mitochondria as a Novel Therapy for Muscle Degeneration After Rotator Cuff Tears

BACKGROUND

Rotator cuff tears (RCTs) commonly lead to muscle atrophy, fatty infiltration, and fibrosis, resulting in pain, weakness, and impaired shoulder mobility. These pathological changes are often irreversible and pose substantial treatment challenges. The aim of this study was to evaluate the therapeutic potential of muscle-derived mitochondria (Mito) in mitigating muscle degeneration and fibrosis following RCTs.

METHODS

Sprague Dawley rats were assigned to 3 groups: sham surgery, RCTs treated with Mito, or RCTs treated with phosphate-buffered saline solution (PBS). Following RCTs, in vivo Mito or PBS treatments were administered to the supraspinatus muscles (SSPs) of the rats immediately and then biweekly for 12 weeks. Data were collected on muscle morphology, fibrosis, fatty infiltration, oxidative stress, mitochondrial function, macrophage phenotypes, and serum inflammatory cytokines. In vitro experiments included mitochondria tracking in bone marrow-derived macrophages (BMDMs), characterization of macrophage polarization, and inflammatory cytokine profiling.

RESULTS

Isolated mitochondria preserved their morphology and function. Mito treatment improved muscle wet weight (p < 0.0001) and fiber cross-sectional area (p < 0.0001) while reducing fibrosis (p < 0.0001) and fatty infiltration (p < 0.0001). It upregulated mitochondrial markers cytochrome c oxidase (COX IV) and translocase of outer mitochondrial membrane 20 (TOMM20) (p < 0.0001) and enhanced antioxidative activity, as shown by increased superoxide dismutase (SOD) activity (p < 0.0001), elevated glutathione peroxidase (GSH-PX) levels (p = 0.038), and decreased malondialdehyde (MDA) levels (p = 0.0002). Mitochondrial density and morphology were restored in SSPs after Mito treatment. Additionally, Mito treatment induced an anti-inflammatory macrophage phenotype and reduced pro-inflammatory cytokines in vivo and in vitro.

CONCLUSIONS

Mito treatment mitigated muscle degeneration, improved mitochondrial function, and fostered an anti-inflammatory environment through macrophage modulation, demonstrating its potential as a cell-free therapeutic strategy for RCT-related muscle pathologies.

CLINICAL RELEVANCE

Although this is a preclinical study, its approach offers a novel avenue for improving RCT treatment outcomes. However, further validation in large animal models is needed to address the translational applicability of these findings, given the inherent regenerative capacity of rodent muscles.

Mitochondria Isolated From Bone Mesenchymal Stem Cells Restrain Muscle Disuse Atrophy and Fatty Infiltration After Rotator Cuff Tears

BACKGROUND

Rotator cuff tears (RCTs) commonly lead to muscle atrophy, fibrosis, and fatty infiltration, complicating treatment.

PURPOSE

To investigate the use of mitochondria isolated from bone mesenchymal stem cells (BMSC-Mito) for mitigating complications after RCT, focusing on muscle protection.

STUDY DESIGN

Controlled laboratory study.

METHODS

RCTs were induced by transecting the tendons of the supraspinatus and infraspinatus in Sprague-Dawley rats. In vivo, 90 rats were randomized into 3 groups: sham (no intervention), RCTs treated with BMSC-Mito, and RCTs treated with phosphate-buffered saline. After 6 weeks of intramuscular injections of BMSC-Mito or phosphate-buffered saline, supraspinatus muscles were harvested for analysis. Evaluations included wet muscle weight, muscle fiber cross-sectional area, fibrosis, fatty infiltration, slow-fast myofiber types and muscle biomechanics, capillary density, mitochondria respiratory chain complex activity, adenosine triphosphate (ATP) concentration, oxidative stress, and mitochondrial ultrastructure. In vitro experiments utilized primary rat skeletal muscle cells pretreated with rhodamine 6G to induce mitochondrial dysfunction, assessing the effects of BMSC-Mito on cell viability, mitochondrial membrane potential, and oxidative stress levels.

RESULTS

BMSC-Mito can be effectively transplanted into muscles and integrated into the local mitochondrial network. After RCT, the supraspinatus showed significant mass loss, reduced fiber cross-sectional area, fatty infiltration, and a shift from slow to fast myofiber types, which negatively affected muscle biomechanics. These changes were reversed by BMSC-Mito. BMSC-Mito also preserved vascularity (CD31 and α-SMA) impaired by RCT. Additionally, BMSC-Mito notably improved disuse-induced mitochondrial changes, leading to increased mitochondrial number and COX IV expression; furthermore, BMSC-Mito protected mitochondria morphology and enhanced cytosolic superoxide dismutase activity. This treatment also improved mitochondria respiratory chain complex activity and ATP concentration, reducing oxidative stress. In vitro, BMSC-Mito treatment effectively maintained the mitochondrial membrane potential of skeletal muscle cells, improved cell viability, and restored its mitochondrial function and ATP levels.

CONCLUSION

These findings suggest that BMSC-Mito might play a role in preventing muscle atrophy and fatty infiltration after RCT through the protection of mitochondrial function and the promotion of angiogenesis.

CLINICAL RELEVANCE

BMSC-Mito present a promising therapeutic approach for addressing rotator cuff muscle degeneration.

Mitochondria-Rich Extracellular Vesicles From Bone Marrow Stem Cells Mitigate Muscle Degeneration in Rotator Cuff Tears in a Rat Model Through Macrophage M2 Phenotype Conversion

PURPOSE

To investigate the protective effects of extracellular vesicles derived from bone marrow stem cells (BMSC-EVs) on muscle degeneration in a rat model of rotator cuff tendon and suprascapular nerve (SSN) transection (termed the RCT-SSN model), focusing on mitochondrial transfer.

METHODS

The EVs were identified and characterized. The RCT-SSN model was established by transecting the supraspinatus, infraspinatus tendons, and suprascapular nerve. Ninety-six rats were divided into 4 groups (n = 24 each): sham surgery, RCT-SSN treated with BMSC-EVs, RCT-SSN treated with EVs from rhodamine 6G-pretreated BMSCs (Rho-EVs), or phosphate-buffered saline. Intramuscular injections were administered every 2 weeks. After 12 weeks, supraspinatus muscles were analyzed for atrophy, fibrosis, oxidative stress, macrophage phenotypes, serum cytokines, and mitochondrial characteristics. In vitro experiments included EVs tracking in macrophages, macrophage phenotype characterization, and inflammatory cytokine profiling.

RESULTS

BMSC-EVs and Rho-EVs displayed similar morphology, but only BMSC-EVs contained functional mitochondria. BMSC-EVs significantly reduced muscle weight loss (0.047 ± 0.010% vs 0.145 ± 0.013%, P < .001), increased muscle fiber cross-sectional area (2037 ± 231.9 μm2 vs 527.9 ± 92.01 μm2, P < .001), and decreased fibrosis (12.09 ± 3.31% vs 25.69 ± 4.84%, P < .001) compared with phosphate-buffered saline. BMSC-EVs enhanced superoxide dismutase activity (93.3 ± 11.8 U/mg protein vs 53.4 ± 8.0 U/mg protein, P < .001), improved mitochondrial function, density and structure, and induced an anti-inflammatory macrophage shift, suppressing proinflammatory cytokines in vitro and in vivo. Rho-EVs showed no such effects.

CONCLUSIONS

This study showed that transecting the supraspinatus, infraspinatus tendons, and suprascapular nerve in a rat model induced muscle degeneration and fibrosis. BMSC-EVs, but not Rho-EVs, mitigated these effects by promoting an anti-inflammatory macrophage phenotype and protecting mitochondrial function through mitochondrial transfer.

CLINICAL RELEVANCE

Mitochondrial transfer via BMSC-EVs may offer a therapeutic strategy to prevent muscle degeneration in patients with rotator cuff tear.

Synthetic nanoparticles functionalized with cell membrane-mimicking, bone-targeting, and ROS-controlled release agents for osteoporosis treatment

Postmenopausal osteoporosis is a common degenerative disease, with suboptimal clinical outcomes. The targets of current therapeutic agents are both nonspecific and diverse. We synthesized a novel nanoparticle (NP), ALN@BMSCM@PLGA-TK-PEG-SS31. After intravenous injection, the NP evaded immune phagocytosis, targeted bone tissue, and efficiently downregulated bone reactive oxygen species (ROS) generation. The core PLGA-TK-PEG-SS31 NP was ∼100 nm in diameter. The TK chemical bond breaks on exposure to ROS, releasing the novel mitochondrion-targeting peptide SS31. Outer bone marrow mesenchymal stem cell membranes (BMSCMs) were used to coat the NP with surface proteins to ensure membrane functionality. The circulation time was prolonged and immune phagocytosis was evaded. Embedding the DSPE-PEG-ALN lipid within the cell membrane enhanced the bone-targeting ability of the NP. Our results suggest that ALN@BMSCM@PLGA-TK-PEG-SS31 exerted dual effects on bone tissue in vitro, significantly inhibiting RANKL-induced osteoclastogenesis in the presence of H2O2 and promoting osteogenic differentiation in BMSCs. In a mouse model of ovariectomy-induced osteoporosis, ALN@BMSCM@PLGA-TK-PEG-SS31 significantly ameliorated oxidative stress and increased bone mass with no notable systemic side effects. These results suggest that ALN@BMSCM@PLGA-TK-PEG-SS31 is a promising treatment for osteoporosis.

Small Intestinal Submucosa Hydrogel Loaded With Gastrodin for the Repair of Achilles Tendinopathy

Achilles tendinopathy (AT) is an injury caused by overuse of the Achilles tendon or sudden force on the Achilles tendon, with a considerable inflammatory infiltrate. As Achilles tendinopathy progresses, inflammation and inflammatory factors affect the remodeling of the extracellular matrix (ECM) of the tendon. Gastrodin(Gas), the main active ingredient of Astrodia has anti-inflammatory, antioxidant, and anti-apoptotic properties. The small intestinal submucosa (SIS) is a naturally decellularized extracellular matrix(dECM)material and has a high content of growth factors as well as good biocompatibility. However, the reparative effects of SIS and Gas on Achilles tendinopathy and their underlying mechanisms remain unknown. Here, it is found that SIS hydrogel loaded with gastrodin restored the mechanical strength of the Achilles tendon, facilitated ECM remodeling, and restored ordered collagen arrangement by promoting the translocation of protein synthesis. It also decreases the expression of inflammatory factors and reduces the infiltration of inflammatory cells by inhibiting the NF-κB signaling pathway. It is believed that through further research, Gas + SIS may be used in the future for the treatment of Achilles tendinopathy and other Achilles tendon injury disorders.

SS-31 inhibits the inflammatory response by increasing ATG5 and promoting autophagy in lipopolysaccharide-stimulated HepG2 cells

SS-31 is a mitochondria-targeting short peptide. Recent studies have indicated its hepatoprotective effects. In our study, we investigated the impact of SS-31 on LPS-induced autophagy in HepG2 cells. The results obtained from a dual-fluorescence autophagy detection system revealed that SS-31 promotes the formation of autolysosomes and autophagosomes, thereby facilitating autophagic flux to a certain degree. Additionally, both ELISA and qPCR analyses provided further evidence that SS-31 safeguards HepG2 cells against inflammatory responses triggered by LPS through ATG5-dependent autophagy. In summary, our study demonstrates that SS-31 inhibits LPS-stimulated inflammation in HepG2 cells by upregulating ATG5-dependent autophagy.

Translational Research on Orthobiologics in the Treatment of Rotator Cuff Disease: From the Laboratory to the Operating Room

Rotator cuff disease is one of the most common human tendinopathies and can lead to significant shoulder dysfunction. Despite efforts to improve symptoms in patients with rotator cuff tears and healing rates after rotator cuff repair, high rates of failed healing and persistent shoulder morbidity exist. Increasing interest has been placed on the utilization of orthobiologics-scaffolds, cell-based augmentation, platelet right plasma (platelet-rich plasma), and small molecule-based strategies-in the management of rotator cuff disease and the augmentation of rotator cuff repairs. This is a complex topic that involves novel treatment strategies, including patches/scaffolds, small molecule-based, cellular-based, and tissue-derived augmentation techniques. Ultimately, translational research, with a particular focus on preclinical models, has allowed us to gain some insights into the utility of orthobiologics in the treatment of rotator cuff disease and will continue to be critical to our further understanding of the underlying cellular mechanisms moving forward.

Hypoxia-Inducible Factor and Oxidative Stress in Tendon Degeneration: A Molecular Perspective

Tendinopathy is a debilitating condition marked by degenerative changes in the tendons. Its complex pathophysiology involves intrinsic, extrinsic, and physiological factors. While its intrinsic and extrinsic factors have been extensively studied, the role of physiological factors, such as hypoxia and oxidative stress, remains largely unexplored. This review article delves into the contribution of hypoxia-associated genes and oxidative-stress-related factors to tendon degeneration, offering insights into potential therapeutic strategies. The unique aspect of this study lies in its pathway-based evidence, which sheds light on how these factors can be targeted to enhance overall tendon health.

Animal model for tendinopathy

Background

Tendinopathy is a common motor system disease that leads to pain and reduced function. Despite its prevalence, our mechanistic understanding is incomplete, leading to limited efficacy of treatment options. Animal models contribute significantly to our understanding of tendinopathy and some therapeutic options. However, the inadequacies of animal models are also evident, largely due to differences in anatomical structure and the complexity of human tendinopathy. Different animal models reproduce different aspects of human tendinopathy and are therefore suitable for different scenarios. This review aims to summarize the existing animal models of tendinopathy and to determine the situations in which each model is appropriate for use, including exploring disease mechanisms and evaluating therapeutic effects.

Methods

We reviewed relevant literature in the PubMed database from January 2000 to December 2022 using the specific terms ((tendinopathy) OR (tendinitis)) AND (model) AND ((mice) OR (rat) OR (rabbit) OR (lapin) OR (dog) OR (canine) OR (sheep) OR (goat) OR (horse) OR (equine) OR (pig) OR (swine) OR (primate)). This review summarized different methods for establishing animal models of tendinopathy and classified them according to the pathogenesis they simulate. We then discussed the advantages and disadvantages of each model, and based on this, identified the situations in which each model was suitable for application.

Results

For studies that aim to study the pathophysiology of tendinopathy, naturally occurring models, treadmill models, subacromial impingement models and metabolic models are ideal. They are closest to the natural process of tendinopathy in humans. For studies that aim to evaluate the efficacy of possible treatments, the selection should be made according to the pathogenesis simulated by the modeling method. Existing tendinopathy models can be classified into six types according to the pathogenesis they simulate: extracellular matrix synthesis-decomposition imbalance, inflammation, oxidative stress, metabolic disorder, traumatism and mechanical load.

Conclusions

The critical factor affecting the translational value of research results is whether the selected model is matched with the research purpose. There is no single optimal model for inducing tendinopathy, and researchers must select the model that is most appropriate for the study they are conducting.

The translational potential of this article

The critical factor affecting the translational value of research results is whether the animal model used is compatible with the research purpose. This paper provides a rationale and practical guide for the establishment and selection of animal models of tendinopathy, which is helpful to improve the clinical transformation ability of existing models and develop new models.