Mitochondrial transfer from bone-marrow-derived mesenchymal stromal cells to chondrocytes protects against cartilage degenerative mitochondrial dysfunction in rats chondrocytes

Defining Endogenous Mitochondrial Transfer in Muscle After Rotator Cuff Injury

BACKGROUND

Rotator cuff muscle degeneration leads to poor clinical outcomes for patients with rotator cuff tears. Fibroadipogenic progenitors (FAPs) are resident muscle stem cells with the ability to differentiate into fibroblasts as well as white and beige adipose tissue. Induction of the beige adipose phenotype in FAPs has been shown to improve muscle quality after rotator cuff tears, but the mechanisms of how FAPs exert their beneficial effects have not been fully elucidated.

PURPOSE

To study the horizontal transfer of mitochondria from FAPs to myogenic cells and examine the effects of β-agonism on this novel process.

STUDY DESIGN

Controlled laboratory study.

METHODS

In mice that had undergone a massive rotator cuff tear, single-cell RNA sequencing was performed on isolated FAPs for genes associated with mitochondrial biogenesis and transfer. Murine FAPs were isolated by fluorescence-activated cell sorting and treated with a β-agonist versus control. FAPs were stained with mitochondrial dyes and cocultured with recipient C2C12 myoblasts, and the rate of transfer was measured after 24 hours by flow cytometry. PdgfraCreERT/MitoTag mice were generated to study the effects of a rotator cuff injury on mitochondrial transfer. PdgfraCreERT/tdTomato mice were likewise generated to perform lineage tracing of PDGFRA+ cells in this injury model. Both populations of transgenic mice underwent tendon transection and denervation surgery, and MitoTag-labeled mitochondria from Pdgfra+ FAPs were visualized by fluorescent microscopy, spinning disk confocal microscopy, and 2-photon microscopy; overall mitochondrial quantity was compared between mice treated with β-agonists and dimethyl sulfoxide.

RESULTS

Single-cell RNA sequencing in mice that underwent rotator cuff tear demonstrated an association between transcriptional markers of adipogenic differentiation and genes associated with mitochondrial biogenesis. In vitro cocultures of murine FAPs with C2C12 cells revealed that treatment of cells with a β-agonist increased mitochondrial transfer compared to control conditions (17.8% ± 9.9% to 99.6% ± 0.13% P < .0001). Rotator cuff injury in PdgfraCreERT/MitoTag mice resulted in a robust increase in MitoTag signal in adjacent myofibers compared with uninjured mice. No accumulation of tdTomato signal from PDGFRA+ cells was seen in injured fibers at 6 weeks after injury, suggesting that FAPs do not fuse with injured muscle fibers but rather contribute their mitochondria.

CONCLUSION

The authors have described a novel process of endogenous mitochondrial transfer that can occur within the injured rotator cuff between FAPs and myogenic cells. This process may be leveraged therapeutically with β-agonist treatment and represents an exciting target for improving translational therapies available for rotator cuff muscle degeneration.

CLINICAL RELEVANCE

Promoting endogenous mitochondrial transfer may represent a novel translational strategy to address muscle degeneration after rotator cuff tears.

Fusogenic liposomes encapsulating mitochondria as a promising delivery system for osteoarthritis therapy

Many attempts have been made to use mitochondria (MT) to treat human diseases; however, MT are large, making them difficult to deliver effectively. Therefore, a transfer strategy based on membrane fusion was established. Fusogenic mitochondrial capsules (FMCs) comprising a neutral lipid (PE), a cationic lipid (DOTAP), an aromatic lipid (Liss Rhod PE), and three types of liposome (FMC0, FMC1, and FMC2), were designed and synthesized. The amount of DOTAP, which affects membrane fusion efficiency, differed between FMC preparations. The characteristics of these FMCs were analyzed by DLS, TEM, and AFM, and the encapsulation and fusion efficiency between FMC-MT and FMC-chondrocytes were confirmed by FRET, mtDNA copy number, and CLSM, respectively. Compared with naked MT, delivery of FMCs to chondrocytes was faster and more efficient. Moreover, fusion was a more stable delivery method than endocytosis, as evidenced by reduced induction of mitophagy. In vitro and in vivo experiments revealed that FMCs reduced expression of inflammatory cytokines and MMP13, increased expression of extracellular matrix components, and promoted cartilage regeneration. These findings suggest that FMCs are a highly effective and promising strategy for delivery of MT to promote cartilage regeneration, and highlight their potential as a novel platform for MT transfer therapy.

Cell-Based Therapies for Degenerative Musculoskeletal Diseases

Degenerative musculoskeletal diseases (DMDs), including osteoporosis, osteoarthritis, degenerative disc disease, and sarcopenia, present major challenges in the aging population. Patients with DMDs present with pain, functional decline, and reduced exercise tolerance, which result in long-term or permanent deficits in their ability to perform daily activities. Current strategies for dealing with this cluster of diseases focus on relieving pain, but they have a limited capacity to repair function or regenerate tissue. Cell-based therapies have attracted considerable attention in recent years owing to their unique mechanisms of action and remarkable effects on regeneration. In this review, current experimental attempts to use cell-based therapies for DMDs are highlighted, and the modes of action of different cell types and their derivatives, such as exosomes, are generalized. In addition, the latest findings from state-of-the-art clinical trials are reviewed, approaches to improve the efficiency of cell-based therapies are summarized, and unresolved questions and potential future research directions for the translation of cell-based therapies are identified.

Culture-expanded mesenchymal stromal cell therapy: does it work in knee osteoarthritis? A pathway to clinical success

Osteoarthritis (OA) is a degenerative multifactorial disease with concomitant structural, inflammatory, and metabolic changes that fluctuate in a temporal and patient-specific manner. This complexity has contributed to refractory responses to various treatments. MSCs have shown promise as multimodal therapeutics in mitigating OA symptoms and disease progression. Here, we evaluated 15 randomized controlled clinical trials (RCTs) and 11 nonrandomized RCTs using culture-expanded MSCs in the treatment of knee OA, and we found net positive effects of MSCs on mitigating pain and symptoms (improving function in 12/15 RCTs relative to baseline and in 11/15 RCTs relative to control groups at study endpoints) and on cartilage protection and/or repair (18/21 clinical studies). We examined MSC dose, tissue of origin, and autologous vs. allogeneic origins as well as patient clinical phenotype, endotype, age, sex and level of OA severity as key parameters in parsing MSC clinical effectiveness. The relatively small sample size of 610 patients limited the drawing of definitive conclusions. Nonetheless, we noted trends toward moderate to higher doses of MSCs in select OA patient clinical phenotypes mitigating pain and leading to structural improvements or cartilage preservation. Evidence from preclinical studies is supportive of MSC anti-inflammatory and immunomodulatory effects, but additional investigations on immunomodulatory, chondroprotective and other clinical mechanisms of action are needed. We hypothesize that MSC basal immunomodulatory "fitness" correlates with OA treatment efficacy, but this hypothesis needs to be validated in future studies. We conclude with a roadmap articulating the need to match an OA patient subset defined by molecular endotype and clinical phenotype with basally immunomodulatory "fit" or engineered-to-be-fit-for-OA MSCs in well-designed, data-intensive clinical trials to advance the field.

Mitochondrial transfer from bone mesenchymal stem cells protects against tendinopathy both in vitro and in vivo

BACKGROUND

Although mesenchymal stem cells (MSCs) have been effective in tendinopathy, the mechanisms by which MSCs promote tendon healing have not been fully elucidated. In this study, we tested the hypothesis that MSCs transfer mitochondria to injured tenocytes in vitro and in vivo to protect against Achilles tendinopathy (AT).

METHODS

Bone marrow MSCs and H₂O₂-injured tenocytes were co-cultured, and mitochondrial transfer was visualized by MitoTracker dye staining. Mitochondrial function, including mitochondrial membrane potential, oxygen consumption rate, and adenosine triphosphate content, was quantified in sorted tenocytes. Tenocyte proliferation, apoptosis, oxidative stress, and inflammation were analyzed. Furthermore, a collagenase type I-induced rat AT model was used to detect mitochondrial transfer in tissues and evaluate Achilles tendon healing.

RESULTS

MSCs successfully donated healthy mitochondria to in vitro and in vivo damaged tenocytes. Interestingly, mitochondrial transfer was almost completely blocked by co-treatment with cytochalasin B. Transfer of MSC-derived mitochondria decreased apoptosis, promoted proliferation, and restored mitochondrial function in H₂O₂-induced tenocytes. A decrease in reactive oxygen species and pro-inflammatory cytokine levels (interleukin-6 and -1β) was observed. In vivo, mitochondrial transfer from MSCs improved the expression of tendon-specific markers (scleraxis, tenascin C, and tenomodulin) and decreased the infiltration of inflammatory cells into the tendon. In addition, the fibers of the tendon tissue were neatly arranged and the structure of the tendon was remodeled. Inhibition of mitochondrial transfer by cytochalasin B abrogated the therapeutic efficacy of MSCs in tenocytes and tendon tissues.

CONCLUSIONS

MSCs rescued distressed tenocytes from apoptosis by transferring mitochondria. This provides evidence that mitochondrial transfer is one mechanism by which MSCs exert their therapeutic effects on damaged tenocytes.

Potency Assay Considerations for Cartilage Repair, Osteoarthritis and Use of Extracellular Vesicles

Articular cartilage covers the ends of bones in synovial joints acting as a shock absorber that helps movement of bones. Damage of the articular cartilage needs treatment as it does not repair itself and the damage can progress to osteoarthritis. In osteoarthritis all the joint tissues are involved with characteristic progressive cartilage degradation and inflammation. Autologous chondrocyte implantation is a well-proven cell-based treatment for cartilage defects, but a main downside it that it requires two surgeries. Multipotent, aka mesenchymal stromal cell (MSC)-based cartilage repair has gained attention as it can be used as a one-step treatment. It is proposed that a combination of immunomodulatory and regenerative capacities make MSC attractive for the treatment of osteoarthritis. Furthermore, since part of the paracrine effects of MSCs are attributed to extracellular vesicles (EVs), small membrane enclosed particles secreted by cells, EVs are currently being widely investigated for their potential therapeutic effects. Although MSCs have entered clinical cartilage treatments and EVs are used in in vivo efficacy studies, not much attention has been given to determine their potency and to the development of potency assays. This chapter provides considerations and suggestions for the development of potency assays for the use of MSCs and MSC-EVs for the treatment of cartilage defects and osteoarthritis.

Mesenchymal stromal cells donate mitochondria to articular chondrocytes exposed to mitochondrial, environmental, and mechanical stress

Articular cartilage has limited healing capacity and no drugs are available that can prevent or slow the development of osteoarthritis (OA) after joint injury. Mesenchymal stromal cell (MSC)-based regenerative therapies for OA are increasingly common, but questions regarding their mechanisms of action remain. Our group recently reported that although cartilage is avascular and relatively metabolically quiescent, injury induces chondrocyte mitochondrial dysfunction, driving cartilage degradation and OA. MSCs are known to rescue injured cells and improve healing by donating healthy mitochondria in highly metabolic tissues, but mitochondrial transfer has not been investigated in cartilage. Here, we demonstrate that MSCs transfer mitochondria to stressed chondrocytes in cell culture and in injured cartilage tissue. Conditions known to induce chondrocyte mitochondrial dysfunction, including stimulation with rotenone/antimycin and hyperoxia, increased transfer. MSC-chondrocyte mitochondrial transfer was blocked by non-specific and specific (connexin-43) gap-junction inhibition. When exposed to mechanically injured cartilage, MSCs localized to areas of matrix damage and extended cellular processes deep into microcracks, delivering mitochondria to chondrocytes. This work provides insights into the chemical, environmental, and mechanical conditions that can elicit MSC-chondrocyte mitochondrial transfer in vitro and in situ, and our findings suggest a new potential role for MSC-based therapeutics after cartilage injury.

Mitochondrial Transport from Mesenchymal Stromal Cells to Chondrocytes Increases DNA Content and Proteoglycan Deposition In Vitro in 3D Cultures

OBJECTIVE

Allogeneic mesenchymal stromal cells (MSCs) are used in the 1-stage treatment of articular cartilage defects. The aim of this study is to investigate whether transport of mitochondria exists between chondrocytes and MSCs and to investigate whether the transfer of mitochondria to chondrocytes contributes to the mechanism of action of MSCs.

DESIGN

Chondrocytes and MSCs were stained with MitoTracker, and CellTrace was used to distinguish between cell types. The uptake of fluorescent mitochondria was measured in cocultures using flow cytometry. Transport was visualized using fluorescence microscopy. Microvesicles were isolated and the presence of mitochondria was assessed. Mitochondria were isolated from MSCs and transferred to chondrocytes using MitoCeption. Pellets of chondrocytes, chondrocytes with transferred MSC mitochondria, and cocultures were cultured for 28 days. DNA content and proteoglycan content were measured. Mitochondrial DNA of cultured pellets and of repair cartilage tissue was quantified.

RESULTS

Mitochondrial transfer occurred bidirectionally within the first 4 hours until 16 hours of coculture. Transport took place via tunneling nanotubes, direct cell-cell contact, and extracellular vesicles. After 28 days of pellet culture, DNA content and proteoglycan deposition were higher in chondrocyte pellets to which MSC mitochondria were transferred than the control groups. No donor mitochondrial DNA was traceable in the biopsies, whereas an increase in MSC mitochondrial DNA was seen in the pellets.

CONCLUSIONS

These results suggest that mitochondrial transport plays a role in the chondroinductive effect of MSCs on chondrocytes in vitro. However, in vivo no transferred mitochondria could be traced back after 1 year.

Mitochondrial transfer/transplantation: an emerging therapeutic approach for multiple diseases

Mitochondria play a pivotal role in energy generation and cellular physiological processes. These organelles are highly dynamic, constantly changing their morphology, cellular location, and distribution in response to cellular stress. In recent years, the phenomenon of mitochondrial transfer has attracted significant attention and interest from biologists and medical investigators. Intercellular mitochondrial transfer occurs in different ways, including tunnelling nanotubes (TNTs), extracellular vesicles (EVs), and gap junction channels (GJCs). According to research on intercellular mitochondrial transfer in physiological and pathological environments, mitochondrial transfer hold great potential for maintaining body homeostasis and regulating pathological processes. Multiple research groups have developed artificial mitochondrial transfer/transplantation (AMT/T) methods that transfer healthy mitochondria into damaged cells and recover cellular function. This paper reviews intercellular spontaneous mitochondrial transfer modes, mechanisms, and the latest methods of AMT/T. Furthermore, potential application value and mechanism of AMT/T in disease treatment are also discussed.

M1 Microglia Induced Neuronal Injury on Ischemic Stroke via Mitochondrial Crosstalk between Microglia and Neurons

Among the middle-aged and senile populations, ischemic stroke (IS) is a frequently occurring acute condition of the cerebrovascular system. Traditionally, it is recognized that when stroke occurs, microglia are activated into M1 phenotype and release cytotoxic cytokines, reactive oxygen species, proteases, and other factors, thus exacerbating the injury by further destroying or killing nearby neurons. In the latest research, the crucial role of the intercellular mitochondrial crosstalk on the stroke management has been demonstrated. Therefore, we tried to clarify mitochondrial crosstalk between microglia and neurons, and evaluated M1 microglial mitochondria-mediated neurological performance in transient middle cerebral artery occlusion (tMCAO) rats. We found that when microglia was activated into the proinflammatory M1 type after stroke, mitochondrial fission process was accelerated, and damaged mitochondria were released, further transferred to neurons and fused with neuronal mitochondria. As a result, the function of neuronal mitochondria was damaged by decreasing adenosine triphosphate (ATP), mitochondria membrane potential, and increasing excessive reactive oxygen species (ROS), thus inducing mitochondria-mediated neuronal death and finally aggravating ischemia injury. Taken together, it provides a novel neuroglial crosstalk mechanism at the mitochondrial level.

Mesenchymal stromal cell-based therapy for cartilage regeneration in knee osteoarthritis

Osteoarthritis, as a degenerative disease, is a common problem and results in high socioeconomic costs and rates of disability. The most commonly affected joint is the knee and characterized by progressive destruction of articular cartilage, loss of extracellular matrix, and progressive inflammation. Mesenchymal stromal cell (MSC)-based therapy has been explored as a new regenerative treatment for knee osteoarthritis in recent years. However, the detailed functions of MSC-based therapy and related mechanism, especially of cartilage regeneration, have not been explained. Hence, this review summarized how to choose, authenticate, and culture different origins of MSCs and derived exosomes. Moreover, clinical application and the latest mechanistical findings of MSC-based therapy in cartilage regeneration were also demonstrated.