Obesity-Related Adipose Tissue Remodeling in the Light of Extracellular Mitochondria Transfer

Adipose tissue dysfunction is strongly associated with obesity and its metabolic complications such as type 2 diabetes and cardiovascular diseases. It is well established that lipid-overloaded adipose tissue produces a large range of secreted molecules that contribute a pro-inflammatory microenvironment which subsequently disseminates towards multi-organ metabolic homeostasis disruption. Besides physiopathological contribution of adipose-derived molecules, a new paradigm is emerging following the discovery that adipocytes have a propensity to extrude damaged mitochondria in the extracellular space, to be conveyed through the blood and taken up by cell acceptors, in a process called intercellular mitochondria transfer. This review summarizes the discovery of mitochondria transfer, its relation to cell quality control systems and recent data that demonstrate its relevant implication in the context of obesity-related adipose tissue dysfunction.

TAMI-51. HORIZONTAL MITOCHONDRIAL TRANSFER FROM THE TUMOR MICROENVIRONMENT TO GLIOBLASTOMA INCREASES TUMORIGENICITY

Communication between glioblastoma (GBM) and its microenvironment facilitates tumor growth and therapeutic resistance, and is facilitated through a variety of mechanisms. Organelle transfer between cells was recently observed, including mitochondria transfer from astrocytes to neurons after ischemic stroke. Given the dependence of GBM on microenvironmental interactions, we hypothesized that mitochondria transfer from tumor microenvironment to GBM cells could occur and affect metabolism and tumorigenicity. We interrogated this in vivo by establishing intracranial GBM tumors in mito::mKate2 mice (with trackable fluorescent mitochondria) using syngeneic GFP-expressing tumor cells (SB28 and GL261 models). We also cultured stromal cell types from mito::mKate2 mice with tumor cells, enabling sorting of tumor cells with and without exogenous mitochondria. Confocal microscopy revealed horizontal transfer of mKate2+ mitochondria from mouse cells to implanted GBM cells in vivo and was confirmed by flow cytometry where 20-40% of GBM cells acquired exogenous mitochondria. Transfer was negligible in wildtype mice transplanted with mito::mKate2 bone marrow cells, suggesting that brain-resident cells were the main donors. In vitro, astrocytes and microglia exhibited 5 to 10-fold higher mitochondrial transfer rate than bone-marrow derived macrophages. Seahorse metabolic profiling revealed that GBM cells with mKate2+ mitochondria had 40% lower respiratory reserve compared to cells without exogenous mitochondria. Median survival of mice implanted with SB28 that acquired mitochondria was significantly shorter and in vivo limiting dilution confirmed the frequency of tumor-initiating cells was 3-fold higher in SB28 cells with exogenous mitochondria. Our data indicate that horizontal mitochondrial transfer from brain-resident glia to mouse GBM tumors alters tumor cell metabolism and increases their tumorigenicity. Ongoing studies are assessing gene expression in GBM cells acquiring exogenous mitochondria; validating findings in human specimens; and screening for transfer inhibitor drugs. Horizontal mitochondrial transfer represents a foundational tumor microenvironment interaction contributing to glioblastoma plasticity, and is likely to inform next-generation treatment strategies.

Autologous mitochondria transport via transzonal filopodia rejuvenates aged oocytes by UC-MSCs derived granulosa cells-oocyte aggregation

Mitochondria transfer can rescue oocyte aging-related infertility. However, heterologous techniques are suspended due to heteroplasmy. Regarding autologous approaches, the donor source and manipulating procedures require further optimization. Here we propose a strategy using umbilical cord mesenchymal stem cells (UC-MSCs) as mitochondria donor cells and employing intercellular mitochondria transport as the transfer method. We cryopreserved UC-MSCs of the female pup. When the female aged, its UC-MSCs were induced into granulosa cells (iGCs). The zona-weakened GV oocytes were aggregated with autologous iGCs into iGC-oocyte complexes. After cultivation in GDF9-containing media, mitochondria migrated from iGCs into the GV oocyte via transzonal filopodia. The maturation rate, quality, and developmental potential of these oocytes were substantially increased. Furthermore, the birth rate after embryo transfer has been improved. This approach utilized noninvasive procedures to collect mitochondria donor cells and optimized mitochondria transfer manipulations, so may represent a promising advance towards the improvement of aging-related infertility.

Mapping cell-to-cell mitochondria transfer in obesity using high-dimensional spectral flow cytometry

Obesity is a metabolic disease that promotes the development of a number of other pathologies. Despite its high disease burden, the underlying pathophysiology of obesity is poorly understood. Emerging research has indicated that adipocytes transfer their mitochondria to macrophages in white adipose tissue as a mechanism of cell-to-cell communication and that this process is impaired in obesity. However, the diversity of intercellular mitochondria transfer axes that occurs in adipose and its regulation in obesity are not known. Here, we utilized 31-color spectral flow cytometry of adipocyte-specific mitochondria reporter (MitoFat) mice to comprehensively analyze intercellular mitochondria transfer from adipocytes to other cell types in white, beige, and brown adipose tissues. Employing manifold machine learning, we generated reference clusters of cells in 5-month (young) and 20-month-old (aged) MitoFat mice fed a normal chow diet (low fat diet). Using the reference clusters and manifold, we then mapped differences in immune cell populations using nearest neighbor search approximations in MitoFat mice fed normal chow, high-fat diet (HFD), high-fat diet with low palmitate (LP-HFD). The degree of mitochondria transfer from adipocytes to each of the various cell clusters was determined for each tissue and for each condition. We observed that adipocytes transfer their mitochondria to a wide range of immune cell populations, most notably macrophages. Although aged mice develop obesity, surprisingly they do not exhibit decreased mitochondria transfer from adipocytes to macrophages in vivo in white, beige, or brown adipose tissue. In contrast, young mice fed a HFD highly enriched in palmitate exhibit obesity and markedly reduced mitochondria transfer from adipocytes to macrophages. The decrease in mitochondria transfer was largely ameliorated by the replacement of palmitate with medium chain fatty acids, suggesting a potential direct dietary mechanism in the alteration of mitochondria transfer. Overall, the 31-color quantification increased granularity, allowing us to quantify differences in immune populations and mitochondria transfer by tissue, age, and diet. Similar machine-learning approaches could be used to investigate both basic biological and clinical questions by effectively reducing dimensions, mitigating batch effect, and enabling comparisons across different tissues, timepoints, or conditions.

Mitochondria Donation by Mesenchymal Stem Cells: Current Understanding and Mitochondria Transplantation Strategies

The phenomenon of mitochondria donation is found in various tissues of humans and animals and is attracting increasing attention. To date, numerous studies have described the transfer of mitochondria from stem cells to injured cells, leading to increased ATP production, restoration of mitochondria function, and rescue of recipient cells from apoptosis. Mitochondria transplantation is considered as a novel therapeutic approach for the treatment of mitochondrial diseases and mitochondrial function deficiency. Mitochondrial dysfunction affects cells with high energy needs such as neural, skeletal muscle, heart, and liver cells and plays a crucial role in type 2 diabetes, as well as Parkinson’s, Alzheimer’s diseases, ischemia, stroke, cancer, and age-related disorders. In this review, we summarize recent findings in the field of mitochondria donation and mechanism of mitochondria transfer between cells. We review the existing clinical trials and discuss advantages and disadvantages of mitochondrial transplantation strategies based on the injection of stem cells, isolated functional mitochondria, or EVs containing mitochondria.