Oxidative stress facilitates exogenous mitochondria internalization and survival in retinal ganglion precursor-like cells.

Ocular cells are highly dependent on mitochondrial function due to their high demand of energy supply and their constant exposure to oxidative stress. Indeed, mitochondrial dysfunction is highly implicated in various acute, chronic, and genetic disorders of the visual system. It has recently been shown that mitochondrial transplantation (MitoPlant) temporarily protects retinal ganglion cells (RGCs) from cell death during ocular ischemia. Here, we characterized MitoPlant dynamics in retinal ganglion precursor-like cells, in steady state and under oxidative stress. We developed a new method for detection of transplanted mitochondria using qPCR, based on a difference in the mtDNA sequence of C57BL/6 and BALB/c mouse strains. Using this approach, we show internalization of exogenous mitochondria already three hours after transplantation, and a decline in mitochondrial content after twenty four hours. Interestingly, exposure of target cells to moderate oxidative stress prior to MitoPlant dramatically enhanced mitochondrial uptake and extended the survival of mitochondria in recipient cells by more than three fold. Understanding the factors that regulate the exogenous mitochondrial uptake and their survival may promote the application of MitoPlant for treatment of chronic and genetic mitochondrial diseases.

In-vivo imaging for assessing tumor growth in mouse models of ocular melanoma.

Uveal melanoma (UM) and conjunctival melanoma (CM) are ocular malignancies that give rise to life-threatening metastases. Although local disease can often be treated successfully, it is often associated with significant vision impairment and treatments are often not effective against metastatic disease. Novel treatment modalities that preserve vision may enable elimination of small tumors and may prevent subsequent metastatic spread. Very few mouse models of metastatic CM and UM are available for research and for development of novel therapies. One of the challenges is to follow tumor growth in-vivo and to determine the right size for treatment, mainly of the posterior, choroidal melanoma. Hence, the purpose of this study was to establish a simple, noninvasive imaging tool that will simplify visualization and tumor follow-up in mouse models of CM and UM. Tumors were induced by inoculation of murine B16LS9 cells into the sub-conjunctival or the choroidal space of a C57BL/6 mouse eye under a surgical microscope. Five to ten days following injection, tumor size was assessed by Phoenix MicronIV™ image-guided Optical Coherence Tomography (OCT) imaging, which included a real-time camera view and OCT scan of the conjunctiva and the retina. In addition, tumor size was evaluated by ultrasound and histopathological examination of eye sections. Tumor growth was observed 5-9 days following sub-conjunctival or sub-retinal injection of seven-thousand or seventy-thousand cells, respectively. A clear tumor mass was detected at these regions using the MicronIV™ imaging system camera and OCT scans. Histology of eye sections confirmed the presence of tumor tissue. OCT allowed an accurate measurement of tumor size in the UM model and a qualitative assessment of tumor size in the CM model. Moreover, OCT enabled assessing the success rate of the choroidal tumor induction and importantly, predicted final tumor size already on the day of cell inoculation. In conclusion, by using a simple, non-invasive imaging tool, we were able to follow intraocular tumor growth of both CM and UM, and to define, already at the time of cell inoculation, a grading scale to evaluate tumor size. This tool may be utilized for evaluation of new mouse models for CM and UM, as well as for testing new therapies for these diseases.