3D-models based on patient-specific induced pluripotent stem cells are widely used for biomedical research. Thus, non-invasive and continuous comprehensive description of these of 3D-models using FLIM and multiphoton microscopy requires.
KEYWORDS: Fluorescence lifetime imaging, Oxygen, 3D modeling, Luminescence, Biological research, 3D displays, Tissues, Stem cells, Microscopy, Medical research
3D models based on cells differentiated from patient-specific induced pluripotent stem cells (iPSCs) are widely used to identify disease phenotypes, to accurately analyze dysfunctions at the level of human tissues and organs, to screen new drugs, which makes them more promising tool for biomedical research tasks than monolayer cultures, which is associated with their proximity to in vivo. The metabolic activity with oxygenation level of cells, assessed by optical imaging methods, can be used as markers of cell viability, proliferative activity and the degree of differentiation in 3D culture conditions. In this paper we used fluorescence and phosphorescence lifetime imaging microscopies (FLIM and PLIM) to study the metabolic status and the oxygenation level of derived from iPSCs neural stem cells (NSC) cultured in 3D condition. An analysis of the fluorescence intensities and FLIM data showed that NSCs in monolayer and at the periphery of large spheroids have more glycolytic phenotypes, NSCs in the center of large spheroids and NSCs grouped into small spheroids have more oxidative state. For determination of the relative oxygen level in spheroids PLIM of BPTDM stained neurospheres was carried out. As it was supposed, oxygen transport in the spheroid depended on it size. In neurospheres with an average size 600 μm O2 distribution is radial, with the lowest concentration in the center. Thus, the metabolic status and oxygenation level of the NSC in the spheroid composition was assessed in a life-time and noninvasive manner.
The changes in cell metabolism can affect the epigenome-modifying enzymes activity during iPSCs differentiation and thus control the functional potential of the final cell. Therefore, for therapeutic applications, the restoration of a fully functional mitochondrial network specific for the cell types derived from iPSCs will be required to support the energy and other mitochondrial factors. Recently, FLIM method allows to study the metabolic changes that accompanying cell differentiation noninvasively and without additional labels. In this study, we investigated the metabolic changes in iPSCs during neural differentiation using two-photon fluorescence microscopy and FLIM. Cellular metabolism was examined by monitoring the optical redox ratio (FAD/NAD(P)H), the fluorescence lifetime contributions of the free and bound forms of NADH and NADPH. Given that neural differentiation is also accompanied by synthetic processes and oxidative stress, this process was included in the scope of this work. We demonstrated an increased contribution of protein-bound NADH and NADPH in neuron associated with metabolic switch to oxidative phosphorylation and the biosynthetic processes or oxidative stress, respectively. We also found that the optical redox ratio FAD/NAD(P)H decreased during neural differentiation, and this was likely to be explained by the intensive lipid membrane synthesis or ROS generating and the enhanced NADPH production associated with them. The biochemical analysis was carried out to verify the metabolic status of iPSCs and their neural derivatives. Based on the data on glucose consumption, lactate and ATP amount we registered the trend to the metabolic pathways redistribution towards the oxidative phosphorylation in neuron.
The differentiation of endothelial cells from human iPSC has incontestable advantages in diseases research and therapeutic applications. However, the safe use of iPSC derivatives in regenerative medicine requires an enhanced understanding and control of factors that optimize in vitro reprogramming and differentiation protocols. Shifts in cellular metabolism associated with intracellular pH changes affect the enzymes that control epigenetic configuration, which impact chromatin reorganization and gene expression changes during reprogramming and differentiation. FLIM-based metabolic imaging of NADH and FAD is a powerful tool for measuring mitochondrial metabolic state and widely used diagnostic method for identification of neoplastic diseases, skin diseases, ocular pathologies and stem cells differentiation. Therefore, in this study, we used the potential of FLIM-based metabolic imaging and fluorescence microscopy of NADH and FAD to study the metabolic changes during iPSC differentiation in endothelial cells. The evaluation of the intracellular pH was carried out with the fluorescent pH-sensor SypHer-2 and fluorescence microscopy to obtain complete information about metabolic status of iPSC and their endothelial derivatives. Based on the FAD/NAD(P)H optical redox ratios increase and the contributions rise of the NAD(P)H fluorescence lifetime in iPSC during endothelial differentiation, we demonstrated an contribution increase of OXPHOS to cellular metabolism. Based on the shift toward more acidic intracellular pH in endothelial cell derived from iPSCs we verified their oxidative state.
Non-invasive imaging of cell metabolism is a valuable approach to assess the efficacy of stem cell therapy and understand the tissue development. In this study we analyzed metabolic trajectory of the mesenchymal stem cells (MCSs) during differentiation into adipocytes by measuring fluorescence lifetimes of free and bound forms of the reduced nicotinamide adenine dinucleotide (NAD(P)H) and flavine adenine dinucleotide (FAD). Undifferentiated MSCs and MSCs on the 5, 12, 19, 26 days of differentiation were imaged on a Zeiss 710 microscope with fluorescence lifetime imaging (FLIM) system B&H (Germany). Fluorescence of NAD(P)H and FAD was excited at 750 nm and 900 nm, respectively, by a femtosecond Ti:sapphire laser and detected in a range 455-500 nm and 500-550 nm, correspondingly. We observed the changes in the NAD(P)H and FAD fluorescence lifetimes and their relative contributions in the differentiated adipocytes compare to undifferentiated MSCs. Increase of fluorescence lifetimes of the free and bound forms of NAD(P)H and the contribution of protein-bound NAD(P)H was registered, that can be associated with a metabolic switch from glycolysis to oxidative phosphorylation and/or synthesis of lipids in adipogenically differentiated MSCs. We also found that the contribution of protein-bound FAD decreased during differentiation. After carrying out appropriate biochemical measurements, the observed changes in cellular metabolism can potentially serve to monitor stem cell differentiation by FLIM.
Recently, great deal of interest is investigation the function of the stem cells (SC) in tumors. In this study, we studied
«recipient–tumor– fluorescent stem cells » system using the methods of in vivo imaging and laser scanning microscopy
(LSM). We used adipose-derived adult stem (ADAS) cells of human lentiviral transfected with the gene of fluorescent protein Turbo FP635. ADAS cells were administrated into nude mice with transplanted tumor HeLa Kyoto (human cervical carcinoma) at different stages of tumor growth (0-8 days) intravenously or into tumor. In vivo imaging was performed on the experimental setup for epi – luminescence bioimaging (IAP RAS, Nizhny Novgorod). The results of the imaging showed localization of fluorophore tagged stem cells in the spleen on day 5-9 after injection. The sensitivity of the technique may be improved by spectral separation autofluorescence and
fluorescence of stem cells. We compared the results of in vivo imaging and confocal laser scanning microscopy (LSM 510 META, Carl Zeiss, Germany). Internal organs of the animals and tumor tissue were investigated. It was shown that with i.v. injection of ADAS, bright fluorescent structures with spectral characteristics corresponding to TurboFP635 protein are locally accumulated in the marrow, lungs and tumors of animals. These findings indicate that ADAS cells integrate in the animal body with transplanted tumor and can be identified by fluorescence bioimaging techniques in vivo and ex vivo.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.