Name: Single-Cell Dissociation of Murine Islets for Flow Cytometric Analysis of &#946;-Cell Mitophagy
Uploaded: 2023-09-15T14:40:00
Description: Watch this Scientific Journal Video about Single-Cell Dissociation of Murine Islets for Flow Cytometric Analysis of β-Cell Mitophagy at JoVE.com

single-cell dissociation of murine islets for flow cytometric analysis of &#946;-cell mitophagy

Análisis cuantitativo de la mitofagia en células β pancreáticas murinas

Pancreatic &#946;-cells produce and secrete insulin to meet metabolic demands, and &#946;-cell dysfunction is responsible for hyperglycemia and diabetes onset in both type 1 and type 2 diabetes. &#946;-Cells couple glucose metabolism with insulin secretion via mitochondrial energetics and metabolic output, which depend on a reserve of functional mitochondrial mass1,2,3. To maintain optimal &#946;-cell function, &#946;-cells rely on mitochondrial quality control mechanisms to remove aged or damaged mitochondria and preserve functional mitochondrial mass4. Selective mitochondrial autophagy, also known as mitophagy, is a key component of the mitochondrial quality control pathway.
Assessments of mitophagy in live cells often rely on changes in mitochondrial pH that occur during mitophagy. Mitochondria have a slightly alkaline pH, and healthy mitochondria normally reside in the pH-neutral cytosol. During mitophagy, damaged or dysfunctional mitochondria are selectively incorporated into autophagosomes and eventually cleared within acidic lysosomes5. Several in vivo transgenic mitophagy reporter mouse models, such as mt-Keima6, mitoQC7, and CMMR8, as well as transfectable mitophagy probes, such as the Cox8-EGFP-mCherry plasmid9, utilize this pH change to provide quantitative assessments of mitophagy. Use of transgenic mice expressing the mt-Keima pH-sensitive dual-excitation ratiometric probe has been optimized for mitophagy assessments in islets and &#946;-cells via flow cytometry10,11. The ratio of acidic-to-neutral mt-Keima wavelength emissions (the ratio of acidic 561 nm to neutral 480 nm excitation) can be used to robustly quantify mitophagy6,12.
This protocol describes an optimized approach to assess mitophagy flux in primary islets and &#946;-cells isolated from mt-Keima transgenic mice10,11. While mt-Keima is a highly sensitive probe, it requires either complicated animal breeding schemes or the transfection of cells, which can often be challenging when working in combination with other genetic models or with primary human islets. Additionally, the use of multiple fluorescence lasers and detectors to identify neutral and acidic cell populations can limit the combinatorial use of other fluorescent reporters.
To overcome these challenges, this protocol also describes a complementary, single fluorescent channel, dye-based method for robust detection of mitophagy in &#946;-cells from isolated mouse islets. This approach, referred to as the MtPhagy method, utilizes a combination of three cell-permeable dyes to select for &#946;-cells, quantify the cell populations actively undergoing mitophagy, and assess mitochondrial membrane potential (MMP or &#916;&#968;m) simultaneously.
The first of these dyes is Fluozin-3-AM, a cell-permeable Zn2+ indicator with an Ex/Em 494/516 nm13. Mouse islets comprise a heterogeneous population of functionally distinct cells, including &#945;-, &#946;-, &#948;-, and PP cells. &#946;-Cells comprise approximately 80% of cells within the mouse islet and can be distinguished from other islet cell types due to their high Zn2+ concentration within insulin granules14,15, allowing for identification of &#946;-cells as the Fluozin-3-AMhigh population. The MtPhagy dye, a pH-sensitive dye that is immobilized on mitochondria via a chemical bond and emits weak fluorescence, is also utilized in this protocol16. Upon mitophagy induction, damaged mitochondria are incorporated into the acidic lysosome, and the MtPhagy dye increases its fluorescence intensity within the low pH environment (Ex/Em 561/570-700 nm).
Additionally, Tetramethylrhodamine, ethyl ester (TMRE), is used to assess MMP. TMRE is a cell-permeable positively charged dye (Ex/Em 552/575 nm) that is sequestered by healthy mitochondria due to the relative negative charge upheld by their membrane potential17. Damaged or unhealthy mitochondria dissipate their membrane potential, resulting in decreased ability to sequester TMRE. Utilizing these dyes together, &#946;-cells undergoing mitophagy can be identified as the FluozinhighMtPhagyhighTMRElow population via flow cytometry. Since mitophagy is a dynamic rather than static process, this protocol was optimized to assess mitophagy flux using valinomycin, a K+-ionophore that induces mitophagy following dissipation of MMP18. Comparison of mitophagy in the presence and absence of valinomycin allows for assessment of mitophagy flux in different sample groups.
The dye-based nature of the current approach allows it to be extrapolated to human islets and other difficult-to-transfect cell types and circumvents the need for complicated animal breeding schemes, unlike the mt-Keima protocol. The overarching goal of this protocol is to quantify mitophagy in &#946;-cells at the single-cell level via two independent flow cytometry-based methods. Taken together, this protocol describes two powerful and complementary methods that allow for both precision and flexibility in the quantitative study of mitochondrial quality control.

Autor destacado: Evaluación del flujo de mitofagia en las células β pancreáticas utilizando enfoques complementarios efectivos y robustos 

Enfoques complementarios para interrogar el flujo de mitofagia en las células β pancreáticas

Our protocol describes two complementary methods to study beta-cell mitophagy flux at the single-cell resolution via flow cytometry. The mt-Keima protocol utilizes a genetic mitophagy reporter, whereas the MtPhagy protocol combines three fluorescent dyes, which makes it easy to extrapolate to difficult-to-transfect cells in human samples. Assessments of mitophagy using traditional biochemical approaches and imaging approaches are both time consuming and challenging.Thus, it's important to develop new, robust, and effective methods to study mitophagy flux in beta-cells. Both the mt-Keima and MtPhagy method are quantitative assessments that are efficient for studying mitophagy flux in pancreatic beta cells. So, the Soleimanpour lab focuses on the different mechanisms that drive pancreatic beta-cell failure and diabetes.And we specifically focus on the different aspects of mitochondrial lifecycle, including mitophagy, to understand how defects in mitochondrial function drive the development of diabetes.

Watch this Scientific Journal Video about Single-Cell Dissociation of Murine Islets for Flow Cytometric Analysis of β-Cell Mitophagy at JoVE.com

Single-Cell Dissociation of Murine Islets for Flow Cytometric Analysis of &#946;-Cell Mitophagy  

Disociación unicelular de islotes murinos para el análisis citométrico de flujo de la mitofagia de β células

Comience cultivando las muestras de ojales aisladas de ratones de dieta regular en grasas o en ratones de dieta alta en grasas durante la noche a 37 grados centígrados. Diseñar las condiciones experimentales deseadas para el estudio. Para cada condición experimental, usando una pipeta, recoja 100 ollaos en una placa de Petri de seis centímetros que contenga dos mililitros de medio para ojales.Para inducir la mitofagia, trate los ojales en las placas de Petri apropiadas con dos microlitros de 250 nanomolares de valinomicina durante tres horas. Aísle los ojales y, con una pipeta, transfiera los ojales de cada placa de Petri a un tubo de microcentrífuga separado. A continuación, gire los ojales a 350 G durante un minuto a 10 grados centígrados y, con una pipeta, deseche el sobrenadante.Lavar la muestra obtenida dos veces con un mililitro de PBS. Entre los lavados, centrifugar la muestra y desechar el sobrenadante como se demostró anteriormente. Para disociar los ojales en células individuales, agregue 500 microlitros de tripsina al 0,05% precalentada a 37 grados centígrados, a un tubo de muestra.Pipetear el contenido del tubo hacia arriba y hacia abajo repetidamente hasta que los ojales estén visiblemente dispersos. Agregue inmediatamente un mililitro de medio de ojal precalentado para neutralizar la tripsina. Centrifugar las muestras a 500 G durante cinco minutos a 10 grados centígrados.Retire el sobrenadante con cuidado sin alterar el gránulo. A continuación, lave las muestras dos veces con medio de flujo de ojales. Las muestras celulares ya están listas para ser teñidas para el análisis citométrico de flujo de la mitofagia de células beta.

Research

JoVE Journal

Biology

Single-Cell Dissociation of Murine Islets for Flow Cytometric Analysis of &#946;-Cell Mitophagy

Complementary Approaches to Interrogate Mitophagy Flux in Pancreatic &#946;-Cells

Mitophagy is a quality control mechanism necessary to maintain optimal mitochondrial function. Dysfunctional &#946;-cell mitophagy results in insufficient ...

Investigación

Biología

Flow Cytometric Analysis of Mitophagy in Murine Pancreatic &#946;-Cells Using MtPhagy Dye

Análisis citométrico de flujo de la mitofagia en células β pancreáticas murinas utilizando el colorante MtPhagy

Flow Cytometric Analysis of Mitophagy in Murine Pancreatic &#946;-Cells Using the Genetically Encoded mt-Keima Reporter

Análisis citométrico de flujo de la mitofagia en células β pancreáticas murinas utilizando el mt-Keima Reporter codificado genéticamente