flow cytometry of hoechst-stained mouse bone marrow cells for effective detection of side population using high-power 375 nm and 405 nm lasers

Alternative Laser Excitation Method for Easy Side Population Cell Detection

The side population (SP) cells are identified through Hoechst 33342 staining and analyzed using flow cytometry (FCM). The SP cells are characterized by the pumping of the fluorescent DNA dye out of the cells through their ATP-binding cassette (ABC) transporter1,2. The method was originally established for isolating murine bone marrow hematopoietic stem cells (HSCs)1. The bone marrow SP cells were enriched with a population of HSCs characterized by &#160;CD117+Sca-1+Lin-Thy1low&#160;expression3,4. Thereafter, the method was widely used to isolate and enrich stem cells from other tissues, including cardiac muscle5, liver6, lung7, kidney8, and forebrain9. In particular, the method has been applied to isolate cancer stem cells (CSCs) in the past decade. CSCs represent a small population of cells that possess the properties of tumor initiation, self-renewal, resistance to chemotherapy, and metastatic potential10. CSCs were initially identified in hematopoietic malignancies11 and subsequently observed in various solid tumors such as the prostate12, ovarian13, gastric14, breast15, and lung16 carcinomas. Despite the availability of various techniques for CSC identification, the SP technique remains a favored choice owing to its broad applicability across diverse tissues and cell lines. Moreover, it is a valuable technique that isolates CSCs using fluorescence-activated cell sorting (FACS)16,17,18. The experimental findings demonstrate that SP cells exhibit pronounced tumorigenicity and display elevated expression levels of stem cell-associated genes19,20. Our previous study21 has also demonstrated that transcriptomic analysis of isolated SP cells in multiple myeloma reveals enrichment of signaling pathways associated with stem cells, such as the hedgehog pathway. Meanwhile, we performed pathway enrichment analyses on the genes differentially expressed in the SP cells of acute myelogenous leukemia22. The altered genes were enriched in stem cell-related pathways (Wnt/&#946;-catenin, TGF-&#946;, Hedgehog, Notch). We found that 1 x 105 SP cells could form tumors in BALB/c null mice22, whereas non-SP cells could not, indicating that SP cells had characteristics of leukemia stem cells. The efficacy of the Hoechst SP method in the identification of CSCs is evident.
The Hoechst SP protocol has been refined and enhanced through the progression of research. The protocol entails stringent control of the dye concentration, cell density, incubation temperature and duration, buffer composition, and pH value. The cell samples prepared in accordance with this protocol were subjected to flow cytometric analysis. Due to the excitation of Hoechst dye with a UV laser at 355 nm and detection of its fluorescence emission using both a 690/50 nm filter (Hoechst Red) and 450/50 nm filter (Hoechst Blue), a 350 nm laser is required for FCM. However, 350 nm lasers are not commonly equipped in most FCMs because of their high cost. Hence, we attempted to find an alternate approach for&#160;dye excitation for the effective detection of SP cells by flow cytometry. In this study, the capability of the 375 nm and 405 nm lasers in detecting SP cells was assessed and compared with that of the 355 nm laser. Our findings demonstrate a remarkable similarity between the SP cells detected by the 355 nm, 375 nm, and 405 nm lasers. These results suggest that the high-power 375 nm and 405 nm lasers can serve as feasible alternatives to the 355 nm laser for SP cell detection. The inclusion of additional excitation light sources for Hoechst 33342 facilitates the use of more flow cytometry models.

Author Spotlight: Innovative Laser Techniques for Hoechst Staining to Analyze Side Population Cells

Effective Detection of Hoechst Side Population Cells by Flow Cytometry

We use the Hoechst stain population method to detect tumor initiating cells. In this paper, we're trying to find alternative approaches for Hoechst excitation. We found that the high power 375 nanometer and 405 nanometer lasers can serve as feasible alternatives to the traditional 355 millimeter laser.Conventionally, the Hoechst dye is excited with a UV laser at 355 nanometer. Due to the high cost of the UV lasers, they're not commonly equipped in most flow cytometry models. Our protocol expands a range of the lasers that can be used to detect Hoechst staining.For researchers focusing on normal and malignant stem cells, more models of flow cytometry can be used to detect cytopopulation cells.

Flow Cytometry of Hoechst-Stained Mouse Bone Marrow Cells for Effective Detection of Side Population Using High-Power 375 nm and 405 nm Lasers

To begin, stain the murine bone marrow cells with Hoechst 33342. For flow cytometry, launch the required software, then select the QC standardization. Insert the quality control or QC FluoroSphere sample tube into the tube holder before selecting start to begin the QC procedure.To create a new experiment, click on New Experiment in the File menu and specify the file path and save the experiment. Then select Set Channel in the Settings menu. Select the channel signal checkbox, and add the reagent name in the label column.Next, click pseudo color plots icon in the plot area to create plots. Click add tube in the test tube screen to create new sample tubes and change their names. Then select Run to load the sample, view the plots and establish the gates.Adjust the gain and threshold settings and select Record to save the data. To design the gate setting logic, click the x-axis to select FSEW, and click the y-axis to select FSEA. Select Polygon Gate to draw gate A to circle the individual cell and exclude adherent cells.For the second plot, click the x-axis to select FSEA, and click the y-axis to select SSEA. Select Polygon Gate to draw gate B to separate non-fragmentary cells and exclude cellular debris. For the third plot, click the x-axis to select PIA, and click the y-axis to select SSEA.After drawing the gate B, select live cells exhibiting negative propidium iodide and draw gate C to obtain live cells. For the fourth two-dimensional plot, click the x-axis to select Hoechst Red, and click the y-axis to select Hoechst Blue. Right-click the plot and select Property from the dropdown menu.Select linear format for both the x-axis and y-axis and draw the gate for side population cells. Use the 355 nanometer and 405 nanometer lasers simultaneously to detect both the control cells and the experimental cells. Acquire fluorescent signals at the 690 by 50 and 450 by 50 nanometer channels corresponding to the two laser.Observe the effective stimulation of Hoechst 33342 dye with 355 and 405 nanometer lasers to visualize the clear side population cells. For the same samples, use the 375 nanometer and 405 nanometer lasers for cell detection. The 355 nanometer laser effectively excited the Hoechst 33342 dye, resulting in clear observation of SP cells of bone marrow.The SP cells of the same samples detected by the 355 nanometer laser and the 405 nanometer laser were found to be essentially identical. Both 375 nanometer and 405 nanometer lasers effectively excited Hoechst 33342 to obtain SP cells.

flow-cytometry-hoechst-stained-mouse-bone-marrow-cells-for-effective

Research

JoVE Journal

Cancer Research

The side population (SP) cells are identified through Hoechst 33342 staining and analyzed using flow cytometry (FCM). The Hoechst SP method is utilized for the isolation of stem cells based on the dye efflux properties of ATP-binding cassette (ABC) transporters. The method was initially employed for the identification and isolation of hematopoietic stem cells (HSCs), but it has now evolved to primarily focus on the identification and isolation of cancer stem cells (CSCs). The traditional detection method of FCM uses a 355 nm laser to excite the dye to detect SP cells. Through this study, we have successfully identified alternative approaches for dye excitation that can effectively replace the detection of SP cells using a 355 nm laser. This is achieved through the utilization of high-power 375 nm or 405 nm lasers. This allows us to exercise enhanced selectivity in the detection of SP cells rather than being solely limited to the 355 nm laser flow cytometry.

Here, we show that high-power 375 nm and 405 nm lasers can effectively excite Hoechst 33342 and serve as a viable alternative to the 355 nm laser for side population (SP) cell detection, thereby expanding the range of available lasers in flow cytometry applications.

The side population (SP) cells are identified through Hoechst 33342 staining and analyzed using flow cytometry (FCM). The Hoechst SP method is utilized ...

Staining Mouse Bone Marrow Cells with Hoechst to Detect Side Population Cells by Flow Cytometry

To begin, obtain bone marrow cells from the mouse and add five micrograms per milliliter Hoechst 33342 to two milliliters of cell suspension. Prepare the negative control tube as well. Incubate in a water bath at 37 degrees Celsius for 90 minutes with gentle agitation every 30 minutes After incubation, cool the cells on ice for five minutes, and then centrifuge at 250G for five minutes at four degrees Celsius.Resuspend the cells in a cold running solution containing Hank's Balanced Salt Solution with 2%FBS. Centrifuge again at four degrees Celsius for five minutes. Next, resuspend the resulting cell pellet in 500 microliters of running solution per sample.Prior to flow cytometry analysis, supplement cells with two micrograms per milliliter of propidium iodide, and place them on ice for approximately five minutes.