Michael A. Model
- Ph.D, Biophysics, University of Michigan
- M.S., B.S., Physics of Materials, Leningrad Polytechnic Institute
- Biological Light Microscopy
Cell volume and death
Cells can die a peaceful or a violent death. The peaceful way of dying is known as apoptosis, where a series of coordinated processes lead to cell's self-destruction. Proper balance between cell proliferation and death is necessary for normal functioning of the organism: too little apoptosis may lead to cancer, autoimmune and inflammatory diseases, and excessive apoptosis is associated with neurodegeneration, tissue damage and AIDS.
Necrosis is the other common type of death that typically results from a more severe injury. It is often observed in stroke, for example. Necrotic cells spill out their components, which can produce dangerous inflammation.
One major difference between necrotic and apoptotic cells is their volume. Necrotic cells swell and eventually rupture; apoptotic cells shrink. Cell volume is determined mostly by the amount of intracellular water, and water can flow in or out of the cell to maintain osmotic equilibrium. When potassium and chloride ions move out of the cell in response to an apoptotic stimulus, some water follows the ions, and the cell shrinks. Cells are capable of sensing their own volume, and volume changes somehow feed back into the signaling chain. This feedback is important, and sometimes blocking cell shrinkage will prevent further progression of apoptosis.
There are thousands of publications dealing with cell volume control – how cells control their volume and how volume, in turn, affects cell functioning. However, most of research on volume regulation in apoptosis has been done on free-floating and not adherent cells. But with the exception of blood cells, the natural condition for the majority of cell types is to be attached to something. Some cells can exist either attached or detached; for example, cells in cancerous tumors grow attached to the tumor, but once in a while they come loose and migrate to new place where they form metastases. Attachment activates integrins and can profoundly influence cell behavior: therefore, studying only cells in suspension cannot produce a complete picture.
The reason that cell volume in apoptosis has been studied mostly on floating cells is simple: there have been no good techniques to measure the volume of cells adhered to a surface. Strange as it may sound, modern optical microscopy can detect individual molecules and do many other amazing things, but is stumped by such a basic task as measuring cell thickness and volume with sufficient speed and precision.
Transmission-through-dye (TTD) is our local KSU brand of microscopy that permits visualization and measurements of cellular 3D shape and volume. The contrast in images obtained using TTD is directly and quantitatively related to cell thickness: thicker cells look brighter. Because cell volume and surface morphology are difficult to study using traditional optical methods, we believe that TTD, especially when combined with other modern techniques, opens new possibilities in diverse fields. In particular, we are now beginning to look at some unconventional mechanisms that may be responsible for cell volume changes in apoptotic cells. This is an important but little explored corner of biology.
The left panel is a TTD image of HeLa cells at various stages of apoptosis development, and the right panel is a corresponding fluorescence image showing caspase activation (green), the loss of mitochondrial potential (red) and condensation of chromatin (blue).
Kasim NR, Kuželová K, Holoubek A, Model MA. Live fluorescence and transmission-through-dye microscopic study ofactinomycin-induced apoptosis and apoptotic volume decrease. Apoptosis doi: 10.1007/s10495-013-0804-z (2013)
Yurinskaya VE, Moshkov AV., Wibberley AV, Lang F, Model MA, Vereninov AA. Dual response of human leukemiaU937 cells to hypertonic shrinkage: initial regulatory volume increase (RVI) anddelayed apoptotic volume decrease (AVD). Cell.Physiol.Biochem. 30:964-973. (2012)
Model MA. Imaging cell's third dimension. Microsc Today 20, 28-32 (2012)
Lababidi SL, Pelts M, Moitra M, Leff LG, Model MA. Measurement of bacterial volume by transmission-through-dye imaging. J Microbiol Methods, 87, 375-377 (2011)
Pelts M, Pandya SM, Oh CJ, Model MA. Thickness profiling of formaldehyde-fixed cells by transmission-through-dye microscopy. BioTechniques, 50, 389-396 (2011)
Model MA, Fang J, Yuvaraj P, Chen, Y, Zhang Newby B. 3D deconvolution of spherically aberrated images using commercial software. J. Microsc. 241, 94-100 (2011).
Gregg JL, McGuire KM, Focht DC, Model MA. Measurement of the thickness and volume of adherent cells using transmission-through-dye microscopy. Pflugers Arch. 460, 1097-1104 (2010).
Model MA, Reese JL, Fraizer GC. Measurement of wheat germ agglutinin binding with a fluorescence microscope. Cytometry 75A, 874-881 (2009).
Model MA, Khitrin AK, Blank JL. Measurement of the absorption of concentrated dyes and their use for quantitative imaging of surface topography. J. Microsc. 231, 156-167 (2008).
Model MA, Blank JL. Concentrated dyes as a source of two-dimensional fluorescent field for characterization of a confocal microscope. J. Microsc. 229, 12-16 (2008).
Scholarly, Creative & Professional Activities
- Techniques in optical microscopy
- Apoptosis, necrosis
- Cell volume regulation