1. Membrane organization/dynamics
Our goal is to better understand the regulation of membrane organization and dynamics, at the plasma membrane and during endocytic trafficking, and its significance for human diseases.
Membrane organization
Membrane lipids are generally considered to be homogeneously distributed, except for nanometric domains (short-lived lipid rafts and long-lived caveolae). Using vital high-resolution confocal imaging, our group has recently discovered that fluorescent membrane lipid analogs can spontaneously cluster into much larger (micrometric), stable domains (Tyteca et al, 2010). These domains depend on temperature, cholesterol, membrane tension as well as membrane:cytoskeleton anchorage, and are deeply altered in genetic diseases of erythrocytes (Figure; Tyteca et al, 2010; D’auria et al, 2011).
Fluorescent sphingomyelin micrometric domains on erythrocytes can be modulated by pharmacological (b,c) or genetic (d) perturbations of membrane architecture. (a) untreated control erythrocyte; (b) 25% cholesterol depletion by methyl-beta-cyclodextrin; (c) phosphorylation of 4.1R anchorage complexes by PKC activation; (d) untreated spherocytotic patient (live confocal imaging, bars, 2 μm).
To understand the mechanisms underlying their biogenesis and physiopathology, our current projects address whether micrometric lipid domains (i) show differential association with key membrane proteins; (ii) are polarized during cell migration, fission and fusion; and (iii) are involved in the physiopathology of genetic diseases affecting membrane:cytoskeleton anchorage. These investigations rely on manipulations of cell culture, advanced vital bioimaging methods, biochemistry (endocytosis, lipid metabolism, subcellular fractionation...) and will be extended to biophysics.
Membrane dynamics
Emphasis is placed on molecular controls and on the role of cell polarity, with special interest to physiopathology. Kidney proximal tubular cells (PTC) serve as a privileged system, because (i) apical receptor-mediated endocytosis shows an extraordinary efficiency and can be readily probed in vivo; (ii) PTC can be conveniently studied and manipulated in polarized monolayers; (iii) various KO mouse models with defective endocytosis are available; and (iv) protein overload during proteinuria is a major cause of kidney failure.
Current projects address (i) the transcriptional control of key endocytic components by polarity; (ii) regulation by kinases of trafficking at the sorting endosome; (iii) and the contribution of intracellular organelles to signalling.
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