Visualization of hypoxic oligodendrocyte injury in PLP-EGFP transgenic mice

Abstract

White matter injury is an important feature of several acute neurological diseases. To date, none of the immunohistochemical approaches for assessing oligodendrocyte (OL) damage have been entirely satisfactory. We investigated the

usefulness of transgenic mice with oligodendrocyte-specific expression of GFP controlled by a proteolipid promoter (Plp-EGFP; BS Mallon et al., J. Neuroscience, 2002), to study the time course of injury during and after 30 min of oxygen- glucose deprivation (OGD). Acute coronal brain slices (400μm) including corpus callosum were transferred to an interface chamber and superfused with aCSF saturated with 95/5% O2

/CO2

at 33C. OGD was induced by switching to

glucose-free aCSF bubbled with 95/5%N2 /CO2 . Within 1-2 hours there was widespread OL injury, demonstrated by loss of labeling with OL-specific antibody CC-1 (APC) and gain of pyknotic nuclei. Cytochrome c was released from mitochondria during OGD and diffused thereafter. Confocal visualization of GFP-expressing OLs revealed marked swelling of the nucleus and vacuole formation around the cytoplasm. By 2 hours of reperfusion some of the OLs lost their processes and extensive vacuoles were observed along their entire length. EM confirmed OL injury including swollen mitochondria, clumping of chromatin and cytoplasmic vacuoles. Our results demonstrate close correspondence between Plp-EGFP and EM assessment of OL morphology. The observed damage to OLs matches patterns of white matter injury in other models (Pantoni, 1996; Rosenberg, 1999; Valeriani, 2000). Transgenic expression of other fluorescent proteins controlled by cell-specific promoters allows study of selected cell populations (YFP axons, Plp-dsRed Ols and GFP-GFAP astrocytes) and is a valuable tool to study mechanisms of injury in vivo and in vitro.