Expression of 27 kDa heat shock protein (Hsp27) in immature rat brain after a cortical aspiration lesion

The 27 kDa heat shock protein (Hsp27) is a well-known member of the astrogl ial response to injury, playing a protective role against oxidative stress, apoptosis, and cytoskeletal destruction. Although several studies have bee n focused on the damaged adult brain, little is known about Hsp27 expressio n in the immature brain. In this work, we have examined the spatiotemporal pattern of Hsp27 expression in the normal postnatal rat brain following a c ortical aspiration lesion at postnatal day 9. In the immature brain, Hsp27 is mainly observed in the internal capsule, although some scattered cells a re also found in the ependyma, the corpus callosum, the septum, and hypotha lamic glia limitans. In the internal capsule, Hsp27 expression is developme ntally regulated, being significantly decreased from postnatal day 14. Afte r a cortical aspiration lesion, de novo expression of Hsp27 is observed in cortical injured areas as well as in the secondary affected thalamus. In th e cortex, expression of Hsp27 is first seen at day 1 postlesion (PL) surrou nding the neurodegenerative area, becoming restricted to the glial scar at longer survival times. Although a pulse-like expression of Hsp27 is observe d in some microglial cells at day 1 PL, most Hsp27-labeled cells are reacti ve astrocytes, which show GFAP overexpression and coexpress vimentin from d ay 3 PL. In the thalamus, astroglial Hsp27 expression is delayed, being fir st observed at day 5 PL. Thalamic Hsp27-labeled astrocytes do not show vime ntin expression. Our observations demonstrate astroglial expression of Hsp2 7 in areas of tissue damage following postnatal traumatic injury, suggestin g an involvement of this cytoskeleton-stabilizing protein in the remodeling processes following postnatal brain damage. (C) 2001 Wiley-Liss, Inc.