Overexpression of the gene encoding the 70-kDa heat shock protein (hsp70) has previously been shown to protect neuronal cells against subsequent thermal or ischemic stress. It has no protective effect, however, against stimuli that induce apoptosis, although a mild heat shock (sufficient to induce hsp synthesis) does have a protective effect against apoptosis. We have prepared disabled herpes simplex virus-based vectors that are able to produce high level expression of individual hsps in infected neuronal cells without damaging effects. We have used these vectors to show that hsp27 and hsp56 (which have never previously been overexpressed in neuronal cells) as well as hsp70 can protect dorsal root ganglion neurons from thermal or ischemic stress. In contrast, only hsp27 can protect dorsal root ganglion neurons from apoptosis induced by nerve growth factor withdrawal, and hsp27 also protects the ND7 neuronal cell line from retinoic acid-induced apoptosis. However, hsp70 showed no protective effect against apoptosis in contrast to its anti-apoptotic effect in non-neuronal cell types. These results thus identify hsp27 as a novel neuroprotective factor and show that it can mediate this effect when delivered via a high efficiency viral vector.The heat shock proteins (hsps) 1 were originally identified on the basis of their increased synthesis following exposure to elevated temperature. Subsequently, however, they were shown to be induced by a wide variety of other stresses in many different cell types (for review see Refs. 1-3) including neuronal cells exposed to ischemia (4), amphetamine treatment (5), or to sodium arsenite (6). Such induction of the hsps has been shown to have a protective effect against exposure to a subsequent stress in a variety of cell types. Thus, for example, exposure of primary neuronal cultures to a mild heat stress or ischemic stress sufficient to induce the hsps has been shown to be protective against subsequent exposure to the excitotoxin glutamate or to severe heat or ischemic stress (6 -8), whereas similar exposure in vivo can protect against damaging effects caused by subsequent exposure to light (9) or ischemia (10, 11).In a number of cases the protective effect of a mild hspinducing stress can be reproduced by the artificial overexpression of a single hsp. Thus, for example, dorsal root ganglion (DRG) neurons can be protected against thermal or ischemic stress by overexpression of either the 70-kDa hsp (hsp70) or the 90-kDa hsp (hsp90) (12-14), and a similar protective effect of hsp70 and hsp90 has also been observed in the ND7 immortalized cell line derived from sensory neurons (15). Interestingly, Fink et al. (16) were able to protect cultured hippocampal neurons against subsequent heat shock using a herpes simplex virus (HSV)-derived amplicon vector expressing hsp70 indicating that this effect applies to neurons derived from both the central and peripheral nervous systems. Moreover, the use of an HSV-based vector opens up the possibility of testing the protective effect of the h...

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