GTMB 7 - Gene Therapy & Molecular Biology

Gene Therapy and Molecular Biology Vol 7, page 251Hence, hsp27 over-expression has a clear potent protectiveeffect in the nervous system in terms of kainate toxicity,both at the level of whole animal seizure activity andsurvival and at the level of vulnerable neurones within thehippocampus (Akbar et al, 2003). It will evidently be ofconsiderable interest to extend this study by determiningwhether hsp27 can have protective effects against otherdamaging stimuli in the nervous system including, forexample, cerebral ischaemia. It will also be of interest toconduct a detailed study of the hsp27 and hsp70 overexpressingtransgenic animals, to compare the potency ofthese different heat shock proteins against variousdamaging stimuli in both the heart and the brain and toconfirm or deny the suggestion that hsp27 may be morepotent than hsp70 in protecting the nervous system.It is already clear however, that hsp27 does have a clearprotective effect in the nervous system in vivo as well as invitro. This reinforces the need to conduct studies usingdifferent individual hsps and investigating their protectiveeffects, rather than simply focusing on the major heatshock protein hsp70.V. Therapeutic potential of hspsThe experiments described in earlier sections, clearlysuggest that procedures which elevate hsp levels in theheart or the brain may be of significant benefit, forexample, during reperfusion following a period ofischaemia, or in patients undergoing neuronal cell loss dueto neurodegenerative diseases such as Alzheimer’s orParkinson’s diseases. Similarly, elevation of hsp levelsmay be beneficial during cardiac bypass or to preservedonor heart function prior to transplantation. Indeed, inview of the use of cold storage during transportation priorto transplantation, it is of particular interest that reduced aswell as elevated temperature induces hsp expression in theheart (Laios et al, 1997). Moreover, a mild heat treatmentprior to hypothermic storage has been shown to enhancesubsequent recovery of the heart (Gowda et al, 1998a).Such temperature-based manipulations of the hspsmay thus have a role to play in cardiac transplantationprocedures. Similarly, it has been shown that a protectiveeffect across the whole heart can be obtained by using athermal probe to produce local heating of the heart (Goudaet al, 1998b) suggesting that a similar procedure could beused therapeutically.The induction of the hsps by stressful stimuli such aselevated temperature (for review see Morimoto, 1998) orischaemia (Nishizawa et al, 1999) is mediated by the heatshock transcription factor (HSF-1). Thus followingexposure to elevated temperature, the cytoplasmic HSF-1monomer, forms a trimer and moves to the nucleus whereit binds to its target sites (known as heat shock elements)in the regulatory regions of the hsp genes and, followingHSF-1 phosphorylation, it induces hsp gene expression.Interestingly, the induction of the hsps by stressfulstimuli diminishes with age in a variety of tissuesincluding the heart and this has been shown to be due toimpaired activation of HSF-1 by stress in the aged heart(Locke and Tanguay, 1996). Moreover, this effect isassociated with a reduced protective effect of mild heatshock or ischaemia against a subsequent severe ischaemicstress in aged hearts (Locke and Tanguay, 1996; Fenton etal, 2000). As many of the situations where the protectiveeffect of hsps would be valuable involve elderlyindividuals, this suggest that other procedures notinvolving stressful stimuli or HSF-1 may be required forthe therapeutic induction of the hsps.Obviously, such an approach would be dependent onover-expression of the hsps actually having a protectiveeffect in aged cells. To test this, we have recently used ourHSV vectors to over-express individual hsps in neuronesfrom aged rats or peripheral blood lymphocytes from agedhumans. These experiments (Alsbury et al, submitted)clearly showed that hsps do have a protective effect incells from aged humans or animals, if they aresuccessfully over-expressed. Hence, it is indeedappropriate to try and identify procedures which result inover-expression of the hsps in a non-stressful manner.Such procedures can be divided into pharmacological andgene therapy procedures.A. Pharmacological methodsAlthough the hsps were identified on the basis oftheir induction by stressful procedures, they are alsoinduced naturally by specific non-stressful procedures (forreview see Latchman, 1998). For example, the cytokinesinterleukin-6 (Stephanou et al, 1997) and interleukin-10(Ripley et al, 1999) can induce hsp gene expression in anon-stressful manner. It has been shown that theseinducers do not act via HSF-1 but activate hsp expressionvia other transcription factors such as NF-IL6 and STAT3(for review see Stephanou and Latchman, 1999). Based onthe use of these inducers in non-cardiac cells, wedemonstrated that the interleukin-6-like cytokinecardiotrophin-1 (CT-1) was able to induce hsp synthesis incultured cardiac cells and that such treatment protectsthem against subsequent exposure to severe thermal orischaemic stress (Stephanou et al, 1998). Similar inductionof the hsps in cultured cardiac cells and protection againstsubsequent severe stress is also observed with the tyrosinekinase inhibitor herbimycin A (Morris et al, 1996; Condeet al, 1997).These protective effects in cardiac cells in culturehave also been extended to the intact heart. For example,Vigh et al, (1997) showed that bimoclomol, a novelhydroxylamine derivative was able to induce hsp synthesisin the intact perfused heart ex vivo and to produce aprotective effect against a subsequent ischaemia.Similarly, Meng et al, (1996) demonstrated thatnorepinephrine treatment of an intact rat resulted in hspinduction in the heart and protection against ischaemiawhen the heart was subsequently perfused ex vivo.Several compounds thus exist which can induce hspsand produce a protective effect, although it should be notethat in no case has this protective effect been directlyshown to be due to the ability to induce hsps. Before theprotective effect of any of these compounds could beexploited clinically, it is evidently necessary to investigatewhether their protective effect in the heart can be achievedwithout any significant side-effects. For example, CT-1was originally identified on the basis of its ability toinduce cardiac hypertrophy (Pennica et al, 1995) whilst251