Ž . Brain Research 832 1999 112–117 Research report Suppression of post-ischemic-induced Fos protein expression by an antisense oligonucleotide to c-fos mRNA leads to increased tissue damage Yi Zhang a , Marsha A. Widmayer a,b , BenXiao Zhang a,b , Jian-Kun Cui a , David S. Baskin a,b, ) a Department of Neurosurgery, Baylor College of Medicine, Suite 944, 6560 Fannin Street, Houston, TX, 77030 USA b Veterans Affairs Medical Center, Houston, TX, USA Accepted 30 March 1999 Abstract Activation of c-fos, an immediate early gene, and the subsequent upregulation of Fos protein expression occur following neural injury, Ž . including focal cerebral ischemia fci . Fos and Jun form a heterodimer known as activator protein 1, which regulates the expression of many late effector genes. To study the downstream effects of c-fos expression following ischemia, we suppressed the translation of c-fos Ž . Ž . by administering an antisense oligonucleotide AO to c-fos mRNA. Eighteen hours prior to fci, male, Long Evans LE rats received Ž . Ž . intraventricular injections of AO, mismatched AO MS or artificial cerebrospinal fluid aCSF . Fci was induced by permanent right middle cerebral artery occlusion. At 24-h post-occlusion, neurological function was assessed, and the animals were sacrificed. The brains were removed and stained with triphenyltetrazolium chloride for infarct volume determination. Fos immunohistochemistry was performed in separate animals to determine the effects of treatment on Fos expression number of Fos positive cells. AO administration reduced the number of cells with fci-induced Fos expression by ;75%. No differences in neurological scores existed between any of the groups. Ž . Ž AO-treated LE developed larger infarcts 40.1 "1.0%, mean "S.D., p -0.001 than MS- or aCSF-treated controls 34.3 "1.0%, . 34.6 "1.0%, respectively . These results suggest that c-fos activation and subsequent Fos protein expression exerts a neuroprotective effect, which is likely via upregulation of neurotrophins, following focal cerebral ischemia. This response, among others, may contribute to brain adaptation to injury that underlies functional recovery after stroke. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Antisense oligonucleotide; Immediate early gene; c-fos; Cerebral ischemia; Cerebral infarction 1. Introduction Ischemia is a common consequence of injury following Ž . many different forms of central nervous system CNS insult. While a number of biochemical cascades that are activated in ischemia have been extensively studied, the adaptive response of the CNS following ischemia has been less well characterized. The discovery of altered gene expression in ischemic brain using animal stroke models has opened new avenues for exploration of those post- w ischemic molecular events 3,14,19,23,28,30,35,46,51, x 54,58 . These include an increase in extracellular excita- tory amino acid neurotransmitters such as glutamate. Glu- tamate receptor-mediated activation of many phospholi- pases and protein kinases results in alteration of nuclear ) Corresponding author. Suite 944, 6560 Fannin Street, Houston, TX, 77030, USA. Fax: q1-713-798-3227; E-mail: dbaskin@tmh.tmc.edu regulatory processes. This includes the increased expres- sion of immediate early genes such as c-fos, junB, and w x c-jun 24,51 , that reach a peak level within hours follow- w x ing stroke 12,27,31,36,52,54,57 . The Fos, Jun, and JunB proteins have been shown to form activator protein-1 Ž . AP-1 through a conserved dimerization domain, i.e., the w x leucine zipper 53 . AP-1 is a transcription regulator pro- tein that can bind to a specific DNA motif, and is believed to transactivate the expression of a number of late effector w x genes 4,7,11,15,16,21,39 . Increases in AP-1 binding activity in the ischemic brain wx have been demonstrated 3 . However, many genes can be modulated by the transcription regulator AP-1. Whether immediate early gene induction and subsequent late gene regulation after stroke is beneficial or deleterious is un- wx known 2 . Since even a mild injury induces a profound expression of c-fos and Fos protein, such induction is often regarded as an index or marker of injury. In many cases, such induction has been assumed to be detrimental. 0006-8993r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0006-8993 99 01459-6