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Caspase Cascades in Human Immunodeficiency Virus-Associated Neurodegeneration

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Caspase Cascades in Human Immunodeficiency Virus-Associated Neurodegeneration The Journal of Neuroscience, May 15, 2002, 22(10):4015–4024 Caspase Cascades in Human Immunodeficiency Virus-Associated Neurodegeneration Gwenn A. Garden,1,2,3 Samantha L. Budd,2,3 Elena Tsai,3 Lisa Hanson,1 Marcus Kaul,2,3 Danielle M. D’Emilia,3 Robert M. Friedlander,3 Junying Yuan,4 Eliezer Masliah,5 and Stuart A. Lipton2,3,5 1Department of Neurology, University of Washington, Seattle, Washington 98195, 2Center for Neuroscience and Aging, The Burnham Institute, La Jolla, California 92037, 3Neuroapoptosis Laboratory and CNS Research Institute, Department of Neurosurgery, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts 02115, 4Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, and 5Department of Neurosciences, University of California, San Diego, La Jolla, California 92037 Many patients infected with human immunodeficiency virus-1 HIV-induced neuronal apoptosis. Increased caspase-3 proteo- (HIV-1) develop a syndrome of neurologic deterioration known lytic activity and mitochondrial release of cytochrome c were as HIV-associated dementia (HAD). Neurons are not produc- observed in cerebrocortical cultures exposed to the HIV coat tively infected by HIV-1; thus, the mechanism of HIV-induced protein gp120. Specific inhibitors of both the Fas/tumor necro- neuronal injury remains incompletely understood. Several in- sis factor-␣/death receptor pathway and the mitochondrial vestigators have observed evidence of neuronal injury, includ- caspase pathway prevented gp120-induced neuronal apopto- ing dendritic degeneration, and apoptosis in CNS tissue from sis. Caspase inhibition also prevented the dendrite degenera- patients with HAD. Caspase enzymes, proteases associated tion observed in vivo in transgenic mice with CNS expression of with the process of apoptosis, are synthesized as inactive HIV/gp120. These findings suggest that pharmacologic inter- proenzymes and are activated in a proteolytic cascade after ventions aimed at the caspase enzyme pathways may be ben- exposure to apoptotic signals. Here we demonstrate that HAD eficial for the prevention or treatment of HAD. is associated with active caspase-3-like immunoreactivity that is localized to the soma and dendrites of neurons in affected Key words: apoptosis; caspase; dendrite degeneration; de- regions of the human brain. Additionally, the cascade of convolution microscopy; HIV-associated dementia; tumor ne- caspase activation was studied using an in vitro model of crosis factor Approximately 20–40% of patients infected with human immu- et al., 1990; Adamson et al., 1996; New et al., 1997; Kruman et al., nodeficiency virus-1 (HIV-1) develop HIV-associated dementia 1998; Yeung et al., 1998; Huang et al., 2000; Patel et al., 2000; (HAD) (McArthur et al., 1993), a neurodegenerative syndrome Trillo-Pazos et al., 2000) from HIV-infected immune cells (mac- characterized by cognitive decline, personality change, and motor rophages and microglia). Among the viral proteins studied, the deficits (Lipton and Gendelman, 1995). The neuropathology that coat protein gp120 manifests neurotoxic effects in both primary can be associated with HAD includes HIV encephalitis (HIVE) human CNS cultures (Yeung et al., 1995) and transgenic mice with prominent microglial activation, neuronal loss, dendritic (Toggas et al., 1994). HIV-1/gp120 binds to CD4 and to specific simplification, and decreased synaptic density (Masliah et al., chemokine receptors on immune cells. Many neurons and astro- 1996). Nuclear changes characteristic of apoptosis have been cytes also bear chemokine receptors (Hesselgesser et al., 1998; observed in both neurons and non-neuronal cells (Adle-Biassette Lavi et al., 1998; Meucci et al., 1998; Zheng et al., 1999). On et al., 1995; Gelbard et al., 1995; Petito and Roberts, 1995; Shi et isolated neurons, HIV/gp120 may promote apoptosis directly al., 1996). Neurons are not productively infected by HIV-1. (Hesselgesser et al., 1998; Meucci et al., 1998; Zheng et al., 1999). Hence, how HIV infection causes neuronal injury and apoptosis However, we showed previously that, in mixed neuronal–glial is not completely understood (Kaul et al., 2001). cultures, the predominant neurotoxicity of HIV/gp120 depends One proposed mechanism for HIV-related neuronal damage on the activation of microglial chemokine receptors rather than a involves release of viral proteins (Brenneman et al., 1988; Dreyer direct effect on neurons (Kaul and Lipton, 1999). Pathophysi- Received Sept. 14, 2001; revised Feb. 1, 2002; accepted Feb. 15, 2002. ologically relevant (picomolar) concentrations of HIV/gp120 ac- This work was supported by The Wellcome Trust (S.L.B.), AmFAR (M.K.), and tivate macrophage–microglial cells (Giulian et al., 1993; Kaul and National Institutes of Health grants to G.A.G. and S.A.L. We thank Timothy Lipton, 1999) that subsequently release toxic products capable of Lishnak and Satjiv Kohli for technical assistance and Dr. M. Johnson, R. Morrison, inducing apoptosis in neurons (Lipton and Gendelman, 1995). T. Moller, and Y. Kinoshita for comments on this manuscript. We also thank Dr. L. Mucke for the generous gift of gp120 transgenic mice. Human tissue was obtained In other systems, apoptosis is mediated by activation of from the University of California, San Diego HIV Neurobehavioral Research caspases, a family of proteases involved in signal transduction of Center. Correspondence should be addressed to Dr. Gwenn Garden, Department of apoptotic stimuli and ordered cellular disassembly (Stennicke and Neurology, Box 356465, University of Washington, Seattle, WA 98195, E-mail: Salvesen, 2000). Caspases are synthesized as inactive proenzymes [email protected]; or Dr. Stuart A. Lipton, Center for Neuroscience and and are activated by proteolytic cleavage. Multiple caspases may Aging, The Burnham Institute, La Jolla, California 92037, E-mail: [email protected]. activate one another in a sequential cascade manner. Caspase-3 is Copyright © 2002 Society for Neuroscience 0270-6474/02/224015-10$15.00/0 a frequent downstream effector of the cascade (Stennicke and 4016 J. Neurosci., May 15, 2002, 22(10):4015–4024 Garden et al. • Caspases in HAD Table 1. Patient characteristics of cases evaluated for active caspase-3-like immunoreactivity Case Cause of death Time to autopsy HIV status Neuropsych testing Neuropathology 1 Hepatic failure 4 hr HIVϩ Impaired HIVE 2 Pneumonia 24 hr HIVϩ Impaired HIVE 3 Pneumonia 24 hr HIVϩ Impaired HIVE 4 Hepatic failure 3 hr HIVϩ Impaired HIVE 5 Pneumonia 16 hr HIVϩ Impaired HIVE 6 Pneumonia 10 hr HIVϩ Normal None 7 Sepsis 14 hr HIVϩ Normal None 8 Fungal sepsis 24 hr HIVϩ Normal Fungal vasculitis 9 Hepatic failure 24 hr HIVϪ Not available Type II Alzheimer’s gliosis 10 Hepatic failure 7 hr HIVϪ Not available None The age range was 33–55 years. There was no significant difference in mean age or time to autopsy between patients with HIVE and controls. The cause of death for each HAD–HIVE case was also represented in the control group. HIVϩ, HIV positive; HIVϪ, HIV negative. Salvesen, 2000) and is activated in several neurodegenerative presence of the gp120 transgene or the caspase interfering transgene disorders (Namura et al., 1998; Hartmann et al., 2000; Su et al., (Casp-1/C285G) by PCR. The PCR product was assessed by the presence of an appropriate molecular weight band on ethidium bromide-stained 2000). Active caspase-3 was detected by Western blot in human agarose gels. The HIV/gp120 transgenic mice were maintained on a fetal CNS cultures exposed to HIV/gp120 (Zheng et al., 1999), hybrid strain background (C57BL/6 ϫ SJL), and the C285G mice were but the specific cell population undergoing caspase activation was bred into a C57BL/6 strain background for more than five generations not identified. Additionally, postmortem studies on the brains of before this cross. The F2 generation of these initial crosses were used to pediatric patients with HAD manifested an increase in neurons establish breeding pairs between Casp-1/C285G and gp120 transgenic heterozygotes. To avoid any possible impact of strain on the results of immunoreactive for procaspase-3 (James et al., 1999). In that these experiments, all of the animals used in this analysis were F3 study, however, the presence of active caspase-3 was not progeny of established F2 breeding pairs. Genotype was confirmed by examined. repeat tail biopsy at the time the animal was killed. We demonstrate here that neuronal active caspase-3-like im- Primary cerebrocortical cultures. Embryonic rat cerebrocortical cultures munoreactivity is significantly elevated in cerebrocortical neurons were prepared as described previously (Kaul and Lipton, 1999; Budd et al., 2000). Cultures containing neurons, astrocytes, and microglia were from patients with HAD, as well as in cultured rodent neurons incubated in 200 pM recombinant glycosylated HIVSF2gp120 (catalog exposed to HIV/gp120. Neurons exposed to HIV/gp120 undergo #386; National Institutes of Health AIDS Research and Reference activation of two upstream caspases, caspase-8 and caspase-9, and Reagent Program, Bethesda, MD). After a 24 hr exposure to gp120, inhibition of either pathway prevents neuronal apoptosis. Trans- cultures were fixed, permeabilized, and stained with Hoechst dye 33342 genic mice expressing the HIV/gp120 coat protein develop sev- (Sigma, St. Louis, MO). Apoptotic profiles were identified by the pres- ence of a condensed nuclear morphology, and the ratio of apoptotic eral neuropathologic features associated with HAD,
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