(a) Field of the Invention
The invention relates to a transgenic animal for the neuronal expression of HIV-1 gp160.
(b) Description of Prior Art
Human immunodeficiency virus type 1 (HIV-1) is the causative agent of the acquired immune deficiency syndrome (AIDS). As a member of the lentivirinae subfamily of retroviruses, it is recognized for its ability to target the immune system and the nervous tissue (Navia, B. A. et al., 1986 b), Ann. Neurol., 19:525-535; Navia, B. A. et al., 1986 a), Ann. Neurol., 19:517-524).
A few weeks after the primary infection with HIV-1, a burst of virus replication with a high level of viremia occurs, it is during that phase of infection that the virus likely reaches the central nervous system (CNS) (Price, R. W. et al., 1988, Science, 239:586-592). In most cases it remains clinically silent for highly variable periods of time. Occasionally, it produces an acute meningitis or meningoencephalitis. However, in a large number of AIDS patients (30-40%) the virus entry in the CNS intiates a slowly progressive dementing syndrome termed HIV-1-associated motor/cognitive complex (Janssen, R. S., 1991, Neurology, 778:773-785), which impairs cognitive and motor functions and induces behavorial disorders. At autopsy, up to 96% of these patients show neuropathological changes (Budka, H., 1990a), In: Chopra J, Jagannathan K, Sawhney IMS (eds) Advancesin Neurology. Excerpta Medica, Amsterdam, 193-202; price, R. W. et al., 1988, Science, 239:586-592; Weis, S. et al., 1993, Acta Neuropathol, 85:185-189) that typically define the HIV-1 encephalopathy (HIVE) or leukoencephalopathy (HIVL) (Villa, G. et al., 1993, J Neur Neurosurgery Psy, 56:878-884; (Weis, S. et al., 1993, Acta Neuropathol, 85:185-189).
HIVE is mainly characterized by brain atrophy and histological changes that include white matter pallor and multiple loosely delimitated inflammatory foci disseminated in the gray and white matter (Navia, B. A. et al., 1986 a), Ann. Neurol., 19:517-524; Weis, S. et al., 1993, Acta Neuropathol, 85: 185-189). These foci are composed of microglial cells, a few lymphocytes, reactive astrocytes and very charasteristic multinucleated cells of monocyte/macrophages origin (Budka, H., 1990 a), In: Chopra J, Jagannathan K, Sawhney IMS (eds) Advances in Neurology. Excerpta Medica, Amsterdam, 193-202; Budka, H., 1990 b), Acta Neuropathol., 79:611-619; Budka, H. et al., 1991, Brain Patholo., 1:143-152). HIVL is characterized by diffuse myelin loss, gliosis and perivascular infiltration by monocytes and more rarely multinucleated microglia/macrophages. The deep white matter is preferentially and symmetrically affected (Budka, H., 1990 a), In: Chopra J, Jagannathan K, Sawhney IMS (eds) Advances in Neurology. Excerpta Medica, Amsterdam, 193-202; Budka, H., 1990 b), Acta Neuropathol., 79:611-619; Budka, H. et al., 1991, Brain Patholo., 1:143-152). In HIVE as well as in HIVL, the giant multinucleated cells are considered as the pathological hallmark and in both, morphometric studies have clearly demonstrated a significant neuronal loss (Epstein, L. G. et al., 1986, Pediatrics, 78:678-687; Ketzler, S. et al., 1990, Acta Neuropathol. (Berl), 80:92-94; Masliah, E. et al., 1992, Lab. Investigation, 66:285-291; Weis, S. et al., 1993, Acta Neuropathol, 85:185-189). In addition to these CNS changes, the spinal cord of HIV-1 infected patients may also present alterations such as myelitis or a peculiar vacuolar myelopathy for which no clear etiology has been determined yet.
Several investigators have tried to identify the cells which support the expression and replication of the virus. These studies have demonstrated HIV-1 products in mononucleated and multinucleated macrophages glial cells (Cheng-Mayer, C. et al., 1987, Proc. Natl. Acad. Sci. U.S.A., 84:3526-3530; Epstein, L. G. et al., 1986, Pediatrics, 78:678-687; Gyorkey, F. et al., 1987, J. Infect. Diseases, 155:870-876; Koenig, S. et al., 1986, Science, 233:1089-1093; Stoler, M. H. et al., 1986, JAMA, 256:2360-2364; Vazeux, R. et al., 1987, American J. Pathol., 126:403-410; Wiley, C. A. et al., 1986, Proc. Natl. Acad. Sci. U.S.A., 83:7086-7093) endothelial cells and astrocytes (Epstein, L. G. et al., 1993, Ann. Neurol., 33:429-436; Wiley, C. A. et al., 1986, Proc. Natl. Acad. Sci. U.S.A., 83:7086-7093) microglial cells, but not in neurons (Savio, T. et al., 1993, J. Neurosc. Res., 34:265-272; Sweetnam, P. M. et al., 1993, Eur. J. Neurosc., 5:276-283). Furthermore, HIV-1 has been rescued from brain tissue and cerebrospinal fluid, but not from neurons (Pulliam, L. et al., 1993, AIDS Res Hum Retroviruses, 9:439-444). These findings appear rather paradoxical, considering the cognitive/motor dysfunctions, the dementing illness and the neuronal loss observed in many HIV-1 patients.
In absence of evidence for neuronal infectivity, several direct and indirect mechanisms have been proposed to account for the motor/cognitive disorders. a) It has been postulated that HIV-1 infection of monocytes or macrophages may activate inappropriate secretion of cytokines, such as interleukine-1 or tumor necrosis factor (TNF), that may impair neuronal and/or glial cell function or compromise the integrity of the blood-brain barrier (Wigdahl, B. et al., 1989, AIDS Res. Hum. Retroviruses, 5:369-374). b) Based on experimental observations showing that HIV-1 glycoprotein gpl20 could inhibit the growth of neurons in the presence of neuroleukin, but not in the presence of nerve growth factor (Lee, M. R. et al., 1987, Science, 237:1047-1051), it has been suggested that the HIV-1 env protein may bind to and compete for neuroleukin receptors (Brenneman, D. E. et al., 1988, Nature (London), 335:639-642; Lee, M. R. et al., 1987, Science, 237:1047-1051). As a consequence, gpl20 could directly interfere with neuronal cell function and/or cause neuronal cell death. c) Recent studies have shown that both native and recombinant gpl20, added at very low concentrations to neuronal cultures produce a striking increase in free calcium within the cells and cause cell death within 24 hours, an effect which could be abolished by adding nimodipine (100 nM), the dihydropyridine calcium channel antagonist (Dreyer, E. B. et al., 1990, Science, 248:364-367), vasoactive intestinal peptide (Brenneman, D. E. et al., 1988, Nature (London), 335:639-642), anti-gpl 20 antibodies (Dreyer, E. B. et al., 1990, Science, 248:364-367) or NMDA antagonists (Brenneman, D. E. et al., 1988, Nature (London), 335:639-642; Lipton, S., 1991, Brain Pathology, 1:193-199). The neurotoxicity of gpl20 may thus be conferred either through the NMDA receptor, via a second messenger, or directly by calcium channels (Levy, J. A. et al., 1985, Lancet, ii: 586-588; Lipton, S. A., 1992, Trends Neurosci., 15: 76-80; Sweetnam, P. M. et al., 1993, Eur. J. Neurosc., 5:276-283). Since gpl20 shares certain sequence homology with vasoactive intestinal peptide it might also compete for the same binding sites and block this neurotransmission (Lee, M. R. et al., 1987, Science, 237:1047-1051). All these studies carried out in vitro have indicated possible mechanisms by which HIV infection could lead to AIDS dementia. However, many aspects related to AIDS neurophysiopathology are still obscure and could not be approached by in vitro techniques.
It would be highly desirable to be provided with transgenic mice carrying the HIV-1 env gene under the neuron specific promoter of human neurofilament light gene (NFL) (Julien, J. P. et al., 1987, Genes & Development, 1:1085-1095) to further define the role of gpl20 in neurotoxicity. Such an animal model could provide some information on the effect(s) of gpl20 when expressed in neuronal cells and should help identify the mechanism(s) involved in AIDS clinical syndrome and neuropathology.
It would be highly desirable to be provided with transgenic animals with the neuronal expression of gpl20 and preliminary findings of the pathological evaluation.