Neurotoxicity of the 22 kDa Thrombin-Cleavage Fragment of Apolipoprotein E and Related Synthetic Peptides Is Receptor-Mediated

Abstract

Potent neurotoxicity is associated with both apolipoprotein E (apoE)-related synthetic peptides and the 22 kDa N-terminal thrombin-cleavage fragment of apoE. Furthermore, the E4 isoform of the 22 kDa fragment is significantly more toxic than the same fragment derived from the E3 isoform, suggesting the possibility of a direct role of apoE-associated neurotoxicity in the pathophysiology of Alzheimer's disease. In the present study, the potential role of cell surface receptors in mediating neurotoxicity was assessed by using a variety of agents that should block the heparinbinding and receptor-binding activity of apoE. Effective inhibitors of neurotoxicity of both the apoE peptides and the apoE fragment include heparin, heparan sulfate, sodium chlorate and heparinase, the low-density lipoprotein (LDL) receptor-related protein receptorassociated protein, and a polyclonal anti-LDL receptor-related protein antibody. These results suggest that the neurotoxicity of the 22 kDa thrombin cleavage fragment of apoE and related peptides is receptor-mediated, and that the most likely candidate receptor is a heparan sulfate proteoglycan-LDL receptor-related protein complex. Key words: apolipoprotein E; synthetic peptides; neurotoxicity; LRP; HSPG; Alzheimer's diseaseApolipoprotein E (apoE) has been implicated in the pathogenesis of late-onset Alzheimer's disease (AD) by several lines of evidence. Perhaps the most compelling finding is the association between inheritance of the allele for the E4 isoform and the increased risk (4.5-fold greater), and earlier age of onset (16 years earlier on average), of the disease (Corder et al., 1993; Saunders et al., 1993a,b;Strittmatter et al., 1993a). Although several hypotheses have been proposed to account for the isoform-specific association of apoE with AD, none has yet gained sufficient support to provide a clear explanation of how apoE contributes to the pathology.Based on the demonstration that apoE synthetic peptides exhibit cytotoxicity (C lay et al., 1995) and cause neurite degeneration (Crutcher et al., 1994), apoE has been suggested to play a direct role in AD pathogenesis by contributing directly to neurodegenerative events. This hypothesis has gained additional support from the recent finding that a 22 kDa thrombin cleavage fragment of apoE, which may be analogous to a similar fragment found in brain and C SF, exhibits neurotoxicity and that the E4-derived fragment is significantly more toxic than the E3-derived fragment (Marques et al., 1996). Furthermore, apoE4 has been shown to exhibit greater neurotoxicity than apoE3 . However, the mechanism underlying these toxic effects, including the question of whether the effects are mediated by specific receptors, is unknown. The cytotoxic apoE peptides and the 22 kDa thrombin fragment include residues 141-155, which reside within the receptor-binding region of apoE (residues 140 -160) Weisgraber et al., 1983;Lalazar et al., 1988), as well as the overlapping high-affinity heparin-binding region (residues 142-147) (Weisgraber et al...

Carboxyl-terminal-truncated apolipoprotein E4 causes Alzheimer's disease-like neurodegeneration and behavioral deficits in transgenic mice

“…The importance of this region of apoE in neurotoxicity is consistent with our previous in vitro observations in which the lipid-binding region of apoE is toxic to cultured neuronal cells (22). The amino-terminal 22-kDa thrombin-cleavage fragment (amino acids 1-191) of apoE4 is also neurotoxic in vitro (51,52), but this toxicity appears to require relatively high concentrations of the fragment and has not yet been confirmed in vivo. The apoE fragments generated in AD brains are different from the 22-kDa thrombin-cleavage products (22), which lack the lipid-binding domain (amino acids 244-272).…”

Neuron-Specific Apolipoprotein E4 Proteolysis Is Associated with Increased Tau Phosphorylation in Brains of Transgenic Mice

“…ApoE fragments similar to those observed in our study were generated in primary cultured cortical neurons but not in primary cultured astrocytes obtained from transgenic mice expressing apoE4 in both cell types (Lesuisse et al, 2001). Others have shown that the N-terminal 22 kDa thrombin cleavage fragment (amino acids 1-191) of apoE4 is neurotoxic in vitro (Tolar et al, 1997(Tolar et al, , 1999; however, this toxicity appears to require relatively high concentrations of the fragment and has not yet been confirmed in vivo. In addition, the lipid-binding domain of apoE (amino acids 244 -272; Huang and Mahley, 1999;Huang, 1999, 2000) appears to be essential for apoE fragments to have neurotoxic effects in vivo, as demonstrated in our previous study (Harris et al, 2003).…”

Prominent Axonopathy and Disruption of Axonal Transport in Transgenic Mice Expressing Human Apolipoprotein E4 in Neurons of Brain and Spinal Cord

“…60 This process was suggested to be receptormediated. 58 We did not observe 22-kd ApoE fragments in the ApoE4 transgenic mice with the method that we used, which argues against a role for these fragments in the pathology of the Thy1-ApoE4 transgenic mice.…”