High density lipoprotein inhibits assembly of amyloid beta-peptides into fibrils.

The extracellular deposition of amyloid beta (Abeta) in senile plaques constitutes one of the defining hallmarks of Alzheimer's disease. Abeta peptides can aggregate spontaneously to highly insoluble amyloid fibrils, but several components are likely to influence the kinetics of fibrillogenesis in vivo. We report here that high density lipoprotein (HDL), the predominant lipoprotein in the human brain, reduces amyloid formation in vitro as determined by thioflavin T fluorescence and high speed sedimentation assays. The inhibition occurred in a dose dependent manner, and with concentrations of HDL above 1% resulting in more than 70% inhibition. We also examined the combined effect of apolipoprotein E (apoE) and HDL on Abeta fibrillogenesis. We found that HDL particles enriched with any of the three apoE isoforms inhibited Abeta fibrillogenesis as their native counterparts. Taken together, these findings suggest that HDL-like particles in the brain may prevent the formation of Abeta fibrils.

In vivo protection of nigral dopamine neurons by lentiviral gene transfer of the novel GDNF-family member neublastin/artemin.

The glial cell line-derived neurotrophic factor (GDNF)-family of neurotrophic factors consisted until recently of three members, GDNF, neurturin, and persephin. We describe here the cloning of a new GDNF-family member, neublastin (NBN), identical to artemin (ART), recently published (Baloh et al., 1998). Addition of NBN/ART to cultures of fetal mesencephalic dopamine (DA) neurons increased the number of surviving tyrosine hydroxylase (TH)-immunoreactive neurons by approximately 70%, similar to the maximal effect obtained with GDNF. To investigate the neuroprotective effects in vivo, lentiviral vectors carrying the cDNA for NBN/ART or GDNF were injected into the striatum and ventral midbrain. Three weeks after an intrastriatal 6-hydroxydopamine lesion only about 20% of the nigral DA neurons were left in the control group, while 80-90% of the DA neurons remained in the NBN/ART and GDNF treatment groups, and the striatal TH-immunoreactive innervation was partly spared. We conclude that NBN/ART, similarly to GDNF, is a potent neuroprotective factor for the nigrostriatal DA neurons in vivo.

Amyloid beta neurotoxicity in the cholinergic but not in the serotonergic phenotype of RN46A cells.

Neuropathological examination of brains from AD patients has documented that distinct areas and nuclei are differently affected by the disease. It is unknown as to what extent the neurochemical phenotype plays a role in this process, but particularly acetylcholine (Ach) neurons in the basal forebrain are lost during the progress of the disease. The exact molecular mechanism by which the neuronal death is induced remains unclear, but the amyloid beta peptide (A beta) is cytotoxic in vitro and may be important for the neuronal cell death in vivo. Previous reports have demonstrated that an immortalized neuronal cell line (RN46A) derived from rat raphe nucleus differentiate in the presence of ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) to a cholinergic and a serotonergic phenotype, respectively [J.S. Rudge et al., Mol. Cell Neurosci. 7 (1996) 204-221]. This study takes advantage of the RN46A cell line to investigate whether the sensitivity to A beta is dependent on cell differentiation and neurochemical phenotype. We found that cellular reduction of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) could be inhibited 30-40% by A beta in undifferentiated cells. The cholinergic phenotype induced by CNTF remained sensitive to A beta whereas the serotonergic phenotype induced by BDNF was unaffected by concentrations of A beta up to 10 microM. These findings suggest that differentiation and neurochemical phenotype may play a role for A beta induced lesions in Alzheimer's disease.