Apolipoprotein E4 stimulates sulfation of glycosaminoglycans in neural cells

Heparan Sulfate as a Therapeutic Target in Tauopathies: Insights From Zebrafish

Microtubule-associated protein tau (MAPT) hyperphosphorylation and aggregation, are two hallmarks of a family of neurodegenerative disorders collectively referred to as tauopathies. In many tauopathies, including Alzheimer's disease (AD), progressive supranuclear palsy (PSP) and Pick's disease, tau aggregates are found associated with highly sulfated polysaccharides known as heparan sulfates (HSs). In AD, amyloid beta (Aβ) peptide aggregates associated with HS are also characteristic of disease. Heparin, an HS analog, promotes misfolding, hyperphosphorylation and aggregation of tau protein in vitro. HS also provides cell surface receptors for attachment and uptake of tau seeds, enabling their propagation. These findings point to HS-tau interactions as potential therapeutic targets in tauopathies. The zebrafish genome contains genes paralogous to MAPT, genes orthologous to HS biosynthetic and chain modifier enzymes, and other genes implicated in AD. The nervous system in the zebrafish bears anatomical and chemical similarities to that in humans. These homologies, together with numerous technical advantages, make zebrafish a valuable model for investigating basic mechanisms in tauopathies and identifying therapeutic targets. Here, we comprehensively review current knowledge on the role of HSs in tau pathology and HS-targeting therapeutic approaches. We also discuss novel insights from zebrafish suggesting a role for HS 3-O-sulfated motifs in tau pathology and establishing HS antagonists as potential preventive agents or therapies for tauopathies.

APOE Variants E2, E3, and E4 Can Be Miscalled By Classical PCR-RFLP When The Christchurch Variant Is Also Present

BACKGROUND

The APOE Christchurch (APOECh) is a rare variant (c.543C>A) in codon 154. It was first described in an E2 patient with type III dyslipidemia, and thus initially called E2Ch. Its prevalence and the lipid profile of carriers remain unclear.

METHODS

E2, E3, and E4 screening for the APOE gene was performed by PCR-RFLP. The rare APOECh variant was firstly found after detecting an unexpected 109 base-pair band in the high-resolution agarose gel electrophoresis leading to a genotype misinterpretation: the presence of APOECh alters the restriction-bands pattern. To confirm the Ch variant, a second PCR-RFLP method was specifically designed to detect this variant and Sanger sequencing was also performed for all positive samples.

RESULTS

We identified 12 unrelated subjects for the APOECh among a cohort of 2,560 patients: nine E3/E3Ch, two E3Ch/E4, and one E2/E3Ch or E2Ch/E3. The frequency of the variant is 0.4% in our study population, which represents the highest percentage published so far. If there is a 109 bp band, it is easy to recognize the presence of the variant. However, in APOE routine genotyping, an E4Ch allele is indistinguishable from a standard E3. Therefore, E4Ch alleles might be underrepresented in the results.

CONCLUSION

We recommend APOE exon 4 sequencing to unequivocally detect the common three variants E2, E3, and E4 and the rare variants as well, to find out the real role they play in atherosclerosis and to estimate its real frequency which is nowadays unclear, in part by the small number of cases identified.

Cholesterol modifies classical conditioning of the rabbit (Oryctolagus cuniculus) nictitating membrane response

Cholesterol plays an important role in synapse formation, receptor function, and synaptic plasticity, and animal studies show that modifying cholesterol may improve learning and memory. Other data show that feeding animals cholesterol can induce beta amyloid accumulation. Rabbits (Oryctolagus cuniculus) fed 2% cholesterol for 8 weeks were given trace conditioning of the nictitating membrane response using a 100-ms tone, a 700-ms trace, and periorbital electrical stimulation or airpuff. Rabbits fed cholesterol showed significant facilitation of trace conditioning to airpuff and conditioning-specific reflex modification to periorbital electrical stimulation and airpuff. The cholesterol-fed rabbits had beta amyloid accumulation in the cortex, but little in the hippocampus. The data suggest cholesterol had facilitative effects that outweighed potential amnesic effects of cortical beta amyloid.

Heparan sulfate proteoglycan 2 polymorphism in Alzheimer's disease and correlation with neuropathology

A genetic association of an intronic single nucleotide polymorphism site of heparan sulfate proteoglycan 2 (HSPG2) with Alzheimer's disease (AD) was investigated among Finnish AD patients (n=213) and controls (n=269). No association of the HSPG2 polymorphism alone was observed with AD. However, an association of HSPG2 A allele with AD was detected in apolipoprotein (APOE) epsilon4 allele carriers. The odds ratio for AD was doubled in subjects carrying both epsilon4 and HSPG2 A alleles (OR=6.6) when compared to subjects with epsilon4 allele alone (OR=3.1). The impact of HSPG2 polymorphism on beta amyloid and tau pathology was studied using immunohistochemistry. Paired helical filament labeling was significantly more pronounced in AD patients carrying both epsilon4 and HSPG A alleles when compared to epsilon4 carriers lacking the HSPG2 A allele. In conclusion, HSPG2 A allele may possess an additive risk effect among the APOE epsilon4 carriers in AD.