Effect of plasma lipids and APOE genotype on cognitive decline

Apolipoprotein E genetic variation, atherogenic index and cardiovascular disease risk assessment in an African population: An analysis of HIV and malaria patients in Ghana

BACKGROUND

Apolipoprotein E is involved in lipid transport and clearance of lipoprotein through low-density lipoprotein receptors (LDLR). ApoE variation has been linked to cardiovascular disease (CVD) risk. There are 3 isoforms of ApoE which originate from two non-synonymous single nucleotide polymorphisms denoted as ε2, ε3 and ε4. The ε2 isoform is implicated in higher levels of atherogenic lipoprotein with the ε4 isoform causing LDLR downregulation. This leads to variable effects and differential CVD risk. Malaria and HIV are life-threatening diseases affecting several countries globally especially in sub-Saharan Africa. Parasite and viral activities have been implicated in lipid dysregulation leading to dyslipidaemia. This study examined ApoE variation and CVD risk assessment in malaria and HIV patients.

METHODS

We compared 76 malaria-only, 33 malaria-HIV coinfected, 21-HIV-only and 31 controls from a tertiary health facility in Ghana. Fasting venous blood samples were taken for ApoE genotyping and lipid measurements. Clinical and laboratory data were collected with ApoE genotyping performed using Iplex Gold microarray and PCR-RFLP. Cardiovascular disease risk was calculated using the Framingham BMI and cholesterol risk and Qrisk3 tools.

RESULTS

The frequency of C/C genotype for rs429358 was 9.32%, whiles T/T genotype for rs7412 was found in 2.48% of all participants. ε3/ε3 was the most distributed ApoE genotype accounting for 51.55% of the total participants whiles ε2/ε2 was found in 2.48% of participants, with 1 in malaria-only and 3 in HIV-only patients. There was a significant association between ε4+ and high TG (OR = 0.20, CI; 0.05-0.73; p = 0.015), whiles ε2+ was significantly associated with higher BMI (OR; 0.24, CI; 0.06-0.87; p = 0.030) and higher Castelli Risk Index II in females (OR = 11.26, CI; 1.37-92.30; p = 0.024). A higher proportion of malaria-only participants had a moderate to high 10-year CVD risk.

CONCLUSION

Overall malaria patients seem to have a higher CVD risk though the means through which this occurs may be poorly understood. ε2/ε2 genotypes was observed in our population at a lower frequency. Further studies are vital to determine CVD risk in malaria and how this occurs.

Acidifying Endolysosomes Prevented Low-Density Lipoprotein-Induced Amyloidogenesis

Cholesterol dyshomeostasis has been linked to the pathogenesis of sporadic Alzheimer's disease (AD). In furthering the understanding of mechanisms by which increased levels of circulating cholesterol augments the risk of developing sporadic AD, others and we have reported that low-density lipoprotein (LDL) enters brain parenchyma by disrupting the blood-brain barrier and that endolysosome de-acidification plays a role in LDL-induced amyloidogenesis in neurons. Here, we tested the hypothesis that endolysosome de-acidification was central to amyloid-β (Aβ) generation and that acidifying endolysosomes protects against LDL-induced increases in Aβ levels in neurons. We demonstrated that LDL, but not HDL, de-acidified endolysosomes and increased intraneuronal and secreted levels of Aβ. ML-SA1, an agonist of endolysosome-resident TRPML1 channels, acidified endolysosomes, and TRPML1 knockdown attenuated ML-SA1-induced endolysosome acidification. ML-SA1 blocked LDL-induced increases in intraneuronal and secreted levels of Aβ as well as Aβ accumulation in endolysosomes, prevented BACE1 accumulation in endolysosomes, and decreased BACE1 activity levels. LDL downregulated TRPML1 protein levels, and TRPML1 knockdown worsens LDL-induced increases in Aβ. Our findings suggest that endolysosome acidification by activating TRPML1 may represent a protective strategy against sporadic AD.

Amyloid beta accumulation in HIV-1 infected brain: the role of altered cholesterol homeostasis

The long-term survival of HIV-1 infected individuals credited to the availability and use of effective antiretroviral therapy (ART) is unfortunately now accompanied by an almost 50% prevalence of HIV-1 associated neurocognitive disorder (HAND). Increasingly, it has been realized that HIV-1 infected people on ART have clinical and pathological observations of Alzheimer's disease (AD)-like manifestations including neurocognitive problems, intraneuronal accumulation of amyloid beta (Aβ) protein, and disturbed synaptic integrity. Part of the current challenge facing the medical community and people living with HIV-1 infection is that the pathogenesis of HAND remains unclear, and little is known about how AD-like pathology is developed as a result of HIV-1 infection and/or long-term ART treatment. Here we discuss the potential role of altered plasma cholesterol homeostasis, a prominent feature of HIV-1 infection, on the development of intraneuronal Aβ accumulation in HIV-1 infected brain. We speculate that elevated plasma LDL cholesterol, once it enters brain parenchyma via an increasingly leaky BBB, can be internalized by neurons via receptor-mediated endocytosis, a process that could promote internalization of amyloid beta precursor protein (AβPP). Unlike brain in situ synthesized apoE-cholesterol, apoB-containing LDL-cholesterol could lead to cholesterol accumulation thus disturbing neuronal endolysosome function and ultimately the accumulation of intraneuronal Aβ in HIV-1 infected brain.

Role of endolysosomes and cholesterol in the pathogenesis of Alzheimer's disease: Insights into why statins might not provide clinical benefit

Altered cholesterol homeostasis in general and increased levels of low-density lipoprotein (LDL) cholesterol specifically is a robust risk factor for the pathogenesis of sporadic Alzheimer's disease (AD). Because of this, the family of drugs known as statins have been tried extensively to lower cholesterol levels in attempting to prevent and/or lessen the neuropathogenesis of AD. Unfortunately, evidence accumulated to date is insufficient to support the continued use of statins as a viable pharmacotherapeutic approach against AD. To understand these complex and inter-related issues it is important to review how altered cholesterol homeostasis contributes to AD pathogenesis and why statins have not provided clinical benefit against AD. Apolipoproteins with their different affinities for various lipids and the receptors that control cholesterol uptake can result in drastic differences in cholesterol trafficking into and its distribution within neurons. The presence of the apoE4 or elevated plasma levels of LDL cholesterol can lead to a set of conditions that resembles lysosomal lipid storage disorders observed in Niemann-Pick type C disease such as impaired recycling of cholesterol back to the endoplasmic reticulum (ER), Golgi and plasma membranes, cholesterol deficiencies in plasma membranes, and increased cholesterol accumulation in endolysosomes resulting in endolysosome dysfunction. Consequently, the use of statins to block cholesterol synthesis in ER might not only decrease further plasma membrane cholesterol levels thus disturbing synaptic integrity, but also could also increase cholesterol burden in endolysosomes thus worsening endolysosome dysfunction. Therefore, it is not surprising that the use of cholesterol-lowering strategies with statins has not resulted in clinical benefit for patients living with AD.

Aging and neuroplasticity

Neuroplasticity can be defined as a final common pathway of neurobiological processes, including structural, functional or molecular mechanisms, that result in stability or compensation for age- or disease-related changes. The papers in this issue address the aging process, as well as depression, dementia, and stroke and a range of interventions, including manipulations in behavior (physical and cognitive activity/exercise), physiological factors (caloric restriction, cholesterol), pharmacologic treatments (AMPA receptors) and manipulation of brain magnetic fields and electrical activity (transcranial magnetic stimulation, magnetic seizure therapy, and deep brain stimulation).This editorial will address different facets of neuroplasticity, the need for translational research to interpret neuroimaging data thought to reflect neuroplasticity in the human brain, and the next steps for testing interventions in aging and in disease.