Unraveling the brain's response to COVID-19: How SARS-CoV-2 afflicts dopaminergic neurons

COVID-19 patients often display dysfunctions of the nervous system, indicating an effect of SARS-CoV-2 on neural cells. Yang et al. now show that human stem-cell-derived dopaminergic neurons are susceptible to SARS-CoV-2, triggering inflammation and senescence. The study further identifies three FDA-approved drugs capable of reversing these cellular phenotypes.

Plasma apolipoprotein E levels in longitudinally followed patients with mild cognitive impairment and Alzheimer’s disease

Background

Low levels of plasma apolipoprotein E (apoE) and presence of the APOE ε4 allele are associated with an increased risk of Alzheimer’s disease (AD). Although the increased risk of AD in APOE ε4-carriers is well-established, the protein levels have received limited attention.

Methods

We here report the total plasma apoE and apoE isoform levels at baseline from a longitudinally (24 months) followed cohort including controls (n = 39), patients with stable amnestic mild cognitive impairment during 24 months follow up (MCI-MCI, n = 30), patients with amnestic MCI (aMCI) that during follow-up were clinically diagnosed with AD with dementia (ADD) (MCI-ADD, n = 28), and patients with AD with dementia (ADD) at baseline (ADD, n = 28). We furthermore assessed associations between plasma apoE levels with cerebrospinal fluid (CSF) AD biomarkers and α-synuclein, as well as both CSF and plasma neurofilament light chain (NfL), YKL-40 and kallikrein 6.

Results

Irrespective of clinical diagnosis, the highest versus the lowest apoE levels were found in APOE ε2/ε3 versus APOE ε4/ε4 subjects, with the most prominent differences exhibited in females. Total plasma apoE levels were 32% and 21% higher in the controls versus MCI-ADD and ADD patients, respectively. Interestingly, MCI-ADD patients exhibited a 30% reduction in plasma apoE compared to MCI-MCI patients. This decrease appeared to be associated with brain amyloid-β (Aβ42) pathology regardless of disease status as assessed using the Amyloid, Tau, and Neurodegeneration (A/T/N) classification. In addition to the association between low plasma apoE and low levels of CSF Aβ42, lower apoE levels were also related to higher levels of CSF total tau (t-tau) and tau phosphorylated at Threonine 181 residue (p-tau) and NfL as well as a worse performance on the mini-mental-state-examination. In MCI-ADD patients, low levels of plasma apoE were associated with higher levels of CSF α-synuclein and kallikrein 6. No significant correlations between plasma apoE and the astrocytic inflammatory marker YKL40 were observed.

Conclusions

Our results demonstrate important associations between low plasma apoE levels, Aβ pathology, and progression from aMCI to a clinical ADD diagnosis.

Brain integrity is altered by hepatic APOE ε4 in humanized-liver mice

Liver-generated plasma apolipoprotein E (apoE) does not enter the brain but nonetheless correlates with Alzheimer's disease (AD) risk and AD biomarker levels. Carriers of APOEε4, the strongest genetic AD risk factor, exhibit lower plasma apoE and altered brain integrity already at mid-life versus non-APOEε4 carriers. Whether altered plasma liver-derived apoE or specifically an APOEε4 liver phenotype promotes neurodegeneration is unknown. Here we investigated the brains of Fah-/-, Rag2-/-, Il2rg-/- mice on the Non-Obese Diabetic (NOD) background (FRGN) with humanized-livers of an AD risk-associated APOE ε4/ε4 versus an APOE ε2/ε3 genotype. Reduced endogenous mouse apoE levels in the brains of APOE ε4/ε4 liver mice were accompanied by various changes in markers of synaptic integrity, neuroinflammation and insulin signaling. Plasma apoE4 levels were associated with unfavorable changes in several of the assessed markers. These results propose a previously unexplored role of the liver in the APOEε4-associated risk of neurodegenerative disease.

α-synuclein in the pathophysiology of Alzheimer's disease

The Alzheimer’s disease (AD) afflicted brain is neuropathologically defined by extracellular amyloid-β (Aβ) plaques and intraneuronal neurofibrillary tangles composed of hyperphosphorylated tau protein. However, accumulating evidence suggests that the presynaptic protein α-synuclein (αSyn), mainly associated with synucleinopathies like Parkinson’s disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA), is involved in the pathophysiology of AD. Lewy-related pathology (LRP), primarily comprised of αSyn, is present in a majority of autopsied AD brains, and higher levels of αSyn in the cerebrospinal fluid (CSF) of patients with mild cognitive impairment (MCI) and AD have been linked to cognitive decline. Recent studies also suggest that the asymptomatic accumulation of Aβ plaques is associated with higher CSF αSyn levels in subjects at risk of sporadic AD and in individuals carrying autosomal dominant AD mutations. Experimental evidence has further linked αSyn mainly to tau hyperphosphorylation, but also to the pathological actions of Aβ and the APOEε4 allele, the latter being a major genetic risk factor for both AD and DLB. In this review, we provide a summary of the current evidence proposing an involvement of αSyn either as an active or passive player in the pathophysiological ensemble of AD, and furthermore describe in detail the current knowledge of αSyn structure and inferred function.

The relevance of cerebrospinal fluid α-synuclein levels to sporadic and familial Alzheimer's disease

Accumulating evidence demonstrating higher cerebrospinal fluid (CSF) α-synuclein (αSyn) levels and αSyn pathology in the brains of Alzheimer's disease (AD) patients suggests that αSyn is involved in the pathophysiology of AD. To investigate whether αSyn could be related to specific aspects of the pathophysiology present in both sporadic and familial disease, we quantified CSF levels of αSyn and assessed links to various disease parameters in a longitudinally followed cohort (n = 136) including patients with sporadic mild cognitive impairment (MCI) and AD, and in a cross-sectional sample from the Dominantly Inherited Alzheimer's Network (n = 142) including participants carrying autosomal dominant AD (ADAD) gene mutations and their non-mutation carrying family members.Our results show that sporadic MCI patients that developed AD over a period of two years exhibited higher baseline αSyn levels (p = 0.03), which inversely correlated to their Mini-Mental State Examination scores, compared to cognitively normal controls (p = 0.02). In the same patients, there was a dose-dependent positive association between CSF αSyn and the APOEε4 allele. Further, CSF αSyn levels were higher in symptomatic ADAD mutation carriers versus non-mutation carriers (p = 0.03), and positively correlated to the estimated years from symptom onset (p = 0.05) across all mutation carriers. In asymptomatic (Clinical Dementia Rating < 0.5) PET amyloid-positive ADAD mutation carriers CSF αSyn was positively correlated to ¹¹C-Pittsburgh Compound-B (PiB) retention in several brain regions including the posterior cingulate, superior temporal and frontal cortical areas. Importantly, APOEε4-positive ADAD mutation carriers exhibited an association between CSF αSyn levels and mean cortical PiB retention (p = 0.032). In both the sporadic AD and ADAD cohorts we found several associations predominantly between CSF levels of αSyn, tau and amyloid-β_1-40.Our results suggest that higher CSF αSyn levels are linked to AD pathophysiology at the early stages of disease development and to the onset of cognitive symptoms in both sporadic and autosomal dominant AD. We conclude that APOEε4 may promote the processes driven by αSyn, which in turn may reflect on molecular mechanisms linked to the asymptomatic build-up of amyloid plaque burden in brain regions involved in the early stages of AD development.

Oligonucleotide labeling using BODIPY phosphoramidite

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives were prepared and their photochemical properties were characterized. One such analogue, 4,4-difluoro-4-bora-1,3,5,7-tetramethyl-8-(5-hydroxypentyl)-3a,4a-diaza-s-indacene was transformed into the corresponding phosphoramidite and incorporated into oligodeoxyribonucleotides as a fluorescent reporter group.