Angiotensin I and II Stimulate Cell Invasion of SARS-CoV-2: Potential Mechanism via Inhibition of ACE2 Arm of RAS

Angiotensin-converting enzyme 2 (ACE2), one of the key enzymes of the renin-angiotensin system (RAS), plays an important role in SARS-CoV-2 infection by functioning as a virus receptor. Angiotensin peptides Ang I and Ang II, the substrates of ACE2, can modulate the binding of SARS-CoV-2 Spike protein to the ACE2 receptor. In the present work, we found that co incubation of HEK-ACE2 and Vero E6 cells with the SARS-CoV-2 Spike pseudovirus (PVP) resulted in stimulation of the virus entry at low and high micromolar concentrations of Ang I and Ang II, respectively. The potency of Ang I and Ang II stimulation of virus entry corresponds to their binding affinity to ACE2 catalytic pocket with 10 times higher efficiency of Ang II. The Ang II induced mild increase of PVP infectivity at 20 microM; while at 100 microM the increase (129.74+/-3.99 %) was highly significant (p<0.001). Since the angiotensin peptides act in HEK ACE2 cells without the involvement of angiotensin type I receptors, we hypothesize that there is a steric interaction between the catalytic pocket of the ACE2 enzyme and the SARS-CoV-2 S1 binding domain. Oversaturation of the ACE2 with their angiotensin substrate might result in increased binding and entry of the SARS-CoV-2. In addition, the analysis of angiotensin peptides metabolism showed decreased ACE2 and increased ACE activity upon SARS-CoV-2 action. These effects should be taken into consideration in COVID-19 patients suffering from comorbidities such as the over-activated renin-angiotensin system as a mechanism potentially influencing the SARS-CoV-2 invasion into recipient cells.

AADvac1, an Active Immunotherapy for Alzheimer's Disease and Non Alzheimer Tauopathies: An Overview of Preclinical and Clinical Development

Neurofibrillary tau protein pathology is closely associated with the progression and phenotype of cognitive decline in Alzheimer's disease and other tauopathies, and a high-priority target for disease-modifying therapies. Herein, we provide an overview of the development of AADvac1, an active immunotherapy against tau pathology, and tau epitopes that are potential targets for immunotherapy. The vaccine leads to the production of antibodies that target conformational epitopes in the microtubule-binding region of tau, with the aim to prevent tau aggregation and spreading of pathology, and promote tau clearance. The therapeutic potential of the vaccine was evaluated in transgenic rats and mice expressing truncated, non mutant tau protein, which faithfully replicate of human tau pathology. Treatment with AADvac1 resulted in reduction of neurofibrillary pathology and insoluble tau in their brains, and amelioration of their deleterious phenotype. The vaccine was highly immunogenic in humans, inducing production of IgG antibodies against the tau peptide in 29/30 treated elderly patients with mild-to-moderate Alzheimer's. These antibodies were able to recognise insoluble tau proteins in Alzheimer patients' brains. Treatment with AADvac1 proved to be remarkably safe, with injection site reactions being the only adverse event tied to treatment. AADvac1 is currently being investigated in a phase 2 study in Alzheimer's disease, and a phase 1 study in non-fluent primary progressive aphasia, a neurodegenerative disorder with a high tau pathology component.

Mesenchymal stem cells rescue the Alzheimer's disease cell model from cell death induced by misfolded truncated tau

We have developed a stably transfected human cell model for Alzheimer's disease with doxycycline-inducible expression of human misfolded truncated tau protein (AT tau). We have showed that AT tau reduced the metabolic activity of the AT tau cells, slowed down cell proliferation, and induced caspase-3-independent apoptosis-like programmed cell death, tauoptosis. The aim of this study was to test the possible capability of rat mesenchymal stem cells (MSCs) to interfere with AT tau protein-induced cell death. AT tau cells after treatment with 10 μM all-trans retinoic acid were either co-cultivated with MSCs or supplemented with MSC secretome for 6 and 9 days. We found that both MSCs and MSC secretome promoted survival and increased the metabolic activity of the cells. Moreover stem cells induced cell differentiation and formation of neurites with numerous varicosities. Strikingly, treatment had no effect on tau expression suggesting that MSC induced self-protecting mechanism that prevented AT tau cells from tauoptosis. Our results showed that mesenchymal stem cells and their secretome are able to rescue the Alzheimer's disease cell model from cell death induced by misfolded truncated tau. We suggest that cell therapy may represent an alternative therapeutic avenue for treatment of human Alzheimer's disease and related tauopathies.

The hunt for dying neurons: insight into the neuronal loss in Alzheimer's disease

Neuronal loss is one of the major pathological hallmarks of neurodegenerative disorders including Alzheimer's disease (AD). Using rigorous quantitative methods, the distinct pattern of neuronal loss in pathological conditions such as neurodegeneration and in normal aging was clearly shown. Furthermore, the decrease of total neuronal numbers correlated in a considerable extent with the presence of neurofibrillary degeneration in the same brain regions. However, it appears that neurofibrillary tangles are not the only cause of reduction of neuronal populations, but also alternative triggers could induce neuronal death in this disease. Various inducers, most probably, activate different cell death pathways. Recently, apoptosis has been implicated as a possible mechanism for neuronal death. There is essentially no evidence of apoptosis in AD that would meet all criteria of its classical definition. Therefore it was suggested, that other modes of cell death could contribute to neuronal loss in AD and related disorders (Tab. 2, Ref. 70).