BACE1 and presenilin: two unusual aspartyl proteases involved in Alzheimer's disease

SARS-CoV-2 Infection to Premature Neuronal Aging and Neurodegenerative Diseases: Is there any Connection with Hypoxia?

The pandemic of coronavirus disease-2019 (COVID-19), caused by SARS-CoV-2, has become a global concern as it leads to a spectrum of mild to severe symptoms and increases death tolls around the world. Severe COVID-19 results in acute respiratory distress syndrome, hypoxia, and multi- organ dysfunction. However, the long-term effects of post-COVID-19 infection are still unknown. Based on the emerging evidence, there is a high possibility that COVID-19 infection accelerates premature neuronal aging and increases the risk of age-related neurodegenerative diseases in mild to severely infected patients during the post-COVID period. Several studies correlate COVID-19 infection with neuronal effects, though the mechanism through which they contribute to the aggravation of neuroinflammation and neurodegeneration is still under investigation. SARS-CoV-2 predominantly targets pulmonary tissues and interferes with gas exchange, leading to systemic hypoxia. The neurons in the brain require a constant supply of oxygen for their proper functioning, suggesting that they are more vulnerable to any alteration in oxygen saturation level that results in neuronal injury with or without neuroinflammation. We hypothesize that hypoxia is one of the major clinical manifestations of severe SARS-CoV-2 infection; it directly or indirectly contributes to premature neuronal aging, neuroinflammation, and neurodegeneration by altering the expression of various genes responsible for the survival of the cells. This review focuses on the interplay between COVID-19 infection, hypoxia, premature neuronal aging, and neurodegenerative diseases and provides a novel insight into the molecular mechanisms of neurodegeneration.

Asymmetric peptidomimetics containing L-tartaric acid core inhibit the aspartyl peptidase activity and growth of Leishmania amazonensis promastigotes

Aspartyl-type peptidases are promising chemotherapeutic targets in protozoan parasites. In the present work, we identified an aspartyl peptidase activity from the soluble extract of Leishmania amazonensis promastigotes, which cleaved the fluorogenic peptide 7-methoxycoumarin-4-acetyl-Gly-Lys-Pro-Ile-Leu-Phe-Phe-Arg-Leu-Lys(DNP)-D-Arg-amide (cathepsin D substrate) under acidic pH conditions at 37°C, showing a KM of 0.58 μM and Vmax of 129.87 fluorescence arbitrary units/s mg protein. The leishmanial aspartyl peptidase activity was blocked by pepstatin A (IC50 = 6.8 μM) and diazo-acetyl-norleucinemetilester (IC50 = 10.2 μM), two classical aspartyl peptidase inhibitors. Subsequently, the effects of 6 asymmetric peptidomimetics, containing L-tartaric acid core, were tested on both aspartyl peptidase and growth of L. amazonensis promastigotes. The peptidomimetics named 88, 154 and 158 promoted a reduction of 50% on the leishmanial aspartyl peptidase activity at concentrations ranging from 40 to 85 μM, whereas the peptidomimetic 157 was by far the most effective, presenting IC50 of 0.04 μM. Furthermore, the peptidomimetics 157 and 154 reduced the parasite proliferation in a dose-dependent manner, displaying IC50 values of 33.7 and 44.5 μM, respectively. Collectively, the peptidomimetic 157 was the most efficient compound able to arrest both aspartyl peptidase activity and leishmanial proliferation, which raises excellent perspectives regarding its use against this human pathogenic protozoan.

Recombinant pre-miR-29b for Alzheimer´s disease therapeutics

MicroRNAs are arising as the next generation of diagnostic and therapeutic tools for gene silencing. Studies demonstrated that the miR-29 expression is decreased in Alzheimer’s disease (AD) patients displaying high levels of human β-secretase (hBACE1). Recent advances toward an effective therapy for AD intend to employ miR-29 to suppress hBACE1 expression and subsequent Amyloid-β (Aβ) peptide. However, delivery of mature miRNA has demonstrated modest efficacy in vitro; therefore, the preparation of highly pure and biologically active pre-miRNA arises as one of the most important challenges in the development of these therapeutic strategies. Recently, we described a new strategy based arginine-affinity chromatography to specifically purify the recombinant pre-miR-29b. Following this strategy, the purified pre-miR-29b was successfully encapsulated into polyplexes that were further delivered in cytoplasm. It was verified that Chitosan/pre-miR-29b and Polyethylenimine/pre-miR-29b systems efficiently delivered pre-miR-29b to N2a695 cells, thus reducing the hBACE1 protein expression (around 78% and 86%, respectively) and Aβ₄₂ levels (approximately 44% and 47%, respectively). Furthermore, pre-miR-29b downregulates the hBACE1 mRNA expression in 80%. Overall, it was demonstrated that the recombinant pre-miR-29b using polyplexes allowed to decrease the hBACE1 and Aβ₄₂ expression levels, improving the currently available methodologies of miRNA-based therapeutics.

Aspartic peptidases of human pathogenic trypanosomatids: perspectives and trends for chemotherapy

Aspartic peptidases are proteolytic enzymes present in many organisms like vertebrates, plants, fungi, protozoa and in some retroviruses such as human immunodeficiency virus (HIV). These enzymes are involved in important metabolic processes in microorganisms/virus and play major roles in infectious diseases. Although few studies have been performed in order to identify and characterize aspartic peptidase in trypanosomatids, which include the etiologic agents of leishmaniasis, Chagas’ disease and sleeping sickness, some beneficial properties of aspartic peptidase inhibitors have been described on fundamental biological events of these pathogenic agents. In this context, aspartic peptidase inhibitors (PIs) used in the current chemotherapy against HIV (e.g., amprenavir, indinavir, lopinavir, nelfinavir, ritonavir and saquinavir) were able to inhibit the aspartic peptidase activity produced by different species of Leishmania. Moreover, the treatment of Leishmania promastigotes with HIV PIs induced several perturbations on the parasite homeostasis, including loss of the motility and arrest of proliferation/growth. The HIV PIs also induced an increase in the level of reactive oxygen species and the appearance of irreversible morphological alterations, triggering parasite death pathways such as programed cell death (apoptosis) and uncontrolled autophagy. The blockage of physiological parasite events as well as the induction of death pathways culminated in its incapacity to adhere, survive and escape of phagocytic cells. Collectively, these results support the data showing that parasites treated with HIV PIs have a significant reduction in the ability to cause in vivo infection. Similarly, the treatment of Trypanosoma cruzi cells with pepstatin A showed a significant inhibition on both aspartic peptidase activity and growth as well as promoted several and irreversible morphological changes. These studies indicate that aspartic peptidases can be promising targets in trypanosomatid cells and aspartic proteolytic inhibitors can be benefic chemotherapeutic agents against these human pathogenic microorganisms.

Biomarkers in Alzheimer's disease: a review

Alzheimer's disease is the most common form of dementia affecting millions of individuals worldwide. It is currently diagnosed only via clinical assessments and confirmed by postmortem brain pathology. The development of validated biomarkers for Alzheimer's disease is essential to improve diagnosis and accelerate the development of new therapies. Biochemical and neuroimaging markers could facilitate diagnosis, predict AD progression from a pre-AD state of mild cognitive impairment (MCI), and be used to monitor efficacies of disease-modifying therapies. Cerebrospinal fluid (CSF) levels of Aβ40, Aβ42, total tau, and phosphorylated tau have diagnostic values in AD. Measurements of the above CSF markers in combination are useful in predicting the risk of progression from MCI to AD. New potential biomarkers are emerging, and CSF or plasma marker profiles may eventually become part of the clinician's toolkit for accurate AD diagnosis and management. These biomarkers along with clinical assessment, neuropsychological testing, and neuroimaging could achieve a much higher diagnostic accuracy for AD and related disorders in the future.

Pathological role of hypoxia in Alzheimer's disease

The majority cases of Alzheimer's disease (AD) are sporadic late-onset form not being linked to APP and PS1 gene mutations. It is believed that the environmental risk factors play an important role in the onset and development of AD. Patients suffering from cerebral ischemia and stroke in which hypoxic conditions occur are much more susceptible to AD. Increasing evidence suggests that hypoxia facilitates the pathogenesis of AD through accelerating the accumulation of Abeta, increasing the hyperphosphorylation of tau, impairing the normal functions of blood-brain barrier, and promoting the degeneration of neurons. Further investigations into the relationship between hypoxia and AD may open the avenue for effective preservation and pharmacological treatments of this neurodegenerative disease.

Mechanism-based treatments for Alzheimer's disease

Treatment for Alzheimer's disease is entering a new and exciting phase, with several new drugs beginning clinical trials. Many of these new therapies are based on our best current understanding of the pathogenesis of Alzheimer's disease, and are designed to try to either slow or halt the progression of the disease. There are several different theories underlying the current efforts, and these are briefly reviewed. Therapies directed against some aspect of β-amyloid formation, against neurofibrillary tangle formation and against the inflammatory response are all considered, as are the problems associated with each area. It is as yet unclear which, if any, of these approaches will be successful, but the high level of activity in each of these three fields provides some hope that an effective treatment for Alzheimer's disease is on the horizon.

Multifunctional aspartic peptidase prosegments

The structure-function relationships of aspartic peptidases (APs) (EC 3.4.23.X) have been extensively investigated, yet much remains to be elucidated regarding the various molecular mechanisms of these enzymes. Over the past years, APs have received considerable interest for food applications (e.g. cheese, fermented foods) and as potential targets for pharmaceutical intervention in human diseases including hypertension, cancer, Alzheimer's disease, AIDS (acquired immune deficiency syndrome), and malaria. A deeper understanding of the structure and function of APs, therefore, will have a direct impact on the design of peptidase inhibitors developed to treat such diseases. Most APs are synthesized as zymogens which contain an N-terminal prosegment (PS) domain that is removed at acidic pH by proteolytic cleavage resulting in the active enzyme. While the nature of the AP PS function is not entirely understood, the PS can be important in processes such as the initiation of correct folding, protein stability, blockage of the active site, pH-dependence of activation, and intracellular sorting of the zymogen. This review summarizes the current knowledge of AP PS function (especially within the A1 family), with particular emphasis on protein folding, cellular sorting, and inhibition.

Biomarkers of Mild Cognitive Impairment and Alzheimer’s Disease

Alzheimer’s disease (AD) is currently diagnosed only via clinical assessments and confirmed by postmortem brain pathology. Biochemical and neuroimaging markers could facilitate diagnosis, predict AD progression from a pre-AD state of mild cognitive impairment (MCI), and be used to monitor efficacies of disease-modifying therapies. It is now clear that cerebrospinal fluid (CSF) levels of Aβ40, Aβ42, total tau and phosphorylated tau have diagnostic values in AD. Measurements of the above CSF markers in combination are useful in predicting the risk of progression from MCI to AD. Recent advances further support a notion that plasma Aβ levels, expressed as an Aβ42/Aβ40 ratio, could also be of value. New potential biomarkers are emerging, and CSF or plasma marker profiles may eventually become part of the clinician’s toolkit for accurate AD diagnosis and management. These biomarkers, along with clinical assessment, neuropsychological testing and neuroimaging could achieve a much higher diagnostic accuracy for AD and related disorders in the future. Key words: Alzheimer’s disease, b-amyloid (Ab), Biomarkers, Mild cognitive impairment (MCI), Tau

A differential proteomic approach reveals an evolutionary conserved regulation of Nme proteins by Fe65 in C. elegans and mouse

The function of the APP-Fe65 complex is still not definitively understood. To address this point we studied the phenotype of Fe65 (feh-1) ablation, which results in severe developmental defects in C. elegans, including embryonic and larval arrests. To shed light on the complex phenotype of embryonic arrest, we undertook a systematic approach, aiming at the definition of the altered proteomic profile of feh-1 null worms. We defined a panel of 27 regulated proteins, 16 of which actually participating to embryonic development processes in the nematode. Protein spots corresponding to the products of the F25H2.5 gene, the nematode orthologue of mammalian Nm23/Nme gene family members, were consistently up-regulated in feh-1 -/- embryos. We observed similar up-regulation of Nme1 and Nme2 genes, both at the transcript and the protein levels, in the brain of Fe65 knock-out mice, thus highlighting the occurrence of evolutionary conserved mechanisms of Nme expression in nematodes and mammals.

The expression of microRNA miR-107 decreases early in Alzheimer's disease and may accelerate disease progression through regulation of beta-site amyloid precursor protein-cleaving enzyme 1

MicroRNAs (miRNAs) are small regulatory RNAs that participate in posttranscriptional gene regulation in a sequence-specific manner. However, little is understood about the role(s) of miRNAs in Alzheimer's disease (AD). We used miRNA expression microarrays on RNA extracted from human brain tissue from the University of Kentucky Alzheimer's Disease Center Brain Bank with near-optimal clinicopathological correlation. Cases were separated into four groups: elderly nondemented with negligible AD-type pathology, nondemented with incipient AD pathology, mild cognitive impairment (MCI) with moderate AD pathology, and AD. Among the AD-related miRNA expression changes, miR-107 was exceptional because miR-107 levels decreased significantly even in patients with the earliest stages of pathology. In situ hybridization with cross-comparison to neuropathology demonstrated that particular cerebral cortical laminas involved by AD pathology exhibit diminished neuronal miR-107 expression. Computational analysis predicted that the 3'-untranslated region (UTR) of beta-site amyloid precursor protein-cleaving enzyme 1 (BACE1) mRNA is targeted multiply by miR-107. From the same RNA material analyzed on miRNA microarrays, mRNA expression profiling was performed using Affymetrix Exon Array microarrays on nondemented, MCI, and AD patients. BACE1 mRNA levels tended to increase as miR-107 levels decreased in the progression of AD. Cell culture reporter assays performed with a subset of the predicted miR-107 binding sites indicate the presence of at least one physiological miR-107 miRNA recognition sequence in the 3'-UTR of BACE1 mRNA. Together, the coordinated application of miRNA profiling, Affymetrix microarrays, new bioinformatics predictions, in situ hybridization, and biochemical validation indicate that miR-107 may be involved in accelerated disease progression through regulation of BACE1.

Alzheimer's disease (AD)-like pathology in aged monkeys after infantile exposure to environmental metal lead (Pb): evidence for a developmental origin and environmental link for AD

The sporadic nature of Alzheimer's disease (AD) argues for an environmental link that may drive AD pathogenesis; however, the triggering factors and the period of their action are unknown. Recent studies in rodents have shown that exposure to lead (Pb) during brain development predetermined the expression and regulation of the amyloid precursor protein (APP) and its amyloidogenic beta-amyloid (Abeta) product in old age. Here, we report that the expression of AD-related genes [APP, BACE1 (beta-site APP cleaving enzyme 1)] as well as their transcriptional regulator (Sp1) were elevated in aged (23-year-old) monkeys exposed to Pb as infants. Furthermore, developmental exposure to Pb altered the levels, characteristics, and intracellular distribution of Abeta staining and amyloid plaques in the frontal association cortex. These latent effects were accompanied by a decrease in DNA methyltransferase activity and higher levels of oxidative damage to DNA, indicating that epigenetic imprinting in early life influenced the expression of AD-related genes and promoted DNA damage and pathogenesis. These data suggest that AD pathogenesis is influenced by early life exposures and argue for both an environmental trigger and a developmental origin of AD.

Hypoxia and Alzheimer's disease

Numerous cardiorespiratory disorders result in persistent systemic hypoxia, or at worst (as a consequence of stroke) deprive the brain of oxygen completely for a period of time. Patients suffering from such conditions are much more susceptible to the development of dementias such as AD (Alzheimer's disease). Until recently, the cellular and molecular basis for the predisposition to AD by systemic hypoxia has been completely unknown. However, emerging evidence suggests that pathological cellular remodelling caused by chronic hypoxia shows striking similarities to those observed in the central nervous system as a consequence of AD. Furthermore, prolonged hypoxia can induce formation of Abetas (amyloid beta peptides), the primary neurotoxic elements of AD, which accumulate over years to form the extracellular plaques that are the hallmark feature of the disease. Hypoxia can lead to paradoxical increases in mitochondrial ROS (reactive oxygen species) generation upstream of Abeta formation. The downstream consequences of prolonged hypoxia include remodelling of functional expression of voltage-gated calcium channels and disturbance of intracellular calcium homoeostasis via disrupted calcium buffering and inhibition of calcium extrusion mechanisms. These effects can be mimicked by application of exogenous Abeta and, crucially, appear to depend on Abeta formation. Current knowledge supports the concept that prevention of the deleterious effects of hypoxia may prove beneficial in slowing or preventing the onset of AD.

Presenilins regulate the cellular level of the tumor suppressor PTEN

Alzheimer's Disease (AD) is characterized by amyloid plaques consisting of beta-amyloid (Abeta) peptides and neurofibrillary tangles consisting of hyperphosphorylated tau protein. Abeta is proteolytically derived from its precursor protein through cleavages by beta-secretase and gamma-secretase complex comprising presenilins (PS, PS1/PS2), nicastrin, APH-1 and PEN-2. PS1 is also known to activate the PI3K/Akt cell survival pathway in a gamma-secretase-independent manner. The tumor suppressor PTEN, which antagonizes the PI3K/Akt pathway, has increasingly been recognized to play a key role in neural functions and its level found reduced in AD brains. Here, we demonstrate that the protein level of PTEN is dramatically reduced in cultured cells and embryonic tissues deficient in PS, and in the cortical neurons of PS1/PS2 conditional double knockout mice. Restoration of PS in PS-deficient cells reverses the reduction of PTEN. Regulation of PTEN by PS is independent of the PS/gamma-secretase activity since impaired gamma-secretase by the gamma-secretase inhibitor treatment or due to nicastrin deficiency has little effect on the protein level of PTEN. Our data suggest an important role for PS in signaling pathways involving PI3K/Akt and PTEN that are crucial for physiological functions and the pathogenesis of multiple diseases.