Low dose DMSO treatment induces oligomerization and accelerates aggregation of α-synuclein

The in vitro dynamics of pseudo-vascular network formation

BACKGROUND/OBJECTIVES

Pseudo-vascular network formation in vitro is considered a key characteristic of vasculogenic mimicry. While many cancer cell lines form pseudo-vascular networks, little is known about the spatiotemporal dynamics of these formations.

METHODS

Here, we present a framework for monitoring and characterising the dynamic formation and dissolution of pseudo-vascular networks in vitro. The framework combines time-resolved optical microscopy with open-source image analysis for network feature extraction and statistical modelling. The framework is demonstrated by comparing diverse cancer cell lines associated with vasculogenic mimicry, then in detecting response to drug compounds proposed to affect formation of vasculogenic mimics. Dynamic datasets collected were analysed morphometrically and a descriptive statistical analysis model was developed in order to measure stability and dissimilarity characteristics of the pseudo-vascular networks formed.

RESULTS

Melanoma cells formed the most stable pseudo-vascular networks and were selected to evaluate the response of their pseudo-vascular networks to treatment with axitinib, brucine and tivantinib. Tivantinib has been found to inhibit the formation of the pseudo-vascular networks more effectively, even in dose an order of magnitude less than the two other agents.

CONCLUSIONS

Our framework is shown to enable quantitative analysis of both the capacity for network formation, linked vasculogenic mimicry, as well as dynamic responses to treatment.

ER stress in mouse serotonin neurons triggers a depressive phenotype alleviated by ketamine targeting eIF2α signaling

Depression is a devastating mood disorder that causes significant disability worldwide. Current knowledge of its pathophysiology remains modest and clear biological markers are lacking. Emerging evidence from human and animal models reveals persistent alterations in endoplasmic reticulum (ER) homeostasis, suggesting that ER stress-related signaling pathways may be targets for prevention and treatment. However, the neurobiological basis linking the pathways involved in depression-related ER stress remains unknown. Here, we report that an induced model of ER stress in mouse serotonin (5-HT) neurons is associated with reduced Egr1-dependent 5-HT cellular activity and 5-HT neurotransmission, resulting in neuroplasticity deficits in forebrain regions and a depressive-like phenotype. Ketamine administration engages downstream eIF2α signaling to trigger rapid neuroplasticity events that rescue the depressive-like effects. Collectively, these data identify ER stress in 5-HT neurons as a cellular pathway involved in the pathophysiology of depression and show that eIF2α is critical in eliciting ketamine's fast antidepressant effects.

Exploring structural determinants of neuroprotection bias on novel glypromate conjugates with bioactive amines

Neurodegenerative disorders of the central nervous system (CNS) such as Alzheimer's and Parkinson's diseases, afflict millions globally, posing a significant public health challenge. Despite extensive research, a critical hurdle in effectively treating neurodegenerative diseases is the lack of neuroprotective drugs that can halt or reverse the underlying disease processes. In this work, we took advantage of the neuroprotective properties of the neuropeptide glycyl-l-prolyl-l-glutamic acid (Glypromate) for the development of new peptidomimetics using l-pipecolic acid as a proline surrogate and exploring their chemical conjugation with relevant active pharmaceutical ingredients (API) via a peptide bond. Together with prolyl-based Glypromate conjugates, a total of 36 conjugates were toxicologically and biologically evaluated. In this series, the results obtained showed that a constrained ring (l-proline) at the central position of the peptide motif accounts for enhanced toxicological profiles and biological effects using undifferentiated and differentiated human neuroblastoma SH-SY5Y cells. Additionally, it was shown that biased biological responses are API-dependent. Conjugation with (R)-1-aminoindane led to a 38-43% reduction of protein aggregation induced by Aβ25-35 (10 μM), denoting a 3.2-3.6-fold improvement in comparison with the parent neuropeptide, with no significative difference between functionalization at α and γ-carboxyl ends. On the other hand, the best-performing neuroprotective conjugate against the toxicity elicited by 6-hydroxydopamine (6-OHDA, 125 μM) was obtained by conjugation with memantine at the α-carboxyl end, resulting in a 2.3-fold improvement of the neuroprotection capacity in comparison with Glypromate neuropeptide. Altogether, the chemical strategy explored in this work shows that the neuroprotective capacity of Glypromate can be modified and fine-tuned, opening a new avenue for the development of biased neurotherapeutics for CNS-related disorders.

Monomeric α-synuclein activates the plasma membrane calcium pump

Alpha-synuclein (aSN) is a membrane-associated and intrinsically disordered protein, well known for pathological aggregation in neurodegeneration. However, the physiological function of aSN is disputed. Pull-down experiments have pointed to plasma membrane Ca2+ -ATPase (PMCA) as a potential interaction partner. From proximity ligation assays, we find that aSN and PMCA colocalize at neuronal synapses, and we show that calcium expulsion is activated by aSN and PMCA. We further show that soluble, monomeric aSN activates PMCA at par with calmodulin, but independent of the autoinhibitory domain of PMCA, and highly dependent on acidic phospholipids and membrane-anchoring properties of aSN. On PMCA, the key site is mapped to the acidic lipid-binding site, located within a disordered PMCA-specific loop connecting the cytosolic A domain and transmembrane segment 3. Our studies point toward a novel physiological role of monomeric aSN as a stimulator of calcium clearance in neurons through activation of PMCA.

Protein kinase R dependent phosphorylation of α-synuclein regulates its membrane binding and aggregation

Aggregated α-synuclein (α-syn) accumulates in the neuronal Lewy body (LB) inclusions in Parkinson's disease (PD) and LB dementia. Yet, under nonpathological conditions, monomeric α-syn is hypothesized to exist in an equilibrium between disordered cytosolic- and partially α-helical lipid-bound states: a feature presumably important in synaptic vesicle release machinery. The exact underlying role of α-syn in these processes, and the mechanisms regulating membrane-binding of α-syn remains poorly understood. Herein we demonstrate that Protein kinase R (PKR) can phosphorylate α-syn at several Ser/Thr residues located in the membrane-binding region that is essential for α-syn's vesicle-interactions. α-Syn phosphorylated by PKR or α-syn isolated from PKR overexpressing cells, exhibit decreased binding to lipid membranes. Phosphorylation of Thr64 and Thr72 appears as the major contributor to this effect, as the phosphomimetic Thr64Glu/Thr72Glu-α-syn mutant displays reduced overall attachment to brain vesicles due to a decrease in vesicle-affinity of the last two thirds of α-syn's membrane binding region. This allows enhancement of the "double-anchor" vesicle-binding mechanism that tethers two vesicles and thus promote the clustering of presynaptic vesicles in vitro. Furthermore, phosphomimetic Thr64Glu/Thr72Glu-α-syn inhibits α-syn oligomerization and completely abolishes nucleation, elongation, and seeding of α-syn fibrillation in vitro and in cells, and prevents trans-synaptic spreading of aggregated α-syn pathology in organotypic hippocampal slice cultures. Overall, our findings demonstrate that normal and abnormal functions of α-syn, like membrane-binding, synaptic vesicle clustering and aggregation can be regulated by phosphorylation, e.g., via PKR. Mechanisms that could potentially be modulated for the benefit of patients suffering from α-syn aggregate-related diseases.

Identification of α-Synuclein Proaggregator: Rapid Synthesis and Streamlining RT-QuIC Assays in Parkinson’s Disease

We report the discovery of two compounds, TKD150 and TKD152, that promote the aggregation of α-synuclein (aSN) using a real-time quaking-induced conversion (RT-QuIC) assay to detect abnormal aSN. By utilizing a Pd-catalyzed C–H arylation of benzoxazole with iodoarenes and implementing a planar conformation to the design, we successfully identified TKD150 and TKD152 as proaggregators for aSN. In comparison to a previously reported proaggregator, PA86, the two identified compounds were able to promote aggregation of aSN at twice the rate. Application of TKD150 and TKD152 to the RT-QuIC assay will shorten the inherent lag time and may allow wider use of this assay in clinical settings for the diagnosis of α-synucleinopathy-related diseases.