Taken By Storm: The Rise And Fall Of Tau From Microtubule-Associated To Aggregated To Degraded

Tau is a microtubule-associated protein, which promotes neuronal microtubule assembly and stability. Accumulation of tau into insoluble aggregates known as neurofibrillary tangles (NFTs) is a pathological hallmark of several neurodegenerative diseases, known as tauopathies. Aggregated proteins are normally degraded by the cell’s protein degradation mechanisms, autophagy or the ubiquitin-proteasome system (UPS). In tauopathies, however, the efficiency of these degradation pathways becomes challenged by the abnormal accumulation of the tau protein, which consequently, does not get fully degraded. The current hypothesis is that small, soluble oligomeric tau species preceding NFT formation cause toxicity. However, thus far, visualizing the spatial distribution of tau monomers and oligomers inside cells under physiological or pathological conditions has not been possible. Moreover, it is unclear whether certain tau aggregate species are more resistant to degradation. Here, using single-molecule localization microscopy, we show that tau forms small oligomers on microtubules ex vivo. These oligomers are distinct from those found in cells exhibiting tau aggregation and could be precursors of aggregated tau in pathology. Furthermore, using an unsupervised shape classification algorithm that we developed, we show that different tau phosphorylation states are associated with distinct tau aggregate species. Using machine learning, we also show that autophagy and UPS target distinct classes of tau aggregates for degradation. More specifically, we propose a model where tau fibrils are targeted by UPS for degradation and NFTs are mostly degraded by autophagy, generating more tau monomers and oligomers as well as small fibrils. Our work elucidates tau’s nanoscale composition under nonaggregated and aggregated conditions ex vivo and further informs our understanding of how tau aggregates become degraded by the cell’s degradation pathways

Coordination chemistry and biology of chelators for the treatment of iron overload disorders

Treatment of the medical condition generally referred to as iron overload through the delivery of chelators has recently received a major boost. In 2005 Novartis gained FDA approval for the drug deferasirox, which may be taken orally. Until this time most patients with Fe overload have had to endure long periods of subcutaneous infusions of the orally ineffective drug desferrioxamine (desferal) which has led to major problems with patient compliance. An effective Fe chelator must possess a number of properties for it to be able to complex Fe in vivo and be excreted intact. This Perspective will provide an overview of the current state of chelators for Fe overload; both those currently approved and those undergoing preclinical development

Methylation of HOXA9 and ISL1 predicts patient outcome in high-grade non-invasive bladder cancer

Introduction Inappropriate DNA methylation is frequently associated with human tumour development, and in specific cases, is associated with clinical outcomes. Previous reports of DNA methylation in low/intermediate grade non-muscle invasive bladder cancer (NMIBC) have suggested that specific patterns of DNA methylation may have a role as diagnostic or prognostic biomarkers. In view of the aggressive and clinically unpredictable nature of high-grade (HG) NMIBC, and the current shortage of the preferred treatment option (Bacillus:Calmette-Guerin), novel methylation analyses may similarly reveal biomarkers of disease outcome that could risk-stratify patients and guide clinical management at initial diagnosis. Methods Promoter-associated CpG island methylation was determined in primary tumour tissue of 36 initial presentation high-grade NMIBCs, 12 low/intermediate-grade NMIBCs and 3 normal bladder controls. The genes HOXA9, ISL1, NKX6-2, SPAG6, ZIC1 and ZNF154 were selected for investigation on the basis of previous reports and/or prognostic utility in low/intermediate-grade NMIBC. Methylation was determined by Pyrosequencing of sodium-bisulphite converted DNA, and then correlated with gene expression using RT-qPCR. Methylation was additionally correlated with tumour behaviour, including tumour recurrence and progression to muscle invasive bladder cancer or metastases. Results The ISL1 genes’ promoter-associated island was more frequently methylated in recurrent and progressive high-grade tumours than their non-recurrent counterparts (60.0% vs. 18.2%, p = 0.008). ISL1 and HOXA9 showed significantly higher mean methylation in recurrent and progressive tumours compared to non-recurrent tumours (43.3% vs. 20.9%, p = 0.016 and 34.5% vs 17.6%, p = 0.017, respectively). Concurrent ISL1/HOXA9 methylation in HG-NMIBC reliably predicted tumour recurrence and progression within one year (Positive Predictive Value 91.7%), and was associated with disease-specific mortality (DSM). Conclusions In this study we report methylation differences and similarities between clinical sub-types of high-grade NMIBC. We report the potential ability of methylation biomarkers, at initial diagnosis, to predict tumour recurrence and progression within one year of diagnosis. We found that specific biomarkers reliably predict disease outcome and therefore may help guide patient treatment despite the unpredictable clinical course and heterogeneity of high-grade NMIBC. Further investigation is required, including validation in a larger patient cohort, to confirm the clinical utility of methylation biomarkers in high-grade NMIBC

The biological development of hydroxypyridinone iron chelators

The object of this study was to screen a series of hydroxypyridinones for their potential as oral iron chelators and to determine the properties of such compounds necessary for oral efficacy. The hydroxypyridinones are water soluble neutral bidentate ligands that have high specificity for iron which they coordinate at a 3:1 ratio under physiological conditions. A protocol for screening these compounds involved in vitro studies using monolayer cultures of isolated rat hepatocytes and in vivo studies using iron-overloaded mice and non-iron-overloaded mice and rats. In the cell culture model, hepatocytes were isolated by collagenase perfusion of livers from adult male Wistar rats. After differential centrifugation, hepatocytes of greater than 90% purity were plated onto collagen-plated sterile dishes. After overnight culture at 37°C, the non-adherent cells were washed away leaving a hepatocyte monolayer of greater than 95% viability. These were pulsed for a variable time with human 59Fe-transferrin before further washes and incubation with the test chelator. Release of 59Fe was then measured over a known time period. Cell toxicity was determined at the end of the experiment by measuring the release of lactate dehydrogenase into the incubation media. In the in vivo studies with mice, the latter were iron over-loaded with iron dextran. After an equilibration period the stores were labelled with human 59Fe-lactoferrin given intravenously. Autoradiographic studies have shown that the majority of the 59Fe labelled the hepatocytes. Following a further equilibration period, the test chelators were administered either orally or intraperitoneally at variable doses. Excretion of 59Fe was measured daily in urine and faeces. Residual radioactivity in body organs and carcasses was also measured. In a second in vivo model the hepatic iron stores of adult female rats were labelled with 59Fe-ferritin. After 90 mins, by which time the 59Fe was at maximum availability, the test chelators were administered either orally or intramuscularly at a dose equivalent to the iron binding capacity of 40mg of desferrioxamine. 59Fe was measured in urine, faeces and body organs 4 hours after chelator administration, by which time chelating activity would be complete. In some experiments the bile duct of the rats was cannulated and the radioactivity of hourly fractions of bile was compared with total biliary iron excretion. The results obtained with the hepatocyte culture system paralleled in vivo data. The hydroxypyridin-4-ones that were most effective in the hepatocyte culture system were also the most active in the mouse and rat models. Their effectiveness by the oral route, in contrast to desferrioxamine, means that these compounds may have an important clinical role to play in the treatment of transfusional iron overload. The most lipophilic compounds, which were associated with the most lactate dehydrogenase release in the hepatocyte culture system, were associated with acute toxicity in mice at doses at which the most hydrophilic compounds showed no toxicity. These findings lead to the conclusion that a consideration of lipid solubility and iron binding constants is important in the overall design of iron chelators. Bidentate hydroxypyridin-4-ones with partition coefficients close to 1 represent compounds which are likely to be the most efficient in mobilising iron both at the cellular level and in vivo, as well as, being less toxic than compounds with high lipid solubility

Taken by Storm: The Rise and Fall of Tau from Microtubule-Associated to Aggregated to Degraded

Tau is a microtubule-associated protein, which promotes neuronal microtubule assembly and stability. Accumulation of tau into insoluble aggregates known as neurofibrillary tangles (NFTs) is a pathological hallmark of several neurodegenerative diseases, known as tauopathies. Aggregated proteins are normally degraded by the cell’s protein degradation mechanisms, autophagy or the ubiquitin-proteasome system (UPS). In tauopathies, however, the efficiency of these degradation pathways becomes challenged by the abnormal accumulation of the tau protein, which consequently, does not get fully degraded. The current hypothesis is that small, soluble oligomeric tau species preceding NFT formation cause toxicity. However, thus far, visualizing the spatial distribution of tau monomers and oligomers inside cells under physiological or pathological conditions has not been possible. Moreover, it is unclear whether certain tau aggregate species are more resistant to degradation. Here, using single-molecule localization microscopy, we show that tau forms small oligomers on microtubules ex vivo. These oligomers are distinct from those found in cells exhibiting tau aggregation and could be precursors of aggregated tau in pathology. Furthermore, using an unsupervised shape classification algorithm that we developed, we show that different tau phosphorylation states are associated with distinct tau aggregate species. Using machine learning, we also show that autophagy and UPS target distinct classes of tau aggregates for degradation. More specifically, we propose a model where tau fibrils are targeted by UPS for degradation and NFTs are mostly degraded by autophagy, generating more tau monomers and oligomers as well as small fibrils. Our work elucidates tau’s nanoscale composition under nonaggregated and aggregated conditions ex vivo and further informs our understanding of how tau aggregates become degraded by the cell’s degradation pathways

Lysosome: the cell's `suicidal bag' as a promising cancer target

Lysosomes are organelles with an acidic lumen containing hydrolases, whose role is to break down macromolecules into their subunits. Cathepsins, which are lysosomal proteases, have important roles in cancer. Enhanced cathepsin activity out of the cell is linked to tumor growth, whereas such activity inside the cell is linked to tumor growth inhibition. Recently published studies on the opposing roles of cathepsin in cancer have investigated their potential as biochemical and nanotechnological therapeutic targets