Multimodal Blood-Based Biomarker Panel Reveals Altered Lysosomal Ionic Content in Alzheimer's Disease.

Lysosomal storage disorders (LSDs) and adult neurodegenerative disorders like Alzheimer's disease (AD) share various clinical and pathophysiological features. LSDs are characterized by impaired lysosomal activity caused by mutations in key proteins and enzymes. While lysosomal dysfunction is also linked to AD pathogenesis, its precise role in disease onset or progression remains unclear.

An SLC12A9-dependent ion transport mechanism maintains lysosomal osmolarity.

Ammonia is a ubiquitous, toxic by-product of cell metabolism. Its high membrane permeability and proton affinity cause ammonia to accumulate inside acidic lysosomes in its poorly membrane-permeant form: ammonium (NH). Ammonium buildup compromises lysosomal function, suggesting the existence of mechanisms that protect cells from ammonium toxicity.

Quantitative Chemical Imaging of Organelles.

ConspectusDNA nanodevices are nanoscale assemblies, formed from a collection of synthetic DNA strands, that may perform artificial functions. The pioneering developments of a DNA cube by Nadrian Seeman in 1991 and a DNA nanomachine by Turberfield and Yurke in 2000 spawned an entire generation of DNA nanodevices ranging from minimalist to rococo architectures. Since our first demonstration in 2009 that a DNA nanodevice can function autonomously inside a living cell, it became clear that this molecular scaffold was well-placed to probe living systems.

A mechanism of lysosomal calcium entry.

Lysosomal calcium (Ca) release is critical to cell signaling and is mediated by well-known lysosomal Ca channels. Yet, how lysosomes refill their Ca remains hitherto undescribed. Here, from an RNA interference screen in , we identify an evolutionarily conserved gene, , that facilitates lysosomal Ca entry in and mammalian cells.

The chemistry of next-generation sequencing.

The first large genome fully sequenced by next-generation sequencing (NGS) was that of a bacteriophage using sequencing by synthesis (SBS) as a paradigm. SBS in NGS is underpinned by 'reversible-terminator chemistry'. To grow from proof of concept to being both affordable and practical, SBS needed to overcome a series of challenges, each of which required the invention of new chemistries.

A DNA nanodevice for mapping sodium at single-organelle resolution.

Cellular sodium ion (Na) homeostasis is integral to organism physiology. Our current understanding of Na homeostasis is largely limited to Na transport at the plasma membrane. Organelles may also contribute to Na homeostasis; however, the direction of Na flow across organelle membranes is unknown because organellar Na cannot be imaged.

Detecting organelle-specific activity of potassium channels with a DNA nanodevice.

Cell surface potassium ion (K) channels regulate nutrient transport, cell migration and intercellular communication by controlling K permeability and are thought to be active only at the plasma membrane. Although these channels transit the trans-Golgi network, early and recycling endosomes, whether they are active in these organelles is unknown. Here we describe a pH-correctable, ratiometric reporter for K called pHlicKer, use it to probe the compartment-specific activity of a prototypical voltage-gated K channel, Kv11.

SLC12A9 is a lysosome-detoxifying ammonium - chloride co-transporter.

Ammonia is a ubiquitous, toxic by-product of cell metabolism. Its high membrane permeability and proton affinity causes ammonia to accumulate inside acidic lysosomes in its poorly membrane-permeant form: ammonium (NH ). Ammonium buildup compromises lysosomal function, suggesting the existence of mechanisms that protect cells from ammonium toxicity.

Passive endocytosis in model protocells.

Semipermeable membranes are a key feature of all living organisms. While specialized membrane transporters in cells can import otherwise impermeable nutrients, the earliest cells would have lacked a mechanism to import nutrients rapidly under nutrient-rich circumstances. Using both experiments and simulations, we find that a process akin to passive endocytosis can be recreated in model primitive cells.

Passive endocytosis in model protocells.

Semipermeable membranes are a key feature of all living organisms. While specialized membrane transporters in cells can import otherwise impermeable nutrients, the earliest cells would have lacked a mechanism to import nutrients rapidly under nutrient-rich circumstances. Using both experiments and simulations, we find that a process akin to passive endocytosis can be recreated in model primitive cells.

Endosomal trafficking of two-pore K efflux channel TWIK2 to plasmalemma mediates NLRP3 inflammasome activation and inflammatory injury.

Potassium efflux via the two-pore K channel TWIK2 is a requisite step for the activation of NLRP3 inflammasome, however, it remains unclear how K efflux is activated in response to select cues. Here, we report that during homeostasis, TWIK2 resides in endosomal compartments. TWIK2 is transported by endosomal fusion to the plasmalemma in response to increased extracellular ATP resulting in the extrusion of K.

Plasma membrane depolarization reveals endosomal escape incapacity of cell-penetrating peptides.

Cell-penetrating peptides (CPPs) are short (<30 amino acids), generally cationic, peptides that deliver diverse cargos into cells. CPPs access the cytosol either by direct translocation through the plasma membrane or via endocytosis followed by endosomal escape. Both direct translocation and endosomal escape can occur simultaneously, making it non-trivial to specifically study endosomal escape alone.

The evolution of organellar calcium mapping technologies.

Intracellular Ca fluxes are dynamically controlled by the co-involvement of multiple organellar pools of stored Ca. Endolysosomes are emerging as physiologically critical, yet underexplored, sources and sinks of intracellular Ca. Delineating the role of organelles in Ca signaling has relied on chemical fluorescent probes and electrophysiological strategies.

A lysosome-targeted DNA nanodevice selectively targets macrophages to attenuate tumours.

Activating CD8 T cells by antigen cross-presentation is remarkably effective at eliminating tumours. Although this function is traditionally attributed to dendritic cells, tumour-associated macrophages (TAMs) can also cross-present antigens. TAMs are the most abundant tumour-infiltrating leukocyte.

Tubular lysosomes harbor active ion gradients and poise macrophages for phagocytosis.

Lysosomes adopt dynamic, tubular states that regulate antigen presentation, phagosome resolution, and autophagy. Tubular lysosomes are studied either by inducing autophagy or by activating immune cells, both of which lead to cell states where lysosomal gene expression differs from the resting state. Therefore, it has been challenging to pinpoint the biochemical properties lysosomes acquire upon tubulation that could drive their functionality.

Tissue-specific targeting of DNA nanodevices in a multicellular living organism.

Nucleic acid nanodevices present great potential as agents for logic-based therapeutic intervention as well as in basic biology. Often, however, the disease targets that need corrective action are localized in specific organs, and thus realizing the full potential of DNA nanodevices also requires ways to target them to specific cell types in vivo. Here, we show that by exploiting either endogenous or synthetic receptor-ligand interactions and leveraging the biological barriers presented by the organism, we can target extraneously introduced DNA nanodevices to specific cell types in , with subcellular precision.

Quantifying phagosomal HOCl at single immune-cell resolution.

Neutralization of pathogens by phagocytic immune cells requires the biogenesis of a compartmentalized hotspot of reactive species called the phagosome. One of these reactive species is hypochlorous acid (HOCl), produced by the enzyme myeloperoxidase (MPO) after the phagosome fuses with the lysosome. Mapping HOCl during phagosome maturation can report on pathogen killing and offer insights into regulation of MPO activity, mechanisms of resistance and host-pathogen interactions.

Proton-activated chloride channel PAC regulates endosomal acidification and transferrin receptor-mediated endocytosis.

During vesicular acidification, chloride (Cl), as the counterion, provides the electrical shunt for proton pumping by the vacuolar H ATPase. Intracellular CLC transporters mediate Cl influx to the endolysosomes through their 2Cl/H exchange activity. However, whole-endolysosomal patch-clamp recording also revealed a mysterious conductance releasing Cl from the lumen.

Quantitative Imaging of Biochemistry and at the Nanoscale.

Biochemical reactions in eukaryotic cells occur in subcellular, membrane-bound compartments called organelles. Each kind of organelle is characterized by a unique lumenal chemical composition whose stringent regulation is vital to proper organelle function. Disruption of the lumenal ionic content of organelles is inextricably linked to disease.

A DNA-based voltmeter for organelles.

The role of membrane potential in most intracellular organelles remains unexplored because of the lack of suitable tools. Here, we describe Voltair, a fluorescent DNA nanodevice that reports the absolute membrane potential and can be targeted to organelles in live cells. Voltair consists of a voltage-sensitive fluorophore and a reference fluorophore for ratiometry, and acts as an endocytic tracer.

DNA-based fluorescent probes of NOS2 activity in live brains.

Innate immune cells destroy pathogens within a transient organelle called the phagosome. When pathogen-associated molecular patterns (PAMPs) displayed on the pathogen are recognized by Toll-like receptors (TLRs) on the host cell, it activates inducible nitric oxide synthase (NOS2) which instantly fills the phagosome with nitric oxide (NO) to clear the pathogen. Selected pathogens avoid activating NOS2 by concealing key PAMPs from their cognate TLRs.

Controlled release of bioactive signaling molecules.

Membrane-initiated steroid signaling (MISS) involves rapid second messenger based intracellular signaling without coupling to transcription or translation. MISS activates important cellular signaling cascades such as mitogen-activated protein kinase (MAPK) or adenylate cyclase pathways. Despite its vital role in signaling, the downstream second messengers involved in MISS and their temporal dynamics remain elusive.