Optical profiling of autonomous Ca2+ nanodomains generated by lysosomal TPC2 and TRPML1

Multiple families of Ca2+-permeable channels co-exist on lysosomal Ca2+ stores but how each family couples to its own unique downstream physiology is unclear. We have therefore investigated the Ca2+-signalling architecture underpinning different channels on the same vesicle that drive separate pathways, using phagocytosis as a physiological stimulus. Lysosomal Ca2+-channels are a major Ca2+ source driving particle uptake in macrophages, but different channels drive different aspects of Fc-receptor-mediated phagocytosis: TPC2 couples to dynamin activation, whilst TRPML1 couples to lysosomal exocytosis. We hypothesised that they are driven by discrete local plumes of Ca2+ around open channels (Ca2+ nanodomains). To test this, we optimized Ca2+-nanodomain recordings by screening panels of genetically encoded Ca2+ indicators (GECIs) fused to TPC2 to monitor the [Ca2+] next to the channel. Signal calibration accounting for the distance of the GECI from the channel mouth reveals that, during phagocytosis, TPC2 generates local Ca2+ nanodomains around itself of up to 42 µM, nearly a hundred-fold greater than the global cytosolic [Ca2+] rise. We further show that TPC2 and TRPML1, though on the same lysosomes, generate autonomous Ca2+ nanodomains of high [Ca2+] that are largely insulated from one another, a platform allowing their discrete Ca2+-decoding to promote unique respective physiologies.

NAADP-Mediated Ca2+ Signalling

The discovery of NAADP-evoked Ca²⁺ release in sea urchin eggs and then as a ubiquitous Ca²⁺ mobilizing messenger has introduced several novel paradigms to our understanding of Ca²⁺ signalling, not least in providing a link between cell stimulation and Ca²⁺ release from lysosomes and other acidic Ca²⁺ storage organelles. In addition, the hallmark concentration-response relationship of NAADP-mediated Ca²⁺ release, shaped by striking activation/desensitization mechanisms, influences its actions as an intracellular messenger. There has been recent progress in our understanding of the molecular mechanisms underlying NAADP-evoked Ca²⁺ release, such as the identification of the endo-lysosomal two-pore channel family of cation channels (TPCs) as their principal target and the identity of NAADP-binding proteins that complex with them. The NAADP/TPC signalling axis has gained recent prominence in pathophysiology for their roles in such disease processes as neurodegeneration, tumorigenesis and cellular viral entry.

Acidic Ca2+ stores and immune-cell function

Acidic organelles act as intracellular Ca²⁺ stores; they actively sequester Ca²⁺ in their lumina and release it to the cytosol upon activation of endo-lysosomal Ca²⁺ channels. Recent data suggest important roles of endo-lysosomal Ca²⁺ channels, the Two-Pore Channels (TPCs) and the TRPML channels (mucolipins), in different aspects of immune-cell function, particularly impacting membrane trafficking, vesicle fusion/fission and secretion. Remarkably, different channels on the same acidic vesicles can couple to different downstream physiology. Endo-lysosomal Ca²⁺ stores can act under different modalities, be they acting alone (via local Ca²⁺ nanodomains around TPCs/TRPMLs) or in conjunction with the ER Ca²⁺ store (to either promote or suppress global ER Ca²⁺ release). These different modalities impinge upon functions as broad as phagocytosis, cell-killing, anaphylaxis, immune memory, thrombostasis, and chemotaxis.

Choreographing endo-lysosomal Ca2+ throughout the life of a phagosome

The emergence of endo-lysosomes as ubiquitous Ca²⁺ stores with their unique cohort of channels has resulted in their being implicated in a growing number of processes in an ever-increasing number of cell types. The architectural and regulatory constraints of these acidic Ca²⁺ stores distinguishes them from other larger Ca²⁺ sources such as the ER and influx across the plasma membrane. In view of recent advances in the understanding of the modes of operation, we discuss phagocytosis as a template for how endo-lysosomal Ca²⁺ signals (generated via TPC and TRPML channels) can be integrated in multiple sophisticated ways into biological processes. Phagocytosis illustrates how different endo-lysosomal Ca²⁺ signals drive different phases of a process, and how these can be altered by disease or infection.

A cellular protection racket: How lysosomal Ca2+ fluxes prevent kidney injury

LC3-lipidation is activated by lysosomal damage by mechanisms that are unknown and divergent from canonical autophagy. In this study, Nakamura et al, show that lysosomal damage induced by lysosomotropic agents or oxalate in renal proximal tubule cells causes lipidated LC3 to insert into the lysosomal membrane to activate TRPML1 channels and release Ca²⁺ from lysosomes. This leads to TFEB dephosphorylation and translocation into the nucleus which results in clearance of damaged lysosomes and their contents which may reduce the deleterious effects of crystal nephropathy.

Defective platelet function in Niemann-Pick disease type C1

Niemann-Pick disease type C (NPC) is a neurodegenerative lysosomal storage disorder caused by mutations in either NPC1 (95% of cases) or NPC2. Reduced late endosome/lysosome calcium (Ca2+) levels and the accumulation of unesterified cholesterol and sphingolipids within the late endocytic system characterize this disease. We previously reported impaired lysosome-related organelle (LRO) function in Npc1 -/- Natural Killer cells; however, the potential contribution of impaired acid compartment Ca2+ flux and LRO function in other cell types has not been determined. Here, we investigated LRO function in NPC1 disease platelets. We found elevated numbers of circulating platelets, impaired platelet aggregation and prolonged bleeding times in a murine model of NPC1 disease. Electron microscopy revealed abnormal ultrastructure in murine platelets, consistent with that seen in a U18666A (pharmacological inhibitor of NPC1) treated megakaryocyte cell line (MEG-01) exhibiting lipid storage and acidic compartment Ca2+ flux defects. Furthermore, platelets from NPC1 patients across different ages were found to cluster at the lower end of the normal range when platelet numbers were measured and had platelet volumes that were clustered at the top of the normal range. Taken together, these findings highlight the role of acid compartment Ca2+ flux in the function of platelet LROs.

NAADP-regulated two-pore channels drive phagocytosis through endo-lysosomal Ca2+ nanodomains, calcineurin and dynamin

Macrophages clear pathogens by phagocytosis and lysosomes that fuse with phagosomes are traditionally regarded as to a source of membranes and luminal degradative enzymes. Here, we reveal that endo-lysosomes act as platforms for a new phagocytic signalling pathway in which FcγR activation recruits the second messenger NAADP and thereby promotes the opening of Ca²⁺ -permeable two-pore channels (TPCs). Remarkably, phagocytosis is driven by these local endo-lysosomal Ca²⁺ nanodomains rather than global cytoplasmic or ER Ca²⁺ signals. Motile endolysosomes contact nascent phagosomes to promote phagocytosis, whereas endo-lysosome immobilization prevents it. We show that TPC-released Ca²⁺ rapidly activates calcineurin, which in turn dephosphorylates and activates the GTPase dynamin-2. Finally, we find that different endo-lysosomal Ca²⁺ channels play diverse roles, with TPCs providing a universal phagocytic signal for a wide range of particles and TRPML1 being only required for phagocytosis of large targets.

Mechanistic convergence and shared therapeutic targets in Niemann-Pick disease

Niemann-Pick disease type C (NPC) and Tangier disease are genetically and clinically distinct rare inborn errors of metabolism. NPC is caused by defects in either NPC1 or NPC2; whereas Tangier disease is caused by a defect in ABCA1. Tangier disease is currently without therapy, whereas NPC can be treated with miglustat, a small molecule inhibitor of glycosphingolipid biosynthesis that slows the neurological course of the disease. When a Tangier disease patient was misdiagnosed with NPC and treated with miglustat, her symptoms improved. This prompted us to consider whether there is mechanistic convergence between these two apparently unrelated rare inherited metabolic diseases. In this study, we found that when ABCA1 is defective (Tangier disease) there is secondary inhibition of the NPC disease pathway, linking these two diseases at the level of cellular pathophysiology. In addition, this study further supports the hypothesis that miglustat, as well as other substrate reduction therapies, may be potential therapeutic agents for treating Tangier disease as fibroblasts from multiple Tangier patients were corrected by miglustat treatment.

Revealing the secrets of secretion

An intracellular ion channel may have a central role in the release of cytokines by macrophages.

Pathogenic mycobacteria achieve cellular persistence by inhibiting the Niemann-Pick Type C disease cellular pathway

BACKGROUND

Tuberculosis remains a major global health concern. The ability to prevent phagosome-lysosome fusion is a key mechanism by which intracellular mycobacteria, including Mycobacterium tuberculosis, achieve long-term persistence within host cells. The mechanisms underpinning this key intracellular pro-survival strategy remain incompletely understood. Host macrophages infected with persistent mycobacteria share phenotypic similarities with cells taken from patients suffering from Niemann-Pick Disease Type C (NPC), a rare lysosomal storage disease in which endocytic trafficking defects and lipid accumulation within the lysosome lead to cell dysfunction and cell death. We investigated whether these shared phenotypes reflected an underlying mechanistic connection between mycobacterial intracellular persistence and the host cell pathway dysfunctional in NPC.

METHODS

The induction of NPC phenotypes in macrophages from wild-type mice or obtained from healthy human donors was assessed via infection with mycobacteria and subsequent measurement of lipid levels and intracellular calcium homeostasis. The effect of NPC therapeutics on intracellular mycobacterial load was also assessed.

RESULTS

Macrophages infected with persistent intracellular mycobacteria phenocopied NPC cells, exhibiting accumulation of multiple lipid types, reduced lysosomal Ca²⁺ levels, and defects in intracellular trafficking. These NPC phenotypes could also be induced using only lipids/glycomycolates from the mycobacterial cell wall. These data suggest that persistent intracellular mycobacteria inhibit the NPC pathway, likely via inhibition of the NPC1 protein, and subsequently induce altered acidic store Ca²⁺ homeostasis. Reduced lysosomal calcium levels may provide a mechanistic explanation for the reduced levels of phagosome-lysosome fusion in mycobacterial infection. Treatments capable of correcting defects in NPC mutant cells via modulation of host cell calcium were of benefit in promoting clearance of mycobacteria from infected host cells.

CONCLUSION 

These findings provide a novel mechanistic explanation for mycobacterial intracellular persistence, and suggest that targeting interactions between the mycobacteria and host cell pathways may provide a novel avenue for development of anti-TB therapies.

Pathogenic mycobacteria achieve cellular persistence by inhibiting the Niemann-Pick Type C disease cellular pathway

BACKGROUND

Tuberculosis remains a major global health concern. The ability to prevent phagosome-lysosome fusion is a key mechanism by which intracellular mycobacteria, including Mycobacterium tuberculosis, achieve long-term persistence within host cells. The mechanisms underpinning this key intracellular pro-survival strategy remain incompletely understood. Host macrophages infected with persistent mycobacteria share phenotypic similarities with cells taken from patients suffering from Niemann-Pick Disease Type C (NPC), a rare lysosomal storage disease in which endocytic trafficking defects and lipid accumulation within the lysosome lead to cell dysfunction and cell death. We investigated whether these shared phenotypes reflected an underlying mechanistic connection between mycobacterial intracellular persistence and the host cell pathway dysfunctional in NPC.

METHODS

The induction of NPC phenotypes in macrophages from wild-type mice or obtained from healthy human donors was assessed via infection with mycobacteria and subsequent measurement of lipid levels and intracellular calcium homeostasis. The effect of NPC therapeutics on intracellular mycobacterial load was also assessed.

RESULTS

Macrophages infected with persistent intracellular mycobacteria phenocopied NPC cells, exhibiting accumulation of multiple lipid types, reduced lysosomal Ca2+ levels, and defects in intracellular trafficking. These NPC phenotypes could also be induced using only lipids/glycomycolates from the mycobacterial cell wall. These data suggest that persistent intracellular mycobacteria inhibit the NPC pathway, likely via inhibition of the NPC1 protein, and subsequently induce altered acidic store Ca2+ homeostasis. Reduced lysosomal calcium levels may provide a mechanistic explanation for the reduced levels of phagosome-lysosome fusion in mycobacterial infection. Treatments capable of correcting defects in NPC mutant cells via modulation of host cell calcium were of benefit in promoting clearance of mycobacteria from infected host cells.

CONCLUSION

These findings provide a novel mechanistic explanation for mycobacterial intracellular persistence, and suggest that targeting interactions between the mycobacteria and host cell pathways may provide a novel avenue for development of anti-TB therapies.

Preferential Coupling of the NAADP Pathway to Exocytosis in T-Cells

A cytotoxic T-lymphocyte (CTL) kills an infected or tumorigenic cell by Ca²⁺-dependent exocytosis of cytolytic granules at the immunological synapse formed between the two cells. However, these granules are more than reservoirs of secretory cytolytic proteins but may also serve as unique Ca²⁺ signaling hubs that autonomously generate their own signals for exocytosis. This review discusses a selective role for the Ca²⁺-mobilizing messenger, nicotinic acid adenine dinucleotide phosphate (NAADP) and its molecular targets, two-pore channels (TPCs), in stimulating exocytosis. Given that TPCs reside on the exocytotic granules themselves, these vesicles generate as well as respond to NAADP-dependent Ca²⁺ signals, which may have wider implications for stimulus-secretion coupling, vesicular fusion, and patho-physiology.

Expression of Ca²⁺-permeable two-pore channels rescues NAADP signalling in TPC-deficient cells

The second messenger NAADP triggers Ca²⁺ release from endo-lysosomes. Although two-pore channels (TPCs) have been proposed to be regulated by NAADP, recent studies have challenged this. By generating the first mouse line with demonstrable absence of both Tpcn1 and Tpcn2 expression (Tpcn1/2^−/−), we show that the loss of endogenous TPCs abolished NAADP-dependent Ca²⁺ responses as assessed by single-cell Ca²⁺ imaging or patch-clamp of single endo-lysosomes. In contrast, currents stimulated by PI(3,5)P₂ were only partially dependent on TPCs. In Tpcn1/2^−/− cells, NAADP sensitivity was restored by re-expressing wild-type TPCs, but not by mutant versions with impaired Ca²⁺-permeability, nor by TRPML1. Another mouse line formerly reported as TPC-null likely expresses truncated TPCs, but we now show that these truncated proteins still support NAADP-induced Ca²⁺ release. High-affinity [³²P]NAADP binding still occurs in Tpcn1/2^−/− tissue, suggesting that NAADP regulation is conferred by an accessory protein. Altogether, our data establish TPCs as Ca²⁺-permeable channels indispensable for NAADP signalling.

Synthesis of caged NAADP

Caged derivatives of Ca²⁺-mobilizing messengers, such as nicotinic acid adenine dinucleotide phosphate (NAADP), are particularly useful for establishing the effects of these messengers on Ca²⁺ signaling. Caged NAADP is no longer commercially available but can be synthesized in house, as described here. In brief, a stable precursor of the caging reagent is made and converted to an unstable reactive reagent immediately before addition to the compound to be caged.

Measurement of luminal pH of acidic stores as a readout for NAADP action

In addition to mobilizing Ca²⁺, NAADP plays a role in modulating the luminal pH (pHL) of acidic stores of the endolysosomal system. The effects of NAADP on pHL have been most extensively studied in the sea urchin egg, both in the intact egg and in egg homogenates. Related observations have also been made in mammalian systems (e.g., guinea pig atrial myocytes and pancreatic acinar cells). Although the connection between Ca²⁺ mobilization and increase in pHL is not understood, pHL can be a useful parameter to measure when studying NAADP-mediated signaling. This protocol describes the fluorescent measurement of pHL of acidic stores. It relies on the use of acridine orange (AO), a standard dye for pHL. AO selectively accumulates to high concentrations in the lumen of organelles as a function of acidity; at these high concentrations it self-quenches. When pHL increases, some AO is lost from the vesicle. As a result, the lower luminal AO concentration relieves the quenching and fluorescence increases in the lumen.

Synthesis of NAADP-AM as a membrane-permeant NAADP analog

Nicotinic acid adenine dinucleotide phosphate (NAADP), like the other major messengers for Ca²⁺ mobilization, is passively membrane-impermeant. Instead, a cell-permeant acetoxymethyl ester derivative of NAADP (NAADP-AM) can be synthesized as described here and used to study NAADP-mediated Ca²⁺ release.

Synthesis of [³²P]NAADP for the radioreceptor binding assay

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a major messenger for Ca(2+) mobilization in cells. NAADP-binding proteins are highly selective and have a strong affinity for NAADP. This is the basis of the radioreceptor binding assay, which is used to measure NAADP levels in cells and tissues and to identify cellular stimuli that use NAADP as an intracellular messenger. In the radioreceptor binding assay, radiolabeled NAADP ([(32)P]NAADP) competes with endogenous NAADP present in samples for binding to their receptors. Here, we describe the synthesis of [(32)P]NAADP for use in the radioreceptor binding assay.

Preparation and use of sea urchin egg homogenates for studying NAADP-mediated Ca²⁺ release

NAADP and other Ca(2+)-mobilizing messengers are membrane impermeant and thus must be added directly to cell-free or broken-cell preparations to effect Ca(2+) release. The sea urchin egg homogenate, where the biological activity of NAADP was first reported, remains the gold standard cell-free system for studying NAADP-mediated Ca(2+) release. Here we describe how to prepare sea urchin egg homogenate and use it to measure NAADP-mediated Ca(2+) release.

Cytolytic granules supply Ca(2+) for their own exocytosis via NAADP and resident two-pore channels

When cytotoxic T-lymphocytes (CTLs) kill infected or cancerous cells they secrete cytolytic proteins (perforin and granzymes) into the target cell. These “death factors” are pre-stored in cytolytic granules within the CTL until an increase in the intracellular Ca²⁺ drives granule exocytosis. However, not all sources of Ca²⁺ stimulate exocytosis: we have recently demonstrated that it is the cytolytic granules themselves that are the source of the Ca²⁺ that most efficiently drives their own exocytosis; release of Ca²⁺ from the granules is only activated by the Ca²⁺-mobilizing messenger NAADP (nicotinic acid adenine dinucleotide phosphate) that acts upon target two-pore channels (TPCs) present on the granules. That NAADP is a unique stimulus of exocytosis may be of fundamental importance not only to immunology but to cell biology in general.

Bidirectional Ca²⁺ signaling occurs between the endoplasmic reticulum and acidic organelles

After acidic organelles induce signaling to activate ER calcium ion release, local microdomains of high calcium at ER–acidic organelle junctions feed back to activate further acidic organelle calcium release.

The endoplasmic reticulum (ER) and acidic organelles (endo-lysosomes) act as separate Ca²⁺ stores that release Ca²⁺ in response to the second messengers IP₃ and cADPR (ER) or NAADP (acidic organelles). Typically, trigger Ca²⁺ released from acidic organelles by NAADP subsequently recruits IP₃ or ryanodine receptors on the ER, an anterograde signal important for amplification and Ca²⁺ oscillations/waves. We therefore investigated whether the ER can signal back to acidic organelles, using organelle pH as a reporter of NAADP action. We show that Ca²⁺ released from the ER can activate the NAADP pathway in two ways: first, by stimulating Ca²⁺-dependent NAADP synthesis; second, by activating NAADP-regulated channels. Moreover, the differential effects of EGTA and BAPTA (slow and fast Ca²⁺ chelators, respectively) suggest that the acidic organelles are preferentially activated by local microdomains of high Ca²⁺ at junctions between the ER and acidic organelles. Bidirectional organelle communication may have wider implications for endo-lysosomal function as well as the generation of Ca²⁺ oscillations and waves.

NAADP activates two-pore channels on T cell cytolytic granules to stimulate exocytosis and killing

A cytotoxic T lymphocyte (CTL) kills an infected or tumorigenic cell by Ca²⁺-dependent exocytosis of cytolytic granules at the immunological synapse formed between the two cells. Although inositol 1,4,5-trisphosphate (IP₃)-mediated Ca²⁺ release from the endoplasmic reticulum activates the store-operated Ca²⁺-influx pathway that is necessary for exocytosis, it is not a sufficient stimulus [1–4]. Here we identify the Ca²⁺-mobilizing messenger nicotinic acid adenine dinucleotide phosphate (NAADP) and its recently identified molecular target, two-pore channels (TPCs) [5–7], as being important for T cell receptor signaling in CTLs. We demonstrate that cytolytic granules are not only reservoirs of cytolytic proteins but are also the acidic Ca²⁺ stores mobilized by NAADP via TPC channels on the granules themselves, so that TPCs migrate to the immunological synapse upon CTL activation. Moreover, NAADP activates TPCs to drive exocytosis in a way that is not mimicked by global Ca²⁺ signals induced by IP₃ or ionomycin, suggesting that critical, local Ca²⁺ nanodomains around TPCs stimulate granule exocytosis. Hence, by virtue of the NAADP/TPC pathway, cytolytic granules generate Ca²⁺ signals that lead to their own exocytosis and to cell killing. This study highlights a selective role for NAADP in stimulating exocytosis crucial for immune cell function and may impact on stimulus-secretion coupling in wider cellular contexts.

Relationships among performance, residual feed intake, and product quality of progeny from Red Angus sires divergent for maintenance energy EPD

Energy expenditure is a physiological process that may be closely associated with residual feed intake (RFI). The maintenance energy (ME(M)) EPD was developed by the Red Angus Association of America (RAAA) and is used as an indicator of energy expenditure. The objectives of this study were to evaluate and quantify the following relationships using progeny of Red Angus (RA) sires divergent for ME(M) EPD: 1) postweaning RFI and finishing phase feed efficiency (FE), 2) postweaning RFI and end-product quality, and 3) postweaning RFI and sire ME(M) EPD. A total of 12 RA sires divergent for ME(M) EPD were chosen using the RAAA-generated ME(M) EPD values and were partitioned into 2 groups: high ME(M) EPD (≥4 Mcal/mo) and low ME(M) EPD (<4 Mcal/mo), based on the breed average of 4 Mcal/mo. Commercial crossbred cows were inseminated to produce 3 cohorts of progeny, which were tested for postweaning RFI (cohorts 1, 2, and 3) and finishing phase FE (cohorts 1 and 3). Results indicate that postweaning RFI and finishing phase FE of steer progeny tended to be positively correlated (r = 0.38; P = 0.06) in cohort 1 and were positively correlated (r = 0.50; P = 0.001) in cohort 3. In addition, postweaning RFI was not phenotypically correlated (P > 0.05) with any carcass traits or end-product quality measurements. Sire ME(M) EPD was phenotypically correlated (P < 0.05) with carcass traits in cohort 1 (HCW, LM area, KPH, fat thickness, and yield grade) and cohort 2 (KPH and fat thickness). Since variation in measured LM area was not explained by the genetic potential of rib eye area EPD, and therefore, the observed correlation between sire ME(M) EPD and measured LM area may suggest an association between ME(M) EPD and LM area. A correlation (r = 0.24; P = 0.02) was observed between postweaning RFI and ultrasound intramuscular fat percentage in cohort 2 but was not detected in cohorts 1 or 3. In addition, no phenotypic relationship was observed (P > 0.05) between progeny postweaning RFI and sire ME(M) EPD. Therefore, results suggest 1) RFI measured during the postweaning growth phase is indicative of FE status in the finishing phase, 2) neither RFI nor sire ME(M) EPD negatively affected carcass or end-product quality, and 3) RFI and sire ME(M) EPD are not phenotypically associated.

Infrared monitoring of dinitrotoluenes in sunflower and maize roots

Infrared microspectroscopy (IMS) is emerging as an important analytical tool for the structural analysis of biological tissue. This report describes the use of IMS coupled to a synchrotron source combined with principal components analysis (PCA) to monitor the fate and effect of dinitrotoluenes in the roots of maize and sunflower plants. Infrared imaging revealed that maize roots metabolized 2,4-dinitrotoluene (DNT) and 2,6-DNT. The DNTs and their derivative aromatic amines were predominantly associated with epidermis and xylem. Both isomers of DNT altered the structure and production of pectin and pectic polysaccharides in maize and sunflower plant roots. Infrared peaks diagnostic for aromatic amines were seen at the 5 mg L concentrations for both DNTs in maize and sunflower treated tissue. However, only infrared peaks for nitro groups, not aromatic amines, were present in the maize treated at 10 mg L For sunflower, the 10 mg L level was toxic and also produced very dark root systems making spectra difficult to obtain. Maize and sunflower seem unable to metabolize effectively at concentrations higher than about 5 mg L DNT in hydroponic solution. Based on the results of this study, IMS combined with PCA can be an effective means of determining the fate and metabolism of organic contaminants in plant tissue when isotopically labeled compounds are not available.

Purified TPC isoforms form NAADP receptors with distinct roles for Ca(2+) signaling and endolysosomal trafficking

Intracellular Ca²⁺ signals constitute key elements in signal transduction. Of the three major Ca²⁺ mobilizing messengers described, the most potent, nicotinic acid adenine dinucleotide phosphate (NAADP) is the least well understood in terms of its molecular targets [1]. Recently, we showed that heterologous expression of two-pore channel (TPC) proteins enhances NAADP-induced Ca²⁺ release, whereas the NAADP response was abolished in pancreatic beta cells from Tpcn2 gene knockout mice [2]. However, whether TPCs constitute native NAADP receptors is unclear. Here we show that immunopurified endogenous TPC complexes possess the hallmark properties ascribed to NAADP receptors, including nanomolar ligand affinity [3–5]. Our study also reveals important functional differences between the three TPC isoforms. Thus, TPC1 and TPC2 both mediate NAADP-induced Ca²⁺ release, but the subsequent amplification of this trigger Ca²⁺ by IP₃Rs is more tightly coupled for TPC2. In contrast, TPC3 expression suppressed NAADP-induced Ca²⁺ release. Finally, increased TPC expression has dramatic and contrasting effects on endolysosomal structures and dynamics, implicating a role for NAADP in the regulation of vesicular trafficking. We propose that NAADP regulates endolysosomal Ca²⁺ storage and release via TPCs and coordinates endoplasmic reticulum Ca²⁺ release in a role that impacts on Ca²⁺ signaling in health and disease [6].

Meningococcal disease in a backpackers hostel in Scotland: a risk assessment for prophylaxis

This paper outlines the risk assessment and communication strategy carried out by the Lothian Health Protection Team after notification of a probable case of meningococcal disease (later confirmed as Neisseria meningitidis) in a resident of a city centre backpackers hostel. Six close contacts were identified from the hostel and given rifampicin prophylaxis. Two days after commencing rifampicin one of these contacts was admitted to hospital with a purpuric/petechial rash and thrombocytopenia. The final diagnosis for this contact was thrombocytopenia, either idiopathic or secondary to rifampicin. This example and the potential side effects of administering rifampicin prophylaxis highlight the importance of a thorough risk assessment of contacts of a case to avoid prescribing prophylaxis to anyone other than those at highest risk of becoming a subsequent case.

Phospholipase C zeta undergoes dynamic changes in its pattern of localization in sperm during capacitation and the acrosome reaction

OBJECTIVE

To evaluate the localization of phospholipase C zeta (PLC zeta) in non-capacitated, capacitated, and ionophore-treated sperm.

DESIGN

Phospholipase C zeta was cloned from the hamster, an important model organism for studying fertilization. Next, we used hamster and mouse models to investigate the localization of PLC zeta in non-capacitated and capacitated sperm and in sperm treated with ionophore to induce the acrosome reaction.

SETTING

University laboratory.

ANIMAL(S)

Male mice and hamsters, 4-6 weeks old.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Phospholipase C zeta localization in non-capacitated, capacitated, and ionophore-treated sperm.

RESULT(S)

Full-length hamster PLC zeta complementary DNA is 1953 base pairs in size, encoding an open reading frame of 651 amino acids, sharing 85% amino acid similarity with the mouse. Phospholipase C zeta was localized in acrosomal and post-acrosomal regions of sperm. The post-acrosomal localization, which became more evident after capacitation and was maintained after ionophore treatment, is in line with PLC zeta being the endogenous agent of egg activation. However, the acrosomal PLC zeta population, which was lost after ionophore treatment, suggests that PLC zeta could have other functions besides egg activation.

CONCLUSION(S)

Phospholipase C zeta is localized to acrosomal and post-acrosomal regions and undergoes dynamic changes during capacitation and the acrosome reaction, indicating a potential role regulating not only egg activation but other sperm functions.

Flipping the switch: How a sperm activates the egg at fertilization

Sperm interaction with an egg in animals was first documented 160 years ago in sea urchins by Alphonse Derbès (1847) when he noted the formation of an "envelope" following the sperm's "approach" to the egg. The "envelope" in sea urchins is an obvious phenotype of fertilization in this animal and over the past 35 years has served to indicate a presence of calcium released from cytoplasmic stores essential to activate the egg. The mechanism of calcium release has been intensely studied because it is a universal regulator of cellular activity, and recently several intersecting pathways of calcium release have been defined. Here we examine these various mechanisms with special emphasis on recent work in eggs of both sea urchins and mice.

Effect of adaptive cruise control systems on traffic flow

The flow of traffic composed of vehicles that are equipped with adaptive cruise control (ACC) is studied using simulations. The ACC vehicles are modeled by a linear dynamical equation that has string stability. In platoons of all ACC vehicles, perturbations due to changes in the lead vehicle's velocity do not cause jams. Simulations of merging flows near an onramp show that if the total incoming rate does not exceed the capacity of the single outgoing lane, free flow is maintained. With larger incoming flows, a state closely related to the synchronized flow phase found in manually driven vehicular traffic has been observed. This state, however, should not be considered congested because the flow is maximal for the density. Traffic composed of random sequences of ACC vehicles and manual vehicles has also been studied. At high speeds (approximately 30 m/s ) jamming occurs for concentrations of ACC vehicles of 10% or less. At 20% no jams are formed. The formation of jams is sensitive to the sequence of vehicles (ACC or manual). At lower speeds (approximately 15 m/s ), no critical concentration for complete jam suppression is found. Rather, the average velocity in the pseudojam region increases with increasing ACC concentration. Mixing 50% ACC vehicles randomly with manually driven vehicles on the primary lane in onramp simulations shows only modestly reduced travel times and larger flow rates.

Multilane simulations of traffic phases

The optimal velocity model, as modified by the author, is used in simulations of traffic on a dual-lane highway and a single-lane highway with an on-ramp. The equilibrium solutions of the modified model cover a two-dimensional region of flow-density space beneath the fundamental-diagram curve, rather than just lying on the curve as in the original model. Thus it satisfies a requirement of the three-phase model of Kerner [Phys. Rev. Lett. 81, 3797 (2002)]. Synchronization of velocity across dual lanes due to frequent lane changes is observed in free flow. True synchronized flow, as determined by the region of density-flow space it occupies, is obtained in on-ramp simulations with typical driver reaction times. A gradual change to the formation of a jam is observed for increasing delay times.

Technical note: fate and transport of jet fuel (JP-8) in soils with selected plants

Remediation of soil and groundwater contaminated by leaking fuel storage tanks may be assisted by plants, although plant effects on abiotic and biotic removal processes remain unclear. The objectives of this study were to investigate abiotic and biotic removal of JP-8, a kerosene-based jet fuel, in soils with plants, and to determine the effects of plant-induced water movement. Loss of JP-8 in a dry-soil, control column was 25% after 5 months, primarily due to volatilization and gas-phase diffusion. By comparison, managed treatments with simulated surface spills averaged 86% mass reduction at 5 months, indicating an important contribution of biodegradation. Overall JP-8 mass reduction was similar in surface and subsurface-irrigated systems, indicating water content, not mode of water application, influences bioremediation in near-surface systems. The JP-8 concentration reductions in soil columns contaminated above a simulated watertable were 36% after 3 months and 50% after 12 months for vegetated columns compared to 26% and 34% in unplanted columns. Downward movement of JP-8 in unplanted columns was double that in planted columns. Near the groundwater table, JP-8 persists longer than near the soil surface. Plants promote upward movement of water and help draw spilled JP-8 to aerobic near-surface soil.

Modeling jet fuel (JP-8) fate and transport in soils with plants

Vegetation is often used to clean up soils and groundwater contaminated with organic contaminants. Plant-induced upward water movement may draw organic contaminants spilled near the watertable to the more aerated near-surface soil. The objective of this study was to develop and verify a 1-D model of fate and transport of JP-8, a kerosene-based jet fuel, in soil. The modeling approach considered the advective and dispersive transport of jet fuels dissolved in groundwater, which may undergo simple first-order decay or linear adsorption. The governing partial differential advection dispersion equation was solved in one dimension. Data from an experiment of fate and transport of JP-8 with plant-induced upward water movement were used to verify the model. Simulated results with different scenarios described the experimental results well for different depths above the contaminated zone in both vegetated and unvegetated columns. Advection was the dominant mechanism near the contaminated zone and advection with retardation and decay was used to fit the data away from the contaminated zone. Results indicated that the soil water movement impacted the transport and concentration of JP-8 in the soil columns. This model can be used to simulate the fate of JP-8 associated with phytoremediation and evapotranspiration.

Comment on "Analysis of optimal velocity model with explicit delay"

The effect of including an explicit delay time (due to driver reaction) on the optimal velocity model is studied. For a platoon of vehicles to avoid collisions, many-vehicle simulations demonstrate that delay times must be well below the critical delay time determined by a linear analysis for the response of a single vehicle. Safe platoons require rather small delay times, substantially smaller than typical reaction times of drivers. The present results do not support the conclusion of Bando et al. [M. Bando, K. Hasebe, K. Nakanishi, and A. Nakayama, Phys. Rev. E 58, 5429 (1998)] that explicit delay plays no essential role.

Transport of methyl tert-butyl ether through alfalfa plants

Concentrations measured in alfalfa plant stem segments indicated that plants grown in methyl tert-butyl ether (MTBE)-contaminated soil took up the chemical through their roots. Assuming a cylindrical shape for the plant stem, a mathematical model was developed to describe the transport of MTBE through the stems. Simulation results from uniform and nonuniform initial concentration distributions across the stem radius were compared with steady-state experimental data. With known values of plant stem radius, water usage, water content, and the distance over which the concentration decreased by 50%, the diffusion coefficient of MTBE radial transport across the plant stem was estimated with 95% confidence to be in the range of 8.43-16.2 x 10(-8) cm2/s with a mean of 1.23 x 10(-7) cm2/s. When the diffusion coefficient was calculated based on transient experimental data, the values with 95% confidence interval ranged from 4.14 x 10(-7) to 8.00 x 10(-7) cm2/s with a mean value of 6.07 x 10(-7) cm2/s. The difference between these two results can be reduced by more accurate estimation of the water flow velocity through plant stems. The model is applicable to other species including sunflowers and poplars upon substitution of appropriate parameters.

Using electrophoresis to observe the interaction of nitrogenase with ions

The two protein components of nitrogenase from Klebsiella pneumoniae were shown to interact with metal ions and ADP, altering their electrophoretic mobility in polyacrylamide gel electrophoresis. Both Mg+2 and Mn+2 caused reduced mobility of Fe protein relative to other proteins. The effect was about 50% complete at concentrations around 0.2 mM. Other ions including Fe+2, Ni+2 and Co+2 had no observable effect at levels up to 1 _mM. Both Cd+2 and Zn+2 appeared to interact with the protein; Cd+2 at 0.5 mM dramatically destabilized the protein. The effects of more than a dozen different mutations of the Fe protein on Mg+2 interaction were examined. All mutated proteins appeared to interact with Mg+2 similarly to wild-type. Using relative mobility differences of charge-changed mutants it was estimated that two to three Mg+2 interact with each Fe protein monomer. The MoFe protein also showed interaction with metal ions but the alteration of mobility was much smaller than for the Fe protein because it is larger and less acidic, so that it runs much more slowly than the Fe protein in standard gels. The interaction of ADP with Fe protein was examined in the presence of Mg+2. Increasing ADP partially reversed the mobility decrease observed on Mg+2 binding, and produced a more diffuse protein band indicative of a reaction zone of interconverting conformers. No alteration of MoFe protein mobility was observed with ADP added during electrophoresis.

Interaction with magnesium and ADP stabilizes both components of nitrogenase from Klebsiella pneumoniae against urea denaturation

The nitrogenase enzyme of Klebsiella pneumoniae consists of two separable proteins, each with multiple subunits and one or more oxygen sensitive metallocenters. The wild-type nitrogenase proteins are stable to electrophoresis in high concentrations of urea under anaerobic conditions. Addition of Mg+2 and ADP greatly increases the stability of the smaller Fe protein (from <4 to >6 M for full unfolding), an effect directly analogous to stabilization in p21ras induced by Mg+2 and GDP. Stabilization by Mg+2 is slight for the holo MoFe protein (from approximately 1.5 to approximately 2.4 M) but more dramatic for the apo protein form of the MoFe protein accumulated by certain Fe protein (nifH gene) mutants. The potent product inhibitor of nitrogenase function, MgADP, increases stability of the MoFe protein more than Mg+2 alone, to approximately 3.6 M, showing that nucleotides interact with the MoFe protein. Mutations of the nifM gene result in slower accumulation of less stable Fe protein, indicating that NifM is involved in correct folding of the Fe protein. Mutationally altered proteins are often difficult to purify for study because of their inherent instability, low expression level, or oxygen lability. Crude extracts of 11 different mutants of Fe protein (nifH gene) were examined by transverse urea gradient gels to rapidly screen for stabilizing interactions in the presence or absence of substrate or inhibitor analogs. Amino acid alterations D44N and R188C, at the interface of the dimer, in the vicinity of the nucleotide binding site(s), have significantly lower stability than the wild-type enzyme in the absence of Mg+2 but comparable stability in its presence, showing the importance of Mg+2 in the subunit interactions. Mutations N163S and E266K, in which residues normally involved in hydrogen bonding far from the active site were altered, are more labile than the wild-type even with Mg+2 added. Seven other mutants, though nonfunctional, did not appear altered in stability compared to the wild-type.

Sideport incision paracentesis versus antiglaucoma medication to control postoperative pressure rises after intraocular lens surgery

Twenty-eight patients who had an intraocular pressure greater than 30 mm Hg within 24 hours after cataract surgery were randomly assigned to be treated with medication or by paracentesis through a sideport incision. Paracentesis provided an immediate reduction in intraocular pressure, but within one hour pressures rebounded. Within two to three hours after treatment, the medication group had significantly greater mean reductions in intraocular pressure than the paracentesis group.

Systematics and body size: implications for feeding adaptations in New World monkeys

The relationship between body size and feeding ecology is well established for primates. It is argued that the evolutionary history of modern New World monkeys and, in particular, the path to attainment of current body size is significant in understanding the similarities and differences between dietary strategies and other ecological parameters of similar-sized monkeys. Current interpretations of New World monkey evolutionary relationships are reviewed. Based on a synthesis of available body weights and the assumption that the earliest New World monkeys weighed close to 1 kg, similar to modern Aotus and Callicebus, predicted patterns of body size change in each lineage are given. Restrictions on directions of body size change in primates are discussed, and it is shown that "Stanley's Rule" offers a good explanation for differing body size ranges in New and Old World anthropoids. Predicted ecological correlates to body size drawn from the mammalian literature are offered and tested using data on New World monkeys, which show some concurrence and several interesting departures from predicted patterns. Sexual dimorphism in body weight of New World monkey species is reviewed, based on the new summary of body weight data given.

Two-step isolation of bacterial ribonucleic acid without using a chaotropic agent or cesium chloride centrifugation

A simple RNA isolation method was developed to purify bacterial RNAs from a large number of samples simultaneously in an hour. The method is based on boiling the cells in the presence of Triton X-100 and lysozyme, and then preferential RNA precipitation with ammonium acetate. There is no CsCl centrifugation required. For the nitrogen-fixing bacterium Klebsiella pneumoniae, the depression condition can be maintained during the cell-harvesting process. The intact isolated RNAs appeared to be free of protein, with a yield of 100 micrograms RNA from a 4-ml cell culture of 100 Klett units (10(9) cells/ml). Any DNA present was in a form that did not react with a nifH probe following Northern blotting to nitrocellulose (i.e., was not single-stranded).

Kinetics of protease hydrolysis of extended peptide substrates: measurement by flow-injection analysis

A flow-injection analysis (FIA) system was developed to study the enzyme-catalyzed hydrolysis of synthetic peptides, each of which contained one scissile bond. The concentrations of alpha-amino groups in reactions mixtures were determined by FIA with o-phthalaldehyde as a fluorescence reagent. The method allows a rapid, precise, and sensitive determination of kinetic constants for proteases acting on extended peptide substrates.

Substitution of histidine for arginine-101 of dinitrogenase reductase disrupts electron transfer to dinitrogenase

Dinitrogenase reductase from Klebsiella pneumoniae strain UN1041 has a histidine residue substituted for arginine at position 101. The mutant dinitrogenase reductase was purified and characterized in order to determine the importance of arginine-101 in the interaction between dinitrogenase and dinitrogenase reductase during electron transfer. Purified dinitrogenase reductase from UN1041 is a dimer of 67 kDa, contains a functional 4Fe-4S cluster, undergoes a MgATP-dependent conformational change, and is competent for ATP hydrolysis uncoupled from substrate reduction in the presence of dinitrogenase. However, the mutant protein is unable to support the reduction of protons or acetylene by dinitrogenase. A 100-fold molar excess of Kp2 from UN1041 does not inhibit electron transfer from wild-type dinitrogenase reductase to dinitrogenase. It is concluded that the interaction of dinitrogenase reductase with dinitrogenase during reductant-independent ATP hydrolysis is different than the interaction between the two proteins during electron transfer; the substitution of histidine for arginine at position 101 disrupts only the latter interaction. The same conclusions are reached using wild-type dinitrogenase reductase which has been ADP-ribosylated at arginine-101.