Gamified Smartphone-App Interventions on Behaviour and Metabolic Profile in Patients at Risk of Cardiovascular Disease

This study assesses how effective gamification in smartphone apps is at enhancing lifestyle and cardiometabolic health in adults at risk of cardiovascular disease. Using a systematic review of six databases, it looked at trials that compared gamified and traditional interventions. Although apps scored highly for functionality, averaging a 4.07 rating, they lacked focus on user engagement. The study reveals that gamification can aid in achievable lifestyle changes and improve cardiometabolic factors, providing insights for future digital health approaches targeting CVD risk reduction.

Spatial and Temporal Coordination of Force-generating Actin-based Modules Drives Membrane Remodeling In Vivo

Membrane remodeling drives a broad spectrum of cellular functions, and it is regulated through mechanical forces exerted on the membrane by cytoplasmic complexes. Here, we investigate how actin filaments dynamically tune their structure to control the active transfer of membranes between cellular compartments with distinct compositions and biophysical properties. Using intravital subcellular microscopy in live rodents we show that: a lattice composed of linear filaments stabilizes the granule membrane after fusion with the plasma membrane; and a network of branched filaments linked to the membranes by Ezrin, a regulator of membrane tension, initiates and drives to completion the integration step. Our results highlight how the actin cytoskeleton tunes its structure to adapt to dynamic changes in the biophysical properties of membranes.

Testing the Effects of App-Based Motivational Messages on Physical Activity and Resting Heart Rate Through Smartphone App Compliance in Patients With Vulnerable Coronary Artery Plaques: Protocol for a Microrandomized Trial

BACKGROUND

Achieving the weekly physical activity recommendations of at least 150-300 minutes of moderate-intensity or 75-150 minutes of vigorous-intensity aerobic exercise is important for reducing cardiometabolic risk, but evidence shows that most people struggle to meet these goals, particularly in the mid to long term.

OBJECTIVE

The Messages Improving Resting Heart Health (MIRTH) study aims to determine if (1) sending daily motivational messages through a research app is effective in improving motivation and in promoting adherence to physical activity recommendations in men and women with coronary heart disease randomized to a 12-month intensive lifestyle intervention, and (2) the time of the day when the message is delivered impacts compliance with exercise training.

METHODS

We will conduct a single-center, microrandomized trial. Participants will be randomized daily to either receive or not receive motivational messages over two 90-day periods at the beginning (phase 1: months 4-6) and at the end (phase 2: months 10-12) of the Lifestyle Vulnerable Plaque Study. Wrist-worn devices (Fitbit Inspire 2) and Bluetooth pairing with smartphones will be used to passively collect data for proximal (ie, physical activity duration, steps walked, and heart rate within 180 minutes of receiving messages) and distal (ie, change values for resting heart rate and total steps walked within and across both phases 1 and 2 of the trial) outcomes. Participants will be recruited from a large academic cardiology office practice (Central Sydney Cardiology) and the Royal Prince Alfred Hospital Departments of Cardiology and Radiology. All clinical investigations will be undertaken at the Charles Perkins Centre Royal Prince Alfred clinic. Individuals aged 18-80 years (n=58) with stable coronary heart disease who have low attenuation plaques based on a coronary computed tomography angiography within the past 3 months and have been randomized to an intensive lifestyle intervention program will be included in MIRTH.

RESULTS

The Lifestyle Vulnerable Plaque Study was funded in 2020 and started enrolling participants in February 2022. Recruitment for MIRTH commenced in November 2022. As of September 2023, 2 participants were enrolled in the MIRTH study and provided baseline data.

CONCLUSIONS

This MIRTH microrandomized trial will represent the single most detailed and integrated analysis of the effects of a comprehensive lifestyle intervention delivered through a customized mobile health app on smart devices on time-based motivational messaging for patients with coronary heart disease. This study will also help inform future studies optimizing for just-in-time adaptive interventions.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12622000731796; https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=382861.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/46082.

Vegetarian and vegan diets: benefits and drawbacks

Plant-based diets have become increasingly popular thanks to their purported health benefits and more recently for their positive environmental impact. Prospective studies suggest that consuming vegetarian diets is associated with a reduced risk of developing cardiovascular disease (CVD), diabetes, hypertension, dementia, and cancer. Data from randomized clinical trials have confirmed a protective effect of vegetarian diets for the prevention of diabetes and reductions in weight, blood pressure, glycosylated haemoglobin and low-density lipoprotein cholesterol, but to date, no data are available for cardiovascular event rates and cognitive impairment, and there are very limited data for cancer. Moreover, not all plant-based foods are equally healthy. Unhealthy vegetarian diets poor in specific nutrients (vitamin B12, iron, zinc, and calcium) and/or rich in highly processed and refined foods increase morbidity and mortality. Further mechanistic studies are desirable to understand whether the advantages of healthy, minimally processed vegetarian diets represent an all-or-nothing phenomenon and whether consuming primarily plant-based diets containing small quantities of animal products (e.g. pesco-vegetarian or Mediterranean diets) has beneficial, detrimental, or neutral effects on cardiometabolic health outcomes. Further, mechanistic studies are warranted to enhance our understanding about healthy plant-based food patterns and the biological mechanisms linking dietary factors, CVD, and other metabolic diseases.

Vegetarian Dietary Patterns and Cardiometabolic Risk in People With or at High Risk of Cardiovascular Disease: A Systematic Review and Meta-analysis

IMPORTANCE

Plant-based diets are known to improve cardiometabolic risk in the general population, but their effects on people at high risk of cardiovascular diseases (CVDs) remain inconclusive.

OBJECTIVE

To assess the association of vegetarian diets with major cardiometabolic risk factors, including low-density lipoprotein cholesterol (LDL-C), hemoglobin A1c (HbA1c), systolic blood pressure (SBP), and body weight in people with or at high risk of CVDs.

DATA SOURCES

This meta-analysis was registered before the study was conducted. Systematic searches performed included Embase, MEDLINE, CINAHL, and CENTRAL from inception until July 31, 2021.

STUDY SELECTION

Eligible randomized clinical trials (RCTs) that delivered vegetarian diets in adults with or at high risk of CVDs and measured LDL-C, HbA1c or SBP were included. Of the 7871 records screened, 29 (0.4%; 20 studies) met inclusion criteria.

DATA EXTRACTION AND SYNTHESIS

Two reviewers independently extracted data including demographics, study design, sample size, and diet description, and performed risk of bias assessment. A random-effects model was used to assess mean changes in LDL-C, HbA1c, SBP, and body weight. The overall certainty of evidence was evaluated using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) tool.

MAIN OUTCOMES AND MEASURES

Mean differences between groups in changes (preintervention vs postintervention) of LDL-C, HbA1c, and SBP; secondary outcomes were changes in body weight and energy intake.

RESULTS

Twenty RCTs involving 1878 participants (range of mean age, 28-64 years) were included, and mean duration of intervention was 25.4 weeks (range, 2 to 24 months). Four studies targeted people with CVDs, 7 focused on diabetes, and 9 included people with at least 2 CVD risk factors. Overall, relative to all comparison diets, meta-analyses showed that consuming vegetarian diets for an average of 6 months was associated with decreased LDL-C, HbA1c, and body weight by 6.6 mg/dL (95% CI, -10.1 to -3.1), 0.24% (95% CI, -0.40 to -0.07), and 3.4 kg (95% CI, -4.9 to -2.0), respectively, but the association with SBP was not significant (-0.1 mm Hg; 95% CI, -2.8 to 2.6). The GRADE assessment showed a moderate level of evidence for LDL-C and HbA1c reduction.

CONCLUSIONS AND RELEVANCE

In this study, consuming a vegetarian diet was associated with significant improvements in LDL-C, HbA1c and body weight beyond standard therapy in individuals at high risk of CVDs. Additional high-quality trials are warranted to further elucidate the effects of healthy plant-based diets in people with CVDs.

The Effect of Different Vegetarian Diets on Cardiometabolic Profile in People With or At High Risk of Cardiovascular Diseases: A Systematic Review and Meta-Analysis

Objectives

This systematic review and meta-analysis assesses the effect of various vegetarian diets on cardiometabolic risk factors (systolic blood pressure (SBP), low-density lipoprotein cholesterol (LDL-C), hemoglobin A1c (HbA1c)) in people with cardiovascular diseases (CVDs) or people with at least two risk factors of CVDs.

Methods

We performed systematic searches in EMBASE, MEDLINE, CINAHL and CENTRAL, from inception until 31^st July 2021 for randomised controlled trials of vegetarian diet interventions in people with CVDs or people with at least two risk factors (e.g. being overweight, high blood pressure, high total cholesterol/LDL-C, high blood glucose) of CVDs. Trials had to use a non-vegetarian diet as the comparison diet and measure at least one of these outcomes: LDL-C, HbA1c and SBP. We extracted demographics, study design, sample size, and diet description of intervention and control group from included studies. We assessed the risk of bias of studies using the Cochrane Risk of Bias Assessment Tool 2.0. A random-effects model was used to assess mean changes in LDL-C, HbA1c, SBP and body weight. We evaluated the overall certainty of evidence using the GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) tool.

Results

Of the 7871 records screened, 29 (20 studies) met our inclusion criteria. Four studies targeted people with CVD, seven focused on people with type 2 diabetes mellitus and the remaining included people with at least two risk factors of CVDs. Meta-analyses showed that consuming vegetarian diets for at least 12 weeks significantly decreased LDL-C, HbA1c, and weight, by 6.8mg/dL (95%CI: −10.7, −3.0), 0.25% (95%CI: −0.43, −0.06), 3.4kg (95%CI: −4.6, −2.2), respectively, but the effect on SBP was not significant (−0.1 mmHg, 95%CI: −2.8, 2.6). The GRADE assessment showed a moderate level of evidence for LDL-C and HbA1c reduction.

Conclusions

Consuming vegetarian diets causes a moderate improvement of LDL-C, HbA1c and body weight in people at high risk of CVD, highlighting the protective effects of vegetarian diets in the primary prevention of CVD. Additional high-quality clinical trials are warranted to further explore the effect of this diet in people with CVD.

Funding Sources

Authors are supported by the Australian NHMRC Investigator Grant, Australian Youth and Health Foundation and Philip Bushell Foundation.

Symposium review: Intravital imaging of the lactating mammary gland in live mice reveals novel aspects of milk-lipid secretion

Milk fat comprises membrane-coated droplets of neutral lipid, which constitute the predominant source of lipids for survival of the suckling neonate. From the perspective of the dairy industry, they are the basis for the manufacture of butter and essential ingredients in the production of cheese, yogurt, and specialty dairy produce. To provide mechanistic insight into the assembly and secretion of lipid droplets during lactation, we developed novel intravital imaging techniques using transgenic mice, which express fluorescently tagged marker proteins. The number 4 mammary glands were surgically prepared under a deep plane of anesthesia and the exposed glands positioned as a skin flap with intact vascular supply on the stage of a laser-scanning confocal microscope. Lipid droplets were stained by prior exposure of the glands to hydrophobic fluorescent BODIPY (boron-dipyrromethene) dyes and their formation and secretion monitored by time-lapse subcellular microscopy over periods of 1 to 2 h. Droplets were transported to the cell apex by directed (superdiffusive) motion at relatively slow and intermittent rates (0-2 µm/min). Regardless of size, droplets grew by numerous fusion events during transport and as they were budding from the cell enveloped by apical membranes. Surprisingly, droplet secretion was not constitutive but required an injection of oxytocin to induce contraction of the myoepithelium with subsequent release of droplets into luminal spaces. These novel results are discussed in the context of the current paradigm for milk fat synthesis and secretion and as a template for future innovations in the dairy industry.

Parallel assembly of actin and tropomyosin, but not myosin II, during de novo actin filament formation in live mice

Many actin filaments in animal cells are co-polymers of actin and tropomyosin. In many cases, non-muscle myosin II associates with these co-polymers to establish a contractile network. However, the temporal relationship of these three proteins in the de novo assembly of actin filaments is not known. Intravital subcellular microscopy of secretory granule exocytosis allows the visualisation and quantification of the formation of an actin scaffold in real time, with the added advantage that it occurs in a living mammal under physiological conditions. We used this model system to investigate the de novo assembly of actin, tropomyosin Tpm3.1 (a short isoform of TPM3) and myosin IIA (the form of non-muscle myosin II with its heavy chain encoded by Myh9) on secretory granules in mouse salivary glands. Blocking actin polymerization with cytochalasin D revealed that Tpm3.1 assembly is dependent on actin assembly. We used time-lapse imaging to determine the timing of the appearance of the actin filament reporter LifeAct-RFP and of Tpm3.1-mNeonGreen on secretory granules in LifeAct-RFP transgenic, Tpm3.1-mNeonGreen and myosin IIA-GFP (GFP-tagged MYH9) knock-in mice. Our findings are consistent with the addition of tropomyosin to actin filaments shortly after the initiation of actin filament nucleation, followed by myosin IIA recruitment.

A RhoA-FRET Biosensor Mouse for Intravital Imaging in Normal Tissue Homeostasis and Disease Contexts

The small GTPase RhoA is involved in a variety of fundamental processes in normal tissue. Spatiotemporal control of RhoA is thought to govern mechanosensing, growth, and motility of cells, while its deregulation is associated with disease development. Here, we describe the generation of a RhoA-fluorescence resonance energy transfer (FRET) biosensor mouse and its utility for monitoring real-time activity of RhoA in a variety of native tissues in vivo. We assess changes in RhoA activity during mechanosensing of osteocytes within the bone and during neutrophil migration. We also demonstrate spatiotemporal order of RhoA activity within crypt cells of the small intestine and during different stages of mammary gestation. Subsequently, we reveal co-option of RhoA activity in both invasive breast and pancreatic cancers, and we assess drug targeting in these disease settings, illustrating the potential for utilizing this mouse to study RhoA activity in vivo in real time.

Concerted actions of distinct nonmuscle myosin II isoforms drive intracellular membrane remodeling in live animals

Membrane remodeling plays a fundamental role during a variety of biological events. However, the dynamics and the molecular mechanisms regulating this process within cells in mammalian tissues in situ remain largely unknown. In this study, we use intravital subcellular microscopy in live mice to study the role of the actomyosin cytoskeleton in driving the remodeling of membranes of large secretory granules, which are integrated into the plasma membrane during regulated exocytosis. We show that two isoforms of nonmuscle myosin II, NMIIA and NMIIB, control distinct steps of the integration process. Furthermore, we find that F-actin is not essential for the recruitment of NMII to the secretory granules but plays a key role in the assembly and activation of NMII into contractile filaments. Our data support a dual role for the actomyosin cytoskeleton in providing the mechanical forces required to remodel the lipid bilayer and serving as a scaffold to recruit key regulatory molecules.

Kinetics of milk lipid droplet transport, growth, and secretion revealed by intravital imaging: lipid droplet release is intermittently stimulated by oxytocin

The lipid droplet (LD) fraction of milk has attracted special attention because it supplies preformed lipids for neonatal development, and the assembled LDs are secreted by a unique apocrine mechanism. Because many aspects of this key process remain uncharacterized, we developed a facile method for the intravital imaging of mammary cells in transgenic mice that express fluorescently tagged marker proteins. Using these techniques, we describe the first kinetic analysis of LD growth and secretion at peak lactation in real time. LD transit from basal to apical regions was slow (0-2 μm/min) and frequently intermittent. Droplets grew by the fusion of preexisting droplets, with no restriction on the size of fusogenic partners. Most droplet expansion took several hours and occurred in apical nucleation centers, either close to or in association with the apical surface. Droplets even continued to expand as they were emerging from the cell. Contrary to expectations, LDs attached to the apical plasma membrane but still associated with the cytoplasm were released after oxytocin-mediated contraction of the myoepithelium. Thus milk LD secretion is an intermittently regulated process. This novel procedure will have broad application for investigating trafficking events within the mammary epithelium in real time.

Recruitment Kinetics of Tropomyosin Tpm3.1 to Actin Filament Bundles in the Cytoskeleton Is Independent of Actin Filament Kinetics

The actin cytoskeleton is a dynamic network of filaments that is involved in virtually every cellular process. Most actin filaments in metazoa exist as a co-polymer of actin and tropomyosin (Tpm) and the function of an actin filament is primarily defined by the specific Tpm isoform associated with it. However, there is little information on the interdependence of these co-polymers during filament assembly and disassembly. We addressed this by investigating the recovery kinetics of fluorescently tagged isoform Tpm3.1 into actin filament bundles using FRAP analysis in cell culture and in vivo in rats using intracellular intravital microscopy, in the presence or absence of the actin-targeting drug jasplakinolide. The mobile fraction of Tpm3.1 is between 50% and 70% depending on whether the tag is at the C- or N-terminus and whether the analysis is in vivo or in cultured cells. We find that the continuous dynamic exchange of Tpm3.1 is not significantly impacted by jasplakinolide, unlike tagged actin. We conclude that tagged Tpm3.1 may be able to undergo exchange in actin filament bundles largely independent of the assembly and turnover of actin.

Toward in vivo two-photon analysis of mouse aqueous outflow structure and function

The promise of revolutionary insights into intraocular pressure (IOP) and aqueous humor outflow homeostasis, IOP pathogenesis, and novel therapy offered by engineered mouse models has been hindered by a lack of appropriate tools for studying the aqueous drainage tissues in their original 3-dimensional (3D) environment. Advances in 2-photon excitation fluorescence imaging (TPEF) combined with availability of modalities such as transgenic reporter mice and intravital dyes have placed us on the cusp of unlocking the potential of the mouse model for unearthing insights into aqueous drainage structure and function. Multimodality 2-photon imaging permits high-resolution visualization not only of tissue structural organization but also cells and cellular function. It is possible to dig deeper into understanding the cellular basis of aqueous outflow regulation as the technique integrates analysis of tissue structure, cell biology and physiology in a way that could also lead to fresh insights into human glaucoma. We outline recent novel applications of two-photon imaging to analyze the mouse conventional drainage system in vivo or in whole tissues: (1) collagen second harmonic generation (SHG) identifies the locations of episcleral vessels, intrascleral plexuses, collector channels, and Schlemm's canal in the distal aqueous drainage tract; (2) the prospero homeobox protein 1-green fluorescent protein (GFP) reporter helps locate the inner wall of Schlemm's canal; (3) Calcein AM, siGLO™, the fluorescent reporters m-Tomato and GFP, and coherent anti-Stokes scattering (CARS), are adjuncts to TPEF to identify live cells by their membrane or cytosolic locations; (4) autofluorescence and sulforhodamine-B to identify elastic fibers in the living eye. These tools greatly expand our options for analyzing physiological and pathological processes in the aqueous drainage tissues of live mice as a model of the analogous human system.

RhoA and ROCK mediate histamine-induced vascular leakage and anaphylactic shock

Histamine-induced vascular leakage is an integral component of many highly prevalent human diseases, including allergies, asthma, and anaphylaxis. Yet, how histamine induces the disruption of the endothelial barrier is not well defined. By using genetically modified animal models, pharmacologic inhibitors, and a synthetic biology approach, here we show that the small GTPase RhoA mediates histamine-induced vascular leakage. Histamine causes the rapid formation of focal adherens junctions, disrupting the endothelial barrier by acting on H1R Gα_q-coupled receptors, which is blunted in endothelial Gα_q/11 KO mice. Interfering with RhoA and ROCK function abolishes endothelial permeability, while phospholipase Cβ plays a limited role. Moreover, endothelial-specific RhoA gene deletion prevents vascular leakage and passive cutaneous anaphylaxis in vivo, and ROCK inhibitors protect from lethal systemic anaphylaxis. This study supports a key role for the RhoA signaling circuitry in vascular permeability, thereby identifying novel pharmacological targets for many human diseases characterized by aberrant vascular leakage.

SDF-1/CXCL12 induces directional cell migration and spontaneous metastasis via a CXCR4/Gαi/mTORC1 axis

Multiple human malignancies rely on C-X-C motif chemokine receptor type 4 (CXCR4) and its ligand, SDF-1/CXCL12 (stroma cell-derived factor 1/C-X-C motif chemokine 12), to metastasize. CXCR4 inhibitors promote the mobilization of bone marrow stem cells, limiting their clinical application for metastasis prevention. We investigated the CXCR4-initiated signaling circuitry to identify new potential therapeutic targets. We used HeLa human cancer cells expressing high levels of CXCR4 endogenously. We found that CXCL12 promotes their migration in Boyden chamber assays and single cell tracking. CXCL12 activated mTOR (mechanistic target of rapamycin) potently in a pertussis-sensitive fashion. Inhibition of mTOR complex 1 (mTORC1) by rapamycin [drug concentration causing 50% inhibition (IC50) = 5 nM] and mTORC1/mTORC2 by Torin2 (IC50 = 6 nM), or by knocking down key mTORC1/2 components, Raptor and Rictor, respectively, decreased directional cell migration toward CXCL12. We developed a CXCR4-mediated spontaneous metastasis model by implanting HeLa cells in the tongue of SCID-NOD mice, in which 80% of the animals develop lymph node metastasis. It is surprising that mTORC1 disruption by Raptor knockdown was sufficient to reduce tumor growth by 60% and spontaneous metastasis by 72%, which were nearly abolished by rapamycin. In contrast, disrupting mTORC2 had no effect in tumor growth or metastasis compared with control short hairpin RNAs. These data suggest that mTORC1 may represent a suitable therapeutic target in human malignancies using CXCR4 for their metastatic spread. .

Homeostasis of the apical plasma membrane during regulated exocytosis in the salivary glands of live rodents

In exocrine organs such as the salivary glands, fluids and proteins are secreted into ductal structures by distinct mechanisms that are tightly coupled. In the acinar cells, the major secretory units of the salivary glands, fluids are secreted into the acinar canaliculi through paracellular and intracellular transport, whereas proteins are stored in large granules that undergo exocytosis and fuse with the apical plasma membranes releasing their content into the canaliculi. Both secretory processes elicit a remodeling of the apical plasma membrane that has not been fully addressed in in vitro or ex vivo models. Recently, we have studied regulated exocytosis in the salivary glands of live rodents, focusing on the role that actin and myosin plays in this process. We observed that during exocytosis both secretory granules and canaliculi are subjected to the hydrostatic pressure generated by fluid secretion. Furthermore, the absorption of the membranes of the secretory granules contributes to the expansion and deformation of the canaliculi. Here we suggest that the homeostasis of the apical plasma membranes during exocytosis is maintained by various strategies that include: (1) membrane retrieval via compensatory endocytosis, (2) increase of the surface area via membrane folds and (3) recruitment of a functional actomyosin complex. Our observations underscore the important relationship between tissue architecture and cellular response, and highlight the potential of investigating biological processes in vivo by using intravital microscopy.

Abstract 4050: A central role for mTORC1 in CXCR4-mediated directional migration and metastasis

Tumor cells can co-opt the promigratory activity of chemokines and their cognate G protein-coupled receptors to disseminate to regional lymph nodes and distant organs. Indeed, the migration to SDF-1 of tumor cells expressing its receptor, CXCR4, is implicated in lymphatic and organ-specific metastasis in multiple human malignancies. However, the critical role of CXCR4 in bone marrow stem cell retention has hampered the development of CXCR4 inhibitors for metastasis prevention. Therefore the study of CXCR4 downstream signaling circuitry may provide new opportunities for the treatment of many human malignancies that depend on CXCR4 for their metastatic spread. The PI3K/mTOR pathway represents a major player in normal and aberrant cell growth. Consistently, mTOR inhibitors targeting its complex 1 (mTORC1) alone or mTORC1/mTORC2 have already shown promising therapeutic responses in many tumor types. Our data show that mTOR is activated upon SDF-1 stimulation of CXCR4 on epithelial-derived cancer cells, and that the disruption of mTORC1 or mTORC2 abrogates CXCR4-mediated directional migration. To study the CXCR4/mTOR axis in vivo we developed a simple and robust model for CXCR4-mediated spontaneous metastasis. Surprisingly, disruption of mTORC1 alone was sufficient to decrease tumor cell proliferation, angiogenesis, lymphangiogenesis, and CXCR4-mediated metastasis, whereas mTORC2 impairment had no effect on tumor dissemination or growth in vivo. Taken together, our data suggest that mTORC1 blockade could inhibit the migration of CXCR4 expressing cancer cells to their secondary sites, while disrupting the establishment of a permissive tumor microenvironment thereby halting the spread of highly aggressive tumors that require CXCR4 to metastasize.

Citation Format: Patricia Dillenburg-Pilla, Vyomesh Patel, Constantinos M. Mikelis, Carlos Rodrigo Zarate-Blades, Panomwat Amornphimoltham, Zhiyong Wang, Daniel Martin, Kantima Leelahavanichkul, Colleen L. Doçi, Robert T. Dorsam, Andrius Masedunskas, Nijiro Nohata , Roberto Weigert, Alfredo A. Molinolo, J. Silvio Gutkind . A central role for mTORC1 in CXCR4-mediated directional migration and metastasis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4050. doi:10.1158/1538-7445.AM2014-4050

Lighting up microtubule cytoskeleton dynamics in skeletal muscle

In the past few decades, live cell microscopy techniques in combination with fluorescent tagging have provided a true explosion in our knowledge of the inner functioning of the cell. Dynamic phenomena can be observed inside living cells and the behavior of individual molecules participating in those events can be documented. However, our preference for simple or easy model systems such as cell culture, has come at a cost of chasing artifacts and missing out on understanding real biology as it happens in complex multicellular organisms. We are now entering a new era where developing meaningful, but also tractable model systems to study biological phenomenon dynamically in vivo in a mammal is not only possible; it will become the gold standard for scientific quality and translational potential.^1,2 A study by Oddoux et al. describing the dynamics of the microtubule (MT) cytoskeleton in skeletal muscle is one example that demonstrates the power of developing in vivo/ex vivo models.³ MTs have long attracted attention as targets for cancer therapeutics ⁴ and more recently as mediators of Duchene muscular dystrophy.⁵ The muscle fiber MT cytoskeleton forms an intricate rectilinear lattice beneath the sarcolemma and is essential for the structural integrity of the muscle. Cultured cells do not develop such a specialized organization of the MT cytoskeleton and our understanding of it has come from static snapshots of muscle sections.⁶ In this context, the methodology and the findings reported by Oddoux et al. are a significant step forward.

Neutral lipid stores and lipase PNPLA5 contribute to autophagosome biogenesis

BACKGROUND

Autophagy is a fundamental cell biological process whereby eukaryotic cells form membranes in the cytoplasm to sequester diverse intracellular targets. Although significant progress has been made in understanding the origins of autophagosomal organelles, the source of lipids that support autophagic membrane formation remain an important open question.

RESULTS

Here we show that lipid droplets as cellular stores of neutral lipids including triglycerides contribute to autophagic initiation. Lipid droplets, as previously shown, were consumed upon induction of autophagy by starvation. However, inhibition of autophagic maturation by blocking acidification or using dominant negative Atg4(C74A) that prohibits autophagosomal closure did not prevent disappearance of lipid droplets. Thus, lipid droplets continued to be utilized upon induction of autophagy, but not as autophagic substrates in a process referred to as lipophagy. We considered an alternative model whereby lipid droplets were consumed not as a part of lipophagy, but as a potential contributing source to the biogenesis of lipid precursors for nascent autophagosomes. We carried out a screen for a potential link between triglyceride mobilization and autophagy and identified a neutral lipase, PNPLA5, as being required for efficient autophagy. PNPLA5, which localized to lipid droplets, was needed for optimal initiation of autophagy. PNPLA5 was required for autophagy of diverse substrates, including degradation of autophagic adaptors, bulk proteolysis, mitochondrial quantity control, and microbial clearance.

CONCLUSIONS

Lipid droplets contribute to autophagic capacity by enhancing it in a process dependent on PNPLA5. Thus, neutral lipid stores are mobilized during autophagy to support autophagic membrane formation.

Novel aquatic silk genes Simulium (Psilozia) vittatum (Zett) Diptera: Simuliidae

The silks of arthropods have an elementary role in the natural history of the organisms that spin them, yet they are coded by rapidly evolving genes leading some authors to speculate that silk proteins are non-homologous proteins co-opted multiple times independently for similar functions. However, some general structural patterns are emerging. In this work we identified three major silk gland proteins using a combined biochemical, proteomic, next-generation sequencing and bioinformatic approach. Biochemical characterization determined that they were phosphorylated with multiple isoforms and potentially differential phosphorylation. Structural characterization showed that their structure was more similar to silk proteins from distantly related aquatic Trichopteran species than more closely related terrestrial or aquatic Diptera. Overall, our approach is easily transferable to any non-model species and if used across a larger number of aquatic species, we will be able to better understand the processes involved in linking the secondary structure of silk proteins with their function between in an organisms and its habitat.

CX3CR1-dependent renal macrophage survival promotes Candida control and host survival

Systemic Candida albicans infection causes high morbidity and mortality and is associated with neutropenia; however, the roles of other innate immune cells in pathogenesis are poorly defined. Here, using a mouse model of systemic candidiasis, we found that resident macrophages accumulated in the kidney, the main target organ of infection, and formed direct contacts with the fungus in vivo mainly within the first few hours after infection. Macrophage accumulation and contact with Candida were both markedly reduced in mice lacking chemokine receptor CX3CR1, which was found almost exclusively on resident macrophages in uninfected kidneys. Infected Cx3cr1-/- mice uniformly succumbed to Candida-induced renal failure, but exhibited clearance of the fungus in all other organs tested. Renal macrophage deficiency in infected Cx3cr1-/- mice was due to reduced macrophage survival, not impaired proliferation, trafficking, or differentiation. In humans, the dysfunctional CX3CR1 allele CX3CR1-M280 was associated with increased risk of systemic candidiasis. Together, these data indicate that CX3CR1-mediated renal resident macrophage survival is a critical innate mechanism of early fungal control that influences host survival in systemic candidiasis.

M2-like macrophages are responsible for collagen degradation through a mannose receptor-mediated pathway

Tissue remodeling processes critically depend on the timely removal and remodeling of preexisting collagen scaffolds. Nevertheless, many aspects related to the turnover of this abundant extracellular matrix component in vivo are still incompletely understood. We therefore took advantage of recent advances in optical imaging to develop an assay to visualize collagen turnover in situ and identify cell types and molecules involved in this process. Collagen introduced into the dermis of mice underwent cellular endocytosis in a partially matrix metalloproteinase-dependent manner and was subsequently routed to lysosomes for complete degradation. Collagen uptake was predominantly executed by a quantitatively minor population of M2-like macrophages, whereas more abundant Col1a1-expressing fibroblasts and Cx3cr1-expressing macrophages internalized collagen at lower levels. Genetic ablation of the collagen receptors mannose receptor (Mrc1) and urokinase plasminogen activator receptor-associated protein (Endo180 and Mrc2) impaired this intracellular collagen degradation pathway. This study demonstrates the importance of receptor-mediated cellular uptake to collagen turnover in vivo and identifies a key role of M2-like macrophages in this process.

Intravital microscopy for imaging subcellular structures in live mice expressing fluorescent proteins

Here we describe a procedure to image subcellular structures in live rodents that is based on the use of confocal intravital microscopy. As a model organ, we use the salivary glands of live mice since they provide several advantages. First, they can be easily exposed to enable access to the optics, and stabilized to facilitate the reduction of the motion artifacts due to heartbeat and respiration. This significantly facilitates imaging and tracking small subcellular structures. Second, most of the cell populations of the salivary glands are accessible from the surface of the organ. This permits the use of confocal microscopy that has a higher spatial resolution than other techniques that have been used for in vivo imaging, such as two-photon microscopy. Finally, salivary glands can be easily manipulated pharmacologically and genetically, thus providing a robust system to investigate biological processes at a molecular level. In this study we focus on a protocol designed to follow the kinetics of the exocytosis of secretory granules in acinar cells and the dynamics of the apical plasma membrane where the secretory granules fuse upon stimulation of the beta-adrenergic receptors. Specifically, we used a transgenic mouse that co-expresses cytosolic GFP and a membrane-targeted peptide fused with the fluorescent protein tandem-Tomato. However, the procedures that we used to stabilize and image the salivary glands can be extended to other mouse models and coupled to other approaches to label in vivo cellular components, enabling the visualization of various subcellular structures, such as endosomes, lysosomes, mitochondria, and the actin cytoskeleton.

Rab25 regulates invasion and metastasis in head and neck cancer

PURPOSE

Head and neck squamous cell carcinoma (HNSCC) is one of the 10 most common cancers with a 50% five-year survival rate, which has remained unchanged for the past three decades. One of the major reasons for the aggressiveness of this cancer is that HNSCCs readily metastasize to cervical lymph nodes that are abundant in the head and neck region. Hence, discovering new molecules controlling the metastatic process as well as understanding their regulation at the molecular level are essential for effective therapeutic strategies.

EXPERIMENTAL DESIGN

Rab25 expression level was analyzed in HNSCC tissue microarray. We used a combination of intravital microscopy in live animals and immunofluorescence in an in vitro invasion assay to study the role of Rab25 in tumor cell migration and invasion.

RESULTS

In this study, we identified the small GTPase Rab25 as a key regulator of HNSCC metastasis. We observed that Rab25 is downregulated in HNSCC patients. Next, we determined that reexpression of Rab25 in a metastatic cell line is sufficient to block invasion in a three-dimensional collagen matrix and metastasis to cervical lymph nodes in a mouse model for oral cancer. Specifically, Rab25 affects the organization of F-actin at the cell surface, rather than cell proliferation, apoptosis, or tumor angiogenesis.

CONCLUSION

These findings suggest that Rab25 plays an important role in tumor migration and metastasis, and that understanding its function may lead to the development of new strategies to prevent metastasis in oral cancer patients.

Abstract P1-05-23: Blockade of mTORC1 decreases CXCR4-mediated migration and metastasis

Tumor cells can co-opt the promigratory activity of chemokines and their cognate G protein–coupled receptors (GPCRs) to metastasize to regional lymph nodes or distant organs. Indeed, the migration toward SDF-1 (stromal cell–derived factor 1) of tumor cells bearing CXCR4 [chemokine (C-X-C motif) receptor 4] has been implicated in the lymphatic and organ-specific metastasis of various human malignancies, including breast cancer. The downstream mechanisms of CXCR4-mediated migration are not fully elucidated. The study of the precise signaling pathways involved in cell migration and metastasis in each tumor type may help identify novel therapeutic targets for improving cancer therapy. Here we show that blockade of mTOR complex 1 (mTORC1) by Rapamycin or knocking down Raptor decreases CXCR4-Gαi mediated cell migration. Moreover, using a spontaneous lymph node metastasis model, we were able to show that pharmacological blockade of mTORC1 decreases lymph node metastasis in vivo. Taken together our data suggest that Rapamycin, a FDA-approved drug, could be beneficial to prevent tumor cells spreading from the primary tumor and metastasize. Molecular events underlying the effects of Rapamycin on CXCR4-induced migration will be presented.

This research was supported [in part] by the Intramural Research Program of the NIH, NIDCR.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-05-23.

Linking differences in membrane tension with the requirement for a contractile actomyosin scaffold during exocytosis in salivary glands

In all the major secretory organs regulated exocytosis is a fundamental process that is used for releasing molecules in the extracellular space. Molecules destined for secretion are packaged into secretory vesicles that fuse with the plasma membrane upon the appropriate stimulus. In exocrine glands, large secretory vesicles fuse with specialized domains of the plasma membrane, which form ductal structures that are in direct continuity with the external environment and exhibit various architectures and diameters. In a recent study, we used intravital microscopy to analyze in detail the dynamics of exocytic events in the salivary glands of live rodents under conditions that cannot be reproduced in in vitro or ex vivo model systems. We found that after the opening of the fusion pore large secretory vesicles gradually collapse with their limiting membranes being completely absorbed into the apical plasma membrane canaliculi within 40-60 sec. Moreover, we observed that this controlled collapse requires the contractile activity of actin and its motor myosin II, which are recruited onto the large secretory vesicles immediately after their fusion with the plasma membrane. Here we suggest that the actomyosin complex may be required to facilitate exocytosis in those systems, such as the salivary glands, in which the full collapse of the vesicles is not energetically favorable due to a difference in membrane tension between the large secretory vesicles and the canaliculi.

Intravital microscopy: a practical guide on imaging intracellular structures in live animals

Intravital microscopy is an extremely powerful tool that enables imaging several biological processes in live animals. Recently, the ability to image subcellular structures in several organs combined with the development of sophisticated genetic tools has made possible extending this approach to investigate several aspects of cell biology. Here we provide a general overview of intravital microscopy with the goal of highlighting its potential and challenges. Specifically, this review is geared toward researchers that are new to intravital microscopy and focuses on practical aspects of carrying out imaging in live animals. Here we share the know-how that comes from first-hand experience, including topics such as choosing the right imaging platform and modality, surgery and stabilization techniques, anesthesia and temperature control. Moreover, we highlight some of the approaches that facilitate subcellular imaging in live animals by providing numerous examples of imaging selected organelles and the actin cytoskeleton in multiple organs.

Regulated exocytosis: novel insights from intravital microscopy

Regulated exocytosis is a fundamental process that every secretory cell uses to deliver molecules to the cell surface and the extracellular space by virtue of membranous carriers. This process has been extensively studied using various approaches such as biochemistry, electrophysiology and electron microscopy. However, recent developments in time-lapse light microscopy have made possible imaging individual exocytic events, hence, advancing our understanding of this process at a molecular level. In this review, we focus on intravital microscopy (IVM), a light microscopy-based approach that enables imaging subcellular structures in live animals, and discuss its recent application to study regulated exocytosis. IVM has revealed differences in regulation and modality of regulated exocytosis between in vitro and in vivo model systems, unraveled novel aspects of this process that can be appreciated only in in vivo settings and provided valuable and novel information on its molecular machinery. In conclusion, we make the case for IVM being a mature technique that can be used to investigate the molecular machinery of several intracellular events under physiological conditions.

Decreased lymphangiogenesis and lymph node metastasis by mTOR inhibition in head and neck cancer

Despite our improved understanding of cancer, the 5-year survival rate for head and neck squamous cell carcinomas (HNSCC) patients remains relatively unchanged at 50% for the past three decades. HNSCCs often metastasize to locoregional lymph nodes, and lymph node involvement represents one of the most important prognostic factors of poor clinical outcome. Among the multiple dysregulated molecular mechanism in HNSCCs, emerging basic, preclinical, and clinical findings support the importance of the mTOR signaling route in HNSCC progression. Indeed, we observed here that the activation of mTOR is a widespread event in clinical specimens of HNSCCs invading locoregional lymph nodes. We developed an orthotopic model of HNSCC consisting of the implantation of HNSCC cells into the tongues of immunocompromised mice. These orthotopic tumors spontaneously metastasize to the cervical lymph nodes, where the presence of HNSCC cells can be revealed by histologic and immunohistochemical evaluation. Both primary and metastatic experimental HNSCC lesions exhibited elevated mTOR activity. The ability to monitor and quantitate lymph node invasion in this model system enabled us to explore whether the blockade of mTOR could impact HNSCC metastasis. We found that inhibition of mTOR with rapamycin and the rapalog RAD001 diminished lymphangiogenesis in the primary tumors and prevented the dissemination of HNSCC cancer cells to the cervical lymph nodes, thereby prolonging animal survival. These findings may provide a rationale for the future clinical evaluation of mTOR inhibitors, including rapamycin and its analogues, as part of a molecular-targeted metastasis preventive strategy for the treatment of patients with HNSCC.

Intravital microscopy as a tool to study drug delivery in preclinical studies

The technical developments in the field of non-linear microscopy have made intravital microscopy one of the most successful techniques for studying physiological and pathological processes in live animals. Intravital microscopy has been utilized to address many biological questions in basic research and is now a fundamental tool for preclinical studies, with an enormous potential for clinical applications. The ability to dynamically image cellular and subcellular structures combined with the possibility to perform longitudinal studies have empowered investigators to use this discipline to study the mechanisms of action of therapeutic agents and assess the efficacy on their targets in vivo. The goal of this review is to provide a general overview of the recent advances in intravital microscopy and to discuss some of its applications in preclinical studies.

Intravital microscopy: a novel tool to study cell biology in living animals

Intravital microscopy encompasses various optical microscopy techniques aimed at visualizing biological processes in live animals. In the last decade, the development of non-linear optical microscopy resulted in an enormous increase of in vivo studies, which have addressed key biological questions in fields such as neurobiology, immunology and tumor biology. Recently, few studies have shown that subcellular processes can be imaged dynamically in the live animal at a resolution comparable to that achieved in cell cultures, providing new opportunities to study cell biology under physiological conditions. The overall aim of this review is to give the reader a general idea of the potential applications of intravital microscopy with a particular emphasis on subcellular imaging. An overview of some of the most exciting studies in this field will be presented using resolution as a main organizing criterion. Indeed, first we will focus on those studies in which organs were imaged at the tissue level, then on those focusing on single cells imaging, and finally on those imaging subcellular organelles and structures.

Expression of plasmid DNA in the salivary gland epithelium: novel approaches to study dynamic cellular processes in live animals

The ability to dynamically image cellular and subcellular structures in a live animal and to target genes to a specific cell population in a living tissue provides a unique tool to address many biological questions in the proper physiological context. Here, we describe a powerful approach that is based on the use of rat submandibular salivary glands, which offer the possibility to easily perform intravital imaging and deliver molecules from the oral cavity, and plasmid DNA, which offers the advantage of rapid manipulations. We show that, under different experimental conditions, a reporter molecule can be rapidly expressed in specific compartments of the glands: 1) in the intercalated ducts, when plasmid DNA is administered alone, and 2) in granular ducts, striated ducts, and, to a lesser extent, acini, when plasmid DNA is mixed with replication-deficient adenovirus subtype 5 particles. Remarkably, we also found that gene expression can be directed to acinar cells when plasmid DNA is administered during isoproterenol-stimulated exocytosis, suggesting a novel mechanism of plasmid internalization regulated by compensatory endocytosis. Finally, as a practical application of these strategies, we show how the expression of fluorescently tagged molecules enables the study of the dynamics of various organelles in live animals at a resolution comparable to that achieved in cell cultures.

Targeted killing of cancer cells in vivo and in vitro with EGF-directed carbon nanotube-based drug delivery

Carbon nanotube-based drug delivery holds great promise for cancer therapy. Herein we report the first targeted, in vivo killing of cancer cells using a drug-single wall carbon nanotube (SWNT) bioconjugate, and demonstrate efficacy superior to nontargeted bioconjugates. First line anticancer agent cisplatin and epidermal growth factor (EGF) were attached to SWNTs to specifically target squamous cancer, and the nontargeted control was SWNT-cisplatin without EGF. Initial in vitro imaging studies with head and neck squamous carcinoma cells (HNSCC) overexpressing EGF receptors (EGFR) using Qdot luminescence and confocal microscopy showed that SWNT-Qdot-EGF bioconjugates internalized rapidly into the cancer cells. Limited uptake occurred for control cells without EGF, and uptake was blocked by siRNA knockdown of EGFR in cancer cells, revealing the importance of EGF-EGFR binding. Three color, two-photon intravital video imaging in vivo showed that SWNT-Qdot-EGF injected into live mice was selectively taken up by HNSCC tumors, but SWNT-Qdot controls with no EGF were cleared from the tumor region in <20 min. HNSCC cells treated with SWNT-cisplatin-EGF were also killed selectively, while control systems that did not feature EGF-EGFR binding did not influence cell proliferation. Most significantly, regression of tumor growth was rapid in mice treated with targeted SWNT-cisplatin-EGF relative to nontargeted SWNT-cisplatin.

Intravital two-photon microscopy for studying the uptake and trafficking of fluorescently conjugated molecules in live rodents

In this study, we describe an experimental system based on intravital two-photon microscopy for studying endocytosis in live animals. The rodent submandibular glands were chosen as model organs because they can be exposed easily, imaged without compromising their function and, furthermore, they are amenable to pharmacological and genetic manipulations. We show that the fibroblasts within the stroma of the glands readily internalize systemically injected molecules such as fluorescently conjugated dextran and BSA, providing a robust model to study endocytosis. We dynamically image the trafficking of these probes from the early endosomes to the late endosomes and lysosomes while also visualizing homotypic fusion events between early endosomes. Finally, we demonstrate that pharmacological agents can be delivered specifically to the submandibular salivary glands, thus providing a powerful tool to study the molecular machinery regulating endocytosis in a physiological context.

Activated leukocyte cell adhesion molecule is a component of the endothelial junction involved in transendothelial monocyte migration

Transendothelial leukocyte migration is a major aspect of the innate immune response. It is essential in repair and regeneration of damaged tissues and is regulated by multiple cell adhesion molecules (CAMs) including members of the immunoglobulin (Ig) superfamily. Activated leukocyte cell adhesion molecule (ALCAM/CD166) is an Ig CAM expressed by activated monocytes and endothelial cells. Hitherto, the functional relevance of ALCAM expression by endothelial cells and activated monocytes remained unknown. In this report, we demonstrate soluble recombinant human ALCAM significantly inhibited the rate of transendothelial migration of monocyte cell lines. Direct involvement of ALCAM in transendothelial migration was evident from the robust inhibition of this process by ALCAM blocking antibodies. However, soluble recombinant ALCAM had no impact on monocyte migration or adhesion to endothelium. Localization of ALCAM specifically at cell-cell junctions in endothelial cells supported its role in transendothelial migration. This study is the first to localize ALCAM to endothelial cell junctions and demonstrate a functional relevance for co-expression of ALCAM by activated monocytes and endothelial cells.