A simple secretion assay for assessing new and existing myocilin variants

With the increasing use of molecular genetics approaches for determination of potential disease-causing mutations, it is becoming more important to be able to interpret and act upon the provided results. As an example of such an instance, nearly 300 mutations have been identified in the myocilin (MYOC) gene, which is the most commonly mutated gene causing primary open angle glaucoma. Yet a lack of sufficient information exists for many of these variants, hindering their definitive classification. While the function of MYOC is unclear, biochemically, the vast majority of glaucoma-causing MYOC mutations result in protein non-secretion and intracellular insoluble aggregate formation in cultured cells. Previously we generated a Gaussia luciferase-based MYOC fusion protein to sensitively track secretion of the protein. Herein we applied this same assay to fourteen clinically-derived MYOC variants with varying degrees of predicted pathogenicity and compared the luciferase secretion results with the better established MYOC assay of western blotting. Eight of the variants (G12R, V53A, T204T, P254L, T325T, D380H, D395_E396insDP, and P481S) had not been biochemically assessed previously. Of these, P254L and D395_E396insDP demonstrated significant secretion defects from human embryonic kidney (HEK-293A) cells reminiscent of glaucoma-causing mutations. Overall, we found that the luciferase assay results agreed with western blotting for thirteen of the fourteen variants (93%), suggesting a strong concordance. These results suggest that the Gaussia luciferase assay may be used as a complementary or standalone assay for quickly assessing MYOC variant behavior, and anticipate that these results will be useful in MYOC variant curation and reclassification.

The Powdery Mildew Effector CSEP0027 Interacts With Barley Catalase to Regulate Host Immunity

Powdery mildew is one of the most important fungal pathogen diseases. The genome of barley mildew fungus, Blumeria graminis f. sp. hordei (Bgh), encodes a large number of candidate secreted effector proteins (CSEPs). So far, the function and mechanism of most CSEPs remain largely unknown. Here, we identify a Bgh effector CSEP0027, a member of family 41, triggering cell death in Nicotiana benthamiana. CSEP0027 contains a functional signal peptide (SP), verified by yeast secretion assay. We show that CSEP0027 promotes Bgh virulence in barley infection using transient gene expression and host-induced gene silencing (HIGS). Barley catalase HvCAT1 is identified as a CSEP0027 interactor by yeast two-hybrid (Y2H) screening, and the interaction is verified in yeast, in vitro and in vivo. The coexpression of CSEP0027 and HvCAT1 in barley cells results in altered localization of HvCAT1 from the peroxisome to the nucleus. Barley stripe mosaic virus (BSMV)-silencing and transiently-induced gene silencing (TIGS) assays reveal that HvCAT1 is required for barley immunity against Bgh. We propose that CSEP0027 interacts with barley HvCAT1 to regulate the host immunity and likely reactive oxygen species (ROS) homeostasis to promote fungal virulence during barley infection.

Multiplexed detection and isolation of viable low-frequency cytokine-secreting human B cells using cytokine secretion assay and flow cytometry (CSA-Flow)

The ability to functionally characterize cytokine-secreting immune cells has broad implications in both health and a range of immune-mediated and auto-immune diseases. Low-frequency cytokine-defined immune-cell subsets can play key immune-regulatory roles, yet their detailed study is often hampered by limited clinical sample availability. Commonly used techniques including intracellular cytokine staining require cell fixation, precluding subsequent functional interrogation. The cytokine-secretion assay (CSA) can overcome this limitation, though has mostly been used for detection of relatively high-frequency, single-cytokine secreting cells. We examined how adaptation of the CSA in combination with multiparametric flow-cytometry (CSA-Flow) may enable simultaneous isolation of multiple, low-frequency, cytokine-secreting cells. Focusing on human B cells (traditionally recognized as harder to assay than T cells), we show that single-capture CSA-Flow allows for isolation of highly-purified populations of both low-frequency (IL-10+; GM-CSF+) and high-frequency (TNF+) cytokine-defined B cells. Simultaneous detection and isolation of up to three viable and highly-purified cytokine-secreting B-cell subpopulations is feasible, albeit with some signal loss, with fractions subsequently amenable to gene expression analysis and in vitro cell culture. This multiplexing CSA-Flow approach will be of interest in many human cellular immunology contexts aiming to functionally characterize cytokine-secreting immune cells, especially when sample volumes and cell numbers are limited.

SAT0016 DEVELOPMENT OF FIBROBLAST-LIKE SYNOVIOCYTE ASSAYS FOR TARGET DISCOVERY IN RHEUMATOID ARTHRITIS

Background:The rheumatoid arthritis (RA) synovium is characterized by an overabundance of fibroblast-like synoviocytes (FLS), which play a central role in the initiation and perpetuation of disease via multiple mechanisms.1FLS promote disease progression by producing high levels of proinflammatory factors, migrating to and invading cartilage and bone, and promoting self-proliferation and resistance to apoptosis. Our current understanding of the molecular mechanisms that govern FLS-mediated pathology in the synovial joint remains incomplete. Importantly, almost 30% of treatment-naïve early RA patients exhibit a strong fibroid phenotype that correlates with relatively poor response to disease-modifying anti-rheumatic drugs.2Yet, current therapies in RA are not directly aimed at FLS pathology, creating an opportunity for novel therapeutic target discovery.Objectives:Our aim is to develop a broad suite of screening-amenable assays in RA patient-derived FLS for the discovery of target pathways that control multiple pathological properties, including cytokine secretion, migration, and invasion.Methods:A sensitive high-throughput RA-FLS secretion assay was developed to examine the ability of small-molecule inhibitors to block the production of interleukin (IL)-6 and matrix metalloproteinase (MMP)-3 in response to stimuli. To create a physiologically relevant stimulus, a surrogate synovial fluid cocktail (composed of 12 factors) was defined and titrated for optimal concentration selection. Small-molecule inhibitors (N=170) of diverse biological pathways were screened using the full cocktail or individual stimulation (TNFα, IL-1α, or IL-17) to characterize assay performance. In addition, an FLS platelet-derived growth factor (PDGF)-mediated migration screening assay was developed using a live cell imaging system (IncuCyte) to quantify real-time FLS migration.Results:Due to the variability and limited volume of synovial fluid, we developed a surrogate synovial fluid cocktail to mimic the relevant stimulation of RA-FLS in the inflamed joint. The surrogate cocktail was composed of 12 factors: TNFα, IL-1α, IL-17, IFNγ, OSM, LIF, GM-CSF, IP-10, VEGF, PDGF, AREG, and FGF2. Individual titration of these factors demonstrated that only 3 stimulatory factors (TNFα, IL-1α, and IL-17) resulted in a robust increase of IL-6 production. Importantly, when all 12 factors were combined, a synergistic increase in IL-6 and MMP-3 production by FLS was observed. Screening results identified several reference compounds, including an inhibitor of transforming growth factor-b–activated kinase 1 (TAK1), that was previously reported to block cytokine secretion in FLS.3Treatment with this compound showed complete inhibition of IL-6 and MMP-3 secretion. In addition to the cytokine secretion assay, treatment of FLS with this TAK1 inhibitor resulted in almost complete inhibition of migration (Fig. 1).Conclusion:Novel FLS assays were developed to discover new targets and interrogate pathways involved in multiple disease-driving mechanisms of FLS in RA. In order to mimic the inflammatory environment present in the RA synovium, we developed a 12-factor surrogate synovial fluid cocktail. A synergistic release of both IL-6 and MMP-3 was demonstrated following cocktail stimulation compared to individual cytokines. This points to the important contribution that multiple factors play in the FLS pathogenic processes and will allow us to uncover pathway interactions that may not be captured with single stimuli. In addition, the development of a real-time, 96-well, imaging-based assay to interrogate FLS migration will allow us to identify targets that control this critical pathological function of FLS.References:[1] Bartok B, et al.J Immunol. 2014;192(5):2063-2070.[2] Humby F, et al.Ann Rheum Dis. 2019;78(6):761-772.[3] Jones DS, et al.Nat Chem Bio. 2017;13(1):38-45.Disclosure of Interests:Debbie Ruelas Employee of: Gilead, Chen Chen Employee of: Gilead, Hoa Truong Employee of: Gilead, Victor Lira Employee of: Gilead, Yasamin Moazami Employee of: Gilead, Kevin Currie Employee of: Gilead, Julie A. Di Paolo Employee of: Gilead, Helen Yu Employee of: Gilead, Gundula Min-Oo Employee of: Gilead

The potential of the incorporated collagen microspheres in alginate hydrogel as an engineered three-dimensional microenvironment to attenuate apoptosis in human pancreatic islets

Background: Tissue engineering is considered as a promising tool for remodeling the native cells microenvironment. In the present study, the effect of alginate hydrogel and collagen microspheres integrated with extracellular matrix components were evaluated in the decrement of apoptosis in human pancreatic islets. Methods: For three dimensional culture, the islets were encapsulated in collagen microspheres, containing laminin and collagen IV and embedded in alginate scaffold for one week. After that the islets were examined in terms of viability, apoptosis, genes and proteins expression including BAX, BCL2, active caspase-3, and insulin. Moreover, the islets function was evaluated through glucose-induced insulin and C-peptide secretion assay. In order to evaluate the structure of the scaffolds and the morphology of the pancreatic islets in three-dimensional microenvironments, we performed scanning electron microscopy. Results: Our findings showed that the designed hydrogel scaffolds significantly improved the islets viability using the reduction of activated caspase-3 and TUNEL positive cells. Conclusion: The reconstruction of the destructed matrix with alginate hydrogels and collagen microspheres might be an effective step to promote the culture of the islets.

RAB6 and microtubules restrict protein secretion to focal adhesions

To ensure their homeostasis and sustain differentiated functions, cells continuously transport diverse cargos to various cell compartments and in particular to the cell surface. Secreted proteins are transported along intracellular routes from the endoplasmic reticulum through the Golgi complex before reaching the plasma membrane along microtubule tracks. Using a synchronized secretion assay, we report here that exocytosis does not occur randomly at the cell surface but on localized hotspots juxtaposed to focal adhesions. Although microtubules are involved, the RAB6-dependent machinery plays an essential role. We observed that, irrespective of the transported cargos, most post-Golgi carriers are positive for RAB6 and that its inactivation leads to a broad reduction of protein secretion. RAB6 may thus be a general regulator of post-Golgi secretion.

INSULIN SECRETAGOGUE EFFECT OF ROOTS OF RAVENALA MADAGASCARIENSIS SONN. - AN IN VITRO STUDY

Objective: The objective of this study was to establish the cytotoxicity profile and to evaluate the insulin secretagogue effect of ethanolic root extract of Ravenala madagascariensis Sonn. Methods: The cell viability of rat insulinoma 5F (RIN5F) cell lines over the treatment of plant extract was assessed by 3-(4,5-dimethyl-2-thiazolyl)- 2,5-diphenyltetrazolium bromide assay. The insulin-releasing effect was evaluated by insulin secretion assay over RIN5F cell lines by enzyme-linked immunosorbent assay. Results: The ethanolic extract of the roots of R. madagascariensis Sonn. showed negligible cytotoxicity at 20–40 μg/ml, and hence, concentrations up to 40 μg/ml were used in insulin secretion assay. The ethanolic root extract at 20 and 40 μg/ml significantly (p<0.05 compared to control) stimulated the insulin release in a dose-dependent manner even in the presence of glucose at lower and higher concentrations (5 and 10 mM). Conclusion: Thus, our results validate its traditional claim in the treatment of diabetes by stimulating the secretion of insulin, thereby suggesting a possible mechanism of its antidiabetic effect.