Recognition of apoptotic cells by viable cells is specific, ubiquitous, and species independent: analysis using photonic crystal biosensors.

Apoptotic recognition is innate and linked to a profound immune regulation (innate apoptotic immunity [IAI]) involving anti-inflammatory and immunosuppressive responses. Many of the molecular and mechanistic details of this response remain elusive. Although immune outcomes can be quantified readily, the initial specific recognition events have been difficult to assess. We developed a sensitive, real-time method to detect the recognition of apoptotic cells by viable adherent responder cells, using a photonic crystal biosensor approach. The method relies on characteristic spectral shifts resulting from the specific recognition and dose-dependent interaction of adherent responder cells with nonadherent apoptotic targets. Of note, the biosensor provides a readout of early recognition-specific events in responder cells that occur distal to the biosensor surface. We find that innate apoptotic cell recognition occurs in a strikingly species-independent manner, consistent with our previous work and inferences drawn from indirect assays. Our studies indicate obligate cytoskeletal involvement, although apoptotic cell phagocytosis is not involved. Because it is a direct, objective, and quantitative readout of recognition exclusively, this biosensor approach affords a methodology with which to dissect the early recognition events associated with IAI and immunosuppression.

Nanostructured optical photonic crystal biosensor for HIV viral load measurement.

Detecting and quantifying biomarkers and viruses in biological samples have broad applications in early disease diagnosis and treatment monitoring. We have demonstrated a label-free optical sensing mechanism using nanostructured photonic crystals (PC) to capture and quantify intact viruses (HIV-1) from biologically relevant samples. The nanostructured surface of the PC biosensor resonantly reflects a narrow wavelength band during illumination with a broadband light source. Surface-adsorbed biotarget induces a shift in the resonant Peak Wavelength Value (PWV) that is detectable with <10 pm wavelength resolution, enabling detection of both biomolecular layers and small number of viruses that sparsely populate the transducer surface. We have successfully captured and detected HIV-1 in serum and phosphate buffered saline (PBS) samples with viral loads ranging from 10(4) to 10(8) copies/mL. The surface density of immobilized biomolecular layers used in the sensor functionalization process, including 3-mercaptopropyltrimethoxysilane (3-MPS), N-gamma-Maleimidobutyryl-oxysuccinimide ester (GMBS), NeutrAvidin, anti-gp120, and bovine serum albumin (BSA) were also quantified by the PC biosensor.

Label-free imaging of cell attachment with photonic crystal enhanced microscopy.

We introduce photonic crystal enhanced microscopy (PCEM) as a label-free biosensor imaging technique capable of measuring cell surface attachment and attachment modulation. The approach uses a photonic crystal optical resonator surface incorporated into conventional microplate wells and a microscope-based detection instrument that measures shifts in the resonant coupling conditions caused by localized changes in dielectric permittivity at the cell-sensor interface. Four model systems are demonstrated for studying cancer cells, primary cardiac muscle cells, and stem cells. First, HepG2/C3 hepatic carcinoma cells were cultured and observed via PCEM in order to characterize cell adhesion in the context of growth and locomotion. Second, Panc-1 pancreatic cancer cells were used to verify that cell attachment density decreases in response to staurosporine, a drug that induces apoptosis. Third, we used PCEM to confirm the influence of integrin-mediated signaling on primary neonatal cardiomyocyte growth and development. Rounded cardiomyocytes consistently showed decreased cell attachment density as recorded via PCEM, while spreading cells exhibited greater attachment strength as well as increased contractility. Finally, PCEM was used to monitor the morphological changes and extracellular matrix remodeling of porcine adipose-derived stem cells subjected to a forced differentiation protocol. Each of these experiments yielded information regarding cell attachment density without the use of potentially cytotoxic labels, enabling study of the same cells for up to several days.

Cytotoxicity screening of Bangladeshi medicinal plant extracts on pancreatic cancer cells.

BACKGROUND: There has been a long standing interest in the identification of medicinal plants and derived natural products for developing cancer therapeutics. Our study focuses upon pancreatic cancer, due to its high mortality rate, that is attributed in part to the lack of an effective chemotherapeutic agent. Previous reports on the use of medicinal plant extracts either alone or alongside conventional anticancer agents in the treatment of this cancer have shown promising results. This work aims to investigate the therapeutic properties of a library of medicinal plants from Bangladesh. METHODS: 56 extracts of 44 unique medicinal plants were studied. The extracts were screened for cytotoxicity against the pancreatic adenocarcinoma cell line Panc-1, using a label-free biosensor assay. The top cytotoxic extracts identified in this screen were tested on two additional pancreatic cancer cell lines (Mia-Paca2 and Capan-1) and a fibroblast cell line (Hs68) using an MTT proliferation assay. Finally, one of the most promising extracts was studied using a caspase-3 colorimetric assay to identify induction of apoptosis. RESULTS: Crude extracts of Petunia punctata, Alternanthera sessilis, and Amoora chittagonga showed cytotoxicity to three cancer cell lines with IC50 values ranging between 20.3 - 31.4 µg/mL, 13.08 - 34.9 µg/mL, and 42.8 - 49.8 µg/mL, respectively. Furthermore, treatment of Panc-1 cells with Petunia punctata was shown to increase caspase-3 activity, indicating that the observed cytotoxicity was mediated via apoptosis. Only Amoora chittagonga showed low cytotoxicity to fibroblast cells with an IC50 value > 100 µg/mL. CONCLUSION: Based upon the initial screening work reported here, further studies aimed at the identification of active components of these three extracts and the elucidation of their mechanisms as cancer therapeutics are warranted.

A novel role for the centrosomal protein, pericentrin, in regulation of insulin secretory vesicle docking in mouse pancreatic beta-cells.

The centrosome is important for microtubule organization and cell cycle progression in animal cells. Recently, mutations in the centrosomal protein, pericentrin, have been linked to human microcephalic osteodysplastic primordial dwarfism (MOPD II), a rare genetic disease characterized by severe growth retardation and early onset of type 2 diabetes among other clinical manifestations. While the link between centrosomal and cell cycle defects may account for growth deficiencies, the mechanism linking pericentrin mutations with dysregulated glucose homeostasis and pre-pubertal onset of diabetes is unknown. In this report we observed abundant expression of pericentrin in quiescent pancreatic beta-cells of normal animals which led us to hypothesize that pericentrin may have a critical function in beta-cells distinct from its known role in regulating cell cycle progression. In addition to the typical centrosome localization, pericentrin was also enriched with secretory vesicles in the cytoplasm. Pericentrin overexpression in beta-cells resulted in aggregation of insulin-containing secretory vesicles with cytoplasmic, but not centrosomal, pericentriolar material and an increase in total levels of intracellular insulin. RNAi- mediated silencing of pericentrin in secretory beta-cells caused dysregulated secretory vesicle hypersecretion of insulin into the media. Together, these data suggest that pericentrin may regulate the intracellular distribution and secretion of insulin. Mice transplanted with pericentrin-depleted islets exhibited abnormal fasting hypoglycemia and inability to regulate blood glucose normally during a glucose challenge, which is consistent with our in vitro data. This previously unrecognized function for a centrosomal protein to mediate vesicle docking in secretory endocrine cells emphasizes the adaptability of these scaffolding proteins to regulate diverse cellular processes and identifies a novel target for modulating regulated protein secretion in disorders such as diabetes.

Identifying modulators of protein-protein interactions using photonic crystal biosensors.

Inhibitors and activators of protein-protein interactions are valuable as biological probes and medicinal agents but are often difficult to identify. Herein we describe a high-throughput assay, based upon photonic crystal (PC) biosensors, for the identification of modulators of protein-protein interactions. Through the use of a d-biotin-tris-NTA (BTN) hybrid compound, any His6-tagged protein can be immobilized on the surface of a PC biosensor. Binding of the bound protein to its cognate partner is detected via a shift in the peak wavelength value. We demonstrate this assay with three protein-protein pairs (caspase-9-XIAP, caspase-7-XIAP, FKBP12-FRB) and their small molecule modulators.

A method for identifying small molecule aggregators using photonic crystal biosensor microplates.

Small molecules identified through high-throughput screens are an essential element in pharmaceutical discovery programs. It is now recognized that a substantial fraction of small molecules exhibit aggregating behavior leading to false positive results in many screening assays, typically due to nonspecific attachment to target proteins. Therefore, the ability to efficiently identify compounds within a screening library that aggregate can streamline the screening process by eliminating unsuitable molecules from further consideration. In this work we show that photonic crystal (PC) optical biosensor microplate technology can be utilized to identify and quantify small molecule aggregation. A group of aggregators and nonaggregators were tested using the PC technology, and measurements were compared with those gathered by three alternative methods: dynamic light scattering (DLS), an alpha-chymotrypsin colorimetric assay, and scanning electron microscopy (SEM). The PC biosensor measurements of aggregation were confirmed by visual observation using SEM, and were in general agreement with the alpha-chymotrypsin assay. As a label-free detection method, the PC biosensor aggregation assay is simple to implement and provides a quantitative direct measurement of the mass density of material adsorbed to the transducer surface, while the microplate-based sensor format enables compatibility with high-throughput automated liquid handling methods used in pharmaceutical screening.

CHOP mediates endoplasmic reticulum stress-induced apoptosis in Gimap5-deficient T cells.

Gimap5 (GTPase of the immunity-associated protein 5) has been linked to the regulation of T cell survival, and polymorphisms in the human GIMAP5 gene associate with autoimmune disorders. The BioBreeding diabetes-prone (BBDP) rat has a mutation in the Gimap5 gene that leads to spontaneous apoptosis of peripheral T cells by an unknown mechanism. Because Gimap5 localizes to the endoplasmic reticulum (ER), we hypothesized that absence of functional Gimap5 protein initiates T cell death through disruptions in ER homeostasis. We observed increases in ER stress-associated chaperones in T cells but not thymocytes or B cells from Gimap5(-/-) BBDP rats. We then discovered that ER stress-induced apoptotic signaling through C/EBP-homologous protein (CHOP) occurs in Gimap5(-/-) T cells. Knockdown of CHOP by siRNA protected Gimap5(-/-) T cells from ER stress-induced apoptosis, thereby identifying a role for this cellular pathway in the T cell lymphopenia of the BBDP rat. These findings indicate a direct relationship between Gimap5 and the maintenance of ER homeostasis in the survival of T cells.

A Method for Identifying Small-Molecule Aggregators Using Photonic Crystal Biosensor Microplates.

Small molecules identified through high-throughput screens are an essential element in pharmaceutical discovery programs. It is now recognized that a substantial fraction of small molecules exhibit aggregating behavior leading to false positive results in many screening assays, typically due to nonspecific attachment to target proteins. Therefore, the ability to efficiently identify compounds within a screening library that aggregate can streamline the screening process by eliminating unsuitable molecules from further consideration. In this work, we show that photonic crystal (PC) optical biosensor microplate technology can be used to identify and quantify small-molecule aggregation. A group of aggregators and nonaggregators were tested using the PC technology, and measurements were compared with those gathered by three alternative methods: dynamic light scattering (DLS), an α-chymotrypsin colorimetric assay, and scanning electron microscopy (SEM). The PC biosensor measurements of aggregation were confirmed by visual observation using SEM, and were in general agreement with the α-chymotrypsin assay. DLS measurements, in contrast, demonstrated inconsistent readings for many compounds that are found to form aggregates in shapes, very different from the classical spherical particles assumed in DLS modeling. As a label-free detection method, the PC biosensor aggregation assay is simple to implement and provides a quantitative direct measurement of the mass density of material adsorbed to the transducer surface, whereas the microplate-based sensor format enables compatibility with high-throughput automated liquid-handling methods used in pharmaceutical screening.

Protein kinase C signaling during T cell activation induces the endoplasmic reticulum stress response.

T cell receptor (TCR) ligation (signal one) in the presence of co-stimulation (signal two) results in downstream signals that increase protein production enabling naïve T cells to fully activate and gain effector function. Enhanced production of proteins by a cell requires an increase in endoplasmic reticulum (ER) chaperone expression, which is accomplished through activation of a cellular mechanism known as the ER stress response. The ER stress response is initiated during the cascade of events that occur for the activation of many cells; however, this process has not been comprehensively studied for T cell function. In this study, we used primary T cells and mice circulating TCR transgenic CD8(+) T cells to investigate ER chaperone expression in which TCR signaling was initiated in the presence or absence of co-stimulation. In the presence of both signals, in vitro and in vivo analyses demonstrated induction of the ER stress response, as evidenced by elevated expression of GRP78 and other ER chaperones. Unexpectedly, ER chaperones were also increased in T cells exposed only to signal one, a treatment known to cause T cells to enter the 'nonresponsive' states of anergy and tolerance. Treatment of T cells with an inhibitor to protein kinase C (PKC), a serine/threonine protein kinase found downstream of TCR signaling, indicated PKC is involved in the induction of the ER stress response during the T cell activation process, thus revealing a previously unknown role for this signaling protein in T cells. Collectively, these data suggest that induction of the ER stress response through PKC signaling is an important component for the preparation of a T cell response to antigen.