Prince Eric Perez - Academia.edu (original) (raw)

Papers by Prince Eric Perez

Gut Microbes, 2020

Sleep is a fundamental biological process, that when repeatedly disrupted, can result in severe h... more Sleep is a fundamental biological process, that when repeatedly disrupted, can result in severe health consequences. Recent studies suggest that both sleep fragmentation (SF) and dysbiosis of the gut microbiome can lead to metabolic disorders, though the underlying mechanisms are largely unclear. To better understand the consequences of SF, we investigated the effects of acute (6 days) and chronic (6 weeks) SF on rats by examining taxonomic profiles of microbiota in the distal ileum, cecum and proximal colon, as well as assessing structural and functional integrity of the gastrointestinal barrier. We further assayed the impact of SF on a host function by evaluating inflammation and immune response. Both acute and chronic SF induced microbial dysbiosis, more dramatically in the distal ileum (compared to other two regions studied), as noted by significant perturbations in alpha-and beta-diversity; though, specific microbial populations were significantly altered throughout each of the three regions. Furthermore, chronic SF resulted in increased crypt depth in the distal ileum and an increase in the number of villi lining both the cecum and proximal colon. Additional changes were noted with chronic SF, including: decreased microbial adhesion and penetration in the distal ileum and cecum, elevation in serum levels of the cytokine KC/GRO, and depressed levels of corticotropin. Importantly, our data show that perturbations to microbial ecology and intestinal morphology intensify in response to prolonged SF and these changes are habitat specific. Together, these results reveal consequences to gut microbiota homeostasis and host response following acute and chronic SF in rats.

Polymers in Medicine II, 1986

Mucosal surfaces in contact with the external biological environment are generally covered with a... more Mucosal surfaces in contact with the external biological environment are generally covered with a mucus layer. The primary function of this layer in the oral cavity and in the respiratory, gastrointestinal and reproductive tracts is to lubricate ephithelial cells and protect them from attack by microorganisms, the toxins they produce, and other antigens1–3.

Seminars in oncology, 1994

Recent Advances in Fish Farms, 2011

fish meal and fish oils. Indeed, the aquaculture sector's consumption of fish meal and oils incre... more fish meal and fish oils. Indeed, the aquaculture sector's consumption of fish meal and oils increased respectively from 2.9Mt to 3.7Mt and from 0.6Mt to 0.8Mt between 2000 and 2008 (Tacon and Metian, 2008). Over and above the issue relating to the use of feed with a high biological value for aquaculture production, Naylor et al. (2000) contrast two aquaculture models: the first one, an input-intensive system, in particular as regards fish meal and oils and a priori non sustainable, and the second one, classically described as extensive or semi-extensive, considered to be sustainable. This implicit or explicit assimilation of intensive and extensive/semi-extensive systems with models of respectively weak or strong sustainability can be found in many publications from the 1980s and 1990s (

The Surface Force Apparatus (SFA) measures directly, and with nanoscale resolution, the interacti... more The Surface Force Apparatus (SFA) measures directly, and with nanoscale resolution, the interaction energy vs. distance profile of planar arrays of biological molecules (e.g., lipids, polymers, or proteins). Through recent advances in the reconstitution and deposition of lipid bilayers, it is now possible to use SFA to study the interactions between membrane-incorporated biomolecules and to reveal any conformational changes and intermediate assembly states. Therein we describe two example systems. First, we show that using bilayers functionalized to carry DNA bases on their lipid headgroups, we can measure a macroscopic nucleosidenucleoside adhesion force, from which one can obtain a molecular binding energy. Second, we describe the use of the SFA to study the interaction between SNARE proteins, which are involved in most of intracellular fusion events. Membrane fusion occurs when SNARE proteins assemble between lipid bilayers in the form of SNAREpins. SFA measurements between SNAREs embedded in lipid bilayers allowed us to elucidate the energetics and dynamics of SNAREpin folding, and to capture an intermediate binding state in SNAREpin assembly.

Langmuir, 1995

To help understand the effects of protein adsorption on membrane filtration performance, we have ... more To help understand the effects of protein adsorption on membrane filtration performance, we have measured the molecular interactions between cellulose acetate films and two proteins with different properties (ribonuclease A and human serum albumin) with a surface force apparatus. Comparison of forces between two protein layers with those between a protein layer and a cellulose acetate (CAI film shows that, at high pH, both proteins retained their native conformation on interacting with the CA film while at the isoelectric point (PI) or below the tertiary structure of proteins was disturbed. These measurements provide the first molecular evidence that disruption of protein tertiary structure could be responsible for the reduced permeation flows observed during membrane filtration of protein solutions and suggest that operating at high pH values away from the PI of proteins will reduce such fouling.

OFC/NFOEC 2007 - 2007 Conference on Optical Fiber Communication and the National Fiber Optic Engineers Conference, 2007

Page 1. Ultra-Compact Long-Period Fiber Grating and Grating Pair Fabrication using a Modulation-S... more Page 1. Ultra-Compact Long-Period Fiber Grating and Grating Pair Fabrication using a Modulation-Scanned CO2 Laser Hon M. Chan, Eric Perez, Fares Alhassen, Ivan V. Tomov, and Henry P. Lee Department of Electrical Engineering ...

The Journal of Physical Chemistry B, 2004

A cationic polyelectrolyte was adsorbed on mica from highly concentrated solutions. The friction ... more A cationic polyelectrolyte was adsorbed on mica from highly concentrated solutions. The friction and surface force behaviors of the adsorbed layers in aqueous media were studied using a new homemade surface force apparatus (SFA). The long-range repulsions produced by the pure cationic polymer at low salt concentration indicate that the chains are in an extended conformation. The addition of anionic surfactant or of salt condenses the cationic polymer chains as evidenced by the much shorter range of the repulsions. These forces are, for both conformations, a combination of steric and double-layer forces. During sliding, the friction forces produced by the adsorbed layers increase monotonically with the load. A strong dependence of these forces on the sliding speed is noticeable for the extended conformations, while the dependence vanishes in the coiled conformations. This study shows the important role of the conformational state of adsorbed polymer chains on their tribological properties.

The Journal of Cell Biology, 2004

We have used a modified, dual pipette assay to quantify the strength of cadherin-dependent cell–c... more We have used a modified, dual pipette assay to quantify the strength of cadherin-dependent cell–cell adhesion. The force required to separate E-cadherin–expressing paired cells in suspension was measured as an index of intercellular adhesion. Separation force depended on the homophilic interaction of functional cadherins at the cell surface, increasing with the duration of contact and with cadherin levels. Severing the link between cadherin and the actin cytoskeleton or disrupting actin polymerization did not affect initiation of cadherin-mediated adhesion, but prevented it from developing and becoming stronger over time. Rac and Cdc42, the Rho-like small GTPases, were activated when E-cadherin–expressing cells formed aggregates in suspension. Overproduction of the dominant negative form of Rac or Cdc42 permitted initial E-cadherin–based adhesion but affected its later development; the dominant active forms prevented cell adhesion outright. Our findings highlight the crucial roles p...

Physical Review Letters, 2001

We present a statistical mechanical treatment relating the macroscopic adhesion energy of two sur... more We present a statistical mechanical treatment relating the macroscopic adhesion energy of two surfaces, which can be obtained by micropipette aspiration studies, to the microscopic adhesion energy between individual bonds. The treatment deals with the case of weak reversible bonds, so that the equilibrium partition function has significance. This description is coherent with previous theories. Experiment and theory are compared to probe the nature of weak bonds in membranes, where local equilibria can be obtained. The case of a bead and a vesicle decorated by nucleosides was considered.

Physical Review Letters, 2005

JKR theory is an accurate model for strong adhesion energies of soft slightly deformable material... more JKR theory is an accurate model for strong adhesion energies of soft slightly deformable material. Little is known about the validity of this theory on complex systems such as living cells. We have addressed this problem using a depletion controlled cell adhesion and measured the force necessary to separate the cells with a micropipette technique. We show that the cytoskeleton can provide the cells with a 3-D structure that is sufficiently elastic and has sufficiently low deformability for JKR theory to be valid. When the cytoskeleton is disrupted, JKR theory is no longer applicable.

Nature Structural & Molecular Biology, 2011

The core mechanism of intracellular vesicle fusion consists of SNAREpin zippering between vesicul... more The core mechanism of intracellular vesicle fusion consists of SNAREpin zippering between vesicular and target membranes. Recent studies indicate that the same SNARE-binding protein, Complexin (CPX), can act either as a facilitator or as an inhibitor of membrane fusion, giving rise to a major controversy. Here, we employ energetic measurements using the Surface Forces Apparatus which reveal that CPX acts sequentially on assembling SNAREpins, first facilitating zippering by nearly doubling the distance at which v-and t-SNAREs can engage, and then by clamping them into a half-zippered fusion-incompetent state. Specifically, we find that the central helix of CPX allows SNAREs to form this intermediate energetic state at 9-15 nm, but not when the bilayers are closer than 9 nm. Stabilizing the activated-clamped state at separations < 9 nm requires the accessory helix of CPX, which prevents membrane-proximal assembly of SNAREpins. During regulated exocytosis in synaptic transmission and neuro-endocrine secretion, a pool of neurotransmitter or hormone-containing vesicles accumulate at the plasma membrane awaiting the signal for rapid and synchronous release. To create this readily releasable pool, the molecular machinery of regulated exocytosis needs to bring the vesicles into an activated state which is as close to fusion as possible, all the while preventing them from fusing prematurely 1-3. Calcium-dependent exocytosis is controlled by the pairing between cognate v-and t-SNARE (soluble N-ethylmaleimide sensitive factor attachment protein receptor) proteins, which assemble like a zipper across the membranes that are destined to fuse, thus facilitating their close apposition and subsequent merging 4,5. The assembly of such membrane-bridging complexes, called SNAREpins, is further manipulated by SNARE interacting proteins to allow fusion to be clamped or triggered where and when necessary 1. Complexin (CPX) and synaptotagmin (SYT) proteins are key regulators of calciumdependent neurotransmitter release displaying an intriguing dual activatory-inhibitory role in membrane fusion 2,6-9 .

Nature Structural & Molecular Biology, 2007

Membrane fusion occurs when SNAREpins fold up between lipid bilayers. How much energy is generate... more Membrane fusion occurs when SNAREpins fold up between lipid bilayers. How much energy is generated during SNAREpin folding and how this energy is coupled to the fusion of apposing membranes is unknown. We have used a surface forces apparatus to determine the energetics and dynamics of SNAREpin formation and characterize the different intermediate structures sampled by cognate SNAREs in the course of their assembly. The interaction energy-versus-distance profiles of assembling SNAREpins reveal that SNARE motifs begin to interact when the membranes are 8 nm apart. Even after very close approach of the bilayers (B2-4 nm), the SNAREpins remain partly unstructured in their membrane-proximal region. The energy stabilizing a single SNAREpin in this configuration (35 k B T) corresponds closely with the energy needed to fuse outer but not inner leaflets (hemifusion) of pure lipid bilayers (40-50 k B T).

Langmuir, 2007

Interactions between hydrophobic chains of lipid monolayers and interactions between hydrophilic ... more Interactions between hydrophobic chains of lipid monolayers and interactions between hydrophilic headgroups of lipid bilayers (with or without a molecular recognition step) are now well documented, especially for commonly used lipids. Here, we report force measurements between a new class of fluorinated lipid layers whose headgroups (synthetic ligands of retinoid receptors) display a very unusual polar/apolar character and can interact via a combination of hydrophobic forces and hydrogen bonds. Although these two interactions produce adhesion and are therefore not easily distinguishable, we show that it is possible to extract both contributions unambiguously. Experiments are performed both in pure water, where the adhesion is a combination of hydrophobic forces and hydrogen bonds, and in Tris buffer, where the hydrophobic effect is the dominant short-range attractive force. The contribution of hydrophobic forces scaled down to molecular interactions is deduced from force versus distance profiles, and the same value is found independently in pure water and Tris buffer, about 1 k B T. We also show that retinoid lipid layers attract each other through a very long-range (100 nm) exponential force, which is insensitive to the pH and the salinity. The origin of this long-range attraction is discussed on the basis of previously proposed mechanisms.

Langmuir, 2008

This study focuses on the interaction involved in the adhesion of mouse gametes and on the mechan... more This study focuses on the interaction involved in the adhesion of mouse gametes and on the mechanical properties of the oocyte membrane. The oocyte has an asymmetrical shape, and its membrane is composed of two distinct areas. One is rich in microvilli, and the other is smoother and without microvilli. With a biomembrane force probe (BFP) adapted to cell-cell measurements, we have quantified the separation forces between a spermatozoon and an oocyte. Microvillar and amicrovillar areas of the oocyte surface have been systematically probed and compared. In addition to a substantial difference in the elastic stiffness of these two regions, the experiments have revealed the presence of two types of membrane domains with different mechanical and adhesive properties, both distributed over the entire oocyte surface (i.e., in both microvillar and amicrovillar regions). If gamete contact occurs in the first type of domain, then the oocyte membrane deforms only elastically under traction. The pull-off forces in these domains are higher in the amicrovillar region. For a spermatozoon contact with the other type of domain, there can be a transition from the elastic to viscoelastic regime, and then tethers are extruded from the oocyte membrane.

Journal of Colloid and Interface Science, 1987

The forces between two mica surfaces covered with an adsorbed layer of protein (mucin BSM) across... more The forces between two mica surfaces covered with an adsorbed layer of protein (mucin BSM) across aqueous solution were measured as a function of distance. Parallel adsorption measurements were performed with radiolabeled mucin. The analysis of the force/distance curves for different mucin surface densities and ionic strengths have shown that (1) in all the studied cases, steric repulsive exponentially varying forces were observed, which increased with the mucin surface density. (2) For a low coverage of the mica surfaces by mucin, bridging effects give rise to large-distance attractive interactions. They disappear at high coverages of the mica surfaces. (3) The mucin macromolecules are more rigid at physiological salt concentrations than at low ionic strengths.

Journal of Bone and Mineral Metabolism, 2007

The antigenic phenotype of cultured human osteoblast-like cells, their ability to phagocytose par... more The antigenic phenotype of cultured human osteoblast-like cells, their ability to phagocytose particles of different nature and size, and their capacity to stimulate allogeneic T cells suggest that they are related to other cell populations with which they may also have immunological functions in common. The objective of this study was to investigate the intracytoplasmatic presence of cytokines and their modulation by different biomolecules. Immunocytochemistry and flow cytometry were used to study the expression of IL-4, IL-12, IL-15, IL-18, and IFNgamma cytokines. To investigate whether FGF, TGF, PDGF, IL-1, and IFNgamma modulate expression of these cytokines in cultured human osteoblast-like cells we used flow cytometry. IL-4, IL-12, IL-15, IL-18, and IFNgamma cytokines were expressed by all the cultured human osteoblast-like cells studied. Treatment with FGF and TGFbeta1 reduced the percentage expression and fluorescence intensity of the cytokines. PDGF treatment enhanced their fluorescence intensity but did not modify their expression. IL-1 treatment produced a small reduction in expression and fluorescence intensity of IL-12 and IL-15, but did not produce major changes in the expression of IL-4, IL-18, or IFNgamma. IFNgamma markedly increased the fluorescence intensity of the cytokines. The results indicate that human osteoblast-like cells may perform immunological functions (e.g., synthesizing cytokines with immune regulator function) that can be modulated by different biomolecules related to bone tissue and/or immune response.

IEEE Transactions on Nanobioscience, 2004

With the possibility of creating and handling nanometer-sized objects, it became popular to dream... more With the possibility of creating and handling nanometer-sized objects, it became popular to dream of future miniaturized tools allowing completely new applications in medicine and technology. Mother nature created during evolution many such self-assembled highly sophisticated and robust objects, and it is very tempting to modify them for other purposes: artificial cells as intelligent submarines floating in the bloodstream attacking cancer cells, single-molecule detection and manipulation allowing the bottom-up construction of devices, and so on. Nanobiotechnology became a hot topic and significant budgets have been attributed to it. However, caution has to be paid that unrealistic dreams might have a fairly negative effect on the taxpayer seeing unkept promises. In this paper, we explore the possibilities of using biological substances in material science.