The fatty liver disease-causing protein PNPLA3-I148M alters lipid droplet-Golgi dynamics.

Nonalcoholic fatty liver disease, recently renamed metabolic dysfunction-associated steatotic liver disease (MASLD), is a progressive metabolic disorder that begins with aberrant triglyceride accumulation in the liver and can lead to cirrhosis and cancer. A common variant in the gene PNPLA3, encoding the protein PNPLA3-I148M, is the strongest known genetic risk factor for MASLD. Despite its discovery 20 y ago, the function of PNPLA3, and now the role of PNPLA3-I148M, remain unclear. In this study, we sought to dissect the biogenesis of PNPLA3 and PNPLA3-I148M and characterize changes induced by endogenous expression of the disease-causing variant. Contrary to bioinformatic predictions and prior studies with overexpressed proteins, we demonstrate here that PNPLA3 and PNPLA3-I148M are not endoplasmic reticulum-resident transmembrane proteins. To identify their intracellular associations, we generated a paired set of isogenic human hepatoma cells expressing PNPLA3 and PNPLA3-I148M at endogenous levels. Both proteins were enriched in lipid droplet, Golgi, and endosomal fractions. Purified PNPLA3 and PNPLA3-I148M proteins associated with phosphoinositides commonly found in these compartments. Despite a similar fractionation pattern as the wild-type variant, PNPLA3-I148M induced morphological changes in the Golgi apparatus, including increased lipid droplet-Golgi contact sites, which were also observed in I148M-expressing primary human patient hepatocytes. In addition to lipid droplet accumulation, PNPLA3-I148M expression caused significant proteomic and transcriptomic changes that resembled all stages of liver disease. Cumulatively, we validate an endogenous human cellular system for investigating PNPLA3-I148M biology and identify the Golgi apparatus as a central hub of PNPLA3-I148M-driven cellular change.

The fatty liver disease-causing protein PNPLA3-I148M alters lipid droplet-Golgi dynamics.

Non-alcoholic fatty liver disease (NAFLD), recently renamed metabolic dysfunction-associated steatotic liver disease (MASLD), is a progressive metabolic disorder that begins with aberrant triglyceride accumulation in the liver and can lead to cirrhosis and cancer. A common variant in the gene PNPLA3, encoding the protein PNPLA3-I148M, is the strongest known genetic risk factor for MASLD to date. Despite its discovery twenty years ago, the function of PNPLA3, and now the role of PNPLA3-I148M, remain unclear. In this study, we sought to dissect the biogenesis of PNPLA3 and PNPLA3-I148M and characterize changes induced by endogenous expression of the disease-causing variant. Contrary to bioinformatic predictions and prior studies with overexpressed proteins, we demonstrate here that PNPLA3 and PNPLA3-I148M are not endoplasmic reticulum-resident transmembrane proteins. To identify their intracellular associations, we generated a paired set of isogenic human hepatoma cells expressing PNPLA3 and PNPLA3-I148M at endogenous levels. Both proteins were enriched in lipid droplet, Golgi, and endosomal fractions. Purified PNPLA3 and PNPLA3-I148M proteins associated with phosphoinositides commonly found in these compartments. Despite a similar fractionation pattern as the wild-type variant, PNPLA3-I148M induced morphological changes in the Golgi apparatus, including increased lipid droplet-Golgi contact sites, which were also observed in I148M-expressing primary human patient hepatocytes. In addition to lipid droplet accumulation, PNPLA3-I148M expression caused significant proteomic and transcriptomic changes that resembled all stages of liver disease. Cumulatively, we validate an endogenous human cellular system for investigating PNPLA3-I148M biology and identify the Golgi apparatus as a central hub of PNPLA3-I148M-driven cellular change.

Use of In Vitro Human Skin Models to Assess Potential Immune Activation In Response to Biotherapeutic Attributes and Process-related Impurities.

Subcutaneous (SubQ) injection is a common administration route for biotherapeutics. However, limited tools are available for understanding the dynamic relationships between drug products and resident cells following injection. Advances in tissue engineering have enabled the production of in vitro skin models that recapitulate the morphological structure and functional activity of human skin. Here we explore the use of a commercially available skin model to investigate potential immune activation in response to subcutaneously injected biotherapeutics. Exposure to high levels of a mixture of process-related impurities (that are known potent immune system activators) induced a robust immune response from the skin model, as indicated by enhanced metabolic activity and increased secretion of 19 cytokines and chemokines. The skin model also responded to aggregated antibodies (generated by extreme mechanical stirring and pH-jump stress, which resulted in orders of magnitude higher particle numbers than that found in products), as shown by the secretion of several signature cytokines (GM-CSF, RANTES, and MCP-1). However, the magnitude of the responses to the aggregates were significantly lower than the response to the impurities. These results highlight the promising utility of in vitro skin models for investigating the potential immune response to process-related impurities and biotherapeutic attributes in a subcutaneous environment. The use of skin models for assessing drug safety may provide new insights to help guide drug product and process development, and potentially mitigate the risk of injection site reactions and systemic immunogenic responses that may compromise the safety and efficacy of subcutaneously administered drugs.

Impact of Precipitation of Antibody Therapeutics After Subcutaneous Injection on Pharmacokinetics and Immunogenicity.

Antibody therapeutics with poor solubility in the subcutaneous matrix may carry unintended risks when administered to patients. The objective of this work was to estimate the risk of antibodies that precipitate in vitro at neutral pH by determining the impact of poor solubility on distribution of the drug from the injection site as well as immunogenicity in vivo. Using fluorescence imaging in a mouse model, we show that one such precipitation-prone antibody is retained at the injection site in the subcutaneous space longer than a control antibody. In addition, we demonstrate that retention at the injection site through aggregation is concentration-dependent and leads to macrophage association and germinal center localization. Although there was delayed disposition of the aggregated antibody to draining lymph nodes, no overall impact on the immune response in lymph nodes, systemic exposure of the antibody, or enhancement of the anti-drug antibody response was evident. Unexpectedly, retention of the precipitated antibody in the subcutaneous space delayed the onset of the immune response and led to an immune suppressive response. Thus, we conclude that precipitation due to poor solubility of high doses of antibody formulations delivered subcutaneously may not be of special concern in terms of exposure or immunogenicity.

Novel protein therapeutic joint retention strategy based on collagen-binding Avimers.

Designing drugs to treat diseases associated with articular joints, particularly those targeting chondrocytes, is challenging due to unique local environmental constraints including the avascular nature of cartilage, the absence of a closed joint compartment, and a highly cross-linked extracellular matrix. In an effort to address these challenges, we developed a novel strategy to prolong residence time of intra-articularly administered protein therapeutics. Avimer domains are naturally found in membrane polypeptides and mediate diverse protein-protein interactions. Screening of a phage Avimer domain library led to identification of several low affinity type II collagen-binding Avimers. Following several rounds of mutagenesis and reselection, these initial hits were transformed to high affinity, selective type II collagen-binding Avimers. One such Avimer (M26) persisted in rat knees for at least 1 month following intra-articular administration. Fusion of this Avimer to a candidate therapeutic payload, IL-1Ra, yielded a protein construct which simultaneously bound to type II collagen and to IL-1 receptor. In vitro, IL-1Ra_M26 bound selectively to cartilage explants and remained associated even after extensive washing. Binding appeared to occur preferentially to pericellular regions surrounding chondrocytes. An acute intra-articular IL-1-induced IL-6 challenge rat model was employed to assess in vivo pharmacodynamics. Whereas both IL-1Ra_M26 and native IL-1Ra inhibited IL-6 output when co-administered with the IL-1 challenge, only IL-1Ra_M26 inhibited when administered 1 week prior to IL-1 challenge. Collagen-binding Avimers thus represent a promising strategy for enhancing cartilage residence time of protein therapeutics. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1238-1247, 2018.

Three-dimensional second-harmonic generation imaging of fibrillar collagen in biological tissues.

Multiphoton-induced second-harmonic generation (SHG) has developed into a very powerful approach for in depth visualization of some biological structures with high specificity. In this unit, we describe the basic principles of three-dimensional SHG microscopy. In addition, we illustrate how SHG imaging can be utilized to assess collagen fibrils in biological tissues. Some technical considerations are also addressed.

Intracellular uptake and trafficking of difluoroboron dibenzoylmethane-polylactide nanoparticles in HeLa cells.

In this study, nanoparticles based on difluoroboron dibenzoylmethane-poly(lactic acid) (BF(2)dbmPLA) are prepared. Polylactic acid or polylactide is a commonly used degradable polymer, while the boron dye possesses a large extinction coefficient, high emission quantum yield, two-photon absorption, and sensitivity to the surrounding environment. BF(2)dbmPLA exhibits molecular-weight-dependent emission properties and can be formulated as stable nanoparticles, suggesting that its unique optical properties may be useful in multiple contexts for probing intracellular environments. Here we show that BF(2)dbmPLA nanoparticles are internalized into cultured HeLa cells by endocytosis, and that within the cellular milieu, they retain their fluorescence properties. BF(2)dbmPLA nanoparticles are photostable, resisting laser-induced photobleaching under conditions that destroy the fluorescence of a common photostable probe, LysoTracker Blue. Their endocytosis is also lipid-raft-dependent, as evidenced by their significant colocalization with cholera toxin B subunit in membrane compartments after uptake and their sensitivity of uptake to methyl-beta-cyclodextrin. Additionally, BF(2)dbmPLA nanoparticle endocytosis utilizes microtubules and actin filaments. Internalized BF(2)dbmPLA nanoparticles do not accumulate in acidic late endosomes and lysosomes but within a perinuclear nonlysosomal compartment. These findings demonstrate the feasibility of using novel BF(2)dbmPLA nanoparticles exhibiting diverse emission properties for in situ, live cell imaging and suggest that their endogenous uptake occurs through a lipid-raft-dependent endocytosis mechanism.

Lymphocytic infiltration leads to degradation of lacrimal gland extracellular matrix structures in NOD mice exhibiting a Sjögren's syndrome-like exocrinopathy.

We previously reported that lacrimal glands (LGs) of male non-obese diabetic (NOD) mice, an established mouse model of autoimmune inflammatory LG disease that displays many features of human LGs in patients afflicted with Sjögren's syndrome (SjS), exhibit significant degradation of extracellular matrix (ECM) structures as well as increased expression of matrix metalloproteinases (MMPs). The purpose of the current study was to expand the spectrum of proteases identified, to clarify their probable origin as well as to identify the contribution of these changes to disease pathogenesis. We explored in depth the changes in ECM structures and ECM protease expression at the onset of disease (6 weeks) versus late stage disease (18 weeks) in male NOD mouse LGs, relative to LGs of age-matched male NODscid, a severely immunocompromised congenic strain, and healthy BALB/c mice. LG tissues were examined using routine histological, immunohistochemical, Western Blot and gene expression analyses novel multiphoton imaging technologies. We further characterized the profile of infiltrating immune cells under each condition using flow cytometry. Our results show that the initial infiltrating cells at 6 weeks of age are responsible for increased MMP and cathepsin H expression and therefore initiate the LG ECM degradation in NOD mice. More importantly, NODscid mice exhibited normal LG ECM structures, indicating the lymphocytes seen in the LGs of NOD mice are responsible for the degradation of the LG ECM. The disease-related remodeling of LG ECM structures may play a crucial role in altering the acinar signaling environment, disrupting the signaling scaffolds within the cells, which are required to mobilize the exocytotic trafficking machinery, ultimately leading to a loss of LG function in patients afflicted with SjS.

Cardiomyopathy is associated with structural remodelling of heart valve extracellular matrix.

AIMS: To increase the supply, many countries harvest allograft valves from explanted hearts of transplant recipients with ischaemic (ICM) or dilated cardiomyopathy (DCM). This study determines the structural integrity of valves from cardiomyopathic hearts. METHODS AND RESULTS: Extracellular matrix (ECM) was examined in human valves obtained from normal, ICM, and DCM hearts. To confirm if ECM changes were directly related to the cardiomyopathy, we developed a porcine model of chronic ICM. Histology and immunohistostaining, as well as non-invasive multiphoton and second harmonic generation (SHG) imaging revealed marked disruption of ECM structures in human valves from ICM and DCM hearts. The ECM was unaffected in valves from normal and acute ICM pigs, whereas chronic ICM specimens showed ECM alterations similar to those seen in ICM and DCM patients. Proteins and proteinases implicated in ECM remodelling, including Tenascin C, TGFbeta1, Cathepsin B, MMP2, were upregulated in human ICM and DCM, and porcine chronic ICM specimens. CONCLUSION: Valves from cardiomyopathic hearts showed significant ECM deterioration with a disrupted collagen and elastic fibre network. It will be important to determine the impact of this ECM damage on valve durability and calcification in vivo if allografts are to be used from these donors.

Transduced viral IL-10 is exocytosed from lacrimal acinar secretory vesicles in a myosin-dependent manner in response to carbachol.

The purpose of this study was to determine the intracellular trafficking and release pathways for the therapeutic protein, viral IL-10 (vIL-10), from transduced acinar epithelial cells from rabbit lacrimal gland. Primary cultured rabbit lacrimal gland acinar cells (LGACs) were transduced with adenovirus serotype 5 containing viral interleukin-10 (AdvIL-10). The distribution of vIL-10 was assessed by confocal fluorescence microscopy. Carbachol (CCH)-stimulated release of vIL-10 was quantified by ELISA. vIL-10 localization and exocytosis was probed in response to treatments with agents modulating actin- and myosin-based transport. vIL-10 immunoreactivity was detected in large intracellular vesicles in transduced LGAC. vIL-10 was partially co-localized with biosynthetic but not endosomal compartment markers. vIL-10 release was sensitive to CCH, and the kinetics of release showed an initial burst phase that was similar but not identical to that of the secretory protein, beta-hexosaminidase. Disassembly of actin filaments with latrunculin B significantly increased CCH-stimulated vIL-10 secretion, suggesting that vIL-10 was released from stores sequestered beneath the subapical actin barrier. That release required the activity of actin-dependent myosin motors previously implicated in secretory vesicle exocytosis was confirmed by findings that CCH-stimulated vIL-10 release was reduced by inhibition of non-muscle myosin 2 and myosin 5c function, using ML-7 and overexpression of dominant negative myosin 5c, respectively. These results suggest that the majority of vIL-10 transgene product is packaged into a subpopulation of secretory vesicles that utilize actin-dependent myosin motors for aspects of actin coat assembly, compound fusion and exocytosis at the apical plasma membrane in response to CCH stimulation.

Site-specific labeling of enveloped viruses with quantum dots for single virus tracking.

This study reports a general method of labeling enveloped viruses with semiconductor quantum dots (QDs) for use in single virus trafficking studies. Retroviruses, including human immunodeficiency virus (HIV), could be successfully tagged with QDs through the membrane incorporation of a short acceptor peptide (AP) that is susceptible to site-specific biotinylation and attachment of streptavidin-conjugated QDs. It was found that this AP tag-based QD labeling had little effect on the viral infectivity and allowed for the study of the kinetics of the internalization of the recombinant lentivirus enveloped with vesicular stomatitis virus glycoprotein (VSVG) into the early endosomes. It also allows for the live cell imaging of the trafficking of labeled virus to the Rab5(+) endosomal compartments. This study further demonstrated by direct visualization of QD-labeled virus that VSVG-pseudotyped lentivirus enters cells independent of clatherin- and caveolin-pathways, while the entry of VSVG-pseudotyped retrovirus occurs via the clathrin pathway. The studies monitoring HIV particles using QD-labeling showed that we could detect single virions on the surface of target cells expressing either CD4/CCR5 or DC-SIGN. Further internalization studies of QD-HIV evidently showed that the clathrin pathway is the major route for DC-SIGN-mediated uptake of viruses. Taken together, our data demonstrate the potential of this QD-labeling for visualizing the dynamic interactions between viruses and target cell structures.

Polystyrene nanoparticle trafficking across alveolar epithelium.

We investigated trafficking of polystyrene nanoparticles (PNP; 20 and 100 nm; carboxylate, sulfate, or aldehyde-sulfate modified [negatively charged] and amidine-modified [positively charged]) across rat alveolar epithelial cell monolayers (RAECM). Apical-to-basolateral fluxes of nanoparticles were estimated as functions of apical PNP concentration ([PNP]) and temperature. Uptake of nanoparticles into RAECM was determined using confocal microscopy. Fluxes increased as charge density became less negative/more positive, with positively charged PNPs trafficking 20-40 times faster than highly negatively charged PNP of comparable size. Trafficking rates decreased with increasing PNP diameter. PNP fluxes tended to level off at high apical [PNP]. Fluxes at 4 degrees C were significantly lower than those at 37 degrees C. Confocal microscopy revealed nanoparticles localized to cell cytoplasm, whereas cell junctions and nuclei appeared free of PNP. These data indicate that (1) trafficking of PNP across RAECM is strongly influenced by charge density, size, and temperature, (2) PNP translocate primarily transcellularly, and (3) PNP translocation requires cellular energy.

Quantitative second harmonic generation imaging of cartilage damage.

Cartilage damage was studied using non-invasive multiphoton-excited autofluorescence and quantitative second harmonic generation (SHG) microscopy. Two cryopreservation techniques based upon freezing and vitrification methods, respectively, were employed to determine whether or not the collagen fiber structure of full thickness porcine articular cartilage was affected by cryopreservation and whether the level of collagen damage could be determined quantitatively in non-processed (non-fixed, non-sliced, non-stained) tissues. Multiphoton-induced autofluorescence imaging revealed the presence of chondrocytes, as well as collagenous structures in all fresh, vitrified and frozen cryopreserved cartilage samples. SHG imaging of the frozen cryopreserved specimens showed a dramatic loss of mean gray value intensities when compared to both fresh and vitrified tissues (P<0.05), indicating structural changes of the extracellular matrix, in particular the deformation and destruction of the collagen fibers in the analyzed articular cartilage. A 0.9974 correlation coefficient was observed between the metabolic cell activity assessed by the alamarBlue technique, and retention of collagen structure between the three experimental groups. These studies suggest that multiphoton-induced autofluorescence imaging combined with quantitative SHG signal profiling may prove to be useful tools for the investigation of extracellular matrix changes in preserved cartilage, giving insights on the structural quality prior to implantation.

Increased degradation of extracellular matrix structures of lacrimal glands implicated in the pathogenesis of Sjögren's syndrome.

Lacrimal glands (LGs) of male non-obese diabetic (NOD) mice display many features of human LGs in patients afflicted with the autoimmune disease Sjögren's syndrome (SS), including the loss of secretory functions and a lymphocytic infiltration into the glands by 4 months of age. So far, research has mainly focused on the intracellular events that are involved in initiating LG dysfunction; however, the impact of SS on extracellular matrix (ECM) structures of the diseased LGs has not yet been determined. In this study we identified and compared LG ECM formation and integrity of age-matched male healthy (BALB/c) and diseased (NOD) mice. LG tissues were examined using routine histological, biochemical, immunohistochemical and gene expression analysis. Multiphoton imaging and second-harmonic generation (SHG) microscopy permitted the non-invasive analysis of major LG ECM structures including collagen- and elastin-containing fibers. Biochemical testing demonstrated a significant loss of collagen, glycosaminoglycans and desmosine in NOD LGs when compared to healthy BALB/c LGs. Immunohistochemical staining and gene expression analysis confirmed this disease-related alteration of LG ECM structures. Furthermore, laser-induced autofluorescence and SHG microscopy revealed dramatic changes in the structural organization of most collagenous and elastic fibers of the diseased LG tissues that were more pronounced than those displayed by histological analysis. Our results clearly show an enhanced degradation of ECM proteins accompanied by the severe disorganization and deformation of ECM structures of diseased LG tissues. These new insights into the involvement of ECM degradation in SS may lead to novel therapies for patients suffering from dry eye disease.

Optimized preservation of extracellular matrix in cardiac tissues: implications for long-term graft durability.

BACKGROUND: Cryopreservation of human tissues, particularly heart valves, is widespread in clinical practice although the effects of this process on underlying tissue structures and its potential impact on valve durability have been poorly studied. Multiphoton imaging and second-harmonic generation (SHG) microscopy permit high-resolution, noninvasive analysis of living tissues at a subcellular level. In the present study we used these novel imaging modalities to compare the effects of vitreous and frozen cryopreservation on the extracellular matrix (ECM) of cardiac tissues. METHODS: Conventional histology, electron microscopy, and multiphoton imaging to obtain autofluorescence and SHG images were performed on cardiac tissues to characterize the ECM in fresh, vitrified, and frozen cryopreserved tissues. RESULTS: Autofluorescence and particularly SHG images revealed that conventional frozen cryopreservation of cardiac valves, when compared with fresh or vitrified tissues, leads to the loss of normal ECM structures in valve leaflets. Similar results were found in all other cardiac tissues suggesting that structural deterioration of the ECM is a common consequence of frozen cryopreservation. CONCLUSIONS: Our results demonstrate that conventional cryopreservation, when compared with fresh or vitrified tissues, causes more destruction of normal ECM structure, which might contribute to eventual graft dysfunction. Whether vitrification preservation will translate into greater durability or less valve failure will need to be determined.

Novel fiber-dependent entry mechanism for adenovirus serotype 5 in lacrimal acini.

The established mechanism for infection of most cells with adenovirus serotype 5 (Ad5) involves fiber capsid protein binding to coxsackievirus-adenovirus receptor (CAR) at the cell surface, followed by penton base capsid protein binding to alpha(v) integrins, which triggers clathrin-mediated endocytosis of the virus. Here we determined the identity of the capsid proteins responsible for mediating Ad5 entry into the acinar epithelial cells of the lacrimal gland. Ad5 transduction of primary rabbit lacrimal acinar cells was inhibited by excess Ad5 fiber or knob (terminal region of the fiber) but not excess penton base. Investigation of the interactions of recombinant Ad5 penton base, fiber, and knob with lacrimal acini revealed that the penton base capsid protein remained surface associated, while the knob domain of the fiber capsid protein was rapidly internalized. Introduction of rabbit CAR-specific small interfering RNA (siRNA) into lacrimal acini under conditions that reduced intracellular CAR mRNA significantly inhibited Ad5 transduction, in contrast to a control (nonspecific) siRNA. Preincubation of Ad5 with excess heparin or pretreatment of acini with a heparinase cocktail each inhibited Ad5 transduction by a separate and apparently additive mechanism. Functional and imaging studies revealed that Ad5, fiber, and knob, but not penton base, stimulated macropinocytosis in acini and that inhibition of macropinocytosis significantly reduced Ad5 transduction of acini. However, inhibition of macropinocytosis did not reduce Ad5 uptake. We propose that internalization of Ad5 into lacrimal acini is through a novel fiber-dependent mechanism that includes CAR and heparan sulfate glycosaminoglycans and that the subsequent intracellular trafficking of Ad5 is enhanced by fiber-induced macropinocytosis.

Altered traffic to the lysosome in an ex vivo lacrimal acinar cell model for chronic muscarinic receptor stimulation.

Evidence suggests that lacrimal and salivary epithelial cells constitutively expose potentially pathogenic autoantigens, but that active regulatory networks normally suppress pathological autoimmune responses . Events that potentially disrupt the regulatory networks include increased exposure of constitutive autoantigens and induced exposure of previously cryptic autoantigen epitopes. Chronic muscarinic receptor (MAChR) stimulation in an ex vivo rabbit lacrimal acinar cell model induces functional and biochemical alterations reminiscent of the functional quiescence associated with Sjogren's syndrome . Chronic MAChR stimulation also elicits changes in the compartmental distribution of beta-hexosaminidase, a product that normally is dually targeted into the lysosomal pathway and the regulated apical secretory pathway. Here, we use subcellular fractionation analyses to further explore the nature of the stimulation-induced traffic changes and to identify effectors that might mediate this change. Overnight stimulation of primary cultured rabbit lacrimal gland acinar cells with 10 microM carbachol (CCh) significantly decreased the abundance of mature cathepsin B in the pre-lysosome and lysosome; decreased the abundance of preprocathepsin B in fractions containing the TGN and late endosome; increased the abundance of procathepsin B in fractions containing the basal-lateral membrane; and increased the accumulation of endocytosed [(125)I]-EGF in the recycling endosome. Alterations in distribution or abundance of traffic effectors included: increased abundances of rab5A and rab6 in the TGN; decreased overall abundance of gamma-adaptin; remarkably increased relative abundance of membrane phase-associated actin; redistribution of cytoplasmic dynein from biosynthetic and proximal endocytic compartments to the lysosome; and redistribution of p150(Glued) from the lysosome to biosynthetic or proximal endocytic compartments. We conclude that chronic MAChR stimulation blocks traffic from the early endosome and the TGN to the lysosome, causing lysosomal proteins to reflux to the TGN, endosomes, and basal-lateral membrane. These traffic alterations may be mediated through action on one or more of the effectors noted.

Role of the microtubule cytoskeleton in traffic of EGF through the lacrimal acinar cell endomembrane network.

We have previously documented a novel biphasic traffic pattern for epidermal growth factor (EGF) in the acinar epithelial cell of the lacrimal gland. Different from the typical paradigm observed in many other cell types, EGF initially accumulates in the acinar basal-lateral recycling endosome, then is re-directed to the prelysosomes and lysosomes and degraded. While the cellular content of intact EGF decreases by 40% between 20 and 120 m of continuous incubation at 37 degrees C, the EGF receptor (EGFR) content decreases only modestly [J. Cell Physiol. 199 (2004) 108]. The purpose of the present study was to investigate the role of the microtubule cytoskeleton in this traffic. Primary cultured rabbit lacrimocytes were incubated with [(125)I]-EGF, lysed, and analyzed by subcellular fractionation on sorbitol density gradients. Nocodazole treatment appeared to slightly decrease the initial uptake rate but to have no significant effect on the total amount of [(125)I] accumulation. However, it enhanced accumulation of [(125)I]-EGF and EGFR in the basal-lateral recycling endosome, and it enhanced accumulation of prepro- and pro- cathepsin B in fractions containing late endosomes and prelysosomes. Nocodazole permitted the time-dependent release of [(125)I]-EGF from the recycling endosome, but it partially inhibited [(125)I]-EGF degradation and decreased accumulation of [(125)I]-labeled degradation products in the lysosome. The microtubule-based molecular motors, cytoplasmic dynein and kinesin, were localized in compartments containing the late endosomes, prelysosomes, and lysosomes, consistent with the suggestion that microtubule-based molecular motors play important roles in traffic within the lysosomal pathway. Confocal fluorescence microscopy imaging of FITC-EGF substantiated the effects observed in biochemical studies by demonstrating that nocodazole increased accumulation in a peripheral compartment and decreased traffic to a perinuclear compartment. These data suggest that initial accumulation in the basal-lateral recycling endosome and subsequent release from the recycling endosome to the late endosomes and prelysosome are not microtubule-dependent. On the other hand, microtubule-based motors are more critical for traffic from the prelysosome to the lysosome.

Novel biphasic traffic of endocytosed EGF to recycling and degradative compartments in lacrimal gland acinar cells.

The purpose of this study was to delineate the traffic patterns of EGF and EGF receptors (EGFR) in primary cultured acinar epithelial cells from rabbit lacrimal glands. Uptake of [(125)I]-EGF exhibited saturable and non-saturable, temperature-dependent components, suggesting both receptor-mediated and fluid phase endocytosis. Accumulation of [(125)I] was time-dependent over a 120-min period, but the content of intact [(125)I]-EGF decreased after reaching a maximum at 20 min. Analytical fractionation by sorbitol density gradient centrifugation and phase partitioning indicated that within 20 min at 37 degrees C [(125)I] reached an early endosome, basal-lateral recycling endosome, pre-lysosome, and lysosome. Small components of the label also appeared to reach the Golgi complex and trans-Golgi network. Intact [(125)I]-EGF initially accumulated in the recycling endosome; the content in the recycling endosome subsequently decreased, and by 120 min increased amounts of [(125)I]-labeled degradation products appeared in the pre-lysosomes and lysosomes. Confocal microscopy imaging of FITC-EGF and LysoTrackerRed revealed FITC enriched in a dispersed system of non-acidic compartments at 20 min and in acidic compartments at 120 min. Both confocal immunofluorescence microscopy and analytical fractionation indicated that the intracellular EGFR pool was much larger than the plasma membrane-expressed pool at all times. Cells loaded with [(125)I]-EGF released a mixture of intact EGF and [(125)I]-labeled degradation products. The observations indicate that in lacrimal acinar cells, EGFR and EGF-EGFR complexes continually traffic between the plasma membranes and a system of endomembrane compartments; EGF-stimulation generates time-dependent signals that initially decrease, then increase, EGF-EGFR traffic to degradative compartments.

Modulation of secretory functions in epithelia by adenovirus capsid proteins.

To evaluate the safety of adenovirus-derived capsid proteins for ocular gene delivery, we have investigated their effects on the morphology and function of the acinar epithelial cells of the lacrimal gland. These cells are responsible for basal and stimulated release of proteins and electrolytes into ocular fluid, a process essential in maintaining the health of the ocular surface. Acinar epithelial cells from rabbit lacrimal gland were exposed to one of two adenovirus serotype 5 capsid proteins, penton or knob (the carboxy-terminal fragment of the fiber capsid protein). Sustained (16-18 h) exposure to the penton at 20 microg/ml was associated with major changes in the organization of the regulated secretory pathway and cytoskeleton. These changes included an apparent loss of mature secretory vesicles enriched in rab3D around the apical lumen as well as a depletion of apical actin. The microtubule array in penton-treated acini also exhibited bundling and disorganization. None of these effects were elicited by exposure to knob protein. Penton treatment also caused a significant (p < or = 0.05) increase and decrease in basal and carbachol-stimulated release, respectively, of bulk protein. Competition studies showed that RGD peptide partially prevented the penton-induced changes in rab3D-enriched secretory vesicles and actin filaments. These findings suggest that the adenovirus penton protein compromises normal acinar secretory compartment organization and function and that these changes are due at least partly to penton-integrin interactions.