ROCK inhibitors 2. Improving potency, selectivity and solubility through the application of rationally designed solubilizing groups.

Solubilizing groups have been frequently appended to kinase inhibitor drug molecules when solubility is insufficient for pharmaceutical development. Such groups are usually located at substitution sites that have minimal impact on target activity. In this report we describe the incorporation of solubilizing groups in a class of Rho kinase (ROCK) inhibitors that not only confer improved solubility, but also enhance target potency and selectivity against a closely related kinase, PKA.

ROCK inhibitors 3: Design, synthesis and structure-activity relationships of 7-azaindole-based Rho kinase (ROCK) inhibitors.

Rho kinase (ROCK) inhibitors are potential therapeutic agents for the treatment of a variety of disorders including hypertension, glaucoma and erectile dysfunction. Here we disclose a series of potent and selective ROCK inhibitors based on a substituted 7-azaindole scaffold. Substitution of the 3-position of 7-azaindole led to compounds such as 37, which possess excellent ROCK inhibitory potency and high selectivity against the closely related kinase PKA.

Preclinical activity of VX-787, a first-in-class, orally bioavailable inhibitor of the influenza virus polymerase PB2 subunit.

VX-787 is a novel inhibitor of influenza virus replication that blocks the PB2 cap-snatching activity of the influenza viral polymerase complex. Viral genetics and X-ray crystallography studies provide support for the idea that VX-787 occupies the 7-methyl GTP (m(7)GTP) cap-binding site of PB2. VX-787 binds the cap-binding domain of the PB2 subunit with a KD (dissociation constant) of 24 nM as determined by isothermal titration calorimetry (ITC). The cell-based EC50 (the concentration of compound that ensures 50% cell viability of an uninfected control) for VX-787 is 1.6 nM in a cytopathic effect (CPE) assay, with a similar EC50 in a viral RNA replication assay. VX-787 is active against a diverse panel of influenza A virus strains, including H1N1pdm09 and H5N1 strains, as well as strains with reduced susceptibility to neuraminidase inhibitors (NAIs). VX-787 was highly efficacious in both prophylaxis and treatment models of mouse influenza and was superior to the neuraminidase inhibitor, oseltamivir, including in delayed-start-to-treat experiments, with 100% survival at up to 96 h postinfection and partial survival in groups where the initiation of therapy was delayed up to 120 h postinfection. At different doses, VX-787 showed a 1-log to >5-log reduction in viral load (relative to vehicle controls) in mouse lungs. Overall, these favorable findings validate the PB2 subunit of the viral polymerase as a drug target for influenza therapy and support the continued development of VX-787 as a novel antiviral agent for the treatment of influenza infection.

Magnetic resonance and confocal imaging of solute penetration into the lens reveals a zone of restricted extracellular space diffusion.

It has been proposed that in the absence of blood supply, the ocular lens operates an internal microcirculation system that delivers nutrients to internalized fiber cells faster and more efficiently than would occur by passive diffusion alone. To visualize the extracellular space solute fluxes potentially generated by this system, bovine lenses were organ cultured in artificial aqueous humor (AAH) for 4 h in the presence or absence of two gadolinium-based contrast agents, ionic Gd(3+), or a chelated form of Gd(3+), Gd-diethylenetriamine penta-acetic acid (Gd-DTPA; mol mass = 590 Da). Contrast reagent penetration into the lens core was monitored in real time using inversion recovery-spin echo (IR-SE) magnetic resonance imaging (MRI), while steady-state accumulation of [Gd-DTPA](-2) was also determined by calculating T1 values. After incubation, lenses were fixed and cryosectioned, and sections were labeled with the membrane marker wheat germ agglutinin (WGA). Sections were imaged by confocal microscopy using standard and reflectance imaging modalities to visualize the fluorescent WGA label and gadolinium reagents, respectively. Real-time IR-SE MRI showed rapid penetration of Gd(3+) into the outer cortex of the lens and a subsequent bloom of signal in the core. These two areas of signal were separated by an area in the inner cortex that limited entry of Gd(3+). Similar results were obtained for Gd-DTPA, but the penetration of the larger negatively charged molecule into the core could only be detected by calculating T1 values. The presence of Gd-DTPA in the extracellular space of the outer cortex and core, but its apparent absence from the inner cortex was confirmed using reflectance imaging of equatorial sections. In axial sections, Gd-DTPA was associated with the sutures, suggesting these structures provide a pathway from the surface, across the inner cortex barrier to the lens core. Our studies have revealed inner and outer boundaries of a zone within which a narrowing of the extracellular space restricts solute diffusion and acts to direct fluxes into the lens core via the sutures.

Development of a 3D finite element model of lens microcirculation.

BACKGROUND: It has been proposed that in the absence of a blood supply, the ocular lens operates an internal microcirculation system. This system delivers nutrients, removes waste products and maintains ionic homeostasis in the lens. The microcirculation is generated by spatial differences in membrane transport properties; and previously has been modelled by an equivalent electrical circuit and solved analytically. While effective, this approach did not fully account for all the anatomical and functional complexities of the lens. To encapsulate these complexities we have created a 3D finite element computer model of the lens. METHODS: Initially, we created an anatomically-correct representative mesh of the lens. We then implemented the Stokes and advective Nernst-Plank equations, in order to model the water and ion fluxes respectively. Next we complemented the model with experimentally-measured surface ionic concentrations as boundary conditions and solved it. RESULTS: Our model calculated the standing ionic concentrations and electrical potential gradients in the lens. Furthermore, it generated vector maps of intra- and extracellular space ion and water fluxes that are proposed to circulate throughout the lens. These fields have only been measured on the surface of the lens and our calculations are the first 3D representation of their direction and magnitude in the lens. CONCLUSION: Values for steady state standing fields for concentration and electrical potential plus ionic and fluid fluxes calculated by our model exhibited broad agreement with observed experimental values. Our model of lens function represents a platform to integrate new experimental data as they emerge and assist us to understand how the integrated structure and function of the lens contributes to the maintenance of its transparency.

Visualizing ocular lens fluid dynamics using MRI: manipulation of steady state water content and water fluxes.

Studies using various MRI techniques have shown that a water-protein concentration gradient exists in the ocular lens. Because this concentration is higher in the core relative to the lens periphery, a gradient in refractive index is established in the lens. To investigate how the water-protein concentration profile is maintained, bovine lenses were incubated in different solutions, and changes in water-protein concentration ratio monitored using proton density weighted (PD-weighted) imaging in the absence and presence of heavy water (D(2)O). Lenses incubated in artificial aqueous humor (AAH) maintained the steady state water-protein concentration gradient, but incubating lenses in high extracellular potassium (KCl-AAH) or low temperature (Low T-AAH) caused a collapse of the gradient due to a rise in water content in the core of the lens. To visualize water fluxes, lenses were incubated in D(2)O, which acts as a contrast agent. Incubation in KCl-AAH and low T-AAH dramatically slowed the movement of D(2)O into the core but did not affect the movement of D(2)O into the outer cortex. D(2)O seemed to preferentially enter the lens cortex at the anterior and posterior poles before moving circumferentially toward the equatorial regions. This directionality of D(2)O influx into the lens cortex was abolished by incubating lenses in high KCl-AAH or low T-AAH, and resulted in homogenous influx of D(2)O into the outer cortex. Taken together, our results show that the water-protein concentration ratio is actively maintained in the core of the lens and that water fluxes preferentially enter the lens at the poles.

Differentiation-dependent modification and subcellular distribution of aquaporin-0 suggests multiple functional roles in the rat lens.

Using immunohistochemistry and mass spectrometry, differentiation-dependent changes in the subcellular distribution and processing of aquaporin-0 (AQP0) have been mapped in the rat lens. Sections labelled with C-terminal tail AQP0 antibodies yielded two concentric rings of labelling with minimal signal in the lens core. The rings were separated by a transient zone of decreased labelling located prior to the transition of differentiating fiber (DF) cells into mature denucleated fiber (MF) cells. Mass spectrometry showed that the loss of core labelling was due to AQP0 cleavage, while the transient loss of labelling was more likely caused by masking of the antibody epitope. AQP0 subcellular distribution changed with radial distance into the lens. In peripheral DF cells, AQP0 was found throughout both broad and narrow side membranes. In deeper-lying DF cells, AQP0 aggregated into plaque-like structures located on the broad sides. This shift occurred prior to the transient loss of AQP0 signal, and coincided with formation of broad-side membrane invaginations between adjacent fiber cells to which filensin, a known binding partner of AQP0, was also localized. After nuclei loss, AQP0 was once again distributed throughout MF cell membranes. In the absence of protein synthesis, the observed subcellular redistribution of AQP0 in DF and subsequent cleavage of AQP0 in MF are suggestive of a switch in the function of AQP0 from a water channel to a junctional protein.

Structure-based design of 3-aryl-6-amino-triazolo[4,3-b]pyridazine inhibitors of Pim-1 kinase.

A series of substituted 3-aryl-6-amino-triazolo[4,3-b]pyridazines were identified as highly selective inhibitors of Pim-1 kinase. Initial exploration identified compound 24 as a potent, selective inhibitor, limited in its utility by poor solubility and permeability. Understanding the unusual ATP-binding site of the Pim kinases and X-ray crystallographic data on compound 24 led to design improvements in this class of inhibitor. This resulted in compound 29, a selective, soluble and permeable inhibitor of Pim-1.

Classifying protein kinase structures guides use of ligand-selectivity profiles to predict inactive conformations: structure of lck/imatinib complex.

We report a clustering of public human protein kinase structures based on the conformations of two structural elements, the activation segment and the C-helix, revealing three discrete clusters. One cluster includes kinases in catalytically active conformations. Each of the other clusters contains a distinct inactive conformation. Typically, kinases adopt at most one of the inactive conformations in available X-ray structures, implying that one of the conformations is preferred for many kinases. The classification is consistent with selectivity profiles of several well-characterized kinase inhibitors. We show further that inhibitor selectivity profiles guide kinase classification. For example, selective inhibition of lck among src-family kinases by imatinib (Gleevec) suggests that the relative stabilities of inactive conformations of lck are different from other src-family kinases. We report the X-ray structure of the lck/imatinib complex, confirming that the conformation adopted by lck is distinct from other structurally-characterized src-family kinases and instead resembles kinases abl1 and kit in complex with imatinib. Our classification creates new paths for designing small-molecule inhibitors.

ROCK enzymatic assay.

We describe the protocols for measuring Rho-associated coiled-coil-containing kinase (ROCK) activity in vitro. A His-tagged, constitutively active form of the protein (lacking C-terminal inhibitory domains) is expressed in baculovirus. The protein is purified by a combination of metal affinity, ion exchange, and size exclusion chromatography. Enzymatic activity is measured spectrophotometrically in a coupled assay format wherein a molecule of NADH is oxidized to NAD+ each time a phosphate is transferred by ROCK.

Design and Synthesis of a Novel Series of Orally Bioavailable, CNS-Penetrant, Isoform Selective Phosphoinositide 3-Kinase γ (PI3Kγ) Inhibitors with Potential for the Treatment of Multiple Sclerosis (MS).

The lipid kinase phosphoinositide 3-kinase γ (PI3Kγ) has attracted attention as a potential target to treat a variety of autoimmune disorders, including multiple sclerosis, due to its role in immune modulation and microglial activation. By minimizing the number of hydrogen bond donors while targeting a previously uncovered selectivity pocket adjacent to the ATP binding site of PI3Kγ, we discovered a series of azaisoindolinones as selective, brain penetrant inhibitors of PI3Kγ. This ultimately led to the discovery of 16, an orally bioavailable compound that showed efficacy in murine experimental autoimmune encephalomyelitis (EAE), a preclinical model of multiple sclerosis.

Mapping of glutathione and its precursor amino acids reveals a role for GLYT2 in glycine uptake in the lens core.

PURPOSE: To correlate the distribution of glutathione (GSH) and its precursor amino acids (cysteine, glycine, and glutamate) with the expression of their respective amino acid transporters in the rat lens. METHODS: Whole rat lenses were fixed, cryoprotected, and cryosectioned in either an equatorial or axial orientation. Sections were double labeled with cystine, glycine, glutamate, GSH, GLYT1, or GLYT2 antibodies, and the membrane marker wheat germ agglutinin (WGA). Sections were imaged by confocal laser scanning microscopy. Cystine, glycine, glutamate, and GSH labeling were quantified by using image-analysis software and intensity profiles plotted as a function of distance from the lens periphery. Western blot analysis was used to verify regional differences in amino acid transporter expression. RESULTS: Cystine and glycine labeling in equatorial sections was most intense in the outer cortex, was diminished in the inner cortex, but was increased again in the core relative to the inner cortex. Glutamate and GSH labeling was most intense in the outer cortex and was diminished in the inner cortex to a minimum that was sustained throughout the core. The distribution of cystine and glutamate levels correlated well with the expression patterns observed previously for the cystine/glutamate exchanger (Xc-) and the glutamate transporter (EAAT4/5), respectively. Although high levels of glycine labeling in the outer cortex correlated well with the expression of the glycine transporter GLYT1, the absence of GLYT1 in the core, despite an increase of glycine in this region, suggests an alternative glycine uptake system such as GLYT2 exists in the core. Equatorial sections labeled with GLYT2 antibodies, showed that labeling in the outer cortex was predominantly cytoplasmic, but progressively became more membranous with distance into the lens. In the inner cortex and core, GLYT2 labeling was localized around the entire membrane of fiber cells. Western blot analysis confirmed GLYT2 to be expressed in the outer cortex, inner cortex, and core of the lens. Axial sections labeled for glycine revealed a track of high-intensity glycine labeling that extended from the anterior pole through to the core that was associated with the sutures. CONCLUSIONS: The mapping of GSH and its precursor amino acids has shown that an alternative glycine uptake pathway exists in mature fiber cells. Although GLYT1 and -2 are likely to mediate glycine uptake in cortical fiber cells, GLYT2 alone appears responsible for the accumulation of glycine in the center of the lens. Enhancing the delivery of glycine to the core via the sutures may represent a pathway to protect the lens against the protein modifications associated with age-related nuclear cataract.

Regional differences in cystine accumulation point to a sutural delivery pathway to the lens core.

PURPOSE: To develop an imaging technique that maps the distribution of free cystine in the rat lens at subcellular resolution and enables cystine accumulation to be compared with the expression of the cystine-glutamate exchanger (Xc-). METHODS: Whole lenses were fixed, cryoprotected, and then cryosectioned in either an equatorial or axial orientation. Sections were double labeled with either a cystine antibody designed to detect free cystine (the oxidized form of cysteine) or an antibody against the light chain of Xc-, and the membrane marker wheat germ agglutinin. Sections were imaged by confocal laser scanning microscopy. Cystine labeling was quantified using image analysis software and an intensity profile plotted as a function of distance from the lens periphery. High performance liquid chromatography (HPLC) was used to determine cyst(e)ine levels in the outer cortex, inner cortex, and core fractions and verify the cystine profiles derived from immunocytochemistry. RESULTS: Qualitative and quantitative imaging approaches both showed that cystine labeling at the lens equator was most intense in the outer cortex, but diminished in the inner cortex before increasing again in the core. HPLC from the outer cortex, inner cortex, and core fractions confirmed high levels of cyst(e)ine in the core relative to the inner cortex. The bimodal distribution of cystine labeling in the outer cortex and core correlated well with the expression of the cystine-glutamate exchanger in these regions, but this was not the case in the inner cortex. A similar bimodal distribution of cystine labeling was observed in axial sections. However, in these sections a track of high-intensity cystine labeling was observed that was associated with the sutures indicating that the sutures act as a delivery pathway to the core. CONCLUSIONS: These imaging approaches have revealed two distinct regions of cystine uptake in the outer cortex and core of the lens. Furthermore, this bimodal distribution of cystine has been shown to be the result of cystine delivery to the core via the sutures. This newly identified pathway opens an opportunity for the delivery of therapeutic antioxidants aimed at preventing age-related nuclear cataract.

Novel 2-Substituted 7-Azaindole and 7-Azaindazole Analogues as Potential Antiviral Agents for the Treatment of Influenza.

JNJ-63623872 (2) is a first-in-class, orally bioavailable compound that offers significant potential for the treatment of pandemic and seasonal influenza. Early lead optimization efforts in our 7-azaindole series focused on 1,3-diaminocyclohexyl amide and urea substitutions on the pyrimidine-7-azaindole motif. In this work, we explored two strategies to eliminate observed aldehyde oxidase (AO)-mediated metabolism at the 2-position of these 7-azaindole analogues. Substitution at the 2-position of the azaindole ring generated somewhat less potent analogues, but reduced AO-mediated metabolism. Incorporation of a ring nitrogen generated 7-azaindazole analogues that were equipotent to the parent 2-H-7-azaindole, but surprisingly, did not appear to improve AO-mediated metabolism. Overall, we identified multiple 2-substituted 7-azaindole analogues with enhanced AO stability and we present data for one such compound (12) that demonstrate a favorable oral pharmacokinetic profile in rodents. These analogues have the potential to be further developed as anti-influenza agents for the treatment of influenza.

Discovery of Novel, Orally Bioavailable ß-Amino Acid Azaindole Inhibitors of Influenza PB2.

In our efforts to develop novel small-molecule inhibitors for the treatment of influenza, we utilized molecular modeling and the X-ray crystal structure of the PB2 subunit of the influenza polymerase to optimize a series of acyclic ß-amino acid inhibitors, highlighted by compound 4. Compound 4 showed good oral exposure in both rat and mouse. More importantly, it showed strong potency versus multiple influenza-A strains, including pandemic 2009 H1N1 and avian H5N1 strains and showed a strong efficacy profile in a mouse influenza model even when treatment was initiated 48 h after infection. Compound 4 offers good oral bioavailability with great potential for the treatment of both pandemic and seasonal influenza.

Spatially transformed fluorescence image data for ERK-MAPK and selected proteins within human epidermis.

BACKGROUND: Phosphoprotein signalling pathways have been intensively studied in vitro, yet their role in regulating tissue homeostasis is not fully understood. In the skin, interfollicular keratinocytes differentiate over approximately 2 weeks as they traverse the epidermis. The extracellular signal-regulated kinase (ERK) branch of the mitogen-activated protein kinase (MAPK) pathway has been implicated in this process. Therefore, we examined ERK-MAPK activity within human epidermal keratinocytes in situ. FINDINGS: We used confocal microscopy and immunofluorescence labelling to measure the relative abundances of Raf-1, MEK1/2 and ERK1/2, and their phosphorylated (active) forms within three human skin samples. Additionally, we measured the abundance of selected proteins thought to modulate ERK-MAPK activity, including calmodulin, ß1 integrin and stratifin (14-3-3σ); and of transcription factors known to act as effectors of ERK1/2, including the AP-1 components Jun-B, Fra2 and c-Fos. Imaging was performed with sufficient resolution to identify the plasma membrane, cytoplasm and nucleus as distinct domains within cells across the epidermis. The image field of view was also sufficiently large to capture the entire epidermis in cross-section, and thus the full range of keratinocyte differentiation in a single observation. Image processing methods were developed to quantify image data for mathematical and statistical analysis. Here, we provide raw image data and processed outputs. CONCLUSIONS: These data indicate coordinated changes in ERK-MAPK signalling activity throughout the depth of the epidermis, with changes in relative phosphorylation-mediated signalling activity occurring along the gradient of cellular differentiation. We believe these data provide unique information about intracellular signalling as they are obtained from a homeostatic human tissue, and they might be useful for investigating intercellular heterogeneity.

Regulation of ERK-MAPK signaling in human epidermis.

BACKGROUND: The skin is largely comprised of keratinocytes within the interfollicular epidermis. Over approximately two weeks these cells differentiate and traverse the thickness of the skin. The stage of differentiation is therefore reflected in the positions of cells within the tissue, providing a convenient axis along which to study the signaling events that occur in situ during keratinocyte terminal differentiation, over this extended two-week timescale. The canonical ERK-MAPK signaling cascade (Raf-1, MEK-1/2 and ERK-1/2) has been implicated in controlling diverse cellular behaviors, including proliferation and differentiation. While the molecular interactions involved in signal transduction through this cascade have been well characterized in cell culture experiments, our understanding of how this sequence of events unfolds to determine cell fate within a homeostatic tissue environment has not been fully characterized. METHODS: We measured the abundance of total and phosphorylated ERK-MAPK signaling proteins within interfollicular keratinocytes in transverse cross-sections of human epidermis using immunofluorescence microscopy. To investigate these data we developed a mathematical model of the signaling cascade using a normalized-Hill differential equation formalism. RESULTS: These data show coordinated variation in the abundance of phosphorylated ERK-MAPK components across the epidermis. Statistical analysis of these data shows that associations between phosphorylated ERK-MAPK components which correspond to canonical molecular interactions are dependent upon spatial position within the epidermis. The model demonstrates that the spatial profile of activation for ERK-MAPK signaling components across the epidermis may be maintained in a cell-autonomous fashion by an underlying spatial gradient in calcium signaling. CONCLUSIONS: Our data demonstrate an extended phospho-protein profile of ERK-MAPK signaling cascade components across the epidermis in situ, and statistical associations in these data indicate canonical ERK-MAPK interactions underlie this spatial profile of ERK-MAPK activation. Using mathematical modelling we have demonstrated that spatially varying calcium signaling components across the epidermis may be sufficient to maintain the spatial profile of ERK-MAPK signaling cascade components in a cell-autonomous manner. These findings may have significant implications for the wide range of cancer drugs which therapeutically target ERK-MAPK signaling components.

Molecular identification of P-glycoprotein: a role in lens circulation?

PURPOSE: To determine whether P-glycoprotein is expressed in the rat lens and to assess what type of damage occurs when P-glycoprotein inhibitors are applied to organ-cultured lenses. METHODS: An initial screening for the P-glycoprotein isoforms multidrug resistance (mdr)1a, mdr1b, and mdr2 was performed by RT-PCR on RNA extracted from rat lens fiber cells. Northern blot analysis was used to determine whether transcript levels detected by RT-PCR were significant. The presence of P-glycoprotein in the lens was confirmed by Western blot analysis and immunocytochemistry. Organ-cultured lenses, maintained in isotonic artificial aqueous humor, were exposed to various concentrations of the P-glycoprotein inhibitor tamoxifen. Lens opacification was assessed by dark-field microscopy, and the underlying cellular changes were visualized by confocal microscopy of lens sections, using a fluorescent membrane marker. Initial cellular damage was assessed after a 6-hour exposure to 100 micro M tamoxifen. Other P-glycoprotein inhibitors, verapamil, and 1,9-dideoxyforskolin (DDFK) were assessed, and the damage phenotypes were compared with those seen for tamoxifen. RESULTS: Transcript for all three P-glycoprotein isoforms was detected with RT-PCR, but only mdr1a and mdr2 could be detected by Northern blot analysis. P-glycoprotein was localized in the plasma membrane of lens epithelial and fiber cells. Treatment of organ-cultured lenses with increasing doses of the P-glycoprotein inhibitor tamoxifen for 18 hours showed that two distinct damage phenotypes were evident. At a dose of 20 micro M tamoxifen, tissue damage was found in a discrete zone that initially started approximately 100 micro m from the capsule, whereas at higher doses (60-100 micro M tamoxifen), extensive vesiculation of fiber cell membranes occurred throughout the entire lens cortex. Decreasing tamoxifen (100 micro M) exposure to 6 hours showed that the inner zone of damage was caused by the dilation of extracellular space between fiber cells. The extracellular space dilution and fiber cell vesiculation could be reproduced by varying the concentrations of other P-glycoprotein inhibitors, verapamil and DDKF. CONCLUSIONS: The P-glycoproteins mdr1a and mdr2 are expressed in the lens and appear to be functional. The initial cellular damage phenotype of extracellular space dilations caused by the P-glycoprotein inhibitors was identical with that caused by chloride channel inhibitors, indicating that P-glycoprotein may play a role in regulating cell volume in the lens. Whether the secondary damage phenotype of fiber cell vesiculation, induced by high doses of P-glycoprotein inhibitors, was due to the inhibition of additional regulatory activities of P-glycoprotein or to nonspecific effects of the drugs remains to be determined. However, regardless of the precise mode of action, these results indicate that P-glycoprotein should be considered in the regulatory mechanisms associated with the control of lens volume and in the initiation of osmotic cataract.

Gap junction processing and redistribution revealed by quantitative optical measurements of connexin46 epitopes in the lens.

PURPOSE: To map changes in the structure and function of fiber cell gap junctions that occur with lens differentiation. METHODS: Equatorial lens sections were fluorescently labeled with antibodies to the gap junction protein connexin (Cx)46, the membrane marker wheat germ agglutinin, and the nuclear stain propidium iodide. Two-photon microscopy and digital image analysis were used to quantify label and cell morphology as a function of radial distance (r/a) across the lens. Loop- and tail-specific Cx46 antibodies were used to identify regions of posttranslational modification. Local fiber cell coupling was imaged in situ using two-photon flash photolysis of caged fluorescein. RESULTS: Antibody labeling showed that the cytoplasmic tail of Cx46 was removed in two zones (r/a approximately 0.9 and r/a approximately 0.7). In addition, with increasing depth, the large radially aligned plaques of peripheral fiber cells became fragmented and dispersed around the cell membrane, and cells became more circular in cross section. Fluorescein transfer between peripheral fiber cells was highly anisotropic and occurred predominantly within a column of fiber cells, resulting in radially directed transport. In regions beyond the zone of nuclear loss, transport was more isotropic and occurred across columns of fiber cells. CONCLUSIONS: The cleavage of Cx46 is associated with a spatial redistribution of gap junction plaques. The distribution of gap junction plaques around the cell membrane can explain the observed directionality of intercellular solute transfer. The findings suggest that the processing and redistribution of gap junction proteins is central to controlling radial and circumferential solute gradients in different regions within the lens.

Resolving morphology and antibody labeling over large distances in tissue sections.

Protein expression patterns are a primary determinant of tissue function and in this study we developed methods to study protein expression over macroscopic distances at subcellular levels of detail. Using the mammalian lens as a model tissue system, we show that by combining two-photon microscopy with novel image montage methods (fast beam blanking coupled with mathematical alignment tools) we have extended the limited field of view of laser scanning microscopes. To illustrate the utility of our approach, the distribution of connexin-46 was visualized across equatorial sections of the rat mammalian lens. By optimizing fixation protocols, good morphological preservation could be achieved over the thickness of the lens (approximately 4 mm) while preserving antigenicity of lens proteins. Using the same image data, changes in lens fiber cell morphology were mapped quantitatively by automatic image analysis routines. The methods presented should be generally applicable to any tissue system where changes in antibody labeling and tissue structure occur over large and small distances.