Cross-beta order and diversity in nanocrystals of an amyloid-forming peptide

The seven-residue peptide GNNQQNY from the N-terminal region of the yeast prion protein Sup35, which forms amyloid fibers, colloidal aggregates and highly ordered nanocrystals, provides a model system for characterizing the elusively protean cross-beta conformation. Depending on preparative conditions, orthorhombic and monoclinic crystals with similar lath-shaped morphology have been obtained. Ultra high-resolution (<0.5A spacing) electron diffraction patterns from single nanocrystals show that the peptide chains pack in parallel cross-beta columns with approximately 4.86A axial spacing. Mosaic striations 20-50 nm wide observed by electron microscopy indicate lateral size-limiting crystal growth related to amyloid fiber formation. Frequently obtained orthorhombic forms, with apparent space group symmetry P2(1)2(1)2(1), have cell dimensions ranging from /a/=22.7-21.2A, /b/=39.9-39.3A, /c/=4.89-4.86A for wet to dried states. Electron diffraction data from single nanocrystals, recorded in tilt series of still frames, have been mapped in reciprocal space. However, reliable integrated intensities cannot be obtained from these series, and dynamical electron diffraction effects present problems in data analysis. The diversity of ordered structures formed under similar conditions has made it difficult to obtain reproducible X-ray diffraction data from powder specimens; and overlapping Bragg reflections in the powder patterns preclude separated structure factor measurements for these data. Model protofilaments, consisting of tightly paired, half-staggered beta strands related by a screw axis, can be fit in the crystal lattices, but model refinement will require accurate structure factor measurements. Nearly anhydrous packing of this hydrophilic peptide can account for the insolubility of the crystals, since the activation energy for rehydration may be extremely high. Water-excluding packing of paired cross-beta peptide segments in thin protofilaments may be characteristic of the wide variety of anomalously stable amyloid aggregates.     

Hsp10 and Hsp60 suppress ubiquitination of insulin-like growth factor-1 receptor and augment insulin-like growth factor-1 receptor signaling in cardiac muscle: implications on decreased myocardial protection in diabetic cardiomyopathy

We have investigated the effects of two heat shock proteins, Hsp10 and Hsp60, on insulin-like growth factor-1 receptor (IGF-1R) signaling in cardiac muscle cells. Neonatal cardiomyocytes were transduced with Hsp10 or Hsp60 via adenoviral vector. Compared with the cells transduced with a control vector, overexpression of Hsp10 or Hsp60 increased the abundance of IGF-1R and IGF-1-stimulated receptor autophosphorylation. Thus, Hsp10 and Hsp60 overexpression increased the number of functioning receptors and amplified activation of IGF-1R signaling. IGF-1 stimulation of MEK, Erk, p90Rsk, and Akt were accordingly augmented. Transducing cardiomyocytes with antisense Hsp60 oligonucleotides reduced Hsp60 expression, decreased the abundance of IGF-1R, attenuated IGF-1R autophosphorylation, and suppressed the pro-survival action of IGF-1 in cardiomyocytes. Using cycloheximide to inhibit protein synthesis did not alter the effect of Hsp60 on IGF-1R signaling, and IGF-1R mRNA levels were not up-regulated by Hsp10 or Hsp60. Additional experiments showed that Hsp10 and Hsp60 suppressed polyubiquitination of IGF-1 receptor. These data indicate that Hsp10 and Hsp60 can modulate IGF-1R signaling through post-translational modification. In animal models of diabetes, diabetic myocardium is associated with decreased abundance of Hsp60, increased ubiquitination of IGF-1R, and lower level of IGF-1R protein. Declined myocardial protection is a major feature of diabetic cardiomyopathy. These data suggest that decreased Hsp60 expression and subsequent decline of IGF-1R signaling may be a fundamental mechanism underlying the development of diabetic cardiomyopathy.     

Slow inactivation in voltage-gated sodium channels

Slow inactivation in voltage-gated sodium channels is a biophysical process that governs the availability of sodium channels over extended periods of time. Slow inactivation, therefore, plays an important role in controlling membrane excitability, firing properties, and spike frequency adaptation. Defective slow inactivation is associated with several diseases of cell excitability, such as hyperkalemic periodic paralysis, myotonia, idiopathic ventricular fibrillation and long-QT syndrome. These associations underscore the physiological importance of this phenomenon. Nevertheless, our understanding of the molecular substrates for slow inactivation is still fragmentary. This review covers the current state of knowledge concerning the molecular underpinnings of slow inactivation, and its relationship with other biophysical processes of voltage-gated sodium channels.     

Functional studies of the kidney of living animals using multicolor two-photon microscopy

Optical microscopy, when applied to livinganimals, provides a powerful means of studying cell biology in the mostphysiologically relevant setting. The ability of two-photon microscopyto collect optical sections deep into biological tissues has opened upthe field of intravital microscopy to high-resolution studies of the brain, lens, skin, and tumors. Here we present examples of the way inwhich two-photon microscopy can be applied to intravital studies ofkidney physiology. Because the kidney is easily externalized withoutcompromising its function, microscopy can be used to evaluate variousaspects of renal function in vivo. These include cell vitality andapoptosis, fluid transport, receptor-mediated endocytosis, blood flow, and leukocyte trafficking. Efficient two-photon excitation of multiple fluorophores permits comparison of multiple probes andsimultaneous characterization of multiple parameters and yields spectral information that is crucial to the interpretation of imagescontaining uncharacterized autofluorescence. The studies described heredemonstrate the way in which two-photon microscopy can provide a levelof resolution previously unattainable in intravital microscopy,enabling kinetic analyses and physiological studies of the organs ofliving animals with subcellular resolution.

     

CD8 T cells are sufficient to mediate allorecognition and allograft rejection

Different T cell subsets may play different roles in allorecognition and allograft rejection. It has been suggested that CD8 T cells can only initiate rejection with help from CD4 T cells. Since CD8 T cells may have different requirements for allorecognition and for costimulation, it is important to clarify the role of CD8 cells in rejection. We examined the role of CD8 cells in allorecognition using a TCR transgenic mouse transplantation model. In our study, CD8 cells were able to recognize alloantigens and reject allografts in the absence of help from CD4 T cells. Furthermore our study provides a model to study the mechanisms of CD8-mediated allograft rejection. It may be important in the future, to consider that CD8 T cells may need to be targeted independently of CD4 T cells in strategies used to prevent rejection and induce tolerance.     

Glucose deprivation and hypoxia increase the expression of the GLUT1 glucose transporter via a specific mRNA cis-acting regulatory element

The expression of the glucose transporter type-1 (GLUT1) gene is up-regulated in hypoxia and glucose deprivation. A 10 nucleotide (nt) cis-acting regulatory element (CAE), which is located within nt 2181-2190 of the GLUT1 3'-untranslated region (CAE2181-2190), increases the expression of a GLUT1-luciferase reporter gene and decreases its mRNA decay. The present study investigated the role of the GLUT1 CAE2181-2190 in glucose deprivation and hypoxia using stable transfectants. Glucose and O2 deprivation produced a marked increase in the expression of the GLUT1 reporter gene carrying the CAE2181-2190, and this effect was additive. Glucose deprivation and/or hypoxia induced no significant changes in the expression of the reporter gene wherein the GLUT1 CAE2181-2190 was site-directed deleted. Data presented here suggest that the GLUT1 CAE2181-2190 participates in the increase of GLUT1 gene expression in glucose deprivation and hypoxia.     

Bone morphogenetic protein signaling and the initiation of lens fiber cell differentiation

Previous studies showed that the retina produces factors that promote the differentiation of lens fiber cells, and identified members of the fibroblast growth factor (FGF) and insulin-like growth factor (IGF) families as potential fiber cell differentiation factors. A possible role for the bone morphogenetic proteins (BMPs) is suggested by the presence of BMP receptors in chicken embryo lenses. We have now observed that phosphorylated SMAD1, an indicator of signaling through BMP receptors, localizes to the nuclei of elongating lens fiber cells. Transduction of chicken embryo retinas and/or lenses with constructs expressing noggin, a secreted protein that binds BMPs and prevents their interactions with their receptors, delayed lens fiber cell elongation and increased cell death in the lens epithelium. In an in vitro explant system, in which chicken embryo or adult bovine vitreous humor stimulates chicken embryo lens epithelial cells to elongate into fiber-like cells, these effects were inhibited by noggin-containing conditioned medium, or by recombinant noggin. BMP2, 4, or 7 were able to reverse the inhibition caused by noggin. Lens cell elongation in epithelial explants was stimulated by treatment with FGF1 or FGF2, alone or in combination with BMP2, but not to the same extent as vitreous humor. These data indicate that BMPs participate in the differentiation of lens fiber cells, along with at least one additional, and still unknown factor.     

Overexpression of heat shock proteins differentially modulates protein kinase C expression in rat neonatal cardiomyocytes

Previous studies have suggested that protein kinase C (PKC) is involved in heat shock protein (Hsp)-mediated cardioprotection. Therefore, we wanted to determine whether overexpression of Hsps modulates PKC expression, which will give us further insight into understanding the mechanism by which Hsps and PKC interact to protect cells from stress-induced injury. Specifically, we overexpressed the inducible form of Hsp70 (Hsp70i) or Hsp90 in rat neonatal cardiomyocytes and evaluated PKCdelta or PKCepsilon expression by immunoblotting and immunofluorescent confocal microscopy. Western analysis showed that overexpression of Hsp70i or Hsp90 decreased PKCepsilon expression. However, overexpression of Hsp70i or Hsp90 did not modify PKCdelta expression over control levels. Overexpression of constitutively active PKCdelta or PKCepsilon increased Hsp70i expression over control levels. The data suggest that overexpression of Hsps differentially modulates expression of PKC isoforms in rat neonatal cardiomyocytes. Furthermore, PKC may directly play a role in Hsp-mediated cardioprotection by upregulating Hsp70i expression.