Collagen IV of basement membranes: III. Chloride pressure is a primordial innovation that drives and maintains the assembly of scaffolds

Collagen IV scaffold is a primordial innovation enabling the assembly of a fundamental architectural unit of epithelial tissues-a basement membrane attached to polarized cells. A family of six α-chains (α1 to α6) coassemble into three distinct protomers that form supramolecular scaffolds, noted as collagen IVα121, collagen IVα345, and collagen IVα121-α556. Chloride ions play a pivotal role in scaffold assembly, based on studies of NC1 hexamers from mammalian tissues. First, Cl- activates a molecular switch within trimeric NC1 domains that initiates protomer oligomerization, forming an NC1 hexamer between adjoining protomers. Second, Cl- stabilizes the hexamer structure. Whether this Cl--dependent mechanism is of fundamental importance in animal evolution is unknown. Here, we developed a simple in vitro method of SDS-PAGE to determine the role of solution Cl- in hexamer stability. Hexamers were characterized from 34 animal species across 15 major phyla, including the basal Cnidarian and Ctenophora phyla. We found that solution Cl- stabilized the quaternary hexamer structure across all phyla except Ctenophora, Ecdysozoa, and Rotifera. Further analysis of hexamers from peroxidasin knockout mice, a model for decreasing hexamer crosslinks, showed that solution Cl- also stabilized the hexamer surface conformation. The presence of sufficient chloride concentration in solution or "chloride pressure" dynamically maintains the native form of the hexamer. Collectively, our findings revealed that chloride pressure on the outside of cells is a primordial innovation that drives and maintains the quaternary and conformational structure of NC1 hexamers of collagen IV scaffolds.

High salt intake reprioritizes osmolyte and energy metabolism for body fluid conservation

Natriuretic regulation of extracellular fluid volume homeostasis includes suppression of the renin-angiotensin-aldosterone system, pressure natriuresis, and reduced renal nerve activity, actions that concomitantly increase urinary Na+ excretion and lead to increased urine volume. The resulting natriuresis-driven diuretic water loss is assumed to control the extracellular volume. Here, we have demonstrated that urine concentration, and therefore regulation of water conservation, is an important control system for urine formation and extracellular volume homeostasis in mice and humans across various levels of salt intake. We observed that the renal concentration mechanism couples natriuresis with correspondent renal water reabsorption, limits natriuretic osmotic diuresis, and results in concurrent extracellular volume conservation and concentration of salt excreted into urine. This water-conserving mechanism of dietary salt excretion relies on urea transporter-driven urea recycling by the kidneys and on urea production by liver and skeletal muscle. The energy-intense nature of hepatic and extrahepatic urea osmolyte production for renal water conservation requires reprioritization of energy and substrate metabolism in liver and skeletal muscle, resulting in hepatic ketogenesis and glucocorticoid-driven muscle catabolism, which are prevented by increasing food intake. This natriuretic-ureotelic, water-conserving principle relies on metabolism-driven extracellular volume control and is regulated by concerted liver, muscle, and renal actions.

Increased salt consumption induces body water conservation and decreases fluid intake

BACKGROUND

The idea that increasing salt intake increases drinking and urine volume is widely accepted. We tested the hypothesis that an increase in salt intake of 6 g/d would change fluid balance in men living under ultra-long-term controlled conditions.

METHODS

Over the course of 2 separate space flight simulation studies of 105 and 205 days' duration, we exposed 10 healthy men to 3 salt intake levels (12, 9, or 6 g/d). All other nutrients were maintained constant. We studied the effect of salt-driven changes in mineralocorticoid and glucocorticoid urinary excretion on day-to-day osmolyte and water balance.

RESULTS

A 6-g/d increase in salt intake increased urine osmolyte excretion, but reduced free-water clearance, indicating endogenous free water accrual by urine concentration. The resulting endogenous water surplus reduced fluid intake at the 12-g/d salt intake level. Across all 3 levels of salt intake, half-weekly and weekly rhythmical mineralocorticoid release promoted free water reabsorption via the renal concentration mechanism. Mineralocorticoid-coupled increases in free water reabsorption were counterbalanced by rhythmical glucocorticoid release, with excretion of endogenous osmolyte and water surplus by relative urine dilution. A 6-g/d increase in salt intake decreased the level of rhythmical mineralocorticoid release and elevated rhythmical glucocorticoid release. The projected effect of salt-driven hormone rhythm modulation corresponded well with the measured decrease in water intake and an increase in urine volume with surplus osmolyte excretion.

CONCLUSION

Humans regulate osmolyte and water balance by rhythmical mineralocorticoid and glucocorticoid release, endogenous accrual of surplus body water, and precise surplus excretion.

FUNDING

Federal Ministry for Economics and Technology/DLR; the Interdisciplinary Centre for Clinical Research; the NIH; the American Heart Association (AHA); the Renal Research Institute; and the TOYOBO Biotechnology Foundation. Food products were donated by APETITO, Coppenrath und Wiese, ENERVIT, HIPP, Katadyn, Kellogg, Molda, and Unilever.

Abstract P245: High-salt Diet Induces Catabolic Urea Formation and Muscle Wasting to Enable Renal Salt Concentration

Background: We showed previously that a high salt diet (HSD) increases cortisol levels in man. We hypothesized HSD induces catabolic urea generation to facilitate renal water conservation during dietary salt excretion.

Methods: 16 male mice were pair-fed either a low-salt diet (<0.1% NaCl plus tap water) or a HSD (4% NaCl plus 0.9% saline water) for two weeks. We investigated urinary concentration, body weight, MRI lean body mass, tissue urea levels, and enzymatic urea and creatine generation in liver, skeletal muscle, skin and kidney.

Results: HSD increased renal Na clearance, decreased urea clearance and resulted in urinary Na concentration. HSD reduced body weight and lean body mass, indicating catabolic muscle wasting. This catabolic state was paralleled by urea accumulation and increased arginase activity in liver and in skeletal muscle, while renal urea excretion was reduced. Expression of L-arginine:glycine amidinotransferase (AGAT), which generates the creatine precursor guanidino-acetate and is representative for anabolic liver/muscle metabolism, was selectively reduced in the livers of HSD mice.

Conclusion: HSD induces urea production and body urea accumulation to allow for water-economizing urinary Na concentration. The liver regulates Na homeostasis and induces catabolism by favoring urea over creatine production. Catabolic skeletal muscle serves as a glutamine reservoir for urea generation in HSD mice, resulting in sarcopenia.

Perspectives: Cachexia is associated with increased cardiovascular mortality and heart failure in humans. Our findings link this condition to catabolic urea osmolyte generation for maintaining Na balance.

Early detection of NSCLC with scFv selected against IgM autoantibody

Survival of patients with lung cancer could be significantly prolonged should the disease be diagnosed early. Growing evidence indicates that the immune response in the form of autoantibodies to developing cancer is present before clinical presentation. We used a phage-displayed antibody library to select for recombinant scFvs that specifically bind to lung cancer-associated IgM autoantibodies. We selected for scFv recombinant antibodies reactive with circulating IgM autoantibodies found in the serum of patients with early stage lung adenocarcinoma but not matched controls. Discriminatory performance of 6 selected scFvs was validated in an independent set of serum from stage 1 adenocarcinoma and matching control groups using two independent novel methods developed for this application. The panel of 6 selected scFvs predicted cancer based on seroreactivity value with sensitivity of 0.8 and specificity of 0.87. Receiver Operative Characteristic curve (ROC) for combined 6 scFv has an AUC of 0.88 (95%CI, 0.76–1.0) as determined by fluorometric microvolume assay technology (FMAT) The ROC curve generated using a homogeneous bridging Mesa Scale Discovery (MSD) assay had an AUC of 0.72 (95% CI, 0.59–0.85). The panel of all 6 antibodies demonstrated better discriminative power than any single scFv alone. The scFv panel also demonstrated the association between a high score - based on seroreactivity - with poor survival. Selected scFvs were able to recognize lung cancer associated IgM autoantibodies in patient serum as early as 21 months before the clinical presentation of disease. The panel of antibodies discovered represents a potential unique non-invasive molecular tool to detect an immune response specific to lung adenocarcinoma at an early stage of disease.

S100A4 is expressed in myeloid cells invading inflamed pancreatic islets and supports development of Type 1 diabetes (171.33)

Type 1 diabetes (T1D) results from adaptive autoimmune destruction of insulin-producing beta cells in pancreatic islets. Macrophages and dendritic cells (DCs) have also been implicated in the disease process, although their roles are less well-studied than those of T cells. S100A4 is a small calcium-activated molecule that contributes to cancer metastases and fibrosis, and has recently been linked to autoimmunity. We have discovered S100A4 among inflammatory infiltrates in pancreatic islets in a T1D model. Cells expressing S100A4 bear surface markers associated with antigen-presentation, such as MHCII and CD86. These cells include CD11c+ DCs, CD11b+ macrophages, and CD11b+/CD11c+ myeloid populations. Neither plasmacytoid DCs (PDCA1+/Ly6C+/B220+) nor lymphoid DCs (CD8+) express S100A4. S100A4-deficiency was engineered by GFP-targeting and introgressed onto the nonobese diabetic (NOD) mouse model of T1D for &gt;10 generations. S100A4-/-/NOD mice are protected from the development of T1D, with a concomitant reduction in insulitis. However, GFP-expression in S100A4-deficient cells indicates that these cell populations remain in the inflamed islets. When compared to S100A4-sufficient counterparts, S100A4-deficient bone marrow-derived DCs have decreased ability to upregulate CD86, or to present antigen and activate T cells in vitro. Thus, S100A4 may contribute to the development of T1D by supporting myeloid cell antigen-presentation to autoreactive T cells.

Neurotrimin is an estrogen-regulated determinant of peripheral sympathetic innervation

Mechanisms underlying axon degeneration in peripheral neuropathies and during normal remodeling are poorly understood. Because estrogen induces widespread sympathetic axon degeneration in female reproductive tract smooth muscle, we surveyed estrogen-regulated genes in rat myometrium. Microarray analysis revealed that the neural cell adhesion protein neurotrimin (Ntm) was markedly up-regulated 6 hr and down-regulated 24 hr after injection of 17beta-estradiol, and real time RT-PCR confirmed this pattern of expression. Protein analysis by Western blotting showed that uterine Ntm protein is also up-regulated in vivo 6-24 hr following estrogen injection and that Ntm protein is increased selectively in the myometrium during the high-estrogen phase of the estrous cycle. Cultured myometrial smooth muscle cells display perinuclear accumulations of Ntm protein, and 17beta-estradiol also increases intracellular levels of Ntm and its secretion into the culture medium. To determine if neurotrimin is required for estrogen-induced sympathetic pruning, sympathetic neurons were cocultured with uterine smooth muscle cells transfected with siRNA directed against Ntm. Although estrogen inhibited neurite outgrowth in nontransfected cocultures, estrogen's ability to reduce sympathetic outgrowth was impaired substantially following Ntm down-regulation. This supports a role for neurotrimin in mediating estrogen-induced sympathetic pruning in some peripheral targets. Together with earlier studies, these findings support the idea that physiological sympathetic axon degeneration is a multifactorial process requiring dynamic regulation of multiple repellant proteins.

Regulation of macrophage cyclooxygenase-2 gene expression by modifications of histone H3

Some transcription factors involved in the regulation of cyclooxygenase 2 (COX-2) expression in macrophage, including NF-kappaB, interact with p300, which contains histone acetyltransferase (HAT) enzyme complex. Chromatin structure is regulated by modifying enzymes, including HAT, and plays an important role in eukaryotic gene regulation through histone modification. We hypothesized that changes in chromatin structure related to phosphorylation and acetylation of histone H3 adjacent to key DNA binding sequence motif in the COX-2 promoter contribute to COX-2 gene activation in macrophages. Sodium butyrate (NaBT) is a short-chain fatty acid that possesses histone deacetyltransferase-inhibiting activity. Our data show that NaBT accentuates LPS-induced COX-2 gene expression at a transcriptional level, even though NaBT alone does not induce the COX-2 gene expression. Using a chromatin immunoprecipitation assay, we showed that costimulation of RAW 264.7 cells with NaBT and LPS synergistically increases COX-2 gene expression through both acetylation and phosphorylation of histone H3 at the promoter site. Our data show that NaBT accentuates LPS-induced COX-2 gene expression through MAP kinase-dependent increase of phosphorylation and acetylation of histone H3 at the COX-2 promoter site. These data indicate that posttranslational modification of histone H3 has a major effect on COX-2 gene expression by macrophages.

Oestrogen regulates sympathetic neurite outgrowth by modulating brain derived neurotrophic factor synthesis and release by the rodent uterus

Sympathetic innervation of the adult rodent uterus undergoes cyclic remodelling. Terminal sympathetic axons degenerate when oestrogen levels rise and regenerate when oestrogen levels decline. This study examined the role of neurotrophins in oestrogen-mediated uterine sympathetic nerve remodelling. Oestrogen injection of ovariectomized female rats did not affect uterine NT-3 levels 24 h postinjection, and increased endometrial NGF protein, indicating that reduced NGF or NT-3 is not responsible for the oestrogen-induced denervation. Oestrogen also raised BDNF protein and mRNA in myometrium and endometrium. To assess whether increased BDNF affects uterine receptivity to sympathetic outgrowth, sympathetic ganglion explants were co-cultured with myometrium. Myometrium from ovariectomized rats induced neuritogenesis in oestrogen-free conditions, and this was abolished when BDNF was added to the medium. Neuritogenesis induced by ovariectomized myometrium was suppressed by oestrogen, and restored by a BDNF function-blocking antibody. To determine if target BDNF synthesis is required for oestrogen to suppress sympathetic neurite outgrowth, uteri from wild-type mice and mice homozygous or heterozygous for recombinant mutations of the BDNF gene were cultured with rat sympathetic ganglia. Neuritogenesis induced by wild-type uteri was diminished by oestrogen. Neurite formation in the presence of homozygous BDNF mutant uteri was not affected by oestrogen, but was lower than that of wild-type mice. Uteri from mice heterozygous for the BDNF mutation, who have reduced BDNF synthesis, showed normal neuritogenic properties, but were not affected by oestrogen. These findings suggest that oestrogen alters neuritogenic properties of the rodent uterus by regulating BDNF synthesis, which inhibits sympathetic neurite outgrowth.

Sympathetic neurons synthesize and secrete pro-nerve growth factor protein

Postmitotic sympathetic neuronal survival is dependent upon nerve growth factor (NGF) provided by peripheral targets, and this dependency serves as a central tenet of the neurotrophic hypothesis. In some other systems, NGF has been shown to play an autocrine role, although the pervasiveness and significance of this phenomenon within the nervous system remain unclear. We show here that rat sympathetic neurons synthesize and secrete NGF. NGF mRNA is expressed in nearly half of superior cervical ganglion sympathetic neurons at embryonic day 17, rising to over 90% in the early postnatal period, and declining in the adult. Neuronal immunoreactivity is reduced when retrograde transport is interrupted by axotomy, but persists in a subpopulation of neurons despite diminished mRNA expression, suggesting that intrinsic protein synthesis occurs. Cultured neonatal neurons express NGF mRNA, which is maintained even when they are undergoing apoptosis. To determine which NGF isoforms are secreted, we performed metabolic labeling and immunoprecipitation of NGF-immunoreactive proteins synthesized by cultured NGF-dependent and -independent neurons. Conditioned medium contained high molecular weight NGF precursor proteins, which varied depending upon the state of NGF dependence. Mature NGF was undetectable by these methods. High molecular weight NGF isoforms were also detected in ganglion homogenates, and persisted at diminished levels following axotomy. We conclude that sympathetic neurons express NGF mRNA, and synthesize and secrete pro-NGF protein. These findings suggest that a potential NGF-sympathetic neuron autocrine loop may exist in this prototypic target-dependent system, but that the secreted forms of this neurotrophin apparently do not support neuronal survival.