Strain-induced proliferation requires the phosphatidylinositol 3-kinase/AKT/glycogen synthase kinase pathway

Upregulation of the microRNA rno-miR-146b-5p may be involved in the development of intestinal injury through inhibition of Kruppel-like factor 4 in intestinal sepsis

Regulatory mechanisms of microRNAs (miRNAs) in the development of intestinal sepsis are unclear. This study investigated the role of rno-miR-146b-5p in sepsis-induced intestinal injury. A rat sepsis model was created using the cecal ligation and puncture method. The expression profiles of miRNA and mRNA in sepsis rats were examined using miRNA and mRNA sequencing; rno-miR-146b was selected for further investigation. The mimics and inhibitors of rno-miR-146b-5p were transfected into IEC-6 cells and then with or without lipopolysaccharide (LPS) treatment, and the expressions of Kruppel-like factor 4 (Klf4) and Cyclin D2 (Ccnd2) were assessed by quantitative real-time transcriptase-polymerase chain reaction (qRT-PCR) and western blotting. Next, cell counting kit-8 assay was used to detect cell viability, and scratch wound healing assay was used to assess cell migration. In sepsis rat model, crypt cell proliferation was inhibited and crypt cell apoptosis was increased. Compared with the sham control, results of miRNA and mRNA sequencing showed that there were 17 miRNAs and 1617 mRNAs that were upregulated and 123 miRNAs and 1917 mRNAs that were downregulated in the sepsis model group. The network diagrams and qRT-PCR validation indicated that rno-miR-146b-5p may inhibit the expression of Klf4. By adjusting the expression of rno-miR-146b-5p in IEC-6 cells with or without LPS treatment, we found that increased expression of rno-miR-146b-5p inhibited cell proliferation and migration and inhibited the expression of Ccnd2. rno-miR-146b-5p may play a vital role in the development of sepsis intestinal injury through targeting Klf4 expression and affecting promoter activity of Ccnd2.

In Vitro Models of the Small Intestine: Engineering Challenges and Engineering Solutions

Pathologies affecting the small intestine contribute significantly to the disease burden of both the developing and the developed world, which has motivated investigation into the disease mechanisms through in vitro models. Although existing in vitro models recapitulate selected features of the intestine, various important aspects have often been isolated or omitted due to the anatomical and physiological complexity. The small intestine's intricate microanatomy, heterogeneous cell populations, steep oxygen gradients, microbiota, and intestinal wall contractions are often not included in in vitro experimental models of the small intestine, despite their importance in both intestinal biology and pathology. Known and unknown interdependencies between various physiological aspects necessitate more complex in vitro models. Microfluidic technology has made it possible to mimic the dynamic mechanical environment, signaling gradients, and other important aspects of small intestinal biology. This review presents an overview of the complexity of small intestinal anatomy and bioengineered models that recapitulate some of these physiological aspects.

Schlafen 12 mediates the effects of butyrate and repetitive mechanical deformation on intestinal epithelial differentiation in human Caco-2 intestinal epithelial cells

Intestinal epithelial differentiation may be stimulated by diverse pathways including luminal short-chain fatty acids and repetitive mechanical deformation engendered by villous motility and peristalsis. Schlafen 12 (SLFN12) is a cytosolic protein that stimulates sucrase-isomaltase (SI) expression. We hypothesized that two disparate differentiating stimuli, butyrate and repetitive deformation, would each stimulate SLFN12 expression in human Caco-2 intestinal epithelial cells and that increased SLFN12 expression would contribute to the differentiating activity of the human Caco-2 intestinal epithelial cells. We stimulated Caco-2 cells with 1-2 mM butyrate or repetitive mechanical deformation at 10 cycles/min at an average 10% strain, and measured SLFN12 and SI expression by qRT-PCR. Sodium butyrate enhanced SLFN12 expression at both 1 mM and 2 mM although SI expression was only significantly increased at 2 mM. Repetitive deformation induced by cyclic mechanical strain also significantly increased both SLFN12 and SI gene expression. Reducing SLFN12 by siRNA decreased basal, deformation-stimulated, and butyrate-stimulated SLFN12 levels, compared to control cells treated with non-targeting siRNA, although both deformation and butyrate were still able to stimulate SLFN12 expression in siRNA-treated cells compared to control cells treated with the same siRNA. This attenuation of the increase in SLFN12 expression in response to mechanical strain or butyrate was accompanied by parallel attenuation of SI expression. Butyrate stimulated SI-promoter activity, and reducing SLFN12 by siRNA attenuated butyrate-induced SI-promoter activity. These data suggest that SLFN12 mediates at least in part the stimulation by both butyrate and repetitive mechanical deformation of sucrase-isomaltase, a late stage differentiation marker in human intestinal epithelial cells.

Bile acids regulate intestinal cell proliferation by modulating EGFR and FXR signaling

Bile acids (BAs) are synthesized in the liver and secreted into the intestine. In the lumen, enteric bacteria metabolize BAs from conjugated, primary forms into more toxic unconjugated, secondary metabolites. Secondary BAs can be injurious to the intestine and may contribute to disease. The epidermal growth factor receptor (EGFR) and the nuclear farnesoid X receptor (FXR) are known to interact with BAs. In this study we examined the effects of BAs on intestinal epithelial cell proliferation and investigated the possible roles for EGFR and FXR in these effects. We report that taurine-conjugated cholic acid (TCA) induced proliferation, while its unconjugated secondary counterpart deoxycholic acid (DCA) inhibited proliferation. TCA stimulated phosphorylation of Src, EGFR, and ERK 1/2. Pharmacological blockade of any of these pathways or genetic ablation of EGFR abrogated TCA-stimulated proliferation. Interestingly, Src or EGFR inhibitors eliminated TCA-induced phosphorylation of both molecules, suggesting that their activation is interdependent. In contrast to TCA, DCA exposure diminished EGFR phosphorylation, and pharmacological or siRNA blockade of FXR abolished DCA-induced inhibition of proliferation. Taken together, these results suggest that TCA induces intestinal cell proliferation via Src, EGFR, and ERK activation. In contrast, DCA inhibits proliferation via an FXR-dependent mechanism that may include downstream inactivation of the EGFR/Src/ERK pathway. Since elevated secondary BA levels are the result of specific bacterial modification, this may provide a mechanism through which an altered microbiota contributes to normal or abnormal intestinal epithelial cell proliferation.

Cyclic stretch disrupts apical junctional complexes in Caco-2 cell monolayers by a JNK-2-, c-Src-, and MLCK-dependent mechanism

The intestinal epithelium is subjected to various types of mechanical stress. In this study, we investigated the impact of cyclic stretch on tight junction and adherens junction integrity in Caco-2 cell monolayers. Stretch for 2 h resulted in a dramatic modulation of tight junction protein distribution from a linear organization into wavy structure. Continuation of cyclic stretch for 6 h led to redistribution of tight junction proteins from the intercellular junctions into the intracellular compartment. Disruption of tight junctions was associated with redistribution of adherens junction proteins, E-cadherin and β-catenin, and dissociation of the actin cytoskeleton at the actomyosin belt. Stretch activates JNK2, c-Src, and myosin light-chain kinase (MLCK). Inhibition of JNK, Src kinase or MLCK activity and knockdown of JNK2 or c-Src attenuated stretch-induced disruption of tight junctions, adherens junctions, and actin cytoskeleton. Paracellular permeability measured by a novel method demonstrated that cyclic stretch increases paracellular permeability by a JNK, Src kinase, and MLCK-dependent mechanism. Stretch increased tyrosine phosphorylation of occludin, ZO-1, E-cadherin, and β-catenin. Inhibition of JNK or Src kinase attenuated stretch-induced occludin phosphorylation. Immunofluorescence localization indicated that phospho-MLC colocalizes with the vesicle-like actin structure at the actomyosin belt in stretched cells. On the other hand, phospho-c-Src colocalizes with the actin at the apical region of cells. This study demonstrates that cyclic stretch disrupts tight junctions and adherens junctions by a JNK2, c-Src, and MLCK-dependent mechanism.

Periostin induces intracellular cross-talk between kinases and hyaluronan in atrioventricular valvulogenesis

Periostin (PN), a novel fasciclin-related matricellular protein, has been implicated in cardiac development and postnatal remodeling, but the mechanism remains unknown. We examined the role of PN in mediating intracellular kinase activation for atrioventricular valve morphogenesis using well defined explant cultures, gene transfection systems, and Western blotting. The results show that valve progenitor (cushion) cells secrete PN into the extracellular matrix, where it can bind to INTEGRINs and activate INTEGRIN/focal adhesion kinase signaling pathways and downstream kinases, PI3K/AKT and ERK. Functional assays with prevalvular progenitor cells showed that activating these signaling pathways promoted adhesion, migration, and anti-apoptosis. Through activation of PI3K/ERK, PN directly enhanced collagen expression. Comparing PN-null to WT mice also revealed that expression of hyaluronan (HA) and activation of hyaluronan synthase-2 (Has2) are also enhanced upon PN/INTEGRIN/focal adhesion kinase-mediated activation of PI3K and/or ERK, an effect confirmed by the reduction of HA synthase-2 in PN-null mice. We also identified in valve progenitor cells a potential autocrine signaling feedback loop between PN and HA through PI3K and/or ERK. Finally, in a three-dimensional assay to simulate normal valve maturation in vitro, PN promoted collagen compaction in a kinase-dependent fashion. In summary, this study provides the first direct evidence that PN can act to stimulate a valvulogenic signaling pathway.

Regulation of epithelial differentiation in rat intestine by intraluminal delivery of an adenoviral vector or silencing RNA coding for Schlafen 3

Although we stimulate enterocytic proliferation to ameliorate short gut syndrome or mucosal atrophy, less effort has been directed at enterocytic differentiation. Schlafen 3 (Slfn3) is a poorly understood protein induced during IEC-6 enterocytic differentiation. We hypothesized that exogenous manipulation of Slfn3 would regulate enterocytic differentiation in vivo. Adenoviral vector coding for Slfn3 cDNA (Ad-GFP-Slfn3) or silencing RNA for Slfn3 (siSlfn3) was introduced intraluminally into rat intestine. We assessed Slfn3, villin, sucrase-isomaltase (SI), Dpp4, and Glut2 by qRT-PCR, Western blot, and immunohistochemistry. We also studied Slfn3 and these differentiation markers in atrophic defunctionalized jejunal mucosa and the crypt-villus axis of normal jejunum. Ad-GFP-Slfn3 but not Ad-GFP increased Slfn3, villin and Dpp4 expression in human Caco-2 intestinal epithelial cells. Injecting Ad-GFP-Slfn3 into rat jejunum in vivo increased mucosal Slfn3 mRNA three days later vs. intraluminal Ad-GFP. This Slfn3 overexpression was associated with increases in all four differentiation markers. Injecting siSlfn3 into rat jejunum in vivo substantially reduced Slfn3 and all four intestinal mucosal differentiation markers three days later, as well as Dpp4 specific activity. Endogenous Slfn3 was reduced in atrophic mucosa from a blind-end Roux-en-Y anastomosis in parallel with differentiation marker expression together with AKT and p38 signaling. Slfn3 was more highly expressed in the villi than the crypts, paralleling Glut2, SI and Dpp4. Slfn3 is a key intracellular regulator of rat enterocytic differentiation. Understanding how Slfn3 works may identify targets to promote enterocytic differentiation and maintain mucosal function in vivo, facilitating enteral nutrition and improving survival in patients with mucosal atrophy or short gut syndrome.

Genetic and bioinformatic analyses of the expression and function of PI3K regulatory subunit PIK3R3 in an Asian patient gastric cancer library

Background

While there is strong evidence for phosphatidylinositol 3-kinase (PI3K) involvement in cancer development, there is limited information about the role of PI3K regulatory subunits. PIK3R3, the gene that encodes the PI3K regulatory subunit p55γ, is over-expressed in glioblastoma and ovarian cancers, but its expression in gastric cancer (GC) is not known. We thus used genetic and bioinformatic approaches to examine PIK3R3 expression and function in GC, the second leading cause of cancer mortality world-wide and highly prevalent among Asians.

Methods

Primary GC and matched non-neoplastic mucosa tissue specimens from a unique Asian patient gastric cancer library were comprehensively profiled with platforms that measured genome-wide mRNA expression, DNA copy number variation, and DNA methylation status. Function of PIK3R3 was predicted by IPA pathway analysis of co-regulated genes with PIK3R3, and further investigated by siRNA knockdown studies. Cell proliferation was estimated by crystal violet dye elution and BrdU incorporation assay. Cell cycle distribution was analysed by FACS.

Results

PIK3R3 was significantly up-regulated in GC specimens (n = 126, p < 0.05), and 9.5 to 15% tumors showed more than 2 fold increase compare to the paired mucosa tissues. IPA pathway analysis showed that PIK3R3 promoted cellular growth and proliferation. Knockdown of PIK3R3 decreased the growth of GC cells, induced G0/G1 cell cycle arrest, decreased retinoblastoma protein (Rb) phosphorylation, cyclin D1, and PCNA expression.

Conclusion

Using a combination of genetic, bioinformatic, and molecular biological approaches, we showed that PIK3R3 was up-regulated in GC and promoted cell cycle progression and proliferation; and thus may be a potential new therapeutic target for GC.

Role of RhoA and its effectors ROCK and mDia1 in the modulation of deformation-induced FAK, ERK, p38, and MLC motogenic signals in human Caco-2 intestinal epithelial cells

Repetitive deformation enhances intestinal epithelial migration across tissue fibronectin. We evaluated the contribution of RhoA and its effectors Rho-associated kinase (ROK/ROCK) and mammalian diaphanous formins (mDia1) to deformation-induced intestinal epithelial motility across fibronectin and the responsible focal adhesion kinase (FAK), extracellular signal-regulated kinase (ERK), p38, and myosin light chain (MLC) signaling. We reduced RhoA, ROCK1, ROCK2, and mDia1 by smart-pool double-stranded short-interfering RNAs (siRNA) and pharmacologically inhibited RhoA, ROCK, and FAK in human Caco-2 intestinal epithelial monolayers on fibronectin-coated membranes subjected to 10% repetitive deformation at 10 cycles/min. Migration was measured by wound closure. Stimulation of migration by deformation was prevented by exoenzyme C3, Y27632, or selective RhoA, ROCK1, and ROCK2 or mDia1 siRNAs. RhoA, ROCK inhibition, or RhoA, ROCK1, ROCK2, mDia1, and FAK reduction by siRNA blocked deformation-induced nuclear ERK phosphorylation without preventing ERK phosphorylation in the cytoplasmic protein fraction. Furthermore, RhoA, ROCK inhibition or RhoA, ROCK1, ROCK2, and mDia1 reduction by siRNA also blocked strain-induced FAK-Tyr(925), p38, and MLC phosphorylation. These results suggest that RhoA, ROCK, mDia1, FAK, ERK, p38, and MLC all mediate the stimulation of intestinal epithelial migration by repetitive deformation. This pathway may be an important target for interventions to promote mechanotransduced mucosal healing during inflammation.

The "cryptic" mechanism of action of glucagon-like peptide-2

Glucagon-like peptide-2 (GLP-2) is a peptide hormone with multiple beneficial effects on the intestine, including expansion of the mucosal surface area through stimulation of crypt cell proliferation, as well as enhancement of nutrient digestion and absorption. Recent advances in clinical trials involving GLP-2 necessitate elucidation of the exact signaling pathways by which GLP-2 acts. In particular, the GLP-2 receptor has been localized to several intestinal cell types that do not include the proliferating crypt cells, and the actions of GLP-2 have thus been linked to a complex network of indirect mediators that induce diverse signaling pathways. The intestinotropic actions of GLP-2 on the colon have been shown to be mediated through the actions of keratinocyte growth factor and insulin-like growth factor (IGF)-2, whereas small intestinal growth has been linked to IGF-1, IGF-2, and ErbB ligands, as well as the IGF-1 receptor and ErbB. The cellular source of these mediators remains unclear, but it likely includes the intestinal subepithelial myofibroblasts. Conversely, the anti-inflammatory and blood flow effects of GLP-2 are dependent on vasoactive intestinal polypeptide released from submucosal enteric neurons and nitric oxide, respectively. Finally, recent studies have suggested that GLP-2 not only modulates intestinal stem cell behavior but may also promote carcinogenesis in models of sporadic colon cancer. Further consideration of the molecular cross-talk and downstream signaling pathways mediating the intestinotropic effects of GLP-2 is clearly warranted.

Delay of cell cycle progression and induction death of cancer cells on type I collagen fibrils [corrected]

Here, we report the behavior of three kinds of human cancer cell lines (Caco-2, MCF-7, HT-1080) on type I collagen substrates, which are in two-dimensional coated collagen or three-dimensional fibrils form. All tested cells on coated collagen adhered and proliferated. However, in the case of collagen fibrils, the proliferation of cancer cells was suppressed. Furthermore, Akt activation, which is known as a cell-survival signal, was inhibited in cells on collagen fibrils. But the activation of ERK1/2 was not completely inhibited. In Caco-2 cells, delay of cell cycle progression and cell death occurred at the same time. Thus, cell division and cell death occurred at equivalent rates on the collagen fibrils, and cell growth seemed to be stopped. These results imply that the fibril form of collagen plays a potential role in inhibiting the growth of cancer cells.

Hepatitis B x-interacting protein induces HepG2 cell proliferation through activation of the phosphatidylinositol 3-kinase/Akt pathway

Hepatitis B x-interacting protein (HBXIP), a co-factor of survivin, was originally identified by its binding with the C-terminus of the hepatitis B virus x protein (HBx). We have recently shown that HBXIP promotes the growth of both normal liver cells and hepatoma cells in vitro, but the molecular mechanisms of this have not been documented. In this study, we investigated the potential effects of HBXIP on the proliferation of HepG2 cells and the intracellular signaling pathway mediating these changes. Over-expression of the HBXIP gene promoted the proliferation of HepG2 cells, as shown by the MTT assay. We also showed that HBXIP induced cellular accumulation in the S phase concomitantly with up-regulation of cyclinD(1) and down-regulation of p21 and p53 levels. Moreover, HBXIP over-expression cells showed activation of the PI3K/Akt pathway; this activation was accompanied by an increase in phosphorylation of glycogen synthase kinase 3β. LY294002, a specific inhibitor of PI3K, blocked HBXIP-stimulated Akt phosphorylation and suppressed the cell cycle promotion induced by HBXIP in HepG2 cells. The increase in cyclinD(1) protein levels induced by HBXIP was inhibited when cells were incubated with LY294002. In conclusion, our data suggest that the proliferation of HepG2 cells promoted by HBXIP is associated with activation of the PI3K/Akt signaling pathway.

Novel avenues of drug discovery and biomarkers for diabetes mellitus

Globally, developed nations spend a significant amount of their resources on health care initiatives that poorly translate into increased population life expectancy. As an example, the United States devotes 16% of its gross domestic product to health care, the highest level in the world, but falls behind other nations that enjoy greater individual life expectancy. These observations point to the need for pioneering avenues of drug discovery to increase life span with controlled costs. In particular, innovative drug development for metabolic disorders such as diabetes mellitus becomes increasingly critical given that the number of diabetic people will increase exponentially over the next 20 years. This article discusses the elucidation and targeting of novel cellular pathways that are intimately tied to oxidative stress in diabetes mellitus for new treatment strategies. Pathways that involve wingless, β-nicotinamide adenine dinucleotide (NAD(+)) precursors, and cytokines govern complex biological pathways that determine both cell survival and longevity during diabetes mellitus and its complications. Furthermore, the role of these entities as biomarkers for disease can further enhance their utility irrespective of their treatment potential. Greater understanding of the intricacies of these unique cellular mechanisms will shape future drug discovery for diabetes mellitus to provide focused clinical care with limited or absent long-term complications.

ILK mediates the effects of strain on intestinal epithelial wound closure

The intestinal epithelium is subjected to repetitive deformation during normal gut function by peristalsis and villous motility. Such repetitive strain promotes intestinal epithelial migration across fibronectin in vitro, but signaling mediators for this are poorly understood. We hypothesized that integrin-linked kinase (ILK) mediates strain-stimulated migration in intestinal epithelial cells cultured on fibronectin. ILK kinase activity increased rapidly 5 min after strain induction in both Caco-2 and intestinal epithelial cell-6 (IEC-6) cells. Wound closure in response to strain was reduced in ILK small interfering RNA (siRNA)-transfected Caco-2 cell monolayers when compared with control siRNA-transfected Caco-2 cells. Pharmacological blockade of phosphatidylinositol-3 kinase (PI3K) or Src or reducing Src by siRNA prevented strain activation of ILK. ILK coimmunoprecipitated with focal adhesion kinase (FAK), and this association was decreased by mutation of FAK Tyr925 but not FAK Tyr397. Strain induction of FAK Tyr925 phosphorylation but not FAK Tyr397 or FAK Tyr576 phosphorylation was blocked in ILK siRNA-transfected cells. ILK-Src association was stimulated by strain and was blocked by the Src inhibitor PP2. Finally, ILK reduction by siRNA inhibited strain-induced phosphorylation of myosin light chain and Akt. These results suggest a strain-dependent signaling pathway in which ILK association with FAK and Src mediates the subsequent downstream strain-induced motogenic response and suggest that ILK induction by repetitive deformation may contribute to recovery from mucosal injury and restoration of the mucosal barrier in patients with prolonged ileus. ILK may therefore be an important target for intervention to maintain the mucosa in such patients.

ERK regulates strain-induced migration and proliferation from different subcellular locations

Repetitive deformation like that engendered by peristalsis or villous motility stimulates intestinal epithelial proliferation on collagenous substrates and motility across fibronectin, each requiring ERK. We hypothesized that ERK acts differently at different intracellular sites. We stably transfected Caco-2 cells with ERK decoy expression vectors that permit ERK activation but interfere with its downstream signaling. Targeting sequences constrained the decoy inside or outside the nucleus. We assayed proliferation by cell counting and migration by circular wound closure with or without 10% repetitive deformation at 10 cycles/min. Confocal microscopy confirmed localization of the fusion proteins. Inhibition of phosphorylation of cytoplasmic RSK or nuclear Elk confirmed functionality. Both the nuclear-localized and cytosolic-localized ERK decoys prevented deformation-induced proliferation on collagen. Deformation-induced migration on fibronectin was prevented by constraining the decoy in the nucleus but not in the cytosol. Like the nuclear-localized ERK decoy, a Sef-overexpressing adenovirus that sequesters ERK in the cytoplasm also blocked the motogenic and mitogenic effects of strain. Inhibiting RSK or reducing Elk ablated both the mitogenic and motogenic effects of strain. RSK isoform reduction revealed isoform specificity. These results suggest that ERK must translocate to the nucleus to stimulate cell motility while ERK must act in both the cytosol and the nucleus to stimulate proliferation in response to strain. Selectively targeting ERK within different subcellular compartments may modulate or replace physical force effects on the intestinal mucosa to maintain the intestinal mucosal barrier in settings when peristalsis or villous motility are altered and fibronectin is deposited into injured tissue.

Diabetes mellitus: channeling care through cellular discovery

Diabetes mellitus (DM) impacts a significant portion of the world's population and care for this disorder places an economic burden on the gross domestic product for any particular country. Furthermore, both Type 1 and Type 2 DM are becoming increasingly prevalent and there is increased incidence of impaired glucose tolerance in the young. The complications of DM are protean and can involve multiple systems throughout the body that are susceptible to the detrimental effects of oxidative stress and apoptotic cell injury. For these reasons, innovative strategies are necessary for the implementation of new treatments for DM that are generated through the further understanding of cellular pathways that govern the pathological consequences of DM. In particular, both the precursor for the coenzyme beta-nicotinamide adenine dinucleotide (NAD(+)), nicotinamide, and the growth factor erythropoietin offer novel platforms for drug discovery that involve cellular metabolic homeostasis and inflammatory cell control. Interestingly, these agents and their tightly associated pathways that consist of cell cycle regulation, protein kinase B, forkhead transcription factors, and Wnt signaling also function in a broader sense as biomarkers for disease onset and progression.

Schlafen 3 induction by cyclic strain regulates intestinal epithelial differentiation

The intestinal epithelium is subjected to repetitive deformation during normal gut function by peristalsis and villous motility. In vitro, cyclic strain promotes intestinal epithelial proliferation and induces an absorptive phenotype characterized by increased dipeptidyl dipeptidase (DPPIV) expression. Schlafen 3 is a novel gene recently associated with cellular differentiation. We sought to evaluate whether Schlafen 3 mediates the effects of strain on the differentiation of intestinal epithelial cell (IEC)-6 in the absence or presence of cyclic strain. Strain increased Schlafen 3 mRNA and protein. In cells transfected with a control-nontargeting siRNA, strain increased DPPIV-specific activity. However, Schlafen 3 reduction by siRNA decreased basal DPPIV and prevented any stimulation of DPPIV activity by strain. Schlafen 3 reduction also prevented DPPIV induction by sodium butyrate (1 mM) or transforming growth factor (TGF)-beta (0.1 ng/ml), two unrelated differentiating stimuli. However, Schlafen-3 reduction by siRNA did not prevent the mitogenic effect of strain or that of EGF. Blocking Src and phosphatidyl inositol (PI3)-kinase prevented strain induction of Schlafen 3, but Schlafen 3 induction required activation of p38 but not ERK. These results suggest that cyclic strain induces an absorptive phenotype characterized by increased DPPIV activity via Src-, p38-, and PI3-kinase-dependent induction of Schlafen 3 in rat IEC-6 cells on collagen, whereas Schlafen 3 may also be a key factor in the induction of intestinal epithelial differentiation by other stimuli such as sodium butyrate or TGF-beta. The induction of Schlafen 3 or its human homologs may modulate intestinal epithelial differentiation and preserve the gut mucosa during normal gut function.

FoxO3a governs early microglial proliferation and employs mitochondrial depolarization with caspase 3, 8, and 9 cleavage during oxidant induced apoptosis

Microglia of the central nervous system have a dual role in the ability to influence the survival of neighboring cells. During inflammatory cell activation, microglia can lead to the disposal of toxic cellular products and permit tissue regeneration, but microglia also may lead to cellular destruction with phagocytic removal. For these reasons, it is essential to elucidate not only the underlying pathways that control microglial activation and proliferation, but also the factors that determine microglial survival. In this regard, we investigated in the EOC 2 microglial cell line with an oxygen-glucose deprivation (OGD) injury model of oxidative stress the role of the "O" class forkhead transcription factor FoxO3a that in some scenarios is closely linked to immune system function. We demonstrate that FoxO3a is a necessary element in the control of early and late apoptotic injury programs that involve membrane phosphatidylserine externalization and nuclear DNA degradation, since transient knockdown of FoxO3a in microglia preserves cellular survival 24 hours following OGD exposure. However, prior to the onset of apoptotic injury, FoxO3a facilitates the activation and proliferation of microglia as early as 3 hours following OGD exposure that occurs in conjunction with the trafficking of the unphosphorylated and active post-translational form of FoxO3a from the cytoplasm to the cell nucleus. FoxO3a also can modulate apoptotic mitochondrial signal transduction pathways in microglia, since transient knockdown of FoxO3a prevents mitochondrial membrane depolarization as well as the release of cytochrome c during OGD. Control of this apoptotic cascade also extends to progressive caspase activation as early as 1 hour following OGD exposure. The presence of FoxO3a is necessary for the expression of cleaved (active) caspase 3, 8, and 9, since loss of FoxO3a abrogates the induction of caspase activity. Interestingly, elimination of FoxO3a reduced caspase 9 activity to a lesser extent than that noted with caspase 3 and 8 activities, suggesting that FoxO3a in relation to caspase 9 may be more reliant upon other signal transduction pathways potentially independent from caspase 3 and 8.

Pituitary adenylate cyclase-activating polypeptide (PACAP)/PAC1HOP1 receptor activation coordinates multiple neurotrophic signaling pathways: Akt activation through phosphatidylinositol 3-kinase gamma and vesicle endocytosis for neuronal survival

MAPK and Akt pathways are predominant mediators of trophic signaling for many neuronal systems. Among the vasoactive intestinal peptide/secretin/glucagon family of related peptides, pituitary adenylate cyclase-activating polypeptide (PACAP) binding to specific PAC(1) receptor isoforms can engage multiple signaling pathways and promote neuroprotection through mechanisms that are not well understood. Using a primary sympathetic neuronal system, the current studies demonstrate that PACAP activation of PAC(1)HOP1 receptors engages both MAPK and Akt neurotrophic pathways in an integrated program to facilitate neuronal survival after growth factor withdrawal. PACAP not only stimulated prosurvival ERK1/2 and ERK5 activation but also abrogated SAPK/JNK and p38 MAPK signaling in parallel. In contrast to the potent and rapid effects of PACAP in ERK1/2 phosphorylation, PACAP stimulated Akt phosphorylation in a late phase of PAC(1)HOP1 receptor signaling. From inhibitor and immunoprecipitation analyses, the PACAP/PAC(1)HOP1 receptor-mediated Akt responses did not represent transactivation mechanisms but appeared to depend on G alpha(q)/phosphatidylinositol 3-kinase gamma activity and vesicular internalization pathways. Phosphatidylinositol 3-kinase gamma-selective inhibitors blocked PACAP-stimulated Akt phosphorylation in primary neuronal cultures and in PAC(1)HOP1-overexpressing cell lines; RNA interference-mediated knockdown of the receptor effectors attenuated PACAP-mediated Akt activation. Similarly, perturbation of endocytic pathways also blocked Akt phosphorylation. Between ERK and Akt pathways, PACAP-stimulated Akt signaling was the primary cascade that attenuated cultured neuron apoptosis after growth factor withdrawal. The partitioning of PACAP-mediated Akt signaling in endosomes may be a key mechanism contributing to the high spatial and temporal specificity in signal transduction necessary for survival pathways.

Oxidative stress: Biomarkers and novel therapeutic pathways

Oxidative stress significantly impacts multiple cellular pathways that can lead to the initiation and progression of varied disorders throughout the body. It therefore becomes imperative to elucidate the components and function of novel therapeutic strategies against oxidative stress to further clinical diagnosis and care. In particular, both the growth factor and cytokine erythropoietin (EPO) and members of the mammalian forkhead transcription factors of the O class (FoxOs) may offer the greatest promise for new treatment regimens since these agents and the cellular pathways they oversee cover a range of critical functions that directly influence progenitor cell development, cell survival and degeneration, metabolism, immune function, and cancer cell invasion. Furthermore, both EPO and FoxOs function not only as therapeutic targets, but also as biomarkers of disease onset and progression, since their cellular pathways are closely linked and overlap with several unique signal transduction pathways. However, biological outcome with EPO and FoxOs may sometimes be both unexpected and undesirable that can raise caution for these agents and warrant further investigations. Here we present the exciting as well as complicated role EPO and FoxOs possess to uncover the benefits as well as the risks of these agents for cell biology and clinical care in processes that range from stem cell development to uncontrolled cellular proliferation.

Oscillatory flow-induced proliferation of osteoblast-like cells is mediated by alphavbeta3 and beta1 integrins through synergistic interactions of focal adhesion kinase and Shc with phosphatidylinositol 3-kinase and the Akt/mTOR/p70S6K pathway

Interstitial flow in and around bone tissue is oscillatory in nature and affects the mechanical microenvironment for bone cell growth and formation. We investigated the role of oscillatory shear stress (OSS) in modulating the proliferation of human osteoblast-like MG63 cells and its underlying mechanisms. Application of OSS (0.5 +/- 4 dynes/cm(2)) to MG63 cells induced sustained activation of phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR/p70S6K (p70S6 kinase) signaling cascades and hence cell proliferation, which was accompanied by increased expression of cyclins A and D1, cyclin-dependent protein kinases-2, -4, and -6, and bone formation-related genes (c-fos, Egr-1, and Cox-2) and decreased expression of p21(CIP1) and p27(KIP1). OSS-induced activation of PI3K/Akt/mTOR/p70S6K and cell proliferation were inhibited by specific antibodies or small interference RNAs of alpha(v)beta(3) and beta(1) integrins and by dominant-negative mutants of Shc (Shc-SH2) and focal adhesion kinase (FAK) (FAK(F397Y)). Co-immunoprecipitation assay showed that OSS induces sustained increases in association of Shc and FAK with alpha(v)beta(3) and beta(1) integrins and PI3K subunit p85, which were abolished by transfecting the cells with FAK(F397Y) or Shc-SH2. OSS also induced sustained activation of ERK, which was inhibited by the specific PI3K inhibitor LY294002 and was required for OSS-induced activation of mTOR/p70S6K and proliferation in MG63 cells. Our findings provide insights into the mechanisms by which OSS induces osteoblast-like cell proliferation through activation of alpha(v)beta(3) and beta(1) integrins and synergistic interactions of FAK and Shc with PI3K, leading to the modulation of downstream ERK and Akt/mTOR/p70S6K pathways.

New strategies for Alzheimer's disease and cognitive impairment

Approximately five million people suffer with Alzheimer's disease (AD) and more than twenty-four million people are diagnosed with AD, pre-senile dementia, and other disorders of cognitive loss worldwide. Furthermore, the annual cost per patient with AD can approach $200,000 with an annual population aggregate cost of $100 billion. Yet, complete therapeutic prevention or reversal of neurovascular injury during AD and cognitive loss is not achievable despite the current understanding of the cellular pathways that modulate nervous system injury during these disorders. As a result, identification of novel therapeutic targets for the treatment of neurovascular injury would be extremely beneficial to reduce or eliminate disability from diseases that lead to cognitive loss or impairment. Here we describe the capacity of intrinsic cellular mechanisms for the novel pathways of erythropoietin and forkhead transcription factors that may offer not only new strategies for disorders such as AD and cognitive loss, but also function as biomarkers for disease onset and progression.

Erythropoietin, forkhead proteins, and oxidative injury: biomarkers and biology

Oxidative stress significantly impacts multiple cellular pathways that can lead to the initiation and progression of varied disorders throughout the body. It therefore becomes imperative to elucidate the components and function of novel therapeutic strategies against oxidative stress to further clinical diagnosis and care. In particular, both the growth factor and cytokine erythropoietin (EPO), and members of the mammalian forkhead transcription factors of the O class (FoxOs), may offer the greatest promise for new treatment regimens, since these agents and the cellular pathways they oversee cover a range of critical functions that directly influence progenitor cell development, cell survival and degeneration, metabolism, immune function, and cancer cell invasion. Furthermore, both EPO and FoxOs function not only as therapeutic targets, but also as biomarkers of disease onset and progression, since their cellular pathways are closely linked and overlap with several unique signal transduction pathways. Yet, EPO and FoxOs may sometimes have unexpected and undesirable effects that can raise caution for these agents and warrant further investigations. Here we present the exciting as well as the complex role that EPO and FoxOs possess to uncover the benefits as well as the risks of these agents for cell biology and clinical care in processes that range from stem cell development to uncontrolled cellular proliferation.

The vitamin nicotinamide: translating nutrition into clinical care

Nicotinamide, the amide form of vitamin B(3) (niacin), is changed to its mononucleotide compound with the enzyme nicotinic acide/nicotinamide adenylyltransferase, and participates in the cellular energy metabolism that directly impacts normal physiology. However, nicotinamide also influences oxidative stress and modulates multiple pathways tied to both cellular survival and death. During disorders that include immune system dysfunction, diabetes, and aging-related diseases, nicotinamide is a robust cytoprotectant that blocks cellular inflammatory cell activation, early apoptotic phosphatidylserine exposure, and late nuclear DNA degradation. Nicotinamide relies upon unique cellular pathways that involve forkhead transcription factors, sirtuins, protein kinase B (Akt), Bad, caspases, and poly (ADP-ribose) polymerase that may offer a fine line with determining cellular longevity, cell survival, and unwanted cancer progression. If one is cognizant of the these considerations, it becomes evident that nicotinamide holds great potential for multiple disease entities, but the development of new therapeutic strategies rests heavily upon the elucidation of the novel cellular pathways that nicotinamide closely governs.

The effects of mechanical forces on intestinal physiology and pathology

The epithelial and non-epithelial cells of the intestinal wall experience a myriad of physical forces including strain, shear, and villous motility during normal gut function. Pathologic conditions alter these forces, leading to changes in the biology of these cells. The responses of intestinal epithelial cells to forces vary with both the applied force and the extracellular matrix proteins with which the cells interact, with differing effects on proliferation, differentiation, and motility, and the regulation of these effects involves similar but distinctly different signal transduction mechanisms. Although normal epithelial cells respond to mechanical forces, malignant gastrointestinal epithelial cells also respond to forces, most notably by increased cell adhesion, a critical step in tumor metastasis. This review will focus on the phenomenon of mechanical forces influencing cell biology and the mechanisms by which the gut responds these forces in both the normal as well as pathophysiologic states when forces are altered. Although more is known about epithelial responses to force, information regarding mechanosensitivity of vascular, neural, and endocrine cells within the gut wall will also be discussed, as will, the mechanism by which forces can regulate epithelial tumor cell adhesion.