Effect of protein kinase C activation on intracellular Ca2+ signaling and integrity of intestinal epithelial cells

Early statin exposure influences cardiac and skeletal development with implications for ion channel transcriptomes in zebrafish

Statins, widely prescribed for cholesterol management by inhibiting HMG-CoA reductase in the cholesterol biosynthesis pathway, may also influence vertebrate development. In this study, we investigated the developmental effects of two widely used statins, atorvastatin (ATO) and pravastatin (PRA), on zebrafish offspring. For ATO, we administered doses classified as low (1 μM), medium (5 μM), and high (10 μM), while for PRA, the corresponding concentrations were set at low (18 μM), medium (180 μM), and high (270 μM). Our results showed significant reductions in birth and hatching rates, along with decreased body length in offspring at all ATO concentrations and medium to high PRA concentrations. A notable increase in malformation rates, especially in the spine and heart, was observed across all ATO treatments and in medium and high PRA groups. Additionally, we observed reduced heart contraction rates, decreased heart size, lower bone volumes, and diminished expression of mRNA osteogenic markers. Elevated venous sinus-artery bulb (SV-BA) ratios, increased thoracic area, and abnormal cartilage development were also prominent in all ATO-treated groups. Transcriptome analysis revealed alterations in genes predominantly associated with ion channels. These findings provide insights into the potential impacts of specific concentrations of statins on offspring development and highlight potential gene interactions with statins.

Cytoskeletal Responses and Aif-1 Expression in Caco-2 Monolayers Exposed to Phorbol-12-Myristate-13-Acetate and Carnosine

The dis(re)organization of the cytoskeletal actin in enterocytes mediates epithelial barrier dys(re)function, playing a key role in modulating epithelial monolayer's integrity and remodeling under transition from physiological to pathological states. Here, by fluorescence-based morphological and morphometric analyses, we detected differential responses of cytoskeletal actin in intestinal epithelial Caco-2 cell monolayers at two different stages of their spontaneous differentiation, i.e., undifferentiated cells at 7 days post-seeding (dps) and differentiated enterocyte-like cells at 21 dps, upon challenge in vitro with the inflammation-mimicking stimulus of phorbol-12-myristate-13-acetate (PMA). In addition, specific responses were found in the presence of the natural dipeptide carnosine detecting its potential counteraction against PMA-induced cytoskeletal alterations and remodeling in differentiated Caco-2 monolayers. In such an experimental context, by both immunocytochemistry and Western blot assays in Caco-2 monolayers, we identified the expression of the allograft inflammatory factor 1 (AIF-1) as protein functionally related to both inflammatory and cytoskeletal pathways. In 21 dps monolayers, particularly, we detected variations of its intracellular localization associated with the inflammatory stimulus and its mRNA/protein increase associated with the differentiated 21 dps enterocyte-like monolayer compared to the undifferentiated cells.

Activation of PKCβII by PMA facilitates enhanced epithelial wound repair through increased cell spreading and migration

Rapid repair of epithelial wounds is essential for intestinal homeostasis, and involves cell proliferation and migration, which in turn are mediated by multiple cellular signaling events including PKC activation. PKC isoforms have been implicated in regulating cell proliferation and migration, however, the role of PKCs in intestinal epithelial cell (IEC) wound healing is still not completely understood. In the current work we used phorbol 12-myristate 13-acetate (PMA), a well recognized agonist of classical and non-conventional PKC subfamilies to investigate the effect of PKC activation on IEC wound healing. We found that PMA treatment of wounded IEC monolayers resulted in 5.8±0.7-fold increase in wound closure after 24 hours. The PMA effect was specifically mediated by PKCβII, as its inhibition significantly diminished the PMA-induced increase in wound closure. Furthermore, we show that the PKCβII-mediated increase in IEC wound closure after PMA stimulation was mediated by increased cell spreading/cell migration but not proliferation. Cell migration was mediated by PKCβII dependent actin cytoskeleton reorganization, enhanced formation of lamellipodial extrusions at the leading edge and increased activation of the focal adhesion protein, paxillin. These findings support a role for PKCβII in IEC wound repair and further demonstrate the ability of epithelial cells to migrate as a sheet thereby efficiently covering denuded surfaces to recover the intestinal epithelial barrier.

Activation of M3 muscarinic receptor and Ca²⁺ influx by crude fraction from Crotonis Fructus in isolated rabbit jejunum

ETHNOPHARMACOLOGICAL RELEVANCE

Crotonis Fructus is the mature fruit of Croton tiglium L. (Euphorbiaceae), which has been used in traditional Chinese medicine for the treatment of gastrointestinal (GI) diseases, such as constipation, abdominal pain, peptic ulcer, and intestinal inflammation for thousands of years. The aim of this study was to investigate the pharmacological effect of extracts and fractions from Crotonis Fructus on GI tract.

MATERIALS AND METHODS

The activities of methanol extract and fractions from Crotonis Fructus on the smooth muscle contractions were evaluated using isolated rabbit jejunum model.

RESULTS

The results suggest that the n-BuOH and H(2)O fractions showed spasmolytic activity, while the MeOH extract, PE and EtOAc fractions exerted spasmogenic effect. Moreover, bioassay-guided fractionation verified that the EtOAc fraction was more potent than others, followed by PE fraction and methanol extract. Additionally, atropine (10μM), 4-DAMP (10μM) and verapamil (0.1μM) produced a significant inhibition of contractions caused by EtOAc fraction, while either hexamethonium (10μM) or methoctramine (10μM) was inactive. Additionally, a HPLC fingerprint of EtOAc fraction was appraised to ensure its chemical consistency and the main component has been identified as phorbol 12-acetate-13-tiglate.

CONCLUSIONS

These data indicate that the regulatory effect of EtOAc fraction on GI motility are medicated via the activation of M3 muscarinic receptor and Ca(2+) influx through L-type Ca(2+) channel. These provide a scientific basis for the traditional use of Crotonis Fructus in GI disorders.

M3 muscarinic receptor- and Ca2+ influx-mediated muscle contractions induced by croton oil in isolated rabbit jejunum

AIM OF STUDY

Croton oil is the fruit oil of Croton tiglium L., which is well known in folk medicine for the treatment of gastrointestinal (GI) diseases, including constipation, abdominal pain, peptic ulcer, and intestinal inflammation for a long period. This study was to investigate the pharmacological effect of croton oil on GI tract.

MATERIALS AND METHODS

The effect of croton oil on the smooth muscle contractions was investigated in vitro using the isolated rabbit jejunum model.

RESULTS

Croton oil has a biphasic action contracting and relaxing intestinal tissue. At the concentrations of 20-80 microg/mL, croton oil produced a concentration-dependent increase in the amplitude and tension of muscle contractions, whereas at high concentrations (>200 microg/mL) it decreased the contractile amplitude and had no impact on the tension. Moreover, croton oil was less effective in increasing muscle amplitude and tension than Ach, confirming that the effect of croton oil on muscle contractions is not a simply stimulatory or inhibitory action, but a unique modulatory process depending on the concentration of croton oil. In addition, croton oil concentration-dependently suppressed the frequency of muscle contractions. On the other hand, atropine (10 microM) and 4-DAMP (10 microM) produced a significant inhibition of contractions caused by croton oil, while either hexamethonium (10 microM) or methoctramine (10 microM) was inactive, implying that the regulatory effects of croton oil on GI motility are mediated via the activation of M3 muscarinic receptor. Furthermore, muscle contractions induced by croton oil were dramatically reduced by verapamil (0.1 microM) but not by NE (1 microM), suggesting that the action of croton oil on GI motility is also mediated by Ca(2+) influx through L-type Ca(2+) channel.

CONCLUSIONS

The results suggest that croton oil possesses spasmogenic and spasmolytic properties and the regulatory effects of croton oil on GI motility are mediated via the activation of M3 muscarinic receptor and Ca(2+) influx through L-type Ca(2+) channel.

Rottlerin induces calcium influx and protein degradation in cultured lenses independent of effects on protein kinase C delta

Rottlerin has been widely accepted as a specific inhibitor of protein kinase C delta (PKC delta); however, recent data suggest that the specificity of this compound become a question. Herein, we address this issue using a lens organ culture system, as PKC delta might regulate the gap junction permeability in lens. Interestingly, we found that rottlerin induced the degradation of connexin50 more rapidly than that of PKC delta. Furthermore, comparison of rottlerin with a protonophore, carbonylcyanide-4-(trifluoromethoxy)-phenylhydrazone (FCCP) that shares many characteristics with rottlerin, showed that both rottlerin and FCCP dramatically increased lens weight over time. This increase in lens weight was partially reversed by depletion of extracellular calcium with ethyleneglycoltetraacetic acid (EGTA) or by blocking L-type calcium channels with verapamil, suggesting rottlerin may induce calcium influx. Indeed, the rapid degradation of connexin50 (but not PKC delta) induced by rottlerin and FCCP was blocked by EGTA. In addition, rottlerin and FCCP also induced degradation of connexin46, filensin, vimentin and CP49. In order to determine whether this protein degradation is associated with the decrease of ATP due to uncoupling mitochondria by rottlerin, ATP content in lenses with different treatments were examined. The result indicated that EGTA had no effect on lens ATP content. Taken together, these data suggest that rottlerin, like FCCP, induces calcium influx, leading to protein degradation and cleavage in the lens, and that this effect is unrelated to the inhibition of PKC delta. Thus, extreme caution must be taken when considering use of rottlerin as a PKC delta inhibitor.

Role of protein kinase C-delta in the age-dependent secretagogue action of bile acids in mammalian colon

The role of specific PKC isoforms in the regulation of epithelial Cl(-) secretion by Ca(2+)-dependent secretagogues remains controversial. In the developing rabbit distal colon, the bile acid taurodeoxycholate (TDC) acts via intracellular calcium to stimulate Cl(-) transport in adult, but not in young, animals, whereas the PKC activator phorbol dibutyrate (PDB) stimulates Cl(-) transport at all ages. We tested the hypothesis that specific PKC isoforms account for the age-specific effects of TDC. The effects of conventional (cPKC) and novel (nPKC) PKC-specific inhibitors on TDC- and PDB-stimulated Cl(-) transport in adult and weanling colonocytes were assessed by using 6-methoxy-quinolyl acetoethyl ester. In adult colonocytes, the cPKC inhibitor Gö-6976 inhibited PDB action but not TDC action, whereas the cPKC and nPKC inhibitor Gö-6850 blocked both TDC and PDB actions. Additionally, rottlerin and the PKC-delta-specific inhibitor peptide (deltaV1-1) inhibited TDC- and PDB-stimulated Cl(-) transport in adult colonocytes. Rottlerin also decreased TDC-stimulated short-circuit current in intact colonic epithelia. Only Gö-6976, but neither rottlerin nor deltaV1-1, inhibited PDB-stimulated transport in weanling colonocytes. Colonic lysates express PKC-alpha, -lambda, and -iota protein equally at all ages, but they do not express PKC-gamma or -theta at any age. Expression of PKC-beta and PKC-epsilon protein was newborn>adult>weanling, whereas PKC-delta was expressed in adult but not in weanling or newborn colonocytes. TDC (1.6-fold) and PDB (2.0-fold) stimulated PKC-delta enzymatic activity in adult colonocytes but failed to do so in weanling colonocytes. PKC-delta mRNA expression showed age dependence. Thus PKC-delta appears critical for the action of TDC in the adult colon, and its low expression in young animals may account for their inability to secrete in response to bile acids.

Rottlerin inhibits human T cell responses

Rottlerin is a pharmacological inhibitor of protein kinase C (PKC) theta, a novel PKC selectively expressed in T lymphocytes. PKC theta is known to regulate T cell receptor (TCR)/CD28 signalling pathways in T lymphocytes, but the impact of PKC theta inhibition on human T cell responses remains undefined. In this work, we describe the effects of rottlerin on the responses of CD4+ and CD8+ human T lymphocytes upon polyclonal activation. We observed a dose-dependent inhibition of CD4+ and CD8+ T cell proliferation in response to anti-CD3/anti-CD28 antibodies stimulation in the presence of rottlerin. This inhibition was associated with impaired CD25 expression and decreased interleukin (IL)-2 production in activated T cells. In contrast, rottlerin did not alter IL-2-induced T cell proliferation. Furthermore, we demonstrated that rottlerin blocked interferon (IFN) gamma, IL-10 and IL-13 mRNA expression in TCR/CD28 activated CD4+ T cells. These findings place rottlerin as a potent immunosuppressive agent for the development of novel therapies in T cell mediated immune disorders.

Does transformation of microvascular endothelial cells into myofibroblasts play a key role in the etiology and pathology of fibrotic disease?

Fibrosis is a major cause of human death and disability. It has been hypothesized widely that activation of resident tissue fibroblasts is responsible for the increase in matrix protein synthesis present in fibrotic tissue. More recent studies in vitro of the physiology of human dermal microvascular endothelial cells and their transformation into spindle-shaped cells by proinflammatory cytokines may provide a new explanation for the increase in myofibroblasts in fibrotic diseases. In cell culture human dermal microvascular endothelial cells transform reversibly into 2 distinct cell phenotypes observed in the endothelium in vivo: an epithelioid phenotype present in a homeostatic microvasculature and a more spindle-shaped phenotype present in an inflammed and a reactive microvasculature. When epithelioid endothelial cell cultures are exposed to proinflammatory cytokines typically increased in fibrosis in vivo (e.g. TNF-alpha and IL-beta) for sustained periods, epithelioid dermal microvascular endothelial cells transform into a spindle-shaped morphology. Many of the transformed cells are identified as myofibroblast-like cells by electron microscopy (cytoplasmic microfilaments with attachment plaques), matrix protein synthesis (type I collagen, alpha smooth muscle actin, calponin) and by RT-PCR analysis of matrix protein mRNA. Following injury to an endothelial cell culture a similar (but reversible) transformation into myofibroblast-like cells also is induced. Drugs known to slow the clinical progression to fibrosis in vivo (e.g. phosphodiesterase inhibitors, antibodies to inflammatory cytokines) are the the same drug types capable of inhibiting endothelial cell tranformation in vitro. The in vivo and in vitro observations made on blood vessel physiology and pathology following sustained inflammation support a hypothesis that endothelial cell transformation into myofibroblast-like cells may begin to explain the increase in matrix proteins and myofibroblasts pathognomonic of fibrotic disease. The experimental and clinical evidence leading to and supporting this hypothesis is presented and discussed in this report.

EGF stimulates proliferation of mouse embryonic stem cells: involvement of Ca2+influx and p44/42 MAPKs

We examined the effect of EGF on the proliferation of mouse embryonic stem (ES) cells and their related signal pathways. EGF increased [3H]thymidine and 5-bromo-2′-deoxyuridine incorporation in a time- and dose-dependent manner. EGF stimulated the phosphorylation of EGF receptor (EGFR). Inhibition of EGFR tyrosine kinase with AG-1478 or herbimycin A, inhibition of PLC with neomycin or U-73122, inhibition of PKC with bisindolylmaleimide I or staurosporine, and inhibition of L-type Ca2+channels with nifedipine or methoxyverapamil prevented EGF-induced [3H]thymidine incorporation. PKC-α, -βI, -γ, -δ, and -ζ were translocated to the membrane and intracellular Ca2+concentration ([Ca2+]i) was increased in response to EGF. Moreover, inhibition of EGFR tyrosine kinase, PLC, and PKC completely prevented EGF-induced increases in [Ca2+]i. EGF also increased inositol phosphate levels, which were blocked by EGFR tyrosine kinase inhibitors. Furthermore, EGF rapidly increased formation of H2O2, and pretreatment with antioxidant ( N-acetyl-l-cysteine) inhibited EGF-induced increase of [Ca2+]i. In addition, we observed that p44/42 MAPK phosphorylation by EGF and inhibition of EGFR tyrosine kinase, PLC, PKC, or Ca2+channels blocked EGF-induced phosphorylation of p44/42 MAPKs. Inhibition of p44/42 MAPKs with PD-98059 (MEK inhibitor) attenuated EGF-induced increase of [3H]thymidine incorporation. Finally, inhibition of EGFR tyrosine kinase, PKC, Ca2+channels, or p44/42 MAPKs attenuated EGF-stimulated cyclin D1, cyclin E, cyclin-dependent kinase (CDK)2, and CDK4, respectively. In conclusion, EGF partially stimulates proliferation of mouse ES cells via PLC/PKC, Ca2+influx, and p44/42 MAPK signal pathways through EGFR tyrosine kinase phosphorylation.