ABCC4 impacts megakaryopoiesis and protects megakaryocytes against 6-mercaptopurine induced cytotoxicity

The role of ABCC4, an ATP-binding cassette transporter, in the process of platelet formation, megakaryopoiesis, is unknown. Here, we show that ABCC4 is highly expressed in megakaryocytes (MKs). Mining of public genomic data (ATAC-seq and genome wide chromatin interactions, Hi-C) revealed that key megakaryopoiesis transcription factors (TFs) interacted with ABCC4 regulatory elements and likely accounted for high ABCC4 expression in MKs. Importantly these genomic interactions for ABCC4 ranked higher than for genes with known roles in megakaryopoiesis suggesting a role for ABCC4 in megakaryopoiesis. We then demonstrate that ABCC4 is required for optimal platelet formation as in vitro differentiation of fetal liver derived MKs from Abcc4-/- mice exhibited impaired proplatelet formation and polyploidization, features required for optimal megakaryopoiesis. Likewise, a human megakaryoblastic cell line, MEG-01 showed that acute ABCC4 inhibition markedly suppressed key processes in megakaryopoiesis and that these effects were related to reduced cAMP export and enhanced dissociation of a negative regulator of megakaryopoiesis, protein kinase A (PKA) from ABCC4. PKA activity concomitantly increased after ABCC4 inhibition which was coupled with significantly reduced GATA-1 expression, a TF needed for optimal megakaryopoiesis. Further, ABCC4 protected MKs from 6-mercaptopurine (6-MP) as Abcc4-/- mice show a profound reduction in MKs after 6-MP treatment. In total, our studies show that ABCC4 not only protects the MKs but is also required for maximal platelet production from MKs, suggesting modulation of ABCC4 function might be a potential therapeutic strategy to regulate platelet production.

A fluorogenic complementation tool kit for interrogating lipid droplet-organelle interaction

Contact sites between lipid droplets and other organelles are essential for cellular lipid and energy homeostasis. Detection of these contact sites at nanometer scale over time in living cells is challenging. Here, we developed a tool kit for detecting contact sites based on Fluorogen-Activated Bimolecular complementation at CONtact sites, FABCON, using a reversible, low affinity split fluorescent protein, splitFAST. FABCON labels contact sites with minimal perturbation to organelle interaction. Via FABCON, we quantitatively demonstrated that endoplasmic reticulum (ER)- and mitochondria (mito)-lipid droplet contact sites are dynamic foci in distinct metabolic conditions, such as during lipid droplet biogenesis and consumption. An automated analysis pipeline further classified individual contact sites into distinct subgroups based on size, likely reflecting differential regulation and function. Moreover, FABCON is generalizable to visualize a repertoire of organelle contact sites including ER-mito. Altogether, FABCON reveals insights into the dynamic regulation of lipid droplet-organelle contact sites and generates new hypotheses for further mechanistical interrogation during metabolic switch.

Reticulons promote formation of ER-derived double-membrane vesicles that facilitate SARS-CoV-2 replication

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the etiologic agent for the global COVID-19 pandemic, triggers the formation of endoplasmic reticulum (ER)-derived replication organelles, including double-membrane vesicles (DMVs), in the host cell to support viral replication. Here, we clarify how SARS-CoV-2 hijacks host factors to construct the DMVs. We show that the ER morphogenic proteins reticulon-3 (RTN3) and RTN4 help drive DMV formation, enabling viral replication, which leads to productive infection. Different SARS-CoV-2 variants, including the delta variant, use the RTN-dependent pathway to promote infection. Mechanistically, our results reveal that the membrane-embedded reticulon homology domain (RHD) of the RTNs is sufficient to functionally support viral replication and physically engage NSP3 and NSP4, two viral non-structural membrane proteins known to induce DMV formation. Our findings thus identify the ER morphogenic RTN3 and RTN4 membrane proteins as host factors that help promote the biogenesis of SARS-CoV-2-induced DMVs, which can act as viral replication platforms.

GCAF(TMEM251) regulates lysosome biogenesis by activating the mannose-6-phosphate pathway

The mannose-6-phosphate (M6P) biosynthetic pathway for lysosome biogenesis has been studied for decades and is considered a well-understood topic. However, whether this pathway is regulated remains an open question. In a genome-wide CRISPR/Cas9 knockout screen, we discover TMEM251 as the first regulator of the M6P modification. Deleting TMEM251 causes mistargeting of most lysosomal enzymes due to their loss of M6P modification and accumulation of numerous undigested materials. We further demonstrate that TMEM251 localizes to the Golgi and is required for the cleavage and activity of GNPT, the enzyme that catalyzes M6P modification. In zebrafish, TMEM251 deletion leads to severe developmental defects including heart edema and skeletal dysplasia, which phenocopies Mucolipidosis Type II. Our discovery provides a mechanism for the newly discovered human disease caused by TMEM251 mutations. We name TMEM251 as GNPTAB cleavage and activity factor (GCAF) and its related disease as Mucolipidosis Type V.

Lunapark-dependent formation of a virus-induced ER exit site contains multi-tubular ER junctions that promote viral ER-to-cytosol escape

Viruses rearrange host membranes to support different entry steps. Polyomavirus simian virus 40 (SV40) reorganizes the endoplasmic reticulum (ER) membrane to generate focus structures that enable virus ER-to-cytosol escape, a decisive infection step. The molecular architecture of the ER exit site that might illuminate why it is ideally suited for membrane penetration is unknown. Here 3D focused ion beam scanning electron microscopy (FIB-SEM) reconstruction reveals that the ER focus structure consists of multi-tubular ER junctions where SV40 preferentially localizes, suggesting that tubular branch points are virus ER-to-cytosol penetration sites. Functional analysis demonstrates that lunapark-an ER membrane protein that typically stabilizes three-way ER junctions-relocates to the ER foci, where it supports focus formation, leading to SV40 ER escape and infection. Our results reveal how a virus repurposes the activity of an ER membrane protein to form a virus-induced ER substructure required for membrane escape and suggest that ER tubular junctions are vulnerable sites exploited by viruses for membrane penetration.

MMP inhibitors attenuate doxorubicin cardiotoxicity by preventing intracellular and extracellular matrix remodelling

AIMS

Heart failure is a major complication in cancer treatment due to the cardiotoxic effects of anticancer drugs, especially from the anthracyclines such as doxorubicin (DXR). DXR enhances oxidative stress and stimulates matrix metalloproteinase-2 (MMP-2) in cardiomyocytes. We investigated whether MMP inhibitors protect against DXR cardiotoxicity given the role of MMP-2 in proteolyzing sarcomeric proteins in the heart and remodelling the extracellular matrix.

METHODS AND RESULTS

Eight-week-old male C57BL/6J mice were treated with DXR weekly with or without MMP inhibitors doxycycline or ONO-4817 by daily oral gavage for 4 weeks. Echocardiography was used to determine cardiac function and left ventricular remodelling before and after treatment. MMP inhibitors ameliorated DXR-induced systolic and diastolic dysfunction by reducing the loss in left ventricular ejection fraction, fractional shortening, and E'/A'. MMP inhibitors attenuated adverse left ventricular remodelling, reduced cardiomyocyte dropout, and prevented myocardial fibrosis. DXR increased myocardial MMP-2 activity in part also by upregulating N-terminal truncated MMP-2. Immunogold transmission electron microscopy showed that DXR elevated MMP-2 levels within the sarcomere and mitochondria which were associated with myofilament lysis, mitochondrial degeneration, and T-tubule distention. DXR-induced myofilament lysis was associated with increased titin proteolysis in the heart which was prevented by ONO-4817. DXR also increased the level and activity of MMP-2 in human embryonic stem cell-derived cardiomyocytes, which was reduced by ONO-4817.

CONCLUSIONS

MMP-2 activation is an early event in DXR cardiotoxicity and contributes to myofilament lysis by proteolyzing cardiac titin. Two orally available MMP inhibitors ameliorated DXR cardiotoxicity by attenuating intracellular and extracellular matrix remodelling, suggesting their use may be a potential prophylactic strategy to prevent heart injury during chemotherapy.

Junctophilin-2 is a target of matrix metalloproteinase-2 in myocardial ischemia-reperfusion injury

Junctophilin-2 is a structural membrane protein that tethers T-tubules to the sarcoplasmic reticulum to allow for coordinated calcium-induced calcium release in cardiomyocytes. Defective excitation-contraction coupling in myocardial ischemia-reperfusion (IR) injury is associated with junctophilin-2 proteolysis. However, it remains unclear whether preventing junctophilin-2 proteolysis improves the recovery of cardiac contractile dysfunction in IR injury. Matrix metalloproteinase-2 (MMP-2) is a zinc and calcium-dependent protease that is activated by oxidative stress in myocardial IR injury and cleaves both intracellular and extracellular substrates. To determine whether junctophilin-2 is targeted by MMP-2, isolated rat hearts were perfused in working mode aerobically or subjected to IR injury with the selective MMP inhibitor ARP-100. IR injury impaired the recovery of cardiac contractile function which was associated with increased degradation of junctophilin-2 and damaged cardiac dyads. In IR hearts, ARP-100 improved the recovery of cardiac contractile function, attenuated junctophilin-2 proteolysis, and prevented ultrastructural damage to the dyad. MMP-2 was co-localized with junctophilin-2 in aerobic and IR hearts by immunoprecipitation and immunohistochemistry. In situ zymography showed that MMP activity was localized to the Z-disc and sarcomere in aerobic hearts and accumulated at sites where the striated JPH-2 staining was disrupted in IR hearts. In vitro proteolysis assays determined that junctophilin-2 is susceptible to proteolysis by MMP-2 and in silico analysis predicted multiple MMP-2 cleavage sites between the membrane occupation and recognition nexus repeats and within the divergent region of junctophilin-2. Degradation of junctophilin-2 by MMP-2 is an early consequence of myocardial IR injury which may initiate a cascade of sequelae leading to impaired contractile function.

Crystals and Fatty Acid Abnormalities Are Not Present in Circulating Cells From Choroideremia Patients

Purpose

To confirm whether choroideremia (CHM) is a systemic disease characterized by blood lipid abnormalities and crystals found in, or associated with, circulating peripheral blood cells of patients.

Methods

Peripheral blood samples obtained from three subjects with confirmed mutations in the CHM gene and three age-matched normal controls were processed for transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Fatty acids from plasma of nine male CHM subjects were analyzed and compared to reference values for a sample from a Canadian population.

Results

Intracellular crystals were not observed in the cells from choroideremia-affected males. No crystals were found adherent to the external plasma membrane of red blood cells. Fatty acid profiles of patients were similar to reference values, with the exception of lower levels of nervonic acid.

Conclusions

This investigation failed to observe crystals previously reported in peripheral circulating blood cells derived from CHM subjects, and showed no significant fatty acid abnormalities, not supporting the view of CHM as a systemic disease.

Establishing normal metabolism and differentiation in hepatocellular carcinoma cells by culturing in adult human serum

Tissue culture medium routinely contains fetal bovine serum (FBS). Here we show that culturing human hepatoma cells in their native, adult serum (human serum, HS) results in the restoration of key morphological and metabolic features of normal liver cells. When moved to HS, these cells show differential transcription of 22–32% of the genes, stop proliferating, and assume a hepatocyte-like morphology. Metabolic analysis shows that the Warburg-like metabolic profile, typical for FBS-cultured cells, is replaced by a diverse metabolic profile consistent with in vivo hepatocytes, including the formation of large lipid and glycogen stores, increased glycogenesis, increased beta-oxidation and ketogenesis, and decreased glycolysis. Finally, organ-specific functions are restored, including xenobiotics degradation and secretion of bile, VLDL and albumin. Thus, organ-specific functions are not necessarily lost in cell cultures, but might be merely suppressed in FBS. The effect of serum is often overseen in cell culture and we provide a detailed study in the changes that occur and provide insight in some of the serum components that may play a role in the establishment of the differentiated phenotype.

Systematic review and meta-analysis of prostatic artery embolisation for lower urinary tract symptoms related to benign prostatic hyperplasia

AIM

To evaluate the efficacy of prostatic artery embolisation (PAE) in lower urinary tract symptoms (LUTS) related to benign prostatic hyperplasia (BPH) at short- and mid-term follow-up.

MATERIALS AND METHODS

The current study included 484 BPH patients from seven eligible studies. A meta-analysis was performed to determine the mean differences in parameters associated with LUTS, including the international prostate symptom score (IPSS), peak urinary flow (Qmax), post-void residual volume (PVR), quality of life score (QoL), prostate-specific antigen level (PSA), and prostatic volume (PV), between baseline and follow-up periods.

RESULTS

Nearly all parameters at follow-up of 3-24 months were significantly improved compared to the baseline. Mean differences in IPSS at 3, 6, 12, and 24 months were -14.06 (95% confidence interval [CI]: -16.47 to -11.64), -12.32 (95% CI: -15.57 to -9.08), -16.41 (95% CI: -19.81 to -13.02), and -17 (95% CI: -17.91 to -16.09), respectively. In addition, mean differences of Qmax, PVR, PV, and QoL between the follow-up period and baseline were improved significantly; however, there were no significant differences in PSA at 24 months.

CONCLUSION

The present data shows that PAE could improve LUTS by BPH after short- and mid-term follow-up; however, more cumulative studies for long-term follow-up and comparison with other therapeutic modalities will be needed.

Inhibition of Soluble Epoxide Hydrolase Limits Mitochondrial Damage and Preserves Function Following Ischemic Injury

Aims: Myocardial ischemia can result in marked mitochondrial damage leading to cardiac dysfunction, as such identifying novel mechanisms to limit mitochondrial injury is important. This study investigated the hypothesis that inhibiting soluble epoxide hydrolase (sEH), responsible for converting epoxyeicosatrienoic acids to dihydroxyeicosatrienoic acids protects mitochondrial from injury caused by myocardial infarction.

Methods: sEH null and WT littermate mice were subjected to surgical occlusion of the left anterior descending (LAD) artery or sham operation. A parallel group of WT mice received an sEH inhibitor, trans-4-[4-(3-adamantan-1-y1-ureido)-cyclohexyloxy]-benzoic acid (tAUCB; 10 mg/L) or vehicle in the drinking water 4 days prior and 7 days post-MI. Cardiac function was assessed by echocardiography prior- and 7-days post-surgery. Heart tissues were dissected into infarct, peri-, and non-infarct regions to assess ultrastructure by electron microscopy. Complexes I, II, IV, citrate synthase, PI3K activities, and mitochondrial respiration were assessed in non-infarct regions. Isolated working hearts were used to measure the rates of glucose and palmitate oxidation.

Results: Echocardiography revealed that tAUCB treatment or sEH deficiency significantly improved systolic and diastolic function post-MI compared to controls. Reduced infarct expansion and less adverse cardiac remodeling were observed in tAUCB-treated and sEH null groups. EM data demonstrated mitochondrial ultrastructure damage occurred in infarct and peri-infarct regions but not in non-infarct regions. Inhibition of sEH resulted in significant improvements in mitochondrial respiration, ATP content, mitochondrial enzymatic activities and restored insulin sensitivity and PI3K activity.

Conclusion: Inhibition or genetic deletion of sEH protects against long-term ischemia by preserving cardiac function and maintaining mitochondrial efficiency.

Dynamic Alterations to α-Actinin Accompanying Sarcomere Disassembly and Reassembly during Cardiomyocyte Mitosis

Although mammals are thought to lose their capacity to regenerate heart muscle shortly after birth, embryonic and neonatal cardiomyocytes in mammals are hyperplastic. During proliferation these cells need to selectively disassemble their myofibrils for successful cytokinesis. The mechanism of sarcomere disassembly is, however, not understood. To study this, we performed a series of immunofluorescence studies of multiple sarcomeric proteins in proliferating neonatal rat ventricular myocytes and correlated these observations with biochemical changes at different cell cycle stages. During myocyte mitosis, α-actinin and titin were disassembled as early as prometaphase. α-actinin (representing the sarcomeric Z-disk) disassembly precedes that of titin (M-line), suggesting that titin disassembly occurs secondary to the collapse of the Z-disk. Sarcomere disassembly was concurrent with the dissolution of the nuclear envelope. Inhibitors of several intracellular proteases could not block the disassembly of α-actinin or titin. There was a dramatic increase in both cytosolic (soluble) and sarcomeric α-actinin during mitosis, and cytosolic α-actinin exhibited decreased phosphorylation compared to sarcomeric α-actinin. Inhibition of cyclin-dependent kinase 1 (CDK1) induced the quick reassembly of the sarcomere. Sarcomere dis- and re-assembly in cardiomyocyte mitosis is CDK1-dependent and features dynamic differential post-translational modifications of sarcomeric and cytosolic α-actinin.

MMP-2 is localized to the mitochondria-associated membrane of the heart

Matrix metalloproteinase-2 (MMP-2) has been extensively studied in the context of extracellular matrix remodeling but is also localized within cells and can be activated by prooxidants to proteolyze specific intercellular targets. Although there are reports of MMP-2 in mitochondria, a critical source of cellular oxidative stress, these studies did not take into account the presence within their preparations of the mitochondria-associated membrane (MAM), a subdomain of the endoplasmic reticulum (ER). We hypothesized that MMP-2 is situated in the MAM and therefore investigated its subcellular distribution between mitochondria and the MAM. Immunogold electron microscopy revealed MMP-2 localized in mitochondria of heart sections from mice. In contrast, immunofluorescence analysis of an MMP-2:HaloTag fusion protein expressed in HL-1 cardiomyocytes showed an ER-like distribution, with greater colocalization with an ER marker (protein disulfide isomerase) relative to the mitochondrial marker, MitoTracker red. Although MMP-2 protein and enzymatic activity were present in crude mitochondrial fractions, once these were separated into purified mitochondria and MAM, MMP-2 was principally associated with the latter. Thus, although mitochondria may contain minimal levels of MMP-2, the majority of MMP-2 previously identified as "mitochondrial" is in fact associated with the MAM. We also found that calreticulin, an ER- and MAM-resident Ca(2+) handling protein and chaperone, could be proteolyzed by MMP-2 in vitro. MAM-localized MMP-2 could therefore potentially impact mitochondrial function by affecting ER-mitochondrial Ca(2+) signaling via its proteolysis of calreticulin.

Matrix metalloproteinase-2 proteolysis of calponin-1 contributes to vascular hypocontractility in endotoxemic rats

OBJECTIVE

Matrix metalloproteinase (MMP)-2 is activated in aorta during endotoxemia and plays a role in the hypocontractility to vasoconstrictors. Calponin-1 is a regulator of vascular smooth muscle tone with similarities to troponin, a cardiac myocyte protein that is cleaved by MMP-2 in myocardial oxidative stress injuries. We hypothesized that calponin-1 may be proteolyzed by MMP-2 in endotoxemia-induced vascular hypocontractility.

METHODS AND RESULTS

Rats were given a nonlethal dose of bacterial lipopolysaccharide (LPS) or vehicle. Some rats were given the MMP inhibitors ONO-4817 or doxycycline. Six hours later, plasma nitrate+nitrite increased >15-fold in LPS-treated rats, an effect unchanged by doxycycline. Both ONO-4817 and doxycycline prevented LPS-induced aortic hypocontractility to phenylephrine. LPS activated MMP-2 in the aorta by S-glutathiolation. Calponin-1 levels decreased by 25% in endotoxemic aortae, which was prevented by doxycycline. Calponin-1 and MMP-2 coimmunoprecipitated and both exhibited uniform cytosolic staining in medial vascular smooth muscle cells. In vitro incubation of calponin-1 with MMP-2 led to calponin-1 degradation and appearance of its cleavage product.

CONCLUSION

Calponin-1 is a target of MMP-2, which contributes to endotoxemia-induced vascular hypocontractility.

Cyclosporine treatment improves mesenteric perfusion and attenuates necrotizing enterocolitis (NEC)-like intestinal injury in asphyxiated newborn piglets during reoxygenation

PURPOSE

Asphyxia-related intestinal injury in neonates may present similar to necrotizing enterocolitis (NEC) and is partially associated with hypoxia-reoxygenation injury. Cyclosporine has been shown to reduce myocardial cell death following ischemia-reperfusion. We hypothesize that cyclosporine treatment may attenuate NEC-like intestinal injury in asphyxiated newborn piglets during reoxygenation.

METHODS

Twenty piglets (1-4 days old) were acutely anesthetized and instrumented for continuous monitoring of systemic hemodynamics and superior mesenteric arterial (SMA) flow. After stabilization, normocapnic alveolar hypoxia (10-15% oxygen) was instituted for 2 h followed by reoxygenation with 100% oxygen for 0.5 h, then 21% for 3.5 h. The piglets were blindly block-randomized to receive cyclosporine (10 mg/kg) or placebo (normal saline) boluses at 5 min of reoxygenation (n = 8/group). A sham-operated group was included (n = 4) and received no hypoxia-reoxygenation. Intestinal samples were collected for tissue lactate and histological assessment (Park's criteria).

RESULTS

At 2 h of hypoxia, piglets had cardiogenic shock (cardiac output 45% of baseline), hypotension (mean arterial pressure 30 mmHg), acidosis (pH 7.04), and decreased superior mesenteric perfusion (all P < 0.05 vs. sham-operated group, ANOVA). Cyclosporine treatment increased SMA flow (114 ± 6 vs. 78 ± 19% of baseline of controls, respectively) with improved SMA oxygen delivery and intestinal tissue lactate (all P < 0.05). Some control piglets had NEC-like injuries including pneumatosis intestinalis, which were attenuated in cyclosporine-treated piglets (P < 0.05 vs. controls).

CONCLUSIONS

This is the first study to demonstrate that post-resuscitation administration of cyclosporine improves mesenteric perfusion and attenuates NEC-like intestinal injury in newborn piglets following asphyxia-reoxygenation.

Titin is a target of matrix metalloproteinase-2: implications in myocardial ischemia/reperfusion injury

BACKGROUND

Titin is the largest mammalian (≈3000 to 4000 kDa) and myofilament protein that acts as a molecular spring in the cardiac sarcomere and determines systolic and diastolic function. Loss of titin in ischemic hearts has been reported, but the mechanism of titin degradation is not well understood. Matrix metalloproteinase-2 (MMP-2) is localized to the cardiac sarcomere and, on activation in ischemia/reperfusion injury, proteolyzes specific myofilament proteins. Here we determine whether titin is an intracellular substrate for MMP-2 and if its degradation during ischemia/reperfusion contributes to cardiac contractile dysfunction.

METHODS AND RESULTS

Immunohistochemistry and confocal microscopy in rat and human hearts showed discrete colocalization between MMP-2 and titin in the Z-disk region of titin and that MMP-2 is localized mainly to titin near the Z disk of the cardiac sarcomere. Both purified titin and titin in skinned cardiomyocytes were proteolyzed when incubated with MMP-2 in a concentration-dependent manner, and this was prevented by MMP inhibitors. Isolated rat hearts subjected to ischemia/reperfusion injury showed cleavage of titin in ventricular extracts by gel electrophoresis, which was confirmed by reduced titin immunostaining in tissue sections. Inhibition of MMP activity with ONO-4817 prevented ischemia/reperfusion-induced titin degradation and improved the recovery of myocardial contractile function. Titin degradation was also reduced in hearts from MMP-2 knockout mice subjected to ischemia/reperfusion in vivo compared with wild-type controls.

CONCLUSION

MMP-2 localizes to titin at the Z-disk region of the cardiac sarcomere and contributes to titin degradation in myocardial ischemia/reperfusion injury.

Caveolin-1 exists and may function in cardiomyocytes

Whether ventricular cardiac myocytes of mouse contain caveolin-1 is disputed. It has been claimed to be exclusively in nearby endothelial cell profiles. Recently, matrix metalloproteinase-2 (MMP-2) was reported to be present in mouse ventricular cardiac myocytes, colocalized with caveolin-1, and caveolin-1 knockout was found to cause the loss of MMP-2 from mouse ventricular cardiac myocytes and affect their functioning. To resolve this dispute, we labeled cardiac myocytes with caveolin-1 and endothelial cells with caveolin-2. Caveolin-2 is agreed to be present exclusively in endothelial cells. The results showed that mouse ventricular myocytes were labeled with caveolin-1 antibodies independently of any caveolin-2 labeling, and endothelial cells were labeled with both caveolin-1 and caveolin-2 antibodies. This confirms that caveolin-1 is present in mouse ventricular cardiac myocytes as well as endothelial cells. Previous evidence confirms that loss of caveolin-1 affects the function of mouse ventricular cardiac myocytes and suggests that MMP-2 may be involved.

Inhibition of matrix metalloproteinase activity in vivo protects against vascular hyporeactivity in endotoxemia

Persistent arterial hypotension is a hallmark of sepsis and is believed to be caused, at least in part, by excess nitric oxide (NO). NO can combine with superoxide to produce peroxynitrite, which activates matrix metalloproteinases (MMPs). Whether MMP inhibition in vivo protects against vascular hyporeactivity induced by endotoxemia is unknown. Male Sprague-Dawley rats were administered either bacterial lipopolysaccharide (LPS, 4 mg/kg ip) or vehicle (pyrogen-free water). Later (30 min), animals received the MMP inhibitor doxycycline (4 mg/kg ip) or vehicle (pyrogen-free water). After LPS injection (6 h), animals were killed, and aortas were excised. Aortic rings were mounted in organ baths, and contractile responses to phenylephrine or KCl were measured. Aortas and plasma were examined for MMP activity by gelatin zymography. Aortic MMP and inducible nitric oxide synthase (iNOS) were examined by immunoblot and/or immunohistochemistry. Doxycycline prevented the LPS-induced development of ex vivo vascular hyporeactivity to phenylephrine and KCl. iNOS protein was significantly upregulated in aortic homogenates from endotoxemic rats; doxycycline did not alter its level. MMP-9 activity was undetectable in aortic homogenates from LPS-treated rats but significantly upregulated in the plasma; this was attenuated by doxycycline. Plasma MMP-2 activities were unchanged by LPS. Specific MMP-2 activity was increased in aortas from LPS-treated rats. This study demonstrates the in vivo protective effect of the MMP inhibitor doxycycline against the development of vascular hyporeactivity in endotoxemic rats.

Extraction of membrane cholesterol disrupts caveolae and impairs serotonergic (5-HT2A) and histaminergic (H1) responses in bovine airway smooth muscle: role of Rho-kinase

Some receptors and signaling molecules, such as Rho-kinase (ROCK), localize in caveolae. We asked whether the function of histamine receptors (H1) and 5-hydroxytryptamine (serotonin) receptors (5-HT2A) in bovine tracheal smooth muscle are modified after caveolae disruption and if so, whether the altered ROCK activity plays a role in this modification. Methyl-β-cyclodextrin (MβCD), used to deplete membrane cholesterol, was shown to disrupt caveolae and diminish sustained contractions to histamine (∼80%), 5-HT (100%), α-methyl-5-HT (100%), and KCl (∼30%). Cholesterol-loaded MβCD (CL-MβCD) restored the responses to KCl and partially restored the responses to agonists. ROCK inhibition by Y-27632 diminished contractions to histamine (∼85%) and 5-HT (∼59%). 5-HT or histamine stimulation augmented ROCK activity. These increases were reduced by MβCD and partially reestablished by CL-MβCD. The increase in intracellular Ca2+ that was induced by both agonists was reduced by MβCD. The presence of caveolin-1 (Cav-1), H1, 5-HT2A, and ROCK1 was corroborated by immunoblotting of membrane fractions from sucrose gradients and by confocal microscopy. H1 receptors coimmunoprecipitated with Cav-1 in caveolar and noncaveolar membrane fractions, whereas 5-HT2A receptors appeared to be restricted to noncaveolar membrane fractions. We conclude that caveolar and cholesterol integrity are indispensable for the proper functionality of the H1 and 5-HT2A receptors through their Rho/ROCK signaling.

Irradiation-induced shrinkage and expansion mechanisms of SiO2 circle membrane nanopores

20 nm diameter SiO(2) nanopore arrays on gradient-thickness membranes were formed by a focused electron beam with in situ transmission electron microscopy (TEM). Nanopore shrinkage was seen in nanopores on thicker membranes, with the rate of diameter change remaining constant during the shrinkage process. In contrast, pore expansion was observed in thinner membranes, with the expansion rate being constant at the initial stage but with a slight increase at the later stage. The geometry model of shrinkage and expansion of the nanopores in relation to the electron irradiation time was investigated by utilizing the TEM tilting method.

The role of caveolae and caveolin 1 in calcium handling in pacing and contraction of mouse intestine

In mouse intestine, caveolae and caveolin-1 (Cav-1) are present in smooth muscle (responsible for executing contractions) and in interstitial cells of Cajal (ICC; responsible for pacing contractions). We found that a number of calcium handling/dependent molecules are associated with caveolae, including L-type Ca(2+) channels, Na(+)-Ca(2+) exchanger type 1 (NCX1), plasma membrane Ca(2+) pumps and neural nitric oxide synthase (nNOS), and that caveolae are close to the peripheral endo-sarcoplasmic reticulum (ER-SR). Also we found that this assemblage may account for recycling of calcium from caveolar domains to SR through L-type Ca (+) channels to sustain pacing and contractions. Here we test this hypothesis further comparing pacing and contractions under various conditions in longitudinal muscle of Cav-1 knockout mice (lacking caveolae) and in their genetic controls. We used a procedure in which pacing frequencies (indicative of functioning of ICC) and contraction amplitudes (indicative of functioning of smooth muscle) were studied in calcium-free media with 100 mM ethylene glycol tetra-acetic acid (EGTA). The absence of caveolae in ICC inhibited the ability of ICC to maintain frequencies of contraction in the calcium-free medium by reducing recycling of calcium from caveolar plasma membrane to SR when the calcium stores were initially full. This recycling to ICC involved primarily L-type Ca(2+) channels; i.e. pacing frequencies were enhanced by opening and inhibited by closing these channels. However, when these stores were depleted by block of the sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) pump or calcium release was activated by carbachol, the absence of Cav-1 or caveolae had little or no effect. The absence of caveolae had little impact on contraction amplitudes, indicative of recycling of calcium to SR in smooth muscle. However, the absence of caveolae slowed the rate of loss of calcium from SR under some conditions in both ICC and smooth muscle, which may reflect the loss of proximity to store operated Ca channels. We found evidence that these channels were associated with Cav-1. These changes were all consistent with the hypothesis that a reduction of the extracellular calcium associated with caveolae in ICC of the myenteric plexus, the state of L-type Ca(2+) channels or an increase in the distance between caveolae and SR affected calcium handling.

EM 3D contour maps provide protein assembly at the nanoscale within the neuronal porosome complex

The neuronal porosome complex, the secretory machinery at the plasma membrane of nerve terminals, is a 12-17-nm cup-shaped lipoprotein structure possessing a central plug. Since the porosome is a membrane associated, multi-protein complex measuring >650 kD, it has precluded generation of 3D crystals for x-ray diffraction studies, nor structural analysis at the atomic level using solution magnetic resonance spectroscopy. These limitations were partially overcome in the current studies, furthering our understanding of the porosome structure. Using atomic force microscopy, electron microscopy and electron density and 3D contour mapping, finally provides at the nanoscale, the structure and assembly of proteins within the neuronal porosome complex. Results from this study demonstrate a set of eight protein units lining the porosome cup, each connected via spoke-like elements to a central plug region within the structure. The isolation of intact porosomes for near-atomic resolution using cryo-electron diffraction measurements, is finally possible.

Calcium extrusion by plasma membrane calcium pump is impaired in caveolin-1 knockout mouse small intestine

Plasma membrane calcium ATPase (PMCA) is an important calcium extrusion mechanism in smooth muscle cells. PMCA4 is the predominant isoform operating in conditions of high intracellular calcium during contraction. PMCA appears to be localized in lipid rafts and caveolae. In this study we examined the effects of the PMCA4-selective inhibitor caloxin 1c2 (5 microM) in intestine of caveolin-1 knockout mice and in bovine tracheal smooth muscle after caveolae disruption on PMCA4 function. Small intestinal tissues from control mice treated with caloxin 1c2 showed a higher contractile response of the longitudinal smooth muscle to Carbachol (10 microM) when compared to control tissues treated with a similar concentration of a control peptide. This effect of caloxin 1c2 was not found in tissues from caveolin-1 knockout mice. Immunohistochemistry and Western blotting of membrane fractions showed that PMCA was co-localized with caveolin-1 in smooth muscle plasma membrane in control tissues. One of the PMCA4 splice variant bands was missing in the lipid raft-enriched fraction prepared from caveolin-1 knockout tissue. In bovine tracheal smooth muscle tissue, caveolae disruption by cholesterol depletion led to the diminution of caveolin-1 and PMCA4b immunoreactivities, previously co-localized in the smooth muscle plasma membrane, and to the loss of the increase in Carbachol-induced contraction by caloxin 1c2. Our results suggest that the calcium removal function of PMCA4 in smooth muscle cells is dependent on its presence in intact caveolae. We suggest that this is due to the close spatial arrangement that allows calcium extrusion from a privileged cytosolic space between caveolae and sarcoplasmic reticulum.

Smooth muscle NOS, colocalized with caveolin-1, modulates contraction in mouse small intestine

Neuronal nitric oxide synthase (nNOS) in myenteric neurons is activated during peristalsis to produce nitric oxide which relaxes intestinal smooth muscle. A putative nNOS is also found in the membrane of intestinal smooth muscle cells in mouse and dog. In this study we studied the possible functions of this nNOS expressed in mouse small intestinal smooth muscle colocalized with caveolin-1(Cav-1). Cav-1 knockout mice lacked nNOS in smooth muscle and provided control tissues. 60 mM KCl was used to increase intracellular [Ca²⁺] through L-type Ca²⁺ channel opening and stimulate smooth muscle NOS activity in intestinal tissue segments. An additional contractile response to LNNA (100 μM, NOS inhibitor) was observed in KCl-contracted tissues from control mice and was almost absent in tissues from Cav-1 knockout mice. Disruption of caveolae with 40 mM methyl-β cyclodextrin in tissues from control mice led to the loss of Cav-1 and nNOS immunoreactivity from smooth muscle as shown by immunohistochemistry and a reduction in the response of these tissues to N-ω-nitro-L-arginine (LNNA). Reconstitution of membrane cholesterol using water soluble cholesterol in the depleted segments restored the immunoreactivity and the response to LNNA added after KCl. Nicardipine (1 μM) blocked the responses to KCl and LNNA confirming the role of L-type Ca²⁺ channels. ODQ (1 μM, soluble guanylate cyclase inhibitor) had the same effect as inhibition of NOS following KCl. We conclude that the activation of nNOS, localized in smooth muscle caveolae, by calcium entering through L-type calcium channels triggers nitric oxide production which modulates muscle contraction by a cGMP-dependent mechanism.

Matrix metalloproteinase-2, caveolins, focal adhesion kinase and c-Kit in cells of the mouse myocardium

Matrix metalloproteinase-2 (MMP-2) may play roles at intracellular and extracellular sites of the heart in ischaemia/reperfusion injury. Caveolins (Cav-1, -2 and -3) are lipid raft proteins which play roles in cell sig-nalling. This study examined, using immunohistochemistry and two photon confocal microscopy, if MMP-2 and caveolins co-localize at the plasma membrane of cardiac cells: cardiomyocytes (CM), fibroblasts (FB) and capillary endothelial cells (CEC) in the left ventricle (LV) of the Cav-1^+/+ and Cav-1^−/− mouse heart. In Cav-1^+/+ mouse LV MMP-2 and Cav-1 co-localized at CM plasma membranes, and at multiple locations in FB and CEC. MMP-2 co-localized with Cav-2 only at CEC. MMP-2 co-localized with Cav-3 at CM plasma membranes and Z-lines, and partially at FB and CEC. In Cav-1^−/− LV Cav-1 and MMP-2 were absent or reduced everywhere. Cav-2 appeared at CEC despite the absence of Cav-1. Cav-3 appeared at CM plasma membranes and Z-lines, FB and CEC. Also, FAK in FB and c-Kit in interstitial Cajal-like cells (ICLC) were completely absent. By transmission electron microscopy in Cav-1^+/+, regular size caveolae (Cav) were at CEC, irregular size Cav were at CM and a few were at FB. In Cav-1^−/− there were few Cav at CM and FB and some at CEC. To conclude, MMP-2 is closely associated with caveolins at FB and CEC as well as at CM. Also, MMP-2 is closely associated with FAK at FB and c-Kit at ICLC. Thus, Cav-1 expression is not necessary for Cav-2 expression. Cav-3 or Cav-3 with Cav-2 has the capability to make Cav.

Caveolin-1 inhibits matrix metalloproteinase-2 activity in the heart

Apart from its ability to degrade extracellular matrix proteins, matrix metalloproteinase-2 (MMP-2) was recently revealed to have targets and actions within the cardiac myocyte. The localization of MMP-2 in caveolae of endothelial cells suggests that caveolin-1 (Cav-1) may play a role in regulating MMP-2. The caveolin scaffolding domain (CSD) of Cav-1 regulates several proteins including those involved with signaling cascades. Whether Cav-1 is responsible for regulating MMP-2 in the heart is unknown. Hearts from Cav-1(-/-) or Cav-1(+/+) mice were isolated and heart extracts or lipid raft enriched membrane fractions were prepared. MMP-2 activity in Cav-1(-/-) hearts was markedly enhanced when compared with Cav-1(+/+) hearts with no changes in MMP-2 protein levels between groups. In contrast, MMP-2 activity and protein level were greatly reduced in lipid raft enriched fractions of Cav-1(-/-) hearts. Purified CSD inhibited MMP-2 activity in a concentration-dependent manner as assessed using an in vitro degradation assay with a fluorogenic MMP-2 substrate (OmniMMP). These data suggest that Cav-1 plays a role in regulating MMP-2 activity. Cav-1 may thus be a novel mechanism to regulate MMP-2 activity in the heart.

The effects of container materials and buffer additives on decreasing the iodide concentration in a disposal vault for spent nuclear fuel

To retard the migration of iodine released from a spent fuel after the break of a container, the reducing effects on the concentration of the iodide by container corrosion products and some buffer additives were examined in a solution with bentonite. Iron and copper, and their corrosion products scarcely reduced the iodide concentration. And kaolinite, chalcopyrite, pyrite, copper ore and galena, known as having a sorption property for iodine, did not noticeably sorb the iodide. However, palm active carbon, silver metal and Ag2O lowered the iodide concentration. Especially, Ag2O put into a disposal container would effectively hinder the migration of iodine to the outside of a disposal vault without a great loss if the pore size of the compacted buffer layer is maintained below 1 mu m.

Caveolin-1 knockout alters beta-adrenoceptors function in mouse small intestine

beta-Adrenoceptors are G protein-coupled receptors whose functions are closely associated with caveolae in the heart and cultured cell lines. In the gut, they are responsible, at least in part, for the mediation of the sympathetic stimulation that might lead to intestinal paralysis postoperatively. We examined the effect of caveolin-1 knockout on the beta-adrenoceptor response in mouse small intestine. The relaxation response to (-)-isoprenaline in carbachol-contracted small intestinal tissue segments was reduced in caveolin-1 knockout mice (cav1(-/-)) compared with their genetic controls (cav1(+/+)). Immunohistochemical staining showed that beta-adrenoceptor expression was similar in both strains in gut smooth muscle. Selective beta-adrenoceptor blockers shifted the concentration response curve (CRC) of (-)-isoprenaline to the right in cav1(+/+) intestine, but not in cav1(-/-), with greatest shift in case of the beta(3)-blocker, SR59230A. The CRC of the selective beta(3)-agonist BRL 37344 was also shifted to the right in cav1(-/-) compared with cav1(+/+). The cAMP-dependent protein kinase (PKA) inhibitor H-89 shifted the CRC of (-)-isoprenaline to the right in cav1(+/+) but not in cav1(-/-). H-89 reduced the relaxation due to forskolin and dibutyryl cAMP in cav1(+/+) but not in cav1(-/-), suggesting a reduction in PKA activity in cav1(-/-). In cav1(+/+), PKA was colocalized with caveolin-1 in the cell membrane, but PKA immunoreactivity persisted in cav1(-/-). Examination of PKA expression in the lipid raft-rich membrane fraction of the jejunum revealed reduced PKA expression in cav1(-/-) compared with cav1(+/+). The results of the present study show that the function of beta-adrenoceptors is reduced in cav1(-/-) small intestine likely owing to reduced PKA activity.

Caveolae and calcium handling, a review and a hypothesis

Caveolae are associated with molecules crucial for calcium handling. This review considers the roles of caveolae in calcium handling for smooth muscle and interstitial cells of Cajal (ICC). Structural studies showed that the plasma membrane calcium pump (PMCA), a sodium-calcium exchanger (NCX1), and a myogenic nNOS appear to be colocalized with caveolin I, the main constituent of these caveolae. Voltage dependent calcium channels (VDCC) are associated but not co-localized with caveolin 1, as are proteins of the peripheral sarcoplasmic reticulum (SR) such as calreticulin. Only the nNOS is absent from caveolin 1 knockout animals. Functional studies in calcium free media sugest that a source of calcium in tonic smooth muscles exists, partly sequestered from extracellular EGTA. This source supported sustained contractions to carbachol using VDCC and dependent on activity of the SERCA pump. This source is postulated to be caveolae, near peripheral SR. New evidence, presented here, suggests that a similar source exists in phasic smooth muscle of the intestine and its ICC. These results suggest that caveolae and peripheral SR are a functional unit recycling calcium through VDCC and controlling its local concentration. Calcium handling molecules associated with caveolae in smooth muscle and ICC were identified and their possible functions also reviewed.

Impact of caveolin-1 knockout on NANC relaxation in circular muscles of the mouse small intestine compared with longitudinal muscles

Recently, we showed that caveolin-1 (cav1) knockout mice (Cav1(-/-) mice) have impaired nitric oxide (NO) function in the longitudinal muscle (LM) layer of the small intestine. The defect was a reduced responsiveness of the muscles to NO compensated by an increase in the function of apamin-sensitive, nonadrenergic, noncholinergic (NANC) mediators. In the present study, we examined similarly the effects of cav1 knockout on the relaxation in circular muscle (CM) of the mouse small intestine. CM of Cav1(-/-) mice also showed defective NO function, but less than in LM, as well as more activation of apamin-sensitive NANC mediators. CM of Cav1(-/-) mice, like LM, lacked cav1 but retained small amounts of cav3 and caveolae in the outer CM layer. In addition, we also examined the effects of a soluble guanylate cyclase inhibitor, 1H-[1,2,4]oxadiazolo-[4,3-alpha]quinazolin-1-one (ODQ), on electric field stimulation (EFS)-mediated relaxation in both LM and CM. ODQ had an effect similar to the block of NO synthesis. Moreover, we compared the actions of two NO donors in the LM and CM of control and Cav1(-/-) mice. Similar to LM, CM of Cav1(-/-) mice showed a reduced responsiveness to the NO donors sodium nitroprusside and S-nitroso-N-acetyl penicillamine. However, both ODQ and apamin blocked the inhibitory effects of the NO donors in LM, whereas apamin had no effect in CM. In conclusion, cav1 knockout affects NO function in both LM and CM, but its effects in CM differ significantly.

Comparison of the amount of nuclides released from the spent fuel in contact with and without a compacted bentonite block

A spent LWR fuel specimen between Ca-bentonite blocks was leached in a simulated bentonite-saturated granitic water (SBGW) for 165 days and its results were compared with those of a specimen leached without a bentonite block. The amounts of Cs, Sb, Sr, Eu, Am, U and Pu released from a 4.3 mm thickness of a fuel pellet with a 50,400 MWD/MTU burn-up in the SBGW without a bentonite block were 2.2, 0.25, 0.15, 0.02, 0.01, 0.01 and approximately 5 x 10(-4)% of their inventories, respectively. However, the amounts of nuclides released from the specimen between the 1.4 Mg/m(3) bentonite blocks were decreased by three times at least. Moreover, the concentrations of the nuclides in the leachate were very low because most of them were retained in the bentonite blocks.

Colocalization between caveolin isoforms in the intestinal smooth muscle and interstitial cells of Cajal of the Cav1(+/+) and Cav1 (-/-) mouse

Confocal microscopic images were obtained from the immunohistochemical sections of jejeunum to determine the localization/colocalization between caveolin-1, caveolin-2 and caveolin-3 in intestinal smooth muscle cells (SMCs) and interstitial cells of Cajal (ICC) of Cav1(+/+) and Cav1(-/-) mouse. Intestinal regions were segmented [inner circular muscle (icm), outer circular muscle (ocm), myenteric plexus region (mp), and longitudinal muscle (lm)] by LSM 5 and analyzed by ImageJ to show Pearson's correlation (r (p)) and overlap coefficient (r) of colocalization. In the intestine of Cav1(+/+), caveolin-1 (cav1) was colocalized with caveolin-2 (cav2) and caveolin-3 (cav3). Cav2 also was well colocalized with cav3. In the intestine of Cav1(-/-), cav1 and cav2 were absent in all images, but reduced cav3 was expressed in ocm. Caveolae were present in cell types with cav1 in Cav1(+/+), and present with cav3 in ocm of Cav1(-/-). C-kit occurred in deep muscular plexus (ICC-DMP) and myenteric plexus (ICC-MP), in both Cav1(+/+) and Cav1(-/-), and colocalized with cav1 and cav2 in the intestine of Cav1(+/+). Cav3 was absent/present at low immunoreactivity in ICC-DMP and ICC-MP of the intestines of Cav1(+/+) and Cav1(-/-). To conclude, cav1 is necessary for the expression of cav2 in SMC and ICC of intestine and facilitates, but is not necessary for the expression of cav3.

Comparisons of neural and pacing activities in intestinal segments from W/W++ and W/W(V) mice

We studied pacing and neurotransmission in longitudinal (LM) and circular muscle (CM) in intestine of W/W++ and W/W(V) mice. Electrical field-stimulation (EFS) of nerves in LM segments was more inhibitory in W/W(V) mice than in W/W++ mice. No inhibitory input to CM segments of W/W(V) mice was found. The EFS, after nerve block, entrained segments of both W/W++ and mutant mice with 10 ms pulses, and entrained those of mutant mice more readily at 1 and 3 ms pulses. Pacing with external electrodes did not depend on interstitial cells of Cajal in the myenteric plexus (ICC-MP). 2-Aminoethoxydiphenyl borate (2-APB), putative antagonist at IP3 receptors, store-operated channels and the Sacro-endoplasmic reticulum Ca2+ ATPase pump, reduced frequency and amplitudes of pacing of LM segments from W/W(V) mice as it did in BALB/c mice. Thus, its actions may not require ICC-MP. SKF 96365, a putative inhibitor of store-operated channels, reduced frequencies and amplitudes of intestinal segments in W/W++ mice at 10 or 30 micromol L-1. This resulted from blocking L-Ca2+-channels. Thus, no evidence was found that store-operated channels play a role in pacing. In LM segments of W/W(V), SKF 96365 had no effects on frequency of contractions. We conclude, results from models of severely reduced systems may not be applicable to intact ICC networks.

Proteins of interstitial cells of Cajal and intestinal smooth muscle, colocalized with caveolin-1

The murine jejunum and lower esophageal sphincter (LES) were examined to determine the locations of various signaling molecules and their colocalization with caveolin-1 and one another. Caveolin-1 was present in punctate sites of the plasma membranes (PM) of all smooth muscles and diffusely in all classes of interstitial cells of Cajal (ICC; identified by c-kit immunoreactivity), ICC-myenteric plexus (MP), ICC-deep muscular plexus (DMP), ICC-serosa (ICC-S), and ICC-intramuscularis (IM). In general, all ICC also contained the L-type Ca(2+) (L-Ca(2+)) channel, the PM Ca(2+) pump, and the Na(+)/Ca(2+) exchanger-1 localized with caveolin-1. ICC in various sites also contained Ca(2+)-sequestering molecules such as calreticulin and calsequestrin. Calreticulin was present also in smooth muscle, frequently in the cytosol, whereas calsequestrin was present in skeletal muscle of the esophagus. Gap junction proteins connexin-43 and -40 were present in circular muscle of jejunum but not in longitudinal muscle or in LES. In some cases, these proteins were associated with ICC-DMP. The large-conductance Ca(2+)-activated K(+) channel was present in smooth muscle and skeletal muscle of esophagus and some ICC but was not colocalized with caveolin-1. These findings suggest that all ICC have several Ca(2+)-handling and -sequestering molecules, although the functions of only the L-Ca(2+) channel are currently known. They also suggest that gap junction proteins are located at sites where ultrastructural gap junctions are know to exist in circular muscle of intestine but not in other smooth muscles. These findings also point to the need to evaluate the function of Ca(2+) sequestration in ICC.

Hyperpolarization-activated, cyclic AMP-gated, HCN1-like cation channel: the primary, full-length HCN isoform expressed in a saccular hair-cell layer

The expression of transcript for hyperpolarization-activated, cyclic nucleotide-sensitive cation channel (HCN) isoforms underlying hyperpolarization-activated, inward current (I(h)) has been determined for a model hair-cell preparation from the saccule of the rainbow trout, Oncorhynchus mykiss. Based upon identification from homology to known vertebrate HCN cDNA sequence, cloning of PCR products amplified with degenerate primers indicated an expression frequency of 7:2:1 (HCN1:HCN2:HCN4) for the hair-cell sheet compared with 1:1:7 for brain. Full-length sequence has been obtained for the HCN1-like isoform representing the primary HCN transcript expressed in the hair-cell preparation. The channel protein is 938 amino acids in length with 93% amino acid identity for the region extending from the S1-S6 membrane spanning domains through the voltage-pore and cyclic nucleotide-binding domains, compared with HCN1 for rabbit, rat, mouse and human. The N- and C-terminal regions are less homologous, with 39-51% and 43-44% amino acid identities, respectively. Compared with other vertebrate HCN1, the hair-cell HCN1 contains additional consensus phosphorylation sites associated with unique repeats in the carboxy terminus. The HCN1-like transcript has been localized to hair cells of the saccular sensory epithelia by in situ hybridization. Previous electrophysiological studies have identified I(h) as the sole inwardly rectifying ion channel in a specific population of hair cells of the saccule of frogs [J Neurophysiol (1995) 73:1484] and fish [J Physiol (1996) 495:665]. I(h) is an important determinant of the resting membrane potential, and for this population of hair cells, is predicted to maintain the membrane potential within a voltage range allowing the voltage-gated calcium channels to open, permitting "spontaneous" release of transmitter. The molecular properties of the HCN1-like isoform underlying I(h) expressed in the saccular hair cells of the teleost, trout, may consequently impact spontaneous release of transmitter from hair cells of the saccule.

Synthesis, topoisomerase I inhibition and antitumor cytotoxicity of 2,2':6',2"-, 2,2':6',3"- and 2,2':6',4"-terpyridine derivatives

For the development of new anticancer agents, 2,2':6',2"-, 2,2':6',3"- and 2,2':6',4"-terpyridine derivatives were designed and evaluated for their topoisomerase I inhibitory activity and antitumor cytotoxicity. Structure-activity relationship studies indicated that 2,2':6',2"-terpyridine derivatives were highly cytotoxic toward several human tumor cell lines, whereas 2,2':6',3"- and 2,2':6',4"-terpyridine derivatives were potent topoisomerase I inhibitors.

Structure-activity relationship studies of isoquinolinone type anticancer agent

Substituted isoquinolin-1-ones (1) were synthesized to test their in vitro anticancer activity. 3-Biphenyl-N-methylisoquinolin-1-one (7) showed the most potent anticancer activity against five different human cancer cell lines.

Pharmacokinetics of a new antitumor 3-arylisoquinoline derivative, CWJ-a-5

1-(4-Methylpiperazinyl)-3-phenylisoquinoline hydrochloride (CWJ-a-5) is a newly developed from benzo[c]phenanthridine alkaloids and derivative and has exhibited potent antitumor activities, in vitro and in vivo. The pharmacokinetics of this novel antitumor 3-arylisoquinoline derivative was studied after intravenous (i.v.), oral (p.o.) and hepatoportal (p.v.) administration in rats. A simple high performance liquid chromatographic method was developed to determine the concentrations of CWJ-a-5 in plasma, bile and urine. Plasma concentration profiles of CWJ-a-5 were best fitted by the two-compartment model after i.v. administration and showed a linear pharmacokinetic behavior up to 20 mg/kg doses. The half-life of CWJ-a-5 in the post-distributive phase (t1/2beta), total-body plasma clearance (CLt), and volume of distribution at steady-state (Vdss) were 86.9 min, 5.72 l/h per kilogram and 9.79 l/kg, respectively, after i.v. administration of 10 mg/kg. Biliary and urinary excretion of CWJ-a-5 was < 1% after i.v. injection of 10 mg/kg. The bioavailability of CWJ-a-5 after p.o. and p.v. administration (50 and 10 mg/kg, respectively) was 52.9 and 72.2%, respectively. Gastrointestinal bioavailability was calculated to be 73.3%. The apparent partition coefficient (log P) of CWJ-a-5 between n-octanol and water was 2.64. Plasma protein binding of CWJ-a-5 measured by the ultrafiltration method was > 95%.

Involvement of SPARC in in vitro differentiation of skeletal myoblasts

SPARC (secreted protein acidic and rich in cysteine) is an extracellular Ca(2+)-binding glycoprotein associated with the morphogenesis and remodeling of various tissues. Here, involvement of SPARC in the myogenesis of skeletal myoblasts was investigated in vitro. First, the differential expression of SPARC mRNA during the myogenesis was initially identified by a differential display reverse transcription (DDRT)-PCR method. The expression of the SPARC gene was significantly up-regulated during the differentiation of C2C12 mouse myoblasts. Second, the treatment with anti-SPARC antibody almost completely prevented the differentiation of myoblasts. Third, the treatment with EGTA, a Ca(2+) chelator that is known to inhibit the fusion of C2C12 myoblasts, reversibly inhibited the up-regulation of SPARC gene expression. On the other hand, the treatment with A23187, a Ca(2+) ionophore, rapidly and dramatically increased the level of SPARC transcript. Taken together, these results suggest that SPARC may play a critical role(s) in the morphological change of myoblasts, and that the expression of SPARC gene may be controlled by Ca(2+)-dependent pathway in myogenesis.

Convenient synthesis of 2,3,9,10-tetraoxygenated protoberberine alkaloids and their 13-methyl alkaloids

New and convenient synthesis of 2,3,9,10-tetraoxygenated protoberberine alkaloids and their 13-methyl alkaloids through the same intermediates was developed. Acylation of the brominated benzylphenethylamine (13) with alpha-chloro-alpha-(methylthio)acetyl chloride, followed by cyclization with stannic chloride, furnished the key intermediates 4-methylthio-3-phenethylisoquinolin-3-ones (14), which were methylated to provide their methyl derivatives (17). Both isoquinolin-3-ones (14, 17) were easily transformed into protoberberine alkaloids (16) and their 13-methyl alkaloids (21) in good yield.

Synthesis of sesquiterpene derivatives as potential antitumor agents; elemane derivatives

Derivatives of elema-1,3-diene were synthesized in several steps as polar analogs of beta-elemene, antitumor agent under clinical phase. The lactone ring of compound 1 was opened by LiAlH4 to give diol 2 which was selectively protected by TBDPSCl. After acetylation of the secondary alcohol, the acetylated product was ozonolyzed and reduced to give elemane derivative 4 which was converted to diolefin 8 via selenides subsequent deprotection by tetrabutylammonium fluoride gave two compounds 9, 10.

A novel synthesis of benzo[c]phenanthridine skeleton and biological evaluation of isoquinoline derivatives

Benzo[c]phenanthridine skeleton was synthesized from easily available starting N-methyl-o-toluamide 2 and o-methylbenzonitrile 5 in 7 steps. Radical cyclization of styrene 10 afforded 6,11-dimethyl-6,11-dihydro-5H-indeno[1,2-c]isoquinolin-5-one 13. Most 3-arylisoquinolines have displayed strong activities against human tumor cell lines. Especially, indenoisoquinolinone 13 exhibited excellent cytotoxicity (IC50 = 0.002 microgram/ml; HCT 15).

Studies on the synthesis and in vitro antitumor activity of the isoquinolone derivatives

3-Arylisoquinolin-1(2H)-ones (2) are possible bioisosteres of the 5-[4'-(piperidinomethyl)phenyl]-2,3-dihydroimidazo[2,1-a]iso quinoline (1) which is in clinical evaluation for the treatment of cancer. Structure-activity relationship studies of 3-arylisoquinolin-1(2H)-ones (2) led to the synthesis of 3-arylquinolin-2(1H)-ones (3). A number of 3-phenyl substituted quinolin-2(1H)-ones were synthesized and tested for their in vitro antitumor activity against four different human tumor cell lines and 3-phenyl-N-benzyl-3,4-dihydroquinolin-2(1H)-one (12) showed the most potent activity.