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ABSTRACT: The aim of this study was to investigate the regulation of hepatic transport systems during liver regeneration.
A DNA oligonucleotide microarray was developed with probes for 400 transcripts. Data were confirmed using real-time PCR and on a functional level in the perfused rat liver. Liver homogenates were taken 3-48 h following 2/3-hepatectomy in rats and compared with sham-operated and non-operated controls.
A more than two-fold increase or decrease of expression was obtained in 183 genes following partial hepatectomy and in 16 genes in sham-operated rats. A strong induction during liver regeneration was detected for the amino acid transporters LAT4, SN2 and sodium-dependent neutral amino acid transporter (ASCT)2, whereas amino acid transport system (ATA)2 and ATA3 expressions remained unchanged. The upregulation of ASCT2 may be responsible for the increase in sodium-dependent neutral amino acid influx important for liver cell proliferation. Expression of the osmolyte transporters Smit, TauT and Bgt1 was almost unchanged indicating that osmolytes are not involved in the cell volume increase during liver regeneration. The basolateral bile salt transporter Ntcp messenger RNA (mRNA) was significantly downregulated, whereas bile salt export pump (Bsep) and multidrug resistance protein (Mrp)2 expressions remained almost unchanged. An increased mRNA expression following partial hepatectomy was detected for organic anion transporting polypeptide (Oatp)5, Octn1, Octn2 and SGLT2. In contrast, Mrp6, Oatp 2, Oatp 3, Oatp 4 and Oatp 7 were downregulated. A five-fold upregulation at the protein level was shown for the Na(+)-K(+)-2Cl- cotransporter sodium-potassium-2-chloride cotransporter (NKCC1).
The data show a differential regulation of hepatic transport systems during liver regeneration.
Liver international: official journal of the International Association for the Study of the Liver 01/2006; 25(6):1243-58. · 3.82 Impact Factor
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ABSTRACT: The potentially enhanced mitogenic activity of insulin analogs represents a safety risk that requires detailed analysis of new analogs considered for therapeutic applications. We assessed the signaling properties and mitogenic potency of two novel rapid-acting insulin analogs, Lys(B3),Glu(B29) insulin (HMR 1964) and Lys(B3),Ile(B28) insulin (HMR 1153) using myoblasts and cardiomyocytes. In myoblasts, both binding and internalization were two- to threefold higher for Asp(B10) insulin and HMR 1153 when compared with HMR 1964 and regular insulin. This finding correlated with a prominent Shc/IGF-I receptor interaction, tyrosine phosphorylation of Shc, activation of extracellular signal-regulated protein kinase (ERK)-1 and -2, and stimulation of DNA synthesis by HMR 1153 and Asp(B10) insulin. In contrast, HMR 1964 produced a marginal activation of the Shc/ERK kinase cascade and was equipotent to insulin in stimulating DNA synthesis in myoblasts. Further, the in vivo growth-promoting activity of this analog was found to be identical to that of regular human insulin. In myoblasts, HMR 1964 produced a minor activation of insulin receptor substrate (IRS)-1 tyrosine phosphorylation, but a prominent activation of IRS-2, with a significantly stronger effect than insulin in human myoblasts. Predominant activation of IRS-2 was also observed in adult cardiomyocytes where HMR 1964 increased 3-O-methylglucose transport and the activation of Akt and glycogen synthase kinase-3 to the same extent as human insulin. We concluded that 1) the mitogenic properties of insulin analogs may result from a series of initial receptor interactions, including internalization and phosphorylation; 2) the mitogenic and metabolic potential of HMR 1964 is identical to that of insulin; and 3) predominant activation of IRS-2 may open new avenues for optimized insulin therapies.
Diabetes 10/2003; 52(9):2227-38. · 8.29 Impact Factor
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ABSTRACT: The effect of oral taurine supplementation on endotoxin-induced cholestasis was investigated in rat liver. At 12h following lipopolysaccharide (LPS) injection (4mg/kg body weight i.p.) bile flow and bromosulfophthalein (BSP) and taurocholate (TC) excretion were determined in the perfused liver and the expression of the canalicular transporters multidrug resistance protein 2 (Mrp2) and bile salt export pump (Bsep) was analyzed. Injection of LPS induced a significant decrease of bile flow ( 2.2+/-0.2 microl/g liver wet weight/min vs 3.3+/-0.1 microl/g liver wet weight in controls), biliary BSP excretion (10.8+/-2.2 nmol/g/min vs 21.0+/-3.8 nmol/g/min), and biliary TC excretion (114+/-23 nmol/g/min vs 228+/-8 nmol/g/min). These effects were due to transporter retrieval from the canalicular membrane and downregulation of Mrp2 and Bsep expression. In taurine-supplemented rats bile flow was 30% higher than that in untreated rats and the expression of Mrp2 and Bsep protein was increased two- to threefold. In taurine-supplemented rats there was no significant reduction of bile flow or of BSP and TC excretion at 12h following LPS injection. This protective effect of taurine was due to higher Mrp2 and Bsep protein levels compared to nonsupplemented LPS-treated rats, whereas relative Mrp2 retrieval from the canalicular membrane induced by LPS was not significantly different. LPS-induced tumor necrosis factor alpha and interleukin-1beta release were lower in taurine-fed rats; however, downregulation of Mrp2 and Bsep expression by LPS was delayed but not prevented. The data show that oral supplementation of taurine induces Mrp2 and Bsep expression and may prevent LPS-induced cholestasis.
Archives of Biochemistry and Biophysics 06/2003; 413(1):32-40. · 2.93 Impact Factor
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ABSTRACT: Intact actin microfilaments are necessary for insulin-regulated GLUT4 translocation from intracellular pools to the plasma membrane. Products of the lipoxygenase (LO) pathway were shown to be implicated in the regulation of actin cytoskeleton rearrangement. The aim of this study was to examine the role of these LO products for cardiac insulin signaling and glucose uptake, GLUT4 translocation, and actin-based cytoskeleton structure. Exposure of cardiomyocytes to esculetin or NDGA, two structurally different LO inhibitors, induced a complete inhibition of insulin-stimulated glucose uptake, whereas control cells showed a threefold stimulation by insulin. Addition of 12(S)-HETE rendered the NDGA-treated cells insulin-sensitive. Early insulin signaling was not changed in cells exposed to LO inhibitors. Cell surface biotinylation of control cells showed a twofold increase of GLUT4 at the cell surface after insulin stimulation. In contrast, the LO inhibitors induced a complete inhibition of insulin-stimulated GLUT4 translocation. Labeling of the F-actin cytoskeleton revealed a prominent disassembly of actin fibers in cells exposed to the LO inhibitors. In conclusion, we show here that products of the LO reaction participate in the organization of the actin network in ventricular cardiomyocytes. Inhibition of LO blocks GLUT4 translocation without affecting insulin signaling events. These data suggest that products of the LO reaction participate in the regulation of glucose transport by contribution to a rearrangement of actin cytoskeletal elements.
Annals of the New York Academy of Sciences 07/2002; 967:208-16. · 3.15 Impact Factor
