Analysis of the mouse Scnn1a promoter in cortical collecting duct cells and in transgenic mice

We have isolated and characterised the promoter of the mouse Scnn1a (alpha ENaC) gene. Using transient transfections of serial deletion mutants into Scnn1a-expressing cells, we demonstrate that 1.56 kb of 5' upstream sequence is required for cell-specific expression and corticosteroid-mediated regulation. These 5' sequences are not sufficient to drive expression of a lacZ reporter gene or a rat Scnn1a cDNA in transgenic mice, where they failed to rescue Scnn1a deficiency.

Deep brain stimulation of the globus pallidus pars interna in advanced Parkinson's disease

Pallidotomy is now widely performed for the treatment of advanced Parkinson's disease (PD). Preliminary reports of the effect of globus pallidus pars interna deep brain stimulation (GPi DBS) have also been promising. We have analyzed a cohort of 22 consecutive patients enrolled in a multicenter study. Surgery was bilateral in 17 and unilateral in five patients. At 6-month follow-up, the bilaterally GPi-implanted patients demonstrated a marked improvement when examined after drug withdrawal ("off") and under optimal medication ("on") using the Unified Parkinson's Disease Rating Scale (UPDRS). The benefit induced by the stimulation in the "off" medication condition in the total motor score was 31% and in the activities of daily living (ADL) scores was 39%. During the "on" medication period, the reduction in the total "on" dyskinesias score was 66% and in the ADL score was 32%. A similar pattern of improvement was seen in the group of patients with unilateral GPi stimulation, although a second cohort of 12 patients not included in the multicenter study showed greater improvements in "on" motor functioning. Although the effect of DBS is predominantly reversible, electrode insertion alone resulted in measurable clinical effects in the absence of stimulation. Thus, at 6-month follow-up, the benefit observed without stimulation was up to 44% in the "on" dyskinesias score and 29% in timed tapping scores undertaken in the "off" medication state. Complications among 34 patients from all centers included perioperative infection (n=3), hardware fracture (n=2), and premature battery failure (n=3). These results show a positive antiparkinsonian effect of pallidal DBS. No specific complications were observed with bilateral procedures.

Transcriptome of a mouse kidney cortical collecting duct cell line: effects of aldosterone and vasopressin

Aldosterone and vasopressin are responsible for the final adjustment of sodium and water reabsorption in the kidney. In principal cells of the kidney cortical collecting duct (CCD), the integral response to aldosterone and the long-term functional effects of vasopressin depend on transcription. In this study, we analyzed the transcriptome of a highly differentiated mouse clonal CCD principal cell line (mpkCCD(cl4)) and the changes in the transcriptome induced by aldosterone and vasopressin. Serial analysis of gene expression (SAGE) was performed on untreated cells and on cells treated with either aldosterone or vasopressin for 4 h. The transcriptomes in these three experimental conditions were determined by sequencing 169,721 transcript tags from the corresponding SAGE libraries. Limiting the analysis to tags that occurred twice or more in the data set, 14,654 different transcripts were identified, 3,642 of which do not match known mouse sequences. Statistical comparison (at P < 0.05 level) of the three SAGE libraries revealed 34 AITs (aldosterone-induced transcripts), 29 ARTs (aldosterone-repressed transcripts), 48 VITs (vasopressin-induced transcripts) and 11 VRTs (vasopressin-repressed transcripts). A selection of the differentially-expressed, hormone-specific transcripts (5 VITs, 2 AITs and 1 ART) has been validated in the mpkCCD(cl4) cell line either by Northern blot hybridization or reverse transcription-PCR. The hepatocyte nuclear transcription factor HNF-3-alpha (VIT39), the receptor activity modifying protein RAMP3 (VIT48), and the glucocorticoid-induced leucine zipper protein (GILZ) (AIT28) are candidate proteins playing a role in physiological responses of this cell line to vasopressin and aldosterone.

Tissue distribution and subcellular localization of the ClC-5 chloride channel in rat intestinal cells

ClC-5 is the Cl- channel that is mutated in Dent's disease, an X-chromosome-linked disease characterized by low molecular weight proteinuria, hypercalciuria, and kidney stones. It is predominantly expressed in endocytically active renal proximal cells. We investigated whether this Cl- channel could also be expressed in intestinal tissues that have endocytotic machinery. ClC-5 mRNA was detected in the rat duodenum, jejunum, ileum, and colon. Western blot analyses revealed the presence of the 83-kDa ClC-5 protein in these tissues. Indirect immunofluorescence studies showed that ClC-5 was mainly concentrated in the cytoplasm above the nuclei of enterocytes and colon cells. ClC-5 partially colocalized with the transcytosed polymeric immunoglobulin receptor but was not detectable together with the brush-border-anchored sucrase isomaltase. A subfractionation of vesicles obtained by differential centrifugation showed that ClC-5 is associated with the vacuolar 70-kDa H+-ATPase and the small GTPases rab4 and rab5a, two markers of early endosomes. Thus these results indicate that ClC-5 is present in the small intestine and colon of rats and suggest that it plays a role in the endocytotic pathways of intestinal cells.

Vasopressin-stimulated chloride transport in transimmortalized mouse cell lines derived from the distal convoluted tubule and cortical and inner medullary collecting ducts

BACKGROUND

The fine control of NaCl absorption takes place in the distal parts of the renal tubule, but the regulation of Cl(-) transport in this region has not been fully elucidated. We have analysed the effects of dD-arginine vasopressin (dDAVP) on Cl(-) fluxes in cultured mouse distal convoluted tubule (mpkDCT), cortical collecting duct (mpkCCD) and inner medullary collecting duct (mpkIMCD) cell lines.

METHODS

RT-PCR and Western blotting were used to detect the amiloride-sensitive sodium channel (ENaC) and cystic fibrosis transmembrane conductance regulator (CFTR) mRNAs and protein in cultured mpkDCT, mpkCCD and mpkIMCD cells. Cl(-) fluxes were analysed by measuring the short-circuit current (I(sc)) and bidirectional (36)Cl(-) fluxes on confluent cells grown on filters.

RESULTS

All three cell lines expressed ENaC and CFTR and had I(sc) stimulated by dDAVP. The rise in I(sc) caused by dDAVP (10(-8) M) was inhibited by amiloride, and to a lesser extent by 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) in all three cell lines. The dDAVP-dependent I(sc) measured under apical Na(+)-free condition was reduced by Cl(-) channel blockers with a profile (NPPB>glibenclamide>DIDS), similar to that for rat CFTR. dDAVP stimulated the apical-to-basal (36)Cl(-) flux and to a lesser extent the basal-to-apical (36)Cl(-) flux under open-circuit condition in all three cultured cell lines. Adding NPPB to the apical side reduced the basal-to-apical (36)Cl(-) flux but not the opposite (36)Cl(-) flux from dDAVP-treated cells.

CONCLUSION

These results indicate that dDAVP stimulates the bi-directional flux of Cl(-), resulting in net Cl(-)absorption, in these cultured mouse distal and collecting duct cells. I(sc) experiments also suggest the presence of a minor component of electrogenic Cl(-) secretion, possibly mediated by CFTR.

Cyclic AMP increases cell surface expression of functional Na,K-ATPase units in mammalian cortical collecting duct principal cells

Cyclic AMP (cAMP) stimulates the transport of Na(+) and Na,K-ATPase activity in the renal cortical collecting duct (CCD). The aim of this study was to investigate the mechanism whereby cAMP stimulates the Na,K-ATPase activity in microdissected rat CCDs and cultured mouse mpkCCD(c14) collecting duct cells. db-cAMP (10(-3) M) stimulated by 2-fold the activity of Na,K-ATPase from rat CCDs as well as the ouabain-sensitive component of (86)Rb(+) uptake by rat CCDs (1.7-fold) and cultured mouse CCD cells (1.5-fold). Pretreatment of rat CCDs with saponin increased the total Na,K-ATPase activity without further stimulation by db-cAMP. Western blotting performed after a biotinylation procedure revealed that db-cAMP increased the amount of Na,K-ATPase at the cell surface in both intact rat CCDs (1.7-fold) and cultured cells (1.3-fold), and that this increase was not related to changes in Na,K-ATPase internalization. Brefeldin A and low temperature (20 degrees C) prevented both the db-cAMP-dependent increase in cell surface expression and activity of Na,K-ATPase in both intact rat CCDs and cultured cells. Pretreatment with the intracellular Ca(2+) chelator bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid also blunted the increment in cell surface expression and activity of Na,K-ATPase caused by db-cAMP. In conclusion, these results strongly suggest that the cAMP-dependent stimulation of Na,K-ATPase activity in CCD results from the translocation of active pump units from an intracellular compartment to the plasma membrane.

A novel mouse Nedd4 protein suppresses the activity of the epithelial Na+ channel

Liddle's syndrome is a form of inherited hypertension linked to mutations in the genes encoding the epithelial Na+ channel (ENaC). These mutations alter or delete PY motifs involved in protein-protein interactions with a ubiquitin-protein ligase, Nedd4. Here we show that Na+ transporting cells, derived from mouse cortical collecting duct, express two Nedd4 proteins with different structural organization and characteristics of ENaC regulation: 1) the classical Nedd4 (herein referred to as Nedd4-1) containing one amino-terminal C2, three WW, and one HECT-ubiquitin protein ligase domain and 2) a novel Nedd4 protein (Nedd4-2), homologous to Xenopus Nedd4 and comprising four WW, one HECT, yet lacking a C2 domain. Nedd4-2, but not Nedd4-1, inhibits ENaC activity when coexpressed in Xenopus oocytes and this property correlates with the ability to bind to ENaC, as only Nedd4-2 coimmunoprecipitates with ENaC. Furthermore, this interaction depends on the presence of at least one PY motif in the ENaC complex and on WW domains 3 and 4 in Nedd4-2. Thus, these results suggest that the novel suppressor protein Nedd4-2 is the regulator of ENaC and hence a potential susceptibility gene for arterial hypertension.

Protection of autotransplanted pig kidneys from ischemia-reperfusion injury by polyethylene glycol

BACKGROUND

Ischemia-reperfusion injury (IRI) is often responsible for graft rejection and leads to delayed graft function of cadaveric kidneys. We have shown that adding polyethylene glycol (PEG 20M) to the preservation solutions helps protect isolated perfused pig kidneys against cold ischemia and reperfusion injury.

METHODS

We compared the effects of adding PEG to a simplified high-K+ perfusion solution of cold-stored kidneys to Euro-Collins or University of Wisconsin solutions on the function of reperfused autotransplanted pig kidneys. The left kidney was cold-flushed with the preservation solutions and stored for 48 hr at 4 degrees C before reimplantation. Creatinine clearance and fractional excretion of sodium were analyzed 2 days before surgery and over 7 days after transplantation. Histological sections were obtained 40 min after reperfusion and on day 7 after surgery.

RESULTS

Adding PEG to the perfusate significantly reduced IRI from autotransplanted pig kidneys. Creatinine clearance was significantly higher and fractional excretion of sodium was significantly lower in pigs transplanted with kidneys cold-flushed with PEG-supplemented perfusate than in those flushed with Euro-Collins or University of Wisconsin solutions. PEG supplementation also better preserved the integrity of kidney cells and markedly reduced interstitial cell infiltrates.

CONCLUSION

PEG protects against IRI and reduces early cellular inflammation. PEG may impair the recruitment and migration of leukocytes into retransplanted pig kidneys. Cold preservation of donor organs with PEG-supplemented solutions may therefore help limit IRI in human renal transplantation.

Cyclosporine stimulates Na+-K+-Cl- cotransport activity in cultured mouse medullary thick ascending limb cells

BACKGROUND

Cyclosporine (CsA) has been shown to alter the activity of plasma membrane transporters in kidney epithelial cells. In this study, we have investigated the effects of CsA on Na+,K+-ATPase and Na+-K+-Cl- cotransport activities in cultured cells derived from microdissected mouse medullary thick ascending limb (mTAL) cells.

METHODS

Experiments were carried out on subcultured confluent mouse TAL cells. Reverse transcription-polymerase chain reaction experiments showed that they expressed the mNKCC2 electroneutral Na+-K+-Cl- cotransporter and ROM-K1 and ROMK2 potassium channel mRNA. Western blotting also revealed the presence of the 40 kD ROMK protein using an anti-ROMK antibody. The effect of CsA (100 ng/mL) on ion transport was assessed by measuring the influx and efflux of rubidium (86Rb+) and 36Cl-, used as tracers of K+ and Cl- movements, on cells grown on Petri dishes or permeable filters.

RESULTS

CsA inhibited by 38% the ouabain-sensitive component of 86Rb+ influx mediated by the Na+,K+-ATPase pumps. CsA also increased by 38% the ouabain-resistant furosemide-sensitive component (Or-Fs) of 86Rb+ influx, reflecting the Na+-K+-Cl- cotransport activity and stimulated the basolateral efflux of 36Cl- from mTAL cells grown on filters. The CsA-stimulated basal efflux of Cl- was prevented by the basal addition of the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino) benzoate (NPPB, 10-4 mol/L). Apical addition of the K+ channel blocking agent Ba2+ (10-4 mol/L) partially prevented the CsA-stimulated basal efflux of Cl-. Adding Ba2+ to the luminal side of cells grown on Petri dishes also prevented the rise in apical 86Rb+ efflux and the increased Or-Fs component of 86Rb+ influx caused by CsA.

CONCLUSION

These results indicated that CsA may stimulate the Na+-K+-Cl- cotransport activity and also suggested that this immunosuppressive agent may interfere in the recycling of apical K+ in this model of cultured mouse TAL cells.

Influence of cold-storage conditions on renal function of autotransplanted large pig kidneys

BACKGROUND

The consequences of ischemia/reperfusion injury (IRI) on delayed graft function (DGF) and graft survival for kidney recipients remain a matter of debate. Several strategies have been proposed to reduce IRI. We have shown that adding the anti-ischemic drug trimetazidine (TMZ) to different preservation solutions had beneficial effects on the function of reperfused rat and pig kidneys.

METHODS

We analyzed the renal parameters of reperfused, autotransplanted large pigs following transplantation. The left kidneys were first removed and cold flushed with Euro-Collins (EC) and University of Wisconsin (UW) solutions (with or without 10-6 mol/L TMZ) and were stored for 48 hours at 4 degrees C. The kidney was then autotransplanted, and the contralateral kidneys were removed. Creatinine clearance, natriuresis, proteinuria, the degree of interstitial fibrosis, the number of CD4, CD8, and macrophage-positive cells, and the amount of vascular cell adhesion molecule-1 were analyzed on kidney biopsies taken at 2, 4 to 5, and 10 to 12 weeks after surgery.

RESULTS

The functions of the transplanted kidneys were better preserved after cold flushing with TMZ-supplemented solutions than with TMZ-free solutions. Creatinine clearance was higher, and proteinuria was lower in animals transplanted with kidneys cold flushed with TMZ-supplemented solutions than with TMZ-free solutions. The cytoprotective action of TMZ also reduced interstitial fibrosis and the numbers of infiltrating CD4- and CD8-positive cells.

CONCLUSION

These results indicate that the condition of cold preservation may influence long-term kidney graft functions and suggest that, to a certain extent, TMZ reduces the degree of interstitial fibrosis.

Glucose persistence on high-mannose oligosaccharides selectively inhibits the macroautophagic sequestration of N-linked glycoproteins

The macroautophagic-lysosomal pathway is a bulk degradative process for cytosolic proteins and organelles including the endoplasmic reticulum (ER). We have previously shown that the human colonic carcinoma HT-29 cell population is characterized by a high rate of autophagic degradation of N-linked glycoproteins substituted with ER-type glycans. In the present work we demonstrate that glucosidase inhibitors [castanospermine (CST) and deoxynojirimycin] have a stabilizing effect on newly synthesized glucosylated N-linked glycoproteins and impaired their lysosomal delivery as shown by subcellular fractionation on Percoll gradients. The inhibition of macroautophagy was restricted to N-linked glycoproteins because macroautophagic parameters such as the rate of sequestration of cytosolic markers and the fractional volume occupied by autophagic vacuoles were not affected in CST-treated cells. The protection of glucosylated glycoproteins from autophagic sequestration was also observed in inhibitor-treated Chinese hamster ovary (CHO) cells and in Lec23 cells (a CHO mutant deficient in glucosidase I activity). The interaction of glucosylated glycoproteins with the ER chaperone binding protein (BiP) was prolonged in inhibitor-treated cells in comparison with untreated CHO cells. These results show that the removal of glucose from N-glycans of glycoproteins is a key event for their delivery to the autophagic pathway and that interaction with BiP could prevent or delay newly synthesized glucosylated N-linked glycoproteins from being sequestered by the autophagic pathway.

Immortalized kidney cells derived from transgenic mice harboring L-type pyruvate kinase and vimentin promoters

Targeted oncogenesis in transgenic mice, where an oncogene is placed under the control of the regulatory sequences of a cell-specific gene, has been used to derive several new types of differentiated nonepithelial and epithelial cell lines. This review summarizes the properties of cell lines derived from proximal, distal and collecting duct cells. The cells were obtained from kidneys of transgenic mice harboring the 5' regulatory sequences of the L-type pyruvate kinase or vimentin genes controlling the expression of either the large T and little t antigens or the temperature-sensitive large T antigen.

Immortalized kidney epithelial cells as tools for hormonally regulated ion transport studies

The development of transgenic mice carrying the simian virus-40 large T antigen gene or the temperature-sensitive simian virus-40 large T antigen gene, either alone or placed under the control of the 5'-regulatory regions of tissue-specific or ubiquitous genes, has permitted the production of differentiated, polarized kidney epithelial cells. This review covers the immortalized cell lines issued from the various parts of the renal tubule and, in particular, the recently established collecting duct cell lines that have been used as ex-vivo cell models to analyze the regulation of ion transport processes by hormones.

Intestinal dysplasia and adenoma in transgenic mice after overexpression of an activated beta-catenin

Mutations in the adenomatous polyposis coli gene or activating mutations in the beta-catenin gene itself are thought to be responsible for the excessive beta-catenin signaling involved in intestinal carcinogenesis. We generated transgenic mice that expressed large amounts of a NH2-terminally truncated mutant beta-catenin (deltaN131beta-catenin) in the intestine. These mice had multifocal dysplastic lesions in the small intestine, reminiscent of the early lesions observed in the mouse models of familial adenomatous polyposis. The number of apoptotic cells in the villi of these transgenic mice was 3-4-fold higher than in nontransgenic mice. Expression of the truncated beta-catenin mutant in the kidney led to the development of severe polycystic kidney disease. Our findings support the concept that deregulation of the beta-catenin signaling pathway is the major oncogenic consequence of adenomatous polyposis coli mutations in intestinal neoplasia.

Tissue and cell distribution of the multidrug resistance-associated protein (MRP) in mouse intestine and kidney

The multidrug resistance-associated protein (MRP) that is involved in drug resistance and the export of glutathione-conjugated substrates may not have the same epithelial cell membrane distribution as the P-glycoprotein encoded by the MDR gene. Because intestinal and kidney epithelial cells are polarized cells endowed distinct secreting and absorptive ion and protein transport capacities, we investigated the tissue and cell distribution of MRP in adult mouse small intestine, colon, and kidney by immunohistochemistry. Western blot analyses revealed the 190-kD MRP protein in these tissues. MRP was found in the basolateral membranes of intestinal crypt cells, mainly Paneth cells, but not in differentiated enterocytes. All the cells lining the crypt-villous axis of the colon wall contained MRP. MRP was found in the glomeruli, ascending limb cells, and basolateral membranes of the distal and collecting tubule cells of the kidney but not in proximal tubule cells. Cultured mouse intestinal m-ICcl2 cells and renal distal mpkDCT cells that have retained the features typical of intestinal crypt and renal distal epithelial cells, respectively, also possess MRP in their basolateral membranes. The patterns of subcellular and cellular distribution indicate that MRP may have a specific role in the basolateral transport of endogenous compounds in Paneth, renal distal, and collecting tubule cells.

Corticosteroid-dependent sodium transport in a novel immortalized mouse collecting duct principal cell line

The final control of sodium balance takes place in the cortical collecting duct (CCD) of the nephron, where corticosteroid hormones regulate sodium reabsorption by acting through mineralocorticoid (MR) and/or glucocorticoid (GR) receptors. A clone of principal CCD cells (mpkCCDc14) has been established that is derived from a transgenic mouse (SV40 large T antigen under the control of the SV40 enhancer/L-type pyruvate kinase promoter). Cells grown on filters form polarized monolayers with high electrical transepithelial resistance (R(T) approximately 4700 ohm x cm2) and potential difference (P(D) approximately -50 mV) and have an amiloride-sensitive electrogenic sodium transport, as assessed by the short-circuit current method (Isc approximately 11 microA/cm2). Reverse transcription-PCR experiments using rat MR primers, [3H]aldosterone, and [3H]dexamethasone binding and competition studies indicated that the mpkCCDc14 cells exhibit specific MR and GR. Aldosterone increased Isc in a dose- (10(-10) to 10(-6) M) and time-dependent (2 to 72 h) manner, whereas corticosterone only transiently increased Isc (2 to 6 h). Consistent with the expression of 11beta-hydroxysteroid dehydrogenase type 2, which metabolizes glucocorticoids to inactive 11-dehydroderivates, carbenoxolone potentiated the corticosterone-stimulated Isc. Aldosterone (5x10(-7) M)-induced Isc (fourfold) was associated with a three- to fivefold increase in alpha-ENaC mRNA (but not in those for beta- or gamma-ENaC) and three- to 10-fold increases in alpha-ENaC protein synthesis. In conclusion, this new immortalized mammalian CCD clonal cell line has retained a high level of epithelial differentiation and sodium transport stimulated by aldosterone and therefore represents a useful mammalian cell system for identifying the genes controlled by aldosterone.

Mechanisms of altered sequestration and efflux of chemotherapeutic drugs by multidrug-resistant cells

This review considers the mechanisms associated with the pleiotropic resistance of cancer cells to chemotherapeutic drugs, and more particularly those related to intracellular pH (pHi). The multidrug resistance (MDR) phenomenon responsible for the decreased accumulation and increased efflux of cytotoxic drugs is generally associated with excess levels of P-glycoproteins (Pgps) encoded by MDR genes and/or the multidrug resistance-associated protein (MRP). MDR cell lines, derived from normal or tumor cells, frequently exhibit abnormally elevated pHi and changes in the production of various proteins. Recent studies have suggested that, in addition to the impact of the ATP-dependent membrane transporters Pgp and MRP on drug transport, other mechanisms linked to pHi changes in MDR cells may play an important role in drug resistance. We have shown that alkalinization of the acidic compartments (endosomes and lysosomes) by lysosomotropic agents could stimulate the efflux of vinblastine from drug-resistant mouse renal proximal tubule cells. The fact that weak base chemotherapeutic drugs can be sequestered within the acidic organelles of MDR cells sheds new light on the cellular mechanisms of drug resistance.

Lysosomotropic agents increase vinblastine efflux from mouse MDR proximal kidney cells exhibiting vectorial drug transport

Vinblastine (VBL) transport and efflux were studied in mouse proximal tubule PKSV-PR cells and in their multidrug-resistant derivatives PKSV-PRcol50 cells. The PKSV-PRcol50 cells produced more mdr1b transcripts and had higher resistance to various drugs. PKSV-PRcol50 cells had a predominantly basal-to-apical flux of [3H]VBL, 2.7 times larger than that in PKSV-PR cells. This flux was partially inhibited by verapamil (VRP) (10 microM) and cyclosporin A (CsA) (200 nM). [3H]VBL efflux was also greater in PKSV-PRcol50 than in PKSV-PR cells. Treatment with NH4Cl (30 mM), a lysosomotropic weak base, and concanamycin A (CCM A) (20 nM), an inhibitor of the vacuolar H+/ATPase, further increased [3H]VBL efflux from PKSV-PRcol50 cells. The cytoplasmic pH (pHcyt) of these drug-resistant cells transiently increased in the presence of NH4Cl deltapHcyt: +0.4). CCM A caused a moderate, delayed increase in pHcyt (deltapHcyt: +0.1) and made the acidic intralysosomal compartment more alkaline (deltapHlys: +1.3). VRP and CsA prevented the NH4Cl- and CCM A-induced [3H]VBL efflux from PKSV-PRcol50 cells. However, VRP (10 microM) did not significantly affect pHcyt of PKSV-PRcol50 cells, the NH4Cl-and CCM A-induced pHcyt responses, and the effect of CCMA on pHlys. Thus, lysosomotropic agents may affect the kinetics of [3H]VBL efflux. Our results also suggest that the inhibitory action of VRP on VBL efflux was not directly mediated by a pH-dependent process in these drug-resistant renal proximal tubule cells.

Characterization of beta cells developed in vitro from rat embryonic pancreatic epithelium

The present study evaluates the development and functional properties of beta cells differentiated in vitro. The authors have previously demonstrated that when E12.5 rat pancreatic rudiments are cultured in vitro in the absence of mesenchyme, the majority of the epithelial cells differentiate into endocrine beta cells. Thus, depletion of the mesenchyme provokes the expansion of endocrine tissue at the expense of exocrine tissue. The potential use of this procedure for the production of beta cells led the authors to characterize the beta cells differentiated in this model and to compare their properties with those of the endocrine cells of the embryonic and adult pancreas. This study shows that the beta cells that differentiate in vitro in the absence of mesenchyme express the homeodomain protein Nkx6.1, a transcription factor that is characteristic of adult mature beta cells. Further, electron microscopy analysis shows that these beta cells are highly granulated, and the ultrastructural analysis of the granules shows that they are characteristic of mature beta cells. The maturity of these granules was confirmed by a double-immunofluorescence study that demonstrated that Rab3A and SNAP-25, two proteins associated with the secretory pathway of insulin, are strongly expressed. Finally, the maturity of the differentiated beta cells in this model was confirmed when the cells responded to stimulation with 16 mM glucose by a 5-fold increase in insulin release. The authors conclude that the beta cells differentiated in vitro from rat embryonic pancreatic rudiments devoid of mesenchyme are mature beta cells.