Osteocalcin improves insulin resistance and inflammation in obese mice: Participation of white adipose tissue and bone

AIMS/HYPOTHESIS

The discovery of osteocalcin, a protein synthetized by osteoblasts, as a hormone that has positive effects on insulin resistance, contributed to support the concept of bone as an endocrine organ. However, very little is known about the molecular pathways involved in osteocalcin improved-insulin resistance. The present study aimed to investigate the mechanisms of action of osteocalcin on insulin resistance and inflammation in obese mice and 3T3-L1 adipocytes.

METHODS AND RESULTS

Lean control, saline-treated obese and uncarboxylated osteocalcin (uOC)-treated obese mice were subjected to insulin tolerance test in vivo. Blood was collect for biochemical/metabolic profile analysis; and, skeletal muscle, white adipose tissue (WAT) and bone were collected for protein (Western blotting) and mRNA (RT-qPCR) analysis. uOC effects on insulin resistance and inflammation were also investigated in 3T3-L1 adipocytes challenged with tumor necrosis factor. Osteocalcin treatment improved in vivo insulin resistance in obese mice. In WAT, osteocalcin had positive effects such as (1) WAT weight reduction; (2) upregulation of glucose transporter (GLUT) 4 protein and its mRNA (Slc2a4); (3) improved insulin-induced AKT phosphorylation; (4) downregulation of several genes involved in inflammation and inflammassome transcriptional machinery, and (5) reduction of the density of macrophage in crown-like structures (histomorphometrical analysis). Notably, in 3T3-L1 adipocytes, osteocalcin restored Slc2a4/GLUT4 content and reduced the expression of inflammatory genes after TNF-a challenge; moreover, osteocalcin treatment increased AKT phosphorylation induced by insulin. Finally, it was observed that in bone, osteocalcin improves insulin resistance by increasing insulin-induced AKT phosphorylation and reducing the expression of genes involved in bone insulin resistance, resulting in increased secretion of uncarboxylated osteocalcin in circulation.

CONCLUSION

We provided some mechanisms of action for osteocalcin in the amelioration of insulin resistance in obesity: in WAT, osteocalcin improves insulin resistance by decreasing inflammation, and increasing insulin signaling and the expression of Slc2a4/GLUT4; and, in bone, osteocalcin increases the secretion of uncarboxylated osteocalcin by improving insulin resistance.

Stat3 and Socs3 expression patterns during murine placenta development

Signal transducers and activators of transcription 3 (STAT3) has been identified as an important signal transducer in the invasive phenotype of the trophoblasts cells in in vitro studies. However, the in situ distribution and patterns of expression of this molecule in trophoblast cells during the development of the placenta are still under-elucidated. Mice uteri of gestational ages between 7 and 14 days of pregnancy (dop) were fixed in methacarn and processed with immunoperoxidase techniques for detection of STAT3 and its phosphorylation at serine (p-ser727) residues, as well as the suppressor of cytokine signaling 3 (SOCS3) expression. STAT3 was observed at 7 through 9 dop in both the antimesometrial and mesometrial deciduas, while continued immunoreactivity between 10 and 13 dop was seen only in the mesometrial decidua. In the placenta, STAT3 was detected in the cytotrophoblast cells of labyrinth and giant trophoblast cells between 10 and 14 dop. Immunoreactivity for STAT3 was also seen in trophoblast cells surrounding the maternal blood vessels. On days 10 and 11 of pregnancy, p-ser727 was detectable in the mesometrial decidua and in giant trophoblasts, while during 12-14 dop in the spongiotrophoblast region. In addition, SOCS3 was immunodetected in maternal and placental tissues, principally in the giant trophoblast cells during the whole period of the study. The present in situ study shows the distribution of STAT3, its serine activation and SOCS3 in different maternal and fetal compartments during murine placental development, thus further supporting the idea that they play a role during physiological placentation in mice.

Maternal diabetes affects specific extracellular matrix components during placentation

During embryo implantation, invasive trophoblast cells mediate embryo invasion into the decidualized stroma, forming a rich network of lacunae that connect the embryonic tissues to the maternal blood vessels. Placentation is probably guided by the composition and organization of the endometrial extracellular matrix. Certain pathological conditions that occur during pregnancy, including diabetes, have been linked to abnormal placental morphology and consequent fetal morbidity. We used immunoperoxidase techniques to identify members of the collagen, proteoglycan and glycoprotein families in the various compartments of the rat placenta and to determine whether experimentally induced diabetes affects placental morphology and alters the distribution of these molecules during pregnancy. Single injections of alloxan (40 mg kg(-1) i.v.) were used to induce diabetes on day 2 of pregnancy in Wistar rats. Placentas were collected on days 14, 17, and 20. Type I and III collagen, as well as the proteoglycans decorin and biglycan, were found to be distributed throughout the placentas of control and diabetic rats. In both groups, laminin expression decreased at the end of pregnancy. In contrast, fibronectin was detected in the labyrinth region of diabetic rats at all gestational stages studied, whereas it was detected only at term pregnancy in the placentas of control rats. These results show for the first time that some extracellular matrix molecules are modulated during placental development. However, as diabetic rats presented increased fibronectin deposition exclusively in the labyrinth region, we speculate that diabetes alters the microenvironment at the maternal-fetal interface, leading to developmental abnormalities in the offspring.

Characterization and distribution of hyaluronan and the proteoglycans decorin, biglycan and perlecan in the developing embryonic mouse gonad

The morphogenesis of tissues and organs requires dynamic changes in cells and in extracellular matrix components. It is known that various extracellular matrix molecules are of fundamental importance for gonad differentiation and growth. In the adult testis, the extracellular matrix represents an important component of the interstitium, participating in the transport of biologically active substances needed for the communication between different cellular components, as well as for the regulation of spermatogenesis and hormone production. The present study was designed in order to identify the proteoglycans biglycan, decorin and perlecan, as well as the glycosaminoglycan hyaluronan, during testis development in mouse embryos. Our data profile the chronology of testis differentiation, as well as the distribution of these extracellular matrix components during testis development in mice. We show that these extracellular matrix molecules are present early in the development of the gonads, suggesting that they play a role in gonad development. In addition, we found no decorin in the testicular cords. Furthermore, of the proteoglycans analysed, only biglycan was seen surrounding immature Sertoli cells and Leydig cell precursors in the testicular cords. This indicates that specific sets of extracellular matrix molecules are required in the various compartments of the developing gonad.

Granulated decidual cells in the mouse deciduoma: a putative source of decidual prolactin in mice

Decidual cells are endometrial fibroblasts that redifferentiate during pregnancy in several species of mammals. In this work, we describe a subpopulation of resident decidual cells in the mouse endometrium that are joined by intercellular junctions and have cytoplasmic granules. Decidualization was induced in pseudopregnant mice on the 4th day of pseudopregnancy by injection of 30 microl of arachis oil into the uterine lumen. The uteri were collected on day 8 of pseudopregnancy (at 4 p.m., 8 p.m. and 11 p.m.) and on day 9 (at 8 a.m.). The tissues were fixed for light and electron microscopy. During day 8 of pseudopregnancy, granulated cells were present at the antimesometrial pole of the endometrium; they were concentrated at the periphery of the antimesometrial decidua and disappeared on day 9 of pseudopregnancy. The cytoplasm of the granulated decidual cells had acidophilic granules that stained also with periodic acid-Schiff (PAS). These granules stained with anti-rat prolactin antibody in both light and electron microscope immunocytochemical preparations. Vacuoles of various sizes were always present in the granulated cells. A PAS-positive and prolactin-stained material was often deposited at the periphery of the vacuoles. Our results indicate that the granulated decidual cells are the source of decidual prolactin which accumulates in cytoplasmic granules. These granulated cells therefore form a transient gland in the mouse antimesometrial endometrium (granulated decidual gland).

Morphological and cytochemical study of extracellular matrix during the migratory phase of human and mouse primordial germ cells

Primordial germ cells (PGCs), the ancestors of functional gametes in mammals, originate in an extragonadal location, and then migrate to and colonize the genital ridges during early organogenesis period. PGCs move actively from their original site, the wall of the hindgut, through the extracellular matrix (ECM) of the dorsal mesentery. This movement is controlled in part by components of the ECM. Cells are known to bind to individual ECM glycoproteins in a complex and poorly understood way. During migration in embryos, PGCs must alter their overall adhesiveness to the endodermal epithelium to allow locomotion. This study examined the ECM material of the migratory route during mouse and human PGCs migration. Mouse embryos obtained from Swiss Rockefeller mouse and normal human embryos between 4 and 7 weeks of development, collected during salpingectomy performed on patients with tubal ectopic pregnancies, were analyzed. The study was based on a morphological analysis using scanning electron microscopy (SEM), and on the histochemical and ultracytochemical identification of glycosaminoglycans (GAGs) and proteoglycans. In each age group, the mesenchyme was widely separated by intercellular spaces and materials. Fine filamentous strands extended between the surface of mesenchymal cells and the surface of PGCs. Hyaluronan and chondroitin and/or dermatan sulfate were localized in the ECM of the PGC migratory pathway both in mouse and human embryos. Hyaluronan was clearly reduced in the later stage of the migratory processes; on the contrary, the chondroitin sulfate reaction product increased. These results are consistent with previous observations showing that hyaluronan is a major component of the ECM, and are also suggestive of the significant role played by hyaluronan, chondroitin sulfate and dermatan sulfate during migration, thus providing a permissive substrate for cell migration during development. The observed temporal and regional patterns suggest that these GAGs are important morphogenetic factors both in the mouse and human although the precise biological function of the proteoglycans are not currently clear.

Exercise training causes skeletal muscle venular growth and alters hemodynamic responses in spontaneously hypertensive rats

OBJECTIVE

To investigate whether training changes skeletal muscle venular profile and hemodynamic responses to exercise we studied spontanesouly hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats submitted to training programme (T = 50-60% of VO2max).

DESIGN

Training (T) was performed on a treadmill over a period of 13 weeks. Age-matched control groups were kept sedentary (S). T and S rats were chronically instrumented for hindlimb flow (HLF) and arterial pressure (AP) measurements at rest, during dynamic exercise and recovery in two different situations: control and after extensive intravenous blockade (hexamethonium + losartan + Nomega-nitro-L-arginine methyl ester + hydralazine). For morphometric analysis, skeletal muscle samples (gracilis) were obtained after transcardiac perfusion with fixative.

RESULTS

T caused a significant reduction of resting mean arterial pressure (MAP) (-11%) only in the SHR group without changing basal HLF. In the sedentary SHR (SHRs), basal relative hindlimb resistance was increased by 45%, but was significantly reduced after T (P < 0.05). During dynamic exercise, MAP increased similarly (10-20 mmHg) in all groups. HLF increases were similar for the four groups up to 0.8 km/h; at higher workloads, HLF was higher in trained SHR (SHRT) versus trained WKY (WKYT) (3.9- versus 2.9-fold increase over basal HLF, respectively). After blockade (and pressure correction with IV phenylephrine infusion), steady-state exercise was performed with similar hindlimb vasodilation in all groups and was accompanied by MAP reduction (-17 +/- 8 mmHg) only in SHRT group. Skeletal muscle venular profile (density, diameter and lumen cross-sectional area) was similar in WKY(T), WKY(S) and SHR(S), but significantly increased in SHR(T). In this group the two-fold increase in venule density was correlated with both the reduction in baseline MAP and the increase in HLF during dynamic exercise.

CONCLUSIONS

The results suggest that increased venule density is a specific adaptation of SHR skeletal muscle to training. Venular growth may contribute to both the pressure-lowering effect and the large HLF at high exercise intensities observed in the trained SHR.

Exercise training normalizes wall-to-lumen ratio of the gracilis muscle arterioles and reduces pressure in spontaneously hypertensive rats

OBJECTIVE

To investigate mechanisms underlying the training-induced blood pressure-lowering effect we analyzed the hemodynamic responses and morphometric changes of the skeletal muscle microcirculation of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats during an exercise training program. DESIGN TRAINING: (50-60% VO2 max) was performed on a treadmill for 13 weeks and control groups were kept sedentary over the same period of time. Trained and sedentary rats were chronically instrumented for hindlimb flow and arterial pressure (AP) recordings under conscious unrestrained conditions. Gracilis and myocardial muscle samples were obtained for morphometric analysis after transcardiac perfusion of fixative.

RESULTS

SHR, when compared to WKY presented an elevated blood pressure, an increased relative hindlimb vascular resistance, capillary rarefaction in both gracilis and myocardium and an increased wall-to-lumen ratio of gracilis arterioles. Training increased significantly both capillary density and capillary/fiber ratio in the gracilis and myocardium of WKY and SHR groups, causing a complete reversal of capillary rarefaction in trained SHR. In SHR, training also reduced resting blood pressure and caused normalization of both relative hindlimb vascular resistance and gracilis arterioles wall-to-lumen ratio. Regression analysis revealed strong positive correlation between hindlimb vascular resistance and mean AP (MAP) and between arterioles wall-to-lumen ratio and MAP.

CONCLUSIONS

The results suggest that low-intensity training can significantly reduce pressure in SHR while normalizing both the arteriole morphology and the resistance of the skeletal muscle microcirculation.

Ultrastructural cytochemical characterization of collagen-associated proteoglycans in the endometrium of mice

The decidual reaction in mice is characterized by the transformation of a specific population of endometrial fibroblasts into epithelioid cells, known as decidual cells. An important feature of decidualization in mice is a remarkable modification of the endometrial extracellular matrix. The present work is an ultrastructural cytochemical study of matrix with the purpose of analyzing the arrangement of collagen-associated proteoglycans (PGs) at various regions of nulliparous endometrium and of the antimesometrial decidua of mice using the cationic dye cuprolinic blue associated with enzymatic treatments with chondroitinase ABC, chondroitinase AC, and hyaluronidase. The staining with cuprolinic blue showed PGs as rods and granules of several sizes. Rods measuring 40-60 nm in length (named F2-rods) were apposed to thin collagen fibrils whereas granules were associated with thick collagen fibrils, particularly in the region occupied by mature decidual cells on the 7th day of pregnancy. The amount of granules was higher than that of F2-rods. Both F2-rods and granules were affected by chondroitinase ABC or AC treatment, indicating that they were PGs containing chondroitin sulfate and dermatan sulfate chains. However, the granules associated with thick collagen fibrils were more resistant to chondroitinase AC treatment than F2-rods, indicating the presence of dermatan sulfate chains that contain both L-iduronic and D-glucuronic acid sugar residues. We suggest that the differences of the nature and amount of PGs may be associated with the changes of the thickness of collagen fibrils observed during decidualization of the endometrium in the mouse.

Organization of desmin-containing intermediate filaments during differentiation of mouse decidual cells

Decidualization of the mouse endometrium consists of a redifferentiation of the endometrial stromal fibroblasts. During decidualization these fibroblasts undergo growth, change of shape, multinucleation, and establishment of intercellular junctions. One feature of rodent decidual cells is the accumulation of intermediate filaments. In spite of the fact that fibroblasts normally have vimentin intermediate filaments, they acquire a large amount of desmin intermediate filaments while they undergo decidualization. The light and electron microscope immunocytochemical results of the present work show that during the initial stages of decidual transformation the desmin intermediate filaments accumulate around the nuclei, often forming caps around the nuclear envelope. As the decidual cells grow, the filaments form bundles and nets that radiate from the nuclei toward the cell surface. During the final stages of differentiation, on day 8 of pregnancy, staining of differentiated decidual cells decreases and most filaments accumulate under the cell surface. A role for intermediate filaments is suggested for decidualization of mouse endometrial cells.

Influence of enalapril on the endothelial function of DOCA-salt hypertensive rats

In the present study, we investigated whether the correction of endothelial dysfunction can be independent of the normalization of high blood pressure levels by enalapril in deoxycorticosterone (DOCA-salt) hypertensive rats. Aorta morphology and the response of aortas with (E+) and without (E-) endothelium to noradrenaline, acetylcholine, and sodium nitroprusside were studied. DOCA-salt hypertensive and normotensive (control) rats were or were not treated with enalapril (5 mg/day/rat in the drinking fluid) for 1, 7, or 15 days. Blood pressure was measured before and after 1, 3, 7, and 15 days of enalapril treatment. Enalapril normalized the high blood pressure levels in 50% (responders) of the hypertensive rats after 3 to as many as 15 days but not after 1 day of treatment. Initial blood pressure levels were not different between responders and nonresponders. Blood pressure levels of normotensive control rats were not altered by enalapril treatment. The tunica media of aortas of DOCA-salt hypertensive rats treated or not treated with enalapril for 15 days was thicker than aortas from normotensive rats. Enalapril corrected the reduced response to acetylcholine observed in aorta from hypertensive rats from the first day of treatment. This treatment rendered aortas from normotensive control rats more sensitive (lower EC(50)) to acetylcholine without a change in the maximal responses. The responses to sodium nitroprusside, a nitric oxide donor, were unaltered in aorta E+ or E- from control and hypertensive rats before and after enalapril treatment. Enalapril did not correct the increased responses to noradrenaline observed in aorta E+ of hypertensive rats. These results suggest that the high blood pressure in DOCA-salt hypertension is not correlated with the altered response to endothelium-dependent agents (either dilator or constrictors). The endothelium-dependent vasodilation by antihypertensive agents can be corrected independently of normalization of blood pressure levels or the vascular morphology.

Distribution and space-time relationship of proteoglycans in the extracellular matrix of the migratory pathway of primordial germ cells in mouse embryos

In this paper we present an in situ ultrastructural cytochemical study on the distribution and spatial-temporal expression of proteoglycans (PGs) in the extracellular matrix of the migratory pathway of mouse primordial germ cells (PGCs) during the different phases of migration, by the use of the cationic dye ruthenium hexammine trichloride (RHT). Embryos of 9, 10, 11 and 12 days of development were used. The treatment with RHT revealed PGs as electron dense layers, granules, and filaments. Whereas granules prevailed in the extracellular spaces of the migratory route during the whole migratory process, the amount of filamentous structures increased during the migration phase of PGCs. At the end of the migratory process the surface of the PGCs lost its reaction by RHT. There were differences in the size of the granules of PGs at the initial migratory period (9-day-old embryos) as compared with the other days of gestation. There was a strong reaction for PGs in the extracellular spaces, expressed as a meshwork of granules interconnected by filaments, as well as reaction on the basement membranes during the peak of the PGCs migration in 10-day-old embryos. These results support the hypothesis that these molecules may have an important role in the migration of PGCs, although the precise mechanism involved in this process is not yet clear.

Ultrastructural cytochemical study of proteoglycans in the endometrium of pregnant mice using cationic dyes

Decidualization in rodents is accompanied by remarkable modifications of both fibrillar and non-fibrillar components of the endometrial extracellular matrix. Biochemical studies have shown that the levels of synthesis of hyaluronic acid and sulfated glycosaminoglycans change during decidualization in rodents. As the rodent decidua has regions containing cells in different stages of decidual transformation, we decided to analyse, by an ultrastructural cytochemical technique, the distribution of proteoglycans (PGs) in each region of the decidua of mice on different days of pregnancy. Endometria of mice on days 4, 5 and 7 of pregnancy were processed for electron microscopy in the presence of safranin O, a cationic dye which preserves most of the tissue PGs. The endometrium of non-pregnant mice was used as control. We observed evident differences in the arrangement and distribution of the network of PGs between non-pregnant and 4-day pregnant endometria, as well as between different regions of pregnant endometria. The possible relationship between these modifications and cell transformation that occurs during decidualization is discussed.

Autoradiography reveals regional metabolic differences in the endometrium of pregnant and nonpregnant mice

The rodent endometrium undergoes remarkable modifications during pregnancy, resulting from a redifferentiation of its fibroblasts. During this modification (decidualization), the fibroblasts transform into large, polyhedral cells that establish intercellular junctions. Decidualization proceeds from the subepithelial stroma towards the deep stroma situated next to the myometrium and creates regions composed of cells in different stages of differentiation. We studied by autoradiography whether cells of these different regions have different levels of macromolecular synthesis. Radioactive amino acids or radioactive sulfate were administered to mice during estrus or on different days of pregnancy. The animals were killed 30 min after injection of the precursors and the uteri were processed for light microscope autoradiography. Silver grains were counted over cells of different regions of the endometrium and are reported as the number of silver grains per area. Higher levels of incorporation of amino acids were found in pregnant animals as compared to animals in estrus. In pregnant animals, the region of decidual cells or the region of fibroblasts transforming into decidual cells showed the highest levels of synthesis. Radioactive sulfate incorporation, on the other hand, was generally higher in nonpregnant animals. Animals without decidual cell transformation (nonpregnant and 4th day of pregnancy) showed a differential incorporation by subepithelial and deep stroma fibroblasts. This study shows that regional differences in synthetic activity exist in cells that are in different stages of transformation into decidual cells as well as in different regions of the endometrium of nonpregnant mice.

Glutamine utilization by rat neutrophils: presence of phosphate-dependent glutaminase

The capacity of rat neutrophils to utilize glutamine was investigated by 1) determination of oxygen consumption in the presence of glucose or glutamine, 2) measurement of maximal activity of phosphate-dependent glutaminase, 3) Northern blot, Western blot, and immunocytochemical detection of glutaminase, and 4) measurement of glutamine utilization and also production of ammonia, glutamate, aspartate, alanine, and lactate and decarboxylation of [U-14C]glutamine in cells incubated for 1 h. The rate of respiration by isolated neutrophils in the absence of added substrate was 5.0 nmol x min(-1) x 10(7) cells(-1). Maximal activity of phosphate-dependent glutaminase was 56 nmol x min(-1) x mg protein(-1) in freshly obtained neutrophils; the Michaelis-Menten constant was 3.5 mM for glutamine. This enzyme activity was inhibited by 2 mM glutamate, 2 mM oxoglutarate, and 2 mM NH4Cl. The presence of glutaminase protein (65 kDa) was confirmed by Western blot and immunocytochemical detection and the presence of the mRNA (6.0 kb) by Northern blot analysis. Glutamine was utilized by neutrophils incubated for 1 h at a rate of 12.8 nmol x min(-1) x mg protein(-1) when the amino acid was added to the medium at 2 mM, which is three to four times higher than the physiological concentration. In the presence of 0.5 mM glutamine, the amino acid was utilized at a rate of 2.9 nmol x min(-1) x mg protein(-1). The addition of 0.5 mM glutamate to the incubation medium caused a marked reduction (by 70%) in glutamine utilization by neutrophils. Glucose was utilized at 7.7 nmol x min(-1) x mg protein(-1) when cells were incubated in 5 mM glucose. The conversion of [U-14C]glutamine to 14CO2 was very low: <1% was totally oxidized. The formation of ammonia was approximately 27% of glutamine utilization, and the conversion of glutamine to glutamate, aspartate, alanine, and lactate accounted for approximately 84.6% of the total amino acid utilized by neutrophils. In this study, evidence is presented that, in addition to lymphocytes and macrophages, neutrophils also utilize glutamine.

Possible modulatory role of non-activated lymphocytes on insulin secretion

In order to study the probable physiological role of non-activated lymphocytes on islet B-cells, we incubated and perfused rat pancreatic islets in the presence of low (2.8 mM) and high (16.7 mM) glucose concentrations after pre-exposure for 60 min to rat lymphocytes or to substances secreted by lymphocytes. Insulin secretion and 86Rb+, 45Ca2+ and [3H]-phosphoinositide metabolite fluxes were lower compared to controls when islets were pre-exposed to lymphocytes but were not different when islets were pre-exposed to substances secreted by lymphocytes. These alterations in isotope flux suggest that, when lymphocytes and islets are in contact, closure of potassium channels and a paradoxical effect of glucose load on insulin release occur in the presence of low glucose concentrations. The alterations observed are probably due to a swift and direct action of lymphocyte secretion perhaps induced by a direct of islet cells.

Impairment of insulin secretion in pancreatic islets isolated from Walker 256 tumor-bearing rats

Previous study has shown that insulin secretion in response to a glucose stimulus (16.7 mM) is reduced in islets isolated from Walker 256 tumor-bearing rats compared with controls. The ultrastructure, 45Ca2+ and 86Rb+ fractional outflow rate, phosphoinositide hydrolysis, and [U-14C]glucose decarboxylation were examined in islets isolated from tumor-bearing and control rats. The general morphological features of the islets from the control and experimental groups were very similar. The 86Rb+ fractional outflow rate was not changed, whereas the 45Ca2+ fractional outflow rate, [U-14C]glucose decarboxylation, and phosphoinositide metabolism were markedly reduced in islets from tumor-bearing rats. The changes in 45Ca2+ fractional outflow rate in islets from tumor-bearing rats were not due to impaired functioning of voltage-dependent calcium channels. By perifusing the islets in the presence of high potassium concentration, evidence was obtained that phospholipase C from islets from tumor-bearing rats reduced response to calcium. To further examine the mechanism involved in the impairment of insulin secretion by islets from tumor-bearing rats, islets isolated from normal rats were perifused after preincubation in the presence of serum from tumor-bearing rats. The results suggest that a thermolabile circulating factor is partially responsible for the changes described in islets isolated from Walker 256 tumor-bearing rats.

Death and replacement of uterine epithelial cells during oil-induced deciduoma development in the mouse

BACKGROUND

A decidual cell reaction can be induced in rodent endometrium by an intrauterine injection of oil. The epithelial lining is thought to be instrumental to transduce intralumenal stimuli for decidualization. One of the consequences of oil injection is the death of uterine epithelial cells. No information is available on the effect that sustained contact with oil has on the epithelium.

METHODS

A decidual cell reaction was induced in 4-day pseudopregnant mice by injection of 30 microliters of arachis oil into the uterine lumen. Samples from the uteri were collected 24, 48, and 72 h after the injection and prepared for transmission electron microscopy.

RESULTS

Twenty-four hours after the oil injection, some of the initial modifications of epithelial cell surfaces were very similar to those induced by the contact with the blastocyst during normal pregnancy. Uterine epithelial cells internalized injected oil and many cells were seen in various stages of degeneration. At 48 h, many epithelial cells were detached from the basal lamina. At 72 h, the uterine lining was re-established by flattened cells.

CONCLUSIONS

The contact of oil with the uterine epithelium of pseudo pregnant mice induces epithelial cell death in the antimesometrial region of the uterine crypt. There is, however, replacement of epithelial lining by epithelial cells, which probably migrate from the mesometrial region of the crypt. The prolonged presence of oil within the uterine lumen seems to induce cycles of epithelial cell death and replacement.

Incorporation of 3H-amino acids by endometrial stromal cells during decidualization in the mouse. A radioautographical study

The incorporation of 3H-amino acids by endometrial stromal cells was analyzed by radioautography during decidualization in the mouse. 3H-proline was administered to 5- and 6-day pregnant mice and to virgin mice in estrus used as controls. 3H-tryptophan was administered to 6-day pregnant mice. The animals were killed 30 min. after the injection of the radioactive label. The quantitative analysis of the radioautograms showed that the concentration of silver grains per unit area due to 3H-proline incorporation was higher in decidual and predecidual cells on the fifth and sixth day of pregnancy than in fibroblasts of virgin mice. Considering the pregnant endometrium by itself, the incorporation of both 3H-proline and 3H-tryptophan was higher in fully differentiated decidual cells and predecidual cells than in fibroblasts of the periphery of the endometrium and involuting decidual cells. These results show a clear correlation between different endometrial regions recognized by morphological criteria and their metabolic activity. The data also show that different cells of the pregnant endometrium have different metabolic activities, independently of the precursor that was used.

Biosynthesis of glycosaminoglycans in the endometrium during the initial stages of pregnancy of the mouse

Significant changes in the synthesis of glycosaminoglycans occur during the transformation of stromal cells of the endometrium into decidual cells which takes place during the initial stages of pregnancy in mice. Hyaluronic acid, which is practically absent in the endometrium of virgin mice, increases dramatically on the fifth day of pregnancy, reaching its maximal concentration on day 6 followed by a 50% decrease on day 7. Changes in hyaluronic acid concentration also occur in pseudopregnant mice indicating that they are not related to the presence of the embryo in the uterus. The absolute concentration of the sulfated glycosaminoglycans, e.g., heparan sulfate, dermatan sulfate and chondroitin sulfate in the decidua did not change significantly. There was, however, a striking decrease of their biosynthesis in pregnant and pseudopregnant mice when compared to virgin mice, as shown by the use of radioactive inorganic sulfate as a precursor for the study of in vivo synthesis. A radioautographical analysis confirmed that the highest incorporation of radioactive sulfate was observed in virgin endometria when compared to pregnant ones. These studies also have shown a characteristic pattern of labeling in different regions of the endometrium that repeats itself during the different days of pregnancy.

Distribution of desmoplakin I/II in endometrial cells of mice in the artificially induced decidua

The decidual reaction is characterized by the redifferentitation of the endometrial connective tissue into a tissue with epithelioid features formed by decidual cells. An ultrastructural study showed a special type of junction formed between differentiating (predecidual) cells of the mouse from day six of pseudopregnancy onward. These contacts share ultrastructural characteristics of both desmosome and adherens junctions. These junctions have usually been classified as desmosome-like. In the present work, besides the ultrastructural analysis, we investigated with light microscopy the presence of desmoplakins I and II, using streptavidin-biotin immunoperoxidase technique. We found a positive punctate staining around predecidual cells while a scarce reaction was observed in the other regions of the uterus. These results suggest that these junctions belong to the desmosome family.

Histochemical demonstration of phospholipid containing choline in the cytoplasm of murine decidual cells

The localization of lipids in the endometrium of virgin and 6- to 9-day-pregnant mice was detected by histochemical methods. Total lipids (as shown by staining with Sudan black) and phospholipids containing choline (PCC) were detected. Sections subjected to reactions that have been proposed for the demonstration of vitamins E and D and cholesterol gave negative results. In the virgin animals, lipids were found in epithelial cells but not in the endometrial storma. On the other hand in the pregnant animals, the endometrial stroma contained both Sudan-black-stained lipids and PCC. Maximal staining was reached on day 8 of pregnancy. The staining was more conspicuous in the more differentiated decidual cells adjacent to the embryos than in the less differentiated predicidual cells. The nondecidualized stroma, situated peripherally near the myometrium did not stain for lipids. In the cytoplasm of decidual cells the reaction for PCC was observed in the form of granules, which were often arranged in groups surrounding the nuclei. We suggest that decidual cells store PCC to be mobilized as a precursor for mediators of decidualization, such as prostaglandins, that would act as paracrine inducers of the decidual reaction.

Implantation and decidualization in rodents

This article reviews the main events of embryo-implantation and decidualization in rodents. In common laboratory rodents the embryo attaches to the uterine epithelial lining, usually on days 4 to 6 of pregnancy. A progressive degree of proximity between trophoblast and epithelium occurs until the epithelial cells undergo apoptosis and detach from the basement membrane. During the attachment stage, the spindle-shaped connective tissue cells that underlie the epithelium next to the embryos transform into polyhedral and closely packed decidual cells. Following the epithelial detachment and the breaching of the basement membrane the embryo is thus in direct contact with decidual cells. These cells accumulate organelles associated with synthesis of macro-molecules, intermediate filaments, and eventually lipid droplets and glycogen. Another remarkable feature of decidual cells is the establishment of gap and adherens intercellular junctions. Differentiation of fibroblasts into decidual cells advances antimesometrially and mesometrially, creating in the endometrium several regions of cells with different morphology. The whole phenomenon of decidualization which is normally triggered by the embryo can be artificially induced in pseudo-pregnant or hormonally-prepared animals with the use of diverse stimuli. The uterine epithelium is probably responsible for the transduction of the initial stimulus. Prostaglandins have been shown to be important in the induction of decidualization. More recently other substances such as leukotrienes, platelet-activating factor (PAF), and transforming growth factor (TGF) have been thought to play a role in induction. Much evidence points to prostaglandin production by the decidual cells. New proteins such as a luteotropic factor, desmin, and other molecules were shown to be produced after rat stromal cells undergo decidual transformation. The extracellular matrix of the mouse decidua contains very thick collagen fibrils. Mouse decidual cells are also very active in phagocytosing the thick fibrils, contributing to the remodeling and involution of the decidua that accompanies embryonic growth. Radioautographic data indicates that mouse decidual cells produce and secrete collagen and sulfated proteoglycans.

Remodeling of the mouse endometrial stroma during the preimplantation period

An ultrastructural cytochemical study of acid phosphatase activity performed in mouse endometrium on the second day of pregnancy showed that stromal cells which were heavily labeled by the cytochemical reaction had disarranged organelles. On the other hand, the cytoplasm of several stromal cells had collagen-containing phagosomes that were also labeled, indicating that the collagen fibrils were being digested by lysosomal enzymes. It is suggested that cell death and phagocytosis of collagen are events of the remodeling of the mouse endometrium that occur prior to decidualization.

Organization of intermediate filaments and their association with collagen-containing phagosomes in mouse decidual cells

We have analyzed the distribution of intermediate filaments (IF) in the cytoplasm of mature decidual cells of mice. IF were scattered throughout the cytoplasm of these cells although there was a preferential accumulation around the nuclei. In many cells a large area of the cytoplasm was occupied by a rich network of IF that extended from the perinuclear region toward the cell surface. Thin bundles of IF crossed the cytoplasm without a preferential orientation. IF were also seen in close association with nuclear pore complexes, gap junctions, mitochondria, and lysosomes. A very developed network of IF surrounded phagosomes that contained collagen fibrils. Longitudinal and cross sections of these phagosomes showed a very close association of IF with the phagosome membrane.

Diameter increase of collagen fibrils of the mouse endometrium during decidualization

The diameter of collagen fibrils was measured in different regions of the antimesometrial endometrium of mice on days 5, 6, and 7 of pregnancy as well as in the endometrium of virgin mice. The average diameter of fibrils of virgin mice was 39.18 nm (range: 20-80). In the region of fully decidualized cells, the averages and ranges were 45.32 nm (30-170), 89.39 nm (30-270), and 125.88 nm (20-370), respectively, on days 5, 6, and 7 of pregnancy. Thick fibrils larger than 70 nm had irregular profiles. Our results show that the increase in diameter is associated with the decidualization of the mouse endometrium.

Phagocytosis of collagen by mouse decidual cells

Collagen fibrils were present within membrane-bound vacuoles in the cytoplasm of mouse decidual cells on the 7th day of pregnancy. The space between the vacuole membranes and the fibrils was narrow and frequently filled with a granular electron-dense material. The loss of banding of the collagen fibrils, their association with lysosomelike bodies, and the demonstration of acid phosphatase activity in the vacuoles indicate that the fibrils were internalized by the decidual cells and were being digested. It is suggested that phagocytosis of collagen is a mechanism of remodeling of the mouse decidua.

Autoradiographic investigation of effects of high-dose colchicine on dentinogenesis in rat incisors

Twelve female Wistar rats received 1.5 mg/kg of colchicine (CLC) intravenously. Control animals were similarly injected with isotonic saline solution. The animals were killed 5 h, 24 h, 3 days and 7 days after injection. Ninety minutes prior to sacrifice, all animals received an intraperitoneal injection of 3H-proline. Autoradiograms of maxillary incisors showed that CLC increased the retention of the labeled precursor in the odontoblasts. It was also shown that the odontoblasts in the different sectors of the rat incisor present different sensitivities to the CLC action.

Cell proliferation in synovial membrane of young mice

The labelling index (LI) of the synoviocytes of the lining-layer cells and of the underlying connective-tissue cells was determined in the synovial membrane of 5-, 10-, 21-, 30-, and 55 day-old mice, following a pulse labelling with [3H]-thymidine. Both the synoviocytes and underlying connective-tissue cells incorporated [3H]-thymidine within 1 h after injection. No significant difference was observed between the LI of these two regions of the synovial membrane. The results indicate that synoviocytes are capable of cell division even in non-pathological conditions.

Collagen remodeling during decidualization in the mouse

An ultrastructural study of the features and distribution of collagen fibrils was performed in the endometrium of virgin and pregnant (2nd to 11th day) mice. Collagen-containing structures were observed in the cytoplasm of fibroblasts on the 2nd day of pregnancy. Treatment of tissues with lanthanum nitrate established that these structures were intracytoplasmic. Their association with lysosome-like bodies suggested the occurrence of intracellular digestion of collagen, probably connected with remodeling of the endometrial stroma prior to decidualization. On the 4th day of pregnancy, very few collagen fibrils were present in the intercellular space. From the 6th day of pregnancy onwards, "thick" collagen fibrils were observed between decidual cells. The diameter of these fibrils measured up to 300 nm whereas the fibrils present in the endometrium of virgin mice measured 40-68 nm.