Contact-associated interactions between large and small bovine luteal cells during the estrous cycle

Effects of prostaglandin F2α on angiogenic and steroidogenic pathways in the bovine corpus luteum may depend on its route of administration

Prostaglandin (PG) F_2α and its analogs (aPGF_2α) are used to induce regression of the corpus luteum (CL); their administration during the middle stage of the estrous cycle causes luteolysis in cattle. However, the bovine CL is resistant to the luteolytic actions of aPGF_2α in the early stage of the estrous cycle. The mechanisms underlying this differential luteal sensitivity, as well as acquisition of luteolytic sensitivity by the CL, are still not fully understood. Therefore, to characterize possible differences in response to aPGF_2α administration, we aimed to determine changes in expression of genes related to (1) angiogenesis-fibroblast growth factor 2 (FGF2), fibroblast growth factor receptor 1 (FGFR1), fibroblast growth factor receptor 2 (FGFR2), vascular endothelial growth factor A (VEGFA), vascular endothelial growth factor receptor 1 (VEGFR1), vascular endothelial growth factor receptor 2 (VEGFR2); and (2) steroidogenesis-steroidogenic acute regulatory protein (STAR), cytochrome P450 family 11 subfamily A member 1 (P450scc), and hydroxy-delta-5-steroid dehydrogenase, 3 β- and steroid delta-isomerase 1 (HSD3B) in early- and middle-stage CL that accompany local (intra-CL) versus systemic (i.m.) aPGF_2α injection. Cows at d 4 (early stage) or d 10 (middle stage) of the estrous cycle were treated as follows: (1) systemic saline injection, (2) systemic aPGF_2α injection (25 mg), (3) local saline injection, and (4) local aPGF_2α injection (2.5 mg). Progesterone (P₄) concentration was measured in jugular vein blood samples during the entire set of experiments. After 4 h of treatment, CL were collected by ovariectomy, and mRNA and protein expression levels were determined by reverse transcription quantitative-PCR and Western blotting, respectively. Local and systemic aPGF_2α injections upregulated FGF2 expression but decreased expression of VEGFA in both CL stages. Both aPGF_2α injections increased the expression of STAR in early-stage CL, but downregulated it in middle-stage CL. In the early-stage CL, local administration of aPGF_2α upregulated HSD3B, whereas systemic injection decreased its mRNA expression in early- and middle-stage CL. Moreover, we observed a decrease in the P₄ level earlier after local aPGF_2α injection than after systemic administration. These results indicate that aPGF_2α acting locally may play a luteotrophic role in early-stage CL. The systemic effect of aPGF_2α on the mRNA expression of genes participating in steroidogenesis seems to be more substantial than its local effect in middle-stage CL.

Effects of concanavalin A on the progesterone production by bovine steroidogenic luteal cells in vitro

The aim of this study was to evaluate the effects of concanavalin A (CONA) on the progesterone (P4) production by bovine steroidogenic luteal cells (LCs) in vitro. Luteal cells were collected during the mid-luteal stage (at 10-12 days following ovulation) and processed in the laboratory. Luteal cells were grown for 7 days in a humid atmosphere with 5% CO2 , with or without 10% foetal bovine serum, and were subjected to the following treatments: control: no treatment; CONA (10 μg/ml); LH (100 μg/ml); CONA + LH; LH (100 μg/ml) + prostaglandin F2α (PGF2α) (10 ng/ml); CONA + LH + PGF2α. Samples of the culture media were collected on days 1 (D1) and 7 (D7) for P4 quantification. The cells were counted on D7 of culture. Differences between treatments were considered statistically significant at p < .05. Culture in the presence of CONA decreased the P4-secreting capacity of LCs on D7 of culture, particularly in the absence of serum. The cell numbers did not change between treatments.

[Reference ranges of insulin, insulin like growth factor-1 and adrenocorticotropic hormone in ponies]

OBJECTIVES

The aim of this study was to validate a chemiluminescence immunometric assay using the IMMULITE 2000® for the determination of adrenocorticotropic hormone (ACTH), insulin and insulin-like growth factor-1 (IGF-1) from which reference ranges were calculated for ponies.

MATERIAL AND METHODS

Blood samples of 130 ponies aged 3-32 years were collected in the afternoon. The reference ranges were calculated according to the Guideline EP28-A3C of the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) from 2010.

RESULTS

The determined intraday precision for insulin was 3.28%, for ACTH 3.35% and for IGF-1 1.84%. The interday precision (insulin: 3.45%; IGF-1: 2.89%; ACTH: 9.77%) was determined on three consecutive days, where the samples were stored at 4   °C. There was no significant loss of insulin activity nor of ACTH or IGF-1 concentration during this time. The reference ranges of insulin and IGF-1 (2.0-21.2 mU/l and 50.2-357.2 mU/l, respectively) were age independent, whereas for ACTH, an age-dependent reference range was established. Ponies aged 3-12 years had a significantly lower reference range (4.2-19.8 pg/ml) than ponies aged 13-32 years (5.0-22.6 pg/ml).

CONCLUSION

The method used is suitable for the determination of ACTH, IGF-1 and insulin in serum of ponies, but the lowest detection limit for insulin is 2.0 mU/l.

CLINICAL RELEVANCE

The calculated reference ranges of insulin and ACTH are helpful for the diagnosis and clinical monitoring of equine metabolic syndrome and pituitary pars intermedia dysfunction (PPID).

Role of gap junctions in regulation of progesterone secretion by ovine luteal cells in vitro

To evaluate the role of gap junctions in the regulation of progesterone secretion, two experiments were conducted. In Experiment 1, luteal cells obtained on days 5, 10, and 15 were cultured overnight at densities of 50 x 10(3), 100 x 10(3), 300 x 10(3), and 600 x 10(3) cells/dish in medium containing: (1) no treatment (control), (2) LH, or (3) dbcAMP. In Experiment 2, luteal cells from days 5 and 10 of the estrous cycle were transfected with siRNA, which targeted the connexin (Cx) 43 gene. In Experiment 1, progesterone secretion, Cx43 mRNA expression, and the rates of gap junctional intercellular communication (GJIC), were affected by the day of the estrous cycle, cell density, and treatments (LH or dbcAMP). The changes in progesterone secretion were positively correlated with the changes in Cx43 mRNA expression and the rates of GJIC. Cx43 was detected on the luteal cell borders in every culture, and luteal cells expressed 3beta-hydroxysteroid dehydrogenase. In Experiment 2, two Cx43 gene-targeted sequences decreased Cx43 mRNA expression and progesterone production by luteal cells. The changes in Cx43 mRNA expression were positively correlated with changes in progesterone concentration in media. Thus, our data demonstrate a relationship between gap junctions and progesterone secretion that was supported by (1) the positive correlations between progesterone secretion and Cx43 mRNA expression and GJIC of luteal cells and (2) the inhibition of Cx43 mRNA expression by siRNA that resulted in decreased production of progesterone by luteal cells. This suggests that gap junctions may be involved in the regulation of steroidogenesis in the ovine corpus luteum.

Involvement of the cytoskeleton in oxytocin secretion by cultured bovine luteal cells

A number of substances have been implicated in the regulation of oxytocin (OT) secretion from bovine corpus luteum in vivo. However, isolated bovine luteal cells cultured in a monolayer lose the ability to secrete OT in response to stimulatory substances. The present study investigated how cell-to-cell contact and the cytoskeleton affect OT secretion by isolated bovine luteal cells. In experiment 1, bovine midluteal cells (Days 8-12 of the estrous cycle) were stimulated with prostaglandin F2alpha (PGF2alpha; 1 microM), noradrenaline (NA; 10 microM), or growth hormone (GH; 5 nM) in two culture systems: In one system, cell monolayers were incubated in 24-well culture plates, and in the other system, aggregates of cells were incubated in glass tubes in a shaking water bath. The cells cultured in a monolayer underwent considerable spreading and showed a variety of shapes, whereas the cells cultured in glass tubes remained fully rounded during the experimental period and soon formed aggregates of cells. Although PGF2alpha, NA, and GH did not stimulate OT secretion by the monolayer cells, all tested substances stimulated OT secretion by the aggregated cells (P < 0.01). In experiment 2, the monolayer cells were pre-exposed for 1 h to an antimicrofilament agent (cytochalasin B; 1 microM) or two antimicrotubule agents (colchicine or vinblastine; 1 microM) before stimulation with PGF2alpha, NA, or GH. Although PGF2alpha, NA, and GH did not stimulate OT secretion by the monolayer cells in the presence of colchicine or vinblastine, they all stimulated OT secretion in the presence of cytochalasin B (P < 0.001). The overall results show that OT secretion by bovine luteal cells depends on microfilament function and cell shape. Moreover, the aggregate culture system that allows three-dimensional, cell-to-cell contact seems to be a good model for studying OT secretion by isolated bovine luteal cells.

Effects of Prostaglandin F2.ALPHA. and Nitric Oxide on the Secretory Function of Bovine Luteal Cells

The objective of the present study was to investigate the influence of prostaglandin F(2alpha) (PGF (2alpha)) and nitric oxide (NO) on production of steroids and PGs by culturing bovine luteal cells obtained from ovaries on days 8-12 of the estrous cycle with a nitric oxide (NO) donor (Spermine NONOate), and a NO synthase inhibitor (N(G)-nitro-L-arginine methyl ester dihydrochloride: L-NAME). When the cells were exposed for 24 h to PGF(2alpha) (10(-7)-10(-5) M), production of progesterone (P(4)) increased significantly at all doses used (P<0.05). Moreover, PGF(2alpha) stimulated PGF(2alpha) production (P<0.01), depressed testosterone (T) production (P<0.05), but did not affect synthesis of prostaglandin E(2) (PGE(2)). Spermine NONOate decreased P(4) production to 66%, 47% and 34% of the control concentration after treatment with 10(-5) M, 10(-4) M and 10(-3) M, respectively, but did not affect T production, and increased PGF(2alpha) synthesis (P<0.05) and PGE(2) (P<0.01) at all doses used. L-NAME increased production of P(4) (P<0.01) but did not affect (P>0.05) secretion of T, PGF(2alpha) and PGE(2). Estradiol-17beta (E(2)) was detectable on the level of sensitivity of assay and was not significantly altered by any treatments. The overall results suggest that PGF(2alpha) and NO produced locally in bovine CL play roles in the regulation of the secretory function of the bovine CL as auto/paracrine factors.

Influence of nitric oxide on the secretory function of the bovine corpus luteum: dependence on cell composition and cell-to-cell communication

The objective of the present study was to investigate the role of cell-to-cell contact in the influence of nitric oxide (NO) on the secretory function of the bovine corpus luteum (CL). In Experiment 1, separate small luteal cells (SLC) or large (LLC) luteal cells were perfused with 100 micro M spermineNONOate, a NO donor, or with 100 micro M Nomega-nitro-L-arginine methyl ester (L-NAME), a NO synthase (NOS) inhibitor; in Experiment 2, a mixture of LLC and SLC and endothelial cells was cultured and incubated with spermineNONOate or L-NAME; in Experiment 3, spermineNONOate was perfused into the CL (100 mg/4 hr) by a microdialysis system in vivo. Perfusion of isolated SLC and LLC with the NO donor or NOS inhibitor (Experiment 1) did not affect (P > 0.05) secretion of progesterone (P(4)) or oxytocin (OT). L-NAME perfusion increased (P < 0.05) leukotriene C(4) (LTC(4)) secretion by both SLC and LLC cells. Treatment of mixtures of luteal cells with an NO donor (Experiment 2) significantly decreased (P < 0.001) secretion of P(4) and OT and increased (P < 0.001) production of prostaglandin F(2alpha) (PGF(2alpha)) and LTC(4). L-NAME stimulated (P < 0.001) P(4) secretion, but did not influence (P > 0.05) OT, PGF(2alpha) or LTC(4) production. Intraluteal administration (Experiment 3) of spermineNONOate increased (P < 0.001) LTC(4) and PGF(2alpha), decreased OT, but did not change P(4) levels in perfusate samples. These data indicate that cell-to-cell contact and cell composition play important roles in the response of bovine CL to treatment with NO donors or NOS inhibitors, and that paracrine mechanisms are required for the full secretory response of the CL in NO action. Endothelial cells appear to be required for the full secretory response of the CL to NO.

Effects of second messengers on gap junctional intercellular communication of ovine luteal cells throughout the estrous cycle

Corpora lutea (CL) from Days 5, 10, and 15 after superovulation were enzymatically dispersed, and a portion of the cells were elutriated to obtain fractions enriched with small or large luteal cells. Mixed, small, and large luteal cell fractions were incubated with no treatment or with agonists or antagonists of cAMP (dbcAMP or Rp-cAMPS), protein kinase C (PKC; TPA or H-7), or calcium (A23187, EGTA, or A23187 + EGTA). The rate of contact-dependent gap junctional intercellular communication (GJIC) was evaluated by laser cytometry. Media were collected for progesterone (P(4)) radioimmunoassay, and luteal cells cultured with no treatment were fixed for immunocytochemistry or frozen for Western blot analysis. Luteal cells from each stage of the estrous cycle exhibited GJIC. The dbcAMP increased (P < 0.05) GJIC for all cell types across the estrous cycle. The Rp-cAMPS decreased (P < 0.05) GJIC for small luteal cells on Day 5 and for all cell types on Days 10 and 15. The TPA inhibited (P < 0.01), but H-7 did not affect, GJIC for all cell types across the estrous cycle. The A23187 decreased (P < 0.05) GJIC for large luteal cells touching only small or only large luteal cells, whereas A23187 + EGTA decreased (P < 0.05) GJIC for all cell types across the estrous cycle. For the mixed and large luteal cell fractions, dbcAMP increased (P < 0.05), but TPA and A23187 + EGTA decreased (P < 0.05), P(4) secretion. The A23187 alone decreased (P < 0.05) P(4) secretion by large, but not by mixed, luteal cells. For all days and cell types, the rate of GJIC and P(4) secretion were correlated (r = 0.113-0.249; P < 0.01). Connexin 43 was detected in cultured luteal cells by immunofluorescence and Western immunoblotting. Thus, intracellular regulators like cAMP, PKC, or calcium appear to regulate GJIC, which probably is an important mechanism for coordinating function of the ovine CL.

Keratinocyte growth factor expression by the bovine corpus luteum

Communication between cells of the corpus luteum (CL) is thought to be necessary for normal luteal function. Keratinocyte growth factor (KGF) is produced by mesenchymally derived cells in numerous tissues and acts on epithelial cells. In bovine follicles, theca cells produce KGF, which can stimulate granulosa cell proliferation. Whether KGF is produced by ovarian cells after luteinization is unknown. Our objective was to determine whether KGF mRNA and protein were present in bovine luteal tissue, and if so, to determine what type(s) of luteal cells contains KGF. CL (n = 3-4/day) were obtained from specific days throughout diestrus. Presence of KGF mRNA in CL was determined using a porcine KGF anti-sense cRNA probe. Northern analyses of luteal tissue poly(A)+ RNA revealed a single transcript (approximately 2.0 kilobases), the quantity of which did not change throughout diestrus. Western analysis revealed an immunoreactive band (28 kDa) in luteal tissues and theca cell homogenates that was absent from granulosa cell homogenates. Immunocytochemistry showed KGF predominantly in theca and small luteal cells. Results indicate that bovine CL produce and contain KGF, which is primarily localized in small luteal cells. Therefore, KGF may participate in paracrine communication within the bovine CL.

Gap junctional intercellular communication of bovine luteal cells from several stages of the estrous cycle: effects of prostaglandin F2 alpha, protein kinase C and calcium

Cellular interactions mediated by both contact-dependent and contact-independent mechanisms are probably important to maintain luteal function. The present studies were performed to evaluate the effects of luteotropic and luteolytic hormones, and also intracellular regulators, on contact-dependent gap junctional intercellular communication (GJIC) of bovine luteal cells from several stages of luteal development. Bovine corpora lutea (CL) from the early, mid and late luteal phases of the estrous cycle were dispersed with collagenase and incubated with no treatment, LH, PGF or LH + PGF (Experiment 1), or with no treatment, or agonists or antagonists of protein kinase C (TPA or H-7) or calcium (A23187 or EGTA; Experiment 2). After incubation, media were collected for determination of progester-one concentrations. Then the rate of GJIC was evaluated for small luteal cells in contact with small luteal cells, and large luteal cells in contact with small luteal cells by using the fluorescence recovery after photobleaching technique and laser cytometry. Luteal cells from each stage of the estrous cycle exhibited GJIC, but the rate of GJIC was least (P < 0.05) for luteal cells from the late luteal phase. LH increased (P < 0.05) GJIC between small luteal cells from the mid and late but not the early luteal phase. PGF increased (P < 0.05) GJIC between small luteal cells from the mid luteal phase and diminished (P < 0.05) LH-stimulatory effects on GJIC between small luteal cells from the late luteal phase. Throughout the estrous cycle, TPA decreased (P < 0.05) the rate of GJIC between large and small, and between small luteal cells, and A23187 decreased (P < 0.05) the rate of GJIC between large and small luteal cells. LH and LH + PGF, but not PGF alone increased (P < 0.05) progesterone secretion by luteal cells from the mid and late luteal phases. Agonists or antagonists of PKC or calcium did not affect progesterone secretion by luteal cells. These data demonstrate that both luteal cell types communicate with small luteal cells, and the rate of communication depends on the stage of luteal development. LH and PGF affect GJIC between small luteal cells during the fully differentiated (mid-luteal) and regressing (late luteal) stages of the estrous cycle. In contrast, at all stages of luteal development, activation of PKC decreases GJIC between small and between large and small luteal cells, whereas calcium ionophore decreases GJIC only between large and small luteal cells. Luteotropic and luteolytic hormones, and intracellular regulators, may be involved in regulation of cellular interactions within bovine CL which likely is an important mechanism for coordination of luteal function.

Effects of luteinizing hormone and prostaglandin F(2α) on gap junctional intercellular communication of ovine luteal cells throughout the estrous cycle

Cellular interactions mediated by contact-dependent pathways may be important to maintain luteal function. The objective of the present experiment was to evaluate the role of LH and prostaglandin F(2α) (PGF) in regulation of contact-dependent, gap junctional intercellular communication (GJIC) of ovine luteal cells from several stages of luteal development. Corpora lutea (CL) obtained from superovulated ewes on days 5 (n=7), 10 (n=8), and 15 (n=9) after estrus were dispersed with collagenase and cell types were separated by elutriation. Cells were plated as a mixed population (nonelutriated), or as small or large luteal cell fractions, and incubated in serum-free media containing no hormone, LH (100 ng/mL), PGF (100 ng/mL), LH+PGF, or dibutyryl cAMP (dbcAMP; 2 mM) for 18-24 h. Media were collected for evaluation of progesterone (P4) concentrations and replaced with media containing fluorescent dye. Then the rate of GJIC was evaluated by using the fluorescence recovery after photobleaching technique and laser cytometry. The rate of GJIC was determined for selected cells: small luteal cells in contact only with small luteal (S-S) cells; large luteal cells in contact only with small luteal (L-S) cells; and large luteal cells in contact only with large luteal (L-L) cells. LH increased (p<0.01) GJIC for S-S on d 5 and 10 and for L-S cells across the estrous cycle, but did not affect GJIC for L-L cells. PGF increased (p<0.05) GJIC for L-L cells on d 10 and 15, and decreased (p<0.05) GJIC for S-S cells from d 5 and 10 of the estrous cycle. LH+PGF increased (p<0.05) GJIC for S-S cells on d 5 and 10, and for L-S and L-L cells on d 10 and 15 of the estrous cycle. In addition, PGF diminished (p<0.05) LH-stimulatory effects on GJIC for S-S cells from d 5 and 10, and for L-S cells from d 5 of the estrous cycle. Dibutyryl cAMP stimulated (p<0.05) GJIC between all evaluated cell types across the estrous cycle. LH and dbcAMP stimulated (p<0.05) P4 secretion by mixed and small luteal cell fractions, PGF alone did not affect basal P4 secretion, but LH+PGF stimulated (p<0.05) P4 production by small luteal cells across the estrous cycle. PGF diminished (p<0.05) LH-stimulatory effects on P4 production in mixed populations of luteal cells across the estrous cycle.These data demonstrate that both luteal cell types communicate with each other, and the rate of communication was affected by LH, PGF, and dbcAMP. Modulation of gap junctional contact-dependent intercellular communication may be an important mechanism by which regulatory signals are transduced during luteal growth, differentiation, and regression in sheep.

Intercellular communication in the bovine corpus luteum

There is a growing body of evidence that intercellular communication is important in the regulation of luteal function. Although the nature of the interactions between small and large luteal cells are not yet clear, it seems likely that they do exist. Many of the substances to which luteal cells respond, such as prostaglandins, growth factors, oxytocin and progesterone, are produced locally. These substances may act as paracrine factors to modulate the response of luteal cells to hormonal signals. Endothelial cells also produce factors that can modify steroidogenesis, and luteal cell-stimulation of endothelial cell proliferation is necessary for the extensive angiogenesis that occurs during luteinization Finally, bidirectional intercellular communication likely occurs between luteal cells and resident immune cells. Immune cells produce cytokines that can modify progesterone and prostaglandin synthesis by luteal cells. Cytokines may also have direct cytotoxic effects on luteal cells, and dead cells are then phagocytized by resident macrophages. Also, factors secreted by luteal cells can serve as chemoattractants for immune cells, and can enhance or suppress immune cell functions. There is little doubt that intercellular communication within the corpus luteum is very complex. One must remember, however, that nearly all evidence collected thus far is based on in vitro studies. Eventually, technology will allow for study of these interactions in vivo, and may lead to new methods for control of luteal function.