Effect of basal lamina of ovarian follicle on T- and L-type Ca(2+) currents in differentiated granulosa cells

Canstatin modulates L-type calcium channel activity in rat ventricular cardiomyocytes

Excessive increase of cytosolic Ca²⁺ through the activation of L-type Ca²⁺ channels (LTCCs) via β adrenergic receptor induces apoptosis of cardiomyocytes. Canstatin, a cleaved fragment of collagen type IV α2 chain, is abundantly expressed in normal heart tissue. We previously reported that canstatin inhibits β adrenergic receptor-stimulated apoptosis in cardiomyoblasts. Here, we tested the hypothesis that canstatin regulates LTCCs activity in ventricular cardiomyocytes. Collagen type IV α2 chain (COL4A2) small interfering (si) RNA (for canstatin suppression) or control siRNA was injected via jugular vein in Wistar rats. Two days after the injection, electrocardiogram (ECG) was recorded and the left ventricular tissue was isolated using Langendorff apparatus. Immunofluorescence staining was performed to clarify the distribution of canstatin in cardiomyocytes. The knockdown efficiency was confirmed by Western blotting. The L-type Ca²⁺ channel current (I_CaL) of ventricular cardiomyocyte was measured by a whole-cell patch clamp technique. In immunofluorescence staining, colocalization of canstatin and α_v integrin was observed in the isolated ventricular cardiomyocytes. The I_CaL of ventricular cardiomyocyte isolated from COL4A2 siRNA-injected rats was significantly enhanced compared with control siRNA-injected rats. Recombinant canstatin (250 ng/ml) significantly reversed it. ECG analysis showed that QT interval tended to be shortened and amplitude of T wave was significantly increased in the COL4A2 siRNA-injected rats. In summary, we for the first time clarified that suppressing canstatin expression increases the basal I_CaL in ventricular cardiomyocytes. It is proposed that canstatin might play a role in the stabilization of cardiac function through the modulation of LTCC activity in cardiomyocytes.

Feed intake alters immune cell functions and ovarian infiltration in broiler hens: implications for reproductive performance

Leukocytes are known to participate in ovarian activities in several species, but there is a surprising lack of information for the common chicken. Broiler hens consuming feed ad libitum (AL) exhibit a number of ovarian irregularities, but leukocyte functions are unstudied. In contrast to feed-restricted (R) hens, AL feeding for 7 wk significantly reduced egg production and clutch length while increasing pause length and atretic follicle numbers (P < 0.05). Granulosa cells from F1 follicles of AL hens contained less progesterone, and follicle walls were thicker with loose fibrous morphology and had less collagenase-3-like gelatinolytic activity but more IL-1beta (P < 0.05) production, suggestive of slower maturation in ovulatory process and inflamed necrosis. Interestingly, while highly infiltrated with immune cells, particularly heterophils, IL-1beta, MMP-22-like, and gelatinase A activities were reduced in AL hen peripheral heterophils and monocytes (P < 0.05); however, AL monocytes showed an increase in phagocytosis rate (P < 0.05). Generation of reactive oxygen intermediates was also suppressed in AL heterophils but increased in AL monocytes (P < 0.05). In contrast to leukocyte-free control, both AL and R heterophils and monocytes suppressed progesterone production and increased cell death in a dose-dependent manner when coincubated with granulosa cells at different ratios (P < 0.05). AL monocytes suppressed progesterone production more, but AL heterophils were less proapoptotic when compared to their R counterparts (P < 0.05). Alterations of cellular ceramide content (P < 0.05) corresponded to the discrepancy between heterophil and monocyte functionality. In conclusion, leukocyte dysfunction contributes to impaired ovarian activities of overfed broiler hens.

Palmitic acid in chicken granulosa cell death-lipotoxic mechanisms mediate reproductive inefficacy of broiler breeder hens

In vivo and in vitro approaches were used to elucidate mechanisms of palmitate-induced cytotoxicity of follicle granulosa cells in fuel-overloaded broiler hens. In contrast to their energy-restricted counterparts, broiler breeder hens fed ad libitum for 2 wk had dyslipidemia, atresia within hierarchical ovarian follicles, and a 34% reduction in egg production (P < 0.05). Based on vital staining of freshly isolated granulosa cells with annexin V/propidium iodide, there were increases in apoptosis consistent with suppressed Akt activation (P < 0.05). Supplementing primary granulosa cell cultures with 0.5 mM palmitate for 48 or 96 h increased apoptosis (P < 0.05). Palmitate-induced cell death was accompanied by increased acyl-CoA oxidase, carnitine palmitoyl transferase-1, serine palmitoyl transferase, and sphingomyelinase transcripts and increased concentrations of proinflammatory interleukin-1β (P < 0.05). Triacsin-C inhibition of fatty acyl-CoA synthesis blunted interleukin-1β production and rescued granulosa cultures from palmitate-induced cell death. That there was partial to complete prevention of cell death with addition of the free radical scavenger pyrrolidine dithiocarbamate, the sphingomyelinase inhibitor imipramine, or the de novo ceramide synthesis inhibitor fumonisin B1, supported the notion that palmitate-induced granulosa cell cytotoxicity operated through a palmitate-derived metabolite. Palmitoyl-CoA may be channeled into β-oxidation and/or into bioactive metabolites that increase free radical generation, an inflammatory response, and ceramide production. In conclusion, palmitate-derived metabolites activated apoptotic machinery in avian granulosa cells, which caused ovarian follicular atresia and reduced egg production in fuel-overloaded broiler breeder hens.

Absence of SPARC leads to impaired lens circulation

SPARC is a matricellular glycoprotein involved in regulation of extracellular matrix, growth factors, adhesion, and migration. SPARC-null mice have altered basement membranes and develop posterior sub-capsular cataracts with cell swelling and equatorial vacuoles. Exchange of fluid, nutrients, and waste products in the avascular lens is driven by a unique circulating ion current. In the absence of SPARC, increased circulation of fluid, ions, and small molecules led to increased fluorescein distribution in vivo, loss of resting membrane polarization, and altered distribution of small molecules. Microarray analysis of SPARC-null lenses showed changes in gene expression of ion channels and receptors, matrix and adhesion genes, cytoskeleton, immune response genes, and cell signaling molecules. Our results confirm the hypothesis that the regulation of SPARC on cell-capsular matrix interactions can increase the circulation of fluid and ions in the lens, and the phenotype in the SPARC-null mouse lens is the result of multiple intersecting functional pathways.

Cocaine- and amphetamine-regulated transcript regulation of follicle-stimulating hormone signal transduction in bovine granulosa cells

Regulation of estradiol production, central to ovarian follicular development and reproductive function, is mediated by a complex interaction of pituitary gonadotropins such as FSH with locally produced regulatory molecules. We previously demonstrated a negative association of expression of cocaine-and amphetamine-regulated transcript (CART) with follicle health status and a novel local negative role for CART in regulation of basal estradiol production by bovine granulosa cells. However, effects of CART on FSH-induced estradiol production and the underlying mechanism(s) mediating the physiological actions of CART on granulosa cells are not known. Objectives of the present study were to determine effects of CART on basal and FSH-induced intracellular cAMP levels, aromatase mRNA, estradiol accumulation, calcium signaling, and the intracellular signaling pathways involved using primary cultures of bovine granulosa cells. CART treatment potently inhibits the FSH-induced rise in granulosa cell cAMP levels, estradiol accumulation, and aromatase mRNA. Furthermore, results show that calcium is essential for FSH-induced cAMP and estradiol accumulation, and CART significantly inhibits FSH-induced calcium influx. Select G protein and protein kinase inhibitors were used to elucidate pathways involved in CART actions. The inhibitory actions of CART on FSH signaling and estradiol production are mediated via a G(o/i)-dependent pathway, whereas none of the other signaling inhibitors had any effect on CART actions. Results demonstrate novel potent inhibitory effects of CART on multiple components of the FSH signaling pathway linked to estradiol production and follicular development and shed new insight into the mechanism of action of CART potentially pertinent within and beyond the reproductive system.

Ion channels of primate ovarian endocrine cells: identification and functional significance

Ion channels are crucially involved in cellular functions, but little is known about molecular identity, subunit composition and the specific role of ion channels in ovarian endocrine cells in human and nonhuman primates. Using human luteinizing granulosa cells, a few groups have started to address these questions and have begun to show molecular identity of ion channels, electrophysiological functions and the relationship to hormone production, as well as regulation by hormones and intraovarian factors. Functional ion channels that have been identified so far include T- and L-type Ca²⁺ channels (Ca_v3.2, Ca_v1.2), a voltage-dependent Na⁺ channel (Na_v1.7), as well as voltage- (K_v4.2) and Ca²⁺-dependent K⁺ channels (BK_Ca). Since all these ion channels were found to be involved in steroid hormone synthesis and are expressed by endocrine ovarian cells in human and nonhuman ovary, it has been proposed that they are physiological key molecules for ovarian function. Furthermore, they may be novel targets for modulating ovarian functions.

Adhesion, migration, transcriptional, interferon-inducible, and other signaling molecules newly implicated in cancer susceptibility and resistance of JB6 cells by cDNA microarray analyses

Relative expression levels of 9500 genes were determined by cDNA microarray analyses in mouse skin JB6 cells susceptible (P+) and resistant (P-) to 12-O-tetradecanoyl phorbol-13 acetate (TPA)-induced neoplastic transformation. Seventy-four genes in 6 functional classes were differentially expressed: (I) extracellular matrix (ECM) and basement membrane (BM) proteins (20 genes). P+ cells express higher levels than P- cells of several collagens and proteases, and lower levels of protease inhibitors. Multiple genes encoding adhesion molecules are expressed preferentially in P- cells, including six genes implicated in axon guidance and adhesion. (II) Cytoskeletal proteins (13 genes). These include actin isoforms and regulatory proteins, almost all preferentially expressed in P- cells. (III) Signal transduction proteins (12 genes). Among these are Ras-GTPase activating protein (Ras-GAP), the deleted in oral cancer-1 and SLIT2 tumor suppressors, and connexin 43 (Cx43) gap junctional protein, all expressed preferentially in P- cells. (IV) Interferon-inducible proteins (3 genes). These include interferon-inducible protein (IFI)-16, an Sp1 transcriptional regulator expressed preferentially in P- cells. (V) Other transcription factors (4 genes). Paired related homeobox gene 2 (Prx2)/S8 homeobox, and retinoic acid (RA)-regulated nur77 and cellular retinoic acid-binding protein II (CRABPII) transcription factors are expressed preferentially in P- cells. The RIN-ZF Sp-transcriptional suppressor exhibits preferential P+ expression. (VI) Genes of unknown functions (22 sequences). Numerous mesenchymal markers are expressed in both cell types. Data for multiple genes were confirmed by real-time PCR. Overall, 26 genes were newly implicated in cancer. Detailed analyses of the functions of the genes and their interrelationships provided converging evidence for their possible roles in implementing genetic programs mediating cancer susceptibility and resistance. These results, in conjunction with cell wounding and phalloidin staining data, indicated that concerted genetic programs were implemented that were conducive to cell adhesion and tumor suppression in P- cells and that favored matrix turnover, cell motility, and abrogation of tumor suppression in P+ cells. Such genetic programs may in part be orchestrated by Sp-, RA-, and Hox-transcriptional regulatory pathways implicated in this study.

Extracellular matrix of the bovine ovarian membrana granulosa

Much is known about the control of the development of ovarian follicles by growth factors and hormones. The study of extracellular matrix in the ovary, though, is a relatively new area. To date much research has focused on identifying the matrix components present, and more recently, its production and the physiological roles. In this review we focus on the changes that occur in the follicular basal lamina from primordial follicles through to ovulation and formation of the corpus luteum, the changes that occur during follicular atresia, and we discuss our observations of a novel matrix which forms in the membrana granulosa. The follicular basal lamina changes considerably during follicular development in its expression pattern of type IV collagens. Of the laminin chains examined, there appears only to be an increase in amount, except for laminin alpha2. It is expressed only in a small proportion of healthy antral follicles and in the majority of atretic antral follicles. Call-Exner bodies have the same composition as the basal lamina, except they do not contain laminin alpha2, even when the follicular basal lamina does. The novel matrix that develops within the membrana granulosa is similar in composition to Call-Exner bodies which occur predominantly in preantral follicles, except that it is far more common in large antral follicles, does not induce polarization of the surrounding granulosa cells, and does not contain follicular fluid-like material as the Call-Exner bodies of some species do. The expression of this matrix occurs prior to and during the time when granulosa cells express steroidogenic enzymes. It does not exist in corpora lutea. In addition large luteal cells, derived from granulosa cells, do not appear to have a basal lamina. These findings suggest that the maturational changes in the membrana granulosa are accompanied by changes in the matrix.