Integrin alpha6 is involved in follicular growth in mice

A Novel Three-Dimensional Follicle Culture System Decreases Oxidative Stress and Promotes the Prolonged Culture of Human Granulosa Cells

Tissue engineering advancements have made it possible to modify biomaterials to reconstruct a similar three-dimensional structure of the extracellular matrix (ECM) for follicle development and to supply the required biological signals. We postulated that an artificial polysaccharide hydrogel modified with an ECM mimetic peptide may produce efficient irritation signals by binding to specific integrins providing a suitable environment for follicular development and influencing the behavior of human granulosa cells (hGCs). Laminin, an important component of the extracellular matrix, can modulate hGCs and oocyte growth. Specifically, follicles of mice were randomly divided into two-dimensional (2D) and three-dimensional (3D) culture systems established by a hydrogel modified with RGD or laminin mimetic peptides (IKVAV and YIGSR) and RGD (IYR). Our results showed that 3D cultured systems significantly improved follicle survival, growth, and viability. IYR peptides enhanced the oocyte meiosis competence. Additionally, we explored the effect of 3D culture on hGCs, which improved hGCs viability, increased the proportion of S- and G2/M-phase cells, and inhibited cell apoptosis of hGCs. On days 1 and 2, the secretion of progesterone was reduced in 3D-cultured hGCs. Notably, 3D-cultured hGCs exhibited delayed senescence, decreased oxidative stress, and elevated mitochondrial membrane potential. Moreover, the expression levels of cumulus expansion-related genes (COX2, HAS2, and PTX3) and integrin α6β1 were upregulated in 3D-cultured hGCs. In conclusion, a 3D culture utilizing hydrogels modified with Laminin-mimetic peptides can provide a durable physical environment suitable for follicular development. The laminin-mimetic peptides may regulate the biological activity of hGCs by attaching to the integrin α6β1.

RGD-modified dextran hydrogel promotes follicle growth in three-dimensional ovarian tissue culture in mice

In vitro follicle growth is a promising technology to preserve fertility for cancer patients. We previously developed a three-dimensional (3-D) ovarian tissue culture system supported by mouse tumor cell-derived Matrigel. When murine ovarian tissues at 14 days old were cultured in Matrigel drops, antrum formation and oocyte competence were significantly enhanced compared with those cultured without Matrigel. In this study, we tested whether nonanimal-derived dextran hydrogels can support a 3-D ovarian tissue culture. We employed chemically defined dextran hydrogels consisting of dextran polymers crosslinked with polyethylene glycol (PEG)-based cell-degradable crosslinker. To determine the optimal gel elasticity for the 3-D tissue culture, we measured Young's modulus of dextran hydrogels at four concentrations (1.75, 2.25, 2.75, and 3.25 mmol/L), and cultured ovarian tissues in these gels for 7 days. As a result, 2.25 mmol/L dextran hydrogel with Young's modulus of 224 Pa was appropriate to provide physical support as well as to promote follicle expansion in the 3-D system. To mimic the natural extracellular matrix (ECM) environment, we modified the dextran hydrogels with two bioactive factors: ECM-derived Arg-Gly-Asp (RGD) peptides as a cell-adhesive factor, and activin A. The ovarian tissues were cultured in 2.25 mmol/L dextran hydrogels under four different conditions: Activin-/RGD- (A-R-), A + R-, A-R+, and A + R+. On Day 7 of culture, follicle and oocyte sizes were significantly increased in the RGD-modified conditions compared with those without RGD. The RGD-modified hydrogels also promoted mRNA levels of steroidogenic-related genes and estradiol production in the 3-D ovarian tissue culture. In vitro maturation and developmental competence of follicular oocytes were remarkably improved in the presence of RGD. In particular, blastocyst embryos were obtained only from A-R+ or A+R+ conditions after in vitro fertilization. We also determined synergistic effects of the RGD peptides and activin A on follicle growth and oocyte development in the 3-D tissue culture. In conclusion, our results suggest that RGD-modified dextran hydrogels provide an ECM-mimetic bioactive environment to support folliculogenesis in a 3-D ovarian tissue culture system.

Bioengineered airway epithelial grafts with mucociliary function based on collagen IV- and laminin-containing extracellular matrix scaffolds

Current methods to replace damaged upper airway epithelium with exogenous cells are limited. Existing strategies use grafts that lack mucociliary function, leading to infection and the retention of secretions and keratin debris. Strategies that regenerate airway epithelium with mucociliary function are clearly desirable and would enable new treatments for complex airway disease.Here, we investigated the influence of the extracellular matrix (ECM) on airway epithelial cell adherence, proliferation and mucociliary function in the context of bioengineered mucosal grafts. In vitro, primary human bronchial epithelial cells (HBECs) adhered most readily to collagen IV. Biological, biomimetic and synthetic scaffolds were compared in terms of their ECM protein content and airway epithelial cell adherence.Collagen IV and laminin were preserved on the surface of decellularised dermis and epithelial cell attachment to decellularised dermis was greater than to the biomimetic or synthetic alternatives tested. Blocking epithelial integrin α2 led to decreased adherence to collagen IV and to decellularised dermis scaffolds. At air-liquid interface (ALI), bronchial epithelial cells cultured on decellularised dermis scaffolds formed a differentiated respiratory epithelium with mucociliary function. Using in vivo chick chorioallantoic membrane (CAM), rabbit airway and immunocompromised mouse models, we showed short-term preservation of the cell layer following transplantation.Our results demonstrate the feasibility of generating HBEC grafts on clinically applicable decellularised dermis scaffolds and identify matrix proteins and integrins important for this process. The long-term survivability of pre-differentiated epithelia and the relative merits of this approach against transplanting basal cells should be assessed further in pre-clinical airway transplantation models.

Pericytes regulate vascular basement membrane remodeling and govern neutrophil extravasation during inflammation

During inflammation polymorphonuclear neutrophils (PMNs) traverse venular walls, composed of the endothelium, pericyte sheath and vascular basement membrane. Compared to PMN transendothelial migration, little is known about how PMNs penetrate the latter barriers. Using mouse models and intravital microscopy, we show that migrating PMNs expand and use the low expression regions (LERs) of matrix proteins in the vascular basement membrane (BM) for their transmigration. Importantly, we demonstrate that this remodeling of LERs is accompanied by the opening of gaps between pericytes, a response that depends on PMN engagement with pericytes. Exploring how PMNs modulate pericyte behavior, we discovered that direct PMN-pericyte contacts induce relaxation rather than contraction of pericyte cytoskeletons, an unexpected response that is mediated by inhibition of the RhoA/ROCK signaling pathway in pericytes. Taking our in vitro results back into mouse models, we present evidence that pericyte relaxation contributes to the opening of the gaps between pericytes and to the enlargement of the LERs in the vascular BM, facilitating PMN extravasation. Our study demonstrates that pericytes can regulate PMN extravasation by controlling the size of pericyte gaps and thickness of LERs in venular walls. This raises the possibility that pericytes may be targeted in therapies aimed at regulating inflammation.

Molecular mechanisms of ovulation: co-ordination through the cumulus complex

Successful ovulation requires that developmentally competent oocytes are released with appropriate timing from the ovarian follicle. Somatic cells of the follicle sense the ovulatory stimulus and guide resumption of meiosis and release of the oocyte, as well as structural remodelling and luteinization of the follicle. Complex intercellular communication co-ordinates critical stages of oocyte maturation and links this process with release from the follicle. To achieve these outcomes, ovulation is controlled through multiple inputs, including endocrine hormones, immune and metabolic signals, as well as intrafollicular paracrine factors from the theca, mural and cumulus granulosa cells and the oocyte itself. This review focuses on the recent advances in understanding of molecular mechanisms that commence after the gonadotrophin surge and culminate with release of the oocyte. These mechanisms include intracellular signalling, gene regulation and remodelling of tissue structure in each of the distinct ovarian compartments. Most critical ovulatory mediators exert effects through the cumulus cell complex that surrounds and connects with the oocyte. The convergence of ovulatory signals through the cumulus complex co-ordinates the key mechanistic processes that mediate and control oocyte maturation and ovulation.

The in vitro regulation of ovarian follicle development using alginate-extracellular matrix gels

The extracellular matrix (ECM) provides a three-dimensional structure that promotes and regulates cell adhesion and provides signals that direct the cellular processes leading to tissue development. In this report, synthetic matrices that present defined ECM components were employed to investigate these signaling effects on tissue formation using ovarian follicle maturation as a model system. In vitro systems for follicle culture are being developed to preserve fertility for women, and cultures were performed to test the hypothesis that the ECM regulates follicle maturation in a manner that is dependent on both the ECM identity and the stage of follicle development. Immature mouse follicles were cultured within alginate-based matrices that were modified with specific ECM components (e.g., laminin) or RGD peptides. The matrix maintains the in vivo like morphology of the follicle and provides an environment that supports follicle development. The ECM components signal the somatic cells of the follicle, affecting their growth and differentiation, and unexpectedly also affect the meiotic competence of the oocyte. These effects depend upon both the identity of the ECM components and the initial stage of the follicle, indicating that the ECM is a dynamic regulator of follicle development. The development of synthetic matrices that promote follicle maturation to produce meiotically competent oocytes may provide a mechanism to preserve fertility, or more generally, provide design principles for scaffold-based approaches to tissue engineering.

Cytoskeleton reorganization mediates alpha6beta1 integrin-associated actions of laminin on proliferation and survival, but not on steroidogenesis of ovine granulosa cells

BACKGROUND

Laminin (LN) is one of the most abundant extracellular matrix components of the basal lamina and granulosa cell layers of ovarian follicles. Culture of ovine granulosa cells (GC) on LN substratum induces cell spreading, enhances cell survival and proliferation, and promotes luteinization. Previous investigations have shown that these effects are mostly mediated by the alpha6beta1 integrin, but its signalization pathways have not been investigated. This study aimed to assess the importance of the cytoskeleton in the alpha6beta1 integrin-mediated actions of laminin on survival, proliferation and steroidogenesis of ovine GC.

METHODS

The relationships between morphology and functions of ovine GC cultured on substrata containing LN or/and RGD peptides were investigated. The effects of (1) cytochalasin D, an actin cytoskeleton-disrupting drug, (2) a specific function-blocking antibody raised against alpha6 integrin subunit (anti-alpha6 IgG), and (3) an inhibitor of the ERK1/2 signalization pathway (PD98059) were assessed for GC shape, pyknosis and proliferation rates, oestradiol and progesterone secretions.

RESULTS

Cytoskeleton disruption by cytochalasin D induced cell rounding, inhibited proliferation, promoted pyknosis, inhibited progesterone secretion and enhanced oestradiol secretion by GC cultured on LN. When GC were cultured on various substrata containing LN and/or RGD peptides in the presence or absence of anti-alpha6 IgG, both the existence of close correlations between the percentage of round cells, and the GC proliferation rate (r = -0.87) and pyknotic rate (r = 0.76) were established, but no relationship was found between cell shape and steroidogenesis. Inhibition of the ERK1/2 signalization pathway by PD98059 had no effect on GC shape, proliferation or pyknotic rates. However, it dramatically reduced progesterone secretion, expression of cytochrome P450 cholesterol side-chain cleavage and 3beta-hydroxysteroid deshydrogenase enzymes, and enhanced oestradiol secretion, thereby reproducing all the effects of the anti-alpha6 IgG on steroidogenesis of GC cultured on LN.

CONCLUSION

LN may participate in the paracrine control of follicular development through different mechanisms. It could enhance proliferation and survival of GC through its alpha6beta1 integrin-mediated actions on cytoskeleton. In contrast, its stimulating action on GC luteinization could be partly mediated by the ERK1/2 pathway, irrespective of cell shape.

Laminin and fibronectin concentrations of the follicular fluid correlate with granulosa cell luteinization and oocyte quality

Background and Aims:  Progesterone production of human cultured luteinizing granulosa cells was reported to be modified by extracellular matrix, suggesting that extracellular matrix regulates luteinization of granulosa cells after ovulation. In the present study, the relationship among laminin, fibronectin, progesterone and estradiol in follicular fluid along with oocyte quality was analyzed to estimate the physiological role of extracellular matrix in follicular luteinization and oocyte quality during ovulation. Methods and Results:  Follicular fluid was collected at oocyte pick-up from the patients undergoing in vitro fertilization treatment and intracytoplasmic sperm injection. The concentrations of laminin, fibronectin, progesterone and estradiol in the follicular fluid were measured by enzyme immunoassay and radioimmunoassay. The morphology of oocytes were also assessed during the procedure of intracytoplasmic sperm injection and was classified into normal and abnormal groups. The fibronectin concentration was higher in the normal ooplasm group than in the abnormal group, but it did not correlate with estradiol or progesterone concentration. However, laminin concentration significantly correlated with that of progesterone, but not with cytoplasm morphology of oocytes. There was no difference in estradiol or progesterone concentration between the normal and abnormal groups. Conclusion:  These findings suggest that extracellular matrix plays some roles in regulating human granulosa cell luteinization and oocyte quality during ovulation. (Reprod Med Biol 2004; 3: 43-49).

Dynamics of the membrana granulosa during expansion of the ovarian follicular antrum

As an endocrine organ, the ovary has some unique characteristics. The formation, the maturation and the regression of the hormone producing cells really determine the timing, the amount and the type of hormone secreted. Here, we focus on the granulosa cells of ovarian follicles which express 17beta-hydroxysteroid dehydrogenase type 1 and cytochrome P450 aromatase. Follicles only produce estradiol late in follicular development before either ovulation or atresia ensues. We discuss the evidence that the membrana granulosa has many characteristics in common with other epithelia, including that it arises from stem cells. The corollary of this is that individual cells within the membrana granulosa are of different ages or stages of specialization. This is evident as regional differences across the membrana granulosa in terms of cell ages, shapes, gene expression, and even behaviour on cell death. We discuss theoretical considerations of the effects of antrum formation on the behavior of the membrana granulosa, and show evidence for differences between follicles in cell shapes, basal lamina phenotypes and location of younger cells, which we speculate is due to different rates of antrum expansion. Clearly, the membrana granulosa is dynamic, and this could explain much about the differences in the behaviors of cells from within the membrana granulosa, and between ovarian follicles.

Interaction of extracellular matrix and activin-A in the initiation of follicle growth in the mouse ovary

The precise mechanism for the initiation of follicle growth and progression through the earliest stages of follicle development remains largely unknown. Activins play a role during early follicle development, and evidence suggests that the extracellular matrix plays a role during later stages of follicular growth. We investigated the role of activin-A and extracellular matrix in follicle growth initiation and early follicular development in the mouse ovary. Ovaries were collected from 5-day-old mice and cultured for 10 days on polylysine, collagen, or laminin in the presence or absence of recombinant human activin-A. Follicle density, indices of follicle growth initiation (primary:primordial follicle [PY:PD] and primary:total follicle [PY:TF] ratios), ratios of multilayer follicle:total follicle (ML:TF), and follicle growth rates were compared between groups. Follicle densities were significantly higher in the extracellular matrix treatment group compared with the polylysine group (P < 0.01). Also, compared with polylysine, both collagen and laminin significantly increased indices of follicle growth initiation (PY:PD ratio: P < 0.001, odds ratio of 3.3; PY:TF ratio: P < 0.001, odds ratio of 2.5), and these were not altered by activin treatment. In the absence of activin-A, exposure to neither collagen nor laminin had an effect on multilayer follicle development. When activin-A was added, collagen and laminin had opposing effects on multilayer follicle development. Activin-A stimulated multilayer follicle development in the presence of laminin (ML:TF ratio: P = 0.01, odds ratio of 10.8), whereas it suppressed follicle growth in collagen (P = 0.01). Activin-A did not affect the ML:TF ratio in the polylysine-treated groups. These results strongly suggest that extracellular matrix components and activin-A interact with each other, and that they regulate follicle growth initiation and multilayer follicle development.