Graafian ovarian follicles consist of follicular fluid, one single mature oocyte, and several hundred thousands of granulosa cells (GCs). Until now, luteinizing GCs have been considered to be terminally differentiated, destined to undergo death after ovulation. Present concepts of luteal function, endocrine regulation of early pregnancy, and the recruitment of new ovarian follicles are all based on the cyclical renewal of the entire population of GCs. We now demonstrate that luteinizing GCs isolated from the ovarian follicles of infertile patients and sorted with flow cytometry based upon the presence of their specific marker, the follicle-stimulating hormone receptor (FSHR), can be maintained in culture over prolonged periods of time in the presence of the leukemia-inhibiting factor (LIF). Under those conditions the markers of GC function such as FSHR and aromatase gradually disappeared. POU5F1 (POU domain, class 5, homeobox 1), a typical stem cell marker, was expressed throughout the culture, but germ line cell markers such as nanog, vasa, and stellar were not. Mesenchymal lineage markers such as CD29, CD44, CD90, CD105, CD117, and CD166, but not CD73, were expressed by substantial subpopulations of GCs. The multipotency of a subset of GCs was established by in vitro differentiation into other cell types, otherwise not present within ovarian follicles, such as neurons, chondrocytes, and osteoblasts. Follicle-derived stem cells were also able to survive when transplanted into the backs of immunoincompetent mice, in vivo generating tissues of mesenchymal origin. The unexpected findings of multipotency of cells with prolonged lifespans originating from ovarian follicles are likely to have a significant impact on evolving theories in ovarian pathophysiology, particularly with reference to ovarian endometriosis and ovarian cancer.

Antral follicular growth in the ovary is characterized by rapid expansion of granulosa cells accompanied by a rising complexity of their functionality. Within two weeks the number of human granulosa cells increases from less than 500,000 to more than 50 millions cells per follicle and differentiates into groups of cells with a variety of specialized functions involved in steroidogenesis, nursing the oocyte, and forming a functional syncitium. Both the rapid proliferation and different specialized functions of the granulosa cells can only be explained through the involvement of stem cells. However, luteinizing granulosa cells were believed to be terminally differentiated cells. Only recently, stem and progenitor cells with FSH-receptor activity were identified in populations of luteinizing granulosa cells obtained during oocyte collected for assisted reproduction. In the presence of the leukaemia-inhibiting factor (LIF), it was possible to culture a subpopulation of the luteinizing granulosa cells over prolonged time periods. Furthermore, when embedded in a matrix consisting of collagen type I, these cells continued to express the FSH receptor over prolonged time periods, developed globular formations that surrogated as follicle-like structures, providing a promising tool for reproductive biology.

A novel three-dimensional culture system allows prolonged culture of functional human granulosa cells and mimics the ovarian environment AbstractThe development of techniques allowing the growth of primordial follicles to mature follicles in vitro has much potential for both reproductive medicine and developmental research. However, human primordial and preantral follicles fail to grow after isolation from the surrounding ovarian stroma. Granulosa cells (GCs), which normally undergo apoptosis after ovulation, contain a subpopulation of ovarian follicular cells remaining viable in vitro over prolonged time periods when cultured in the presence of leukaemia inhibiting factor (LIF). However, when cultured as monolayers, they progressively lose all their characteristics, such as follicle-stimulating hormone receptor (FSHR) and cytochrome P450-aromatase. Here, we describe a three-dimensional (3D) culture system containing type I collagen, which, together with LIF, allowed the survival and growth of a subpopulation of GCs isolated from mature ovarian follicles and supported them to proliferate into spherical structures exhibiting steroidogenic capacity, as demonstrated by P450-aromatase and 3-hydroxysteroid dehydrogenase. After transplantation into the ovaries of immuno-deficient mice, these cells became localized preferentially within antral follicles and the prolonged expression of FSHR was confirmed as well. With this optimization of the culture conditions an environment was created, which acts as a niche closely mimicking the development of early ovarian follicles in vitro. ENVIRONMENT (doi: 10.1089 This article has been peer-reviewed and accepted for publication, but has yet to undergo copyediting and proof correction. The final published version may differ from this proof. 2 ABSTRACTThe development of techniques allowing the growth of primordial follicles to mature follicles in vitro has much potential for both reproductive medicine and developmental research. However, human primordial and preantral follicles fail to grow after isolation from the surrounding ovarian stroma.Granulosa cells (GCs), which normally undergo apoptosis after ovulation, contain a subpopulation of ovarian follicular cells remaining viable in vitro over prolonged time periods when cultured in the presence of leukaemia inhibiting factor (LIF). However, when cultured as monolayers, they progressively lose all their characteristics, such as follicle-stimulating hormone receptor (FSHR) and cytochrome P450-aromatase. Here, we describe a three-dimensional (3D) culture system containing type I collagen, which, together with LIF, allowed the survival and growth of a subpopulation of GCs isolated from mature ovarian follicles and supported them to proliferate into spherical structures exhibiting steroidogenic capacity, as demonstrated by P450-aromatase and 3β-hydroxysteroid dehydrogenase. After transplantation into the ovaries of immuno-deficient mice, these cells became localized preferentially within antral follicles and the prolonged expressi...