Ovarian hypercytolipidemia induced by obese (ob/ob) and diabetes (db/db) mutations: basis of female reproductive tract involution II

Abstract

The diabetes (db/db) and obese (ob/ob) genotype mutations induce a progressive, hypercytolipidemic condition within the ovarian compartments of the female reproductive tract that results in sterility and premature organ involution in C57BL/KsJ mice. The current studies focus on the ultrastructural changes that occur within the ovarian interstitial, thecal, and follicular granulosa cell layers during the progressive expression of these mutations which promote tissue cytolipidemia-induced organoinvolution. Control (normal: +/?), diabetes (db/db), and obese (ob/ob) genotype groups were prepared for high resolution light (HRLM) and transmission electron microscopic (TEM) analysis of ovarian tissue samples collected from 4 (young)- to 20 (aged)-week-old mice, allowing for the progressive influences of the mutational aberrations on tissue structure to be evaluated. Compared to controls, both (ob/ob) and (db/db) mutations induced a dramatic increase in ovarian interstitial, thecal and follicular granulosa cytolipid vacuole accumulations, which increased in density between 4 and 20 weeks of age. Initially, lipid vacuoles aggregated in the interstitial and thecal regions of ovarian follicles in response to the hyperglycemic-hypertriglyceridemic metabolic conditions typical of both (ob/ob) and (db/db) groups. Progressive cytoplasmic movement of the lipid pools established a perinuclear isolation from associated cytoplasmic organelles. Progressive lipid accumulations forced cytoplasmic organelles to peripheral cell compartments and altered the follicular cell profile towards that of adipocyte-like entities relative to controls. The progressive hypercytolipidemia-induced alterations in cell structure disrupted normal tissue continuity, which culminated in premature ovarian organo-involution and female reproductive sterility.

Introduction

Ovarian structural integrity is compromised by the deleterious influences of the diabetes–obesity syndrome (DOS), which induces well-recognized alterations in female reproductive tract cellular metabolism and cytoarchitecture (Garris, 1985, Garris et al., 1985, Garris et al., 1985, Qiu et al., 2001, Swerdloff et al., 1976). In both humans (Hall and Tillman, 1951) and experimental models (Garris et al., 1986), significant alterations in tissue lipogenic metabolism (Garris and Garris, 2003a, Garris and Garris, 2003b) in ovarian interstitial, thecal and follicular granulosa cell layers induce cellular lipotoxicity which predisposes these female reproductive tract tissues to premature involution (Garris, 1989a, Garris and Garris, 2002). The resulting reproductive incompetence is characterized by ovarian acyclicity, compromised ovarian follicular development, depressed ovarian steroid hormone synthesis, depressed sensitivity and responsivity to endocrine stimulated cellular metabolism and enhanced follicular atresia (Garris, 1989a). The affected ovarian architecture is characterized by an enormous increase in intra- and inter-cellular lipid depositions, resulting from the interstitial perivascular escape and imbibition of elevated circulating triglyceride and free fatty acid concentrations (Garris et al., 1986). Ultimately, exposure to the chronic influences of the DOS-promoted, non-homeostatic, hyperglycemic-hyperinsulinemic metabolic state induces a lipo-atrophic syndrome (Garris et al., 1984a, Garris et al., 1984b), characterized by the progressive accumulation of cytolipid inclusions (Garris, 1989a; Garris and Garris, 2003a, Garris and Garris, 2003b), organelle dissolution, suppressed cellular oxidative metabolism, and cyto-transformation into adipocyte-like dysfunctional cells which are incapable of maintaining ovarian reproductive competency (Garris, 1988a, Garris, 1988b, Garris, 1990; Garris and Garris, 2002, Garris and Garris, 2003a,b). The resulting reproductive tract atrophy underlies the causal associations of obesity and diabetes-associated compromise in reproductive tract maturation (Chieri et al., 1969; Garris et al., 1984a, Garris et al., 1984b; Foreman et al., 1983), hypo-vascular perfusion rates (Garris, 1988a) and depressed follicular development rate (Garris et al., 1982), which characterize the deleterious influences of diabetes on female reproductive tract function (Santonge and Cote, 1983; Garris and Garris, 2003a, Garris and Garris, 2003b).

In C57BL/KsJ obese (ob/ob) and (db/db) diabetic mouse models, an autosomal recessive (Coleman, 1978) genetic mutation promotes utero-ovarian dysfunction (Johnson and Sidman, 1979, Garris and Garris, 2002, Garris and Garris, 2003a,b) following the metabolic expression of systemic hyperglycemia, insulin resistance and phenotypic obesity (Garris et al., 1985, Garris et al., 1985, Garris et al., 1986, Garris, 1987, Garris, 1990). In addition, the (ob/ob) obese mutation promotes truncal obesity and transient hyperinsulinemia (Coleman, 1978; Garris, 1989a, Garris, 1989b; Garris and Garris, 2002), typical of Type II (NIDDM) diabetes conditions, but with a moderated form of systemic hyperglycemia and hyperinsulinemia. These observations indicate that the genomic expression of the (db/db) and (ob/ob) genetic mutations, associated with leptin ligand-receptor deficient gene expression (Leibel et al., 1997), induce the functional compromise of cellular oxidative metabolic parameters in ovarian tissue compartments (Garris et al., 1985, Garris et al., 1985) which underlie the resulting reproductive incompetence that characterizes these experimental models. As previously demonstrated for uterine tissue involution indices (Garris, 2004), comparing the progressive influences of the (ob/ob) and (db/db) mutations on ovarian cytoarchitecture during the development of the obese- and diabetes-metabolic states, the structural basis of hypercytolipidemia-induced reproductive tract failure in both models may be evaluated. The present studies were designed to evaluate the cytoarchitectural influences of the (ob/ob) and (db/db) genomic mutations on the severity of compartmental ovarian hypercytolipidemia which promotes reproductive tract involution and infertility in these experimental models.