Granulosa cell subtypes respond by autophagy or cell death to oxLDL-dependent activation of the oxidized lipoprotein receptor 1 and toll-like 4 receptor

Abstract

Autophagic cell death has been observed in granulosa cell cultures via the oxLDL-dependent activation of lectin-like oxidized low density lipoprotein receptor 1 (LOX-1). This activation might differ for cytokeratin-positive (CK(+)) and CK(-) granulosa cells. In particular, LOX-1 and toll-like receptor 4 (TLR4), one of the pattern recognition receptors of innate immunity, might be diversely regulated. Granulosa cell subtype cultures were established from the follicle harvests of patients undergoing in vitro fertilization (IVF) therapy. In response to oxLDL treatment, the fibroblast-like CK(-) cells upregulated LOX-1 and exhibited reparative autophagy, which could be blocked with anti-LOX-1 antibody. The epithelioid-like CK(+) cells did not regulate LOX-1 expression upon oxLDL application, but the expression of TLR4 and CD14 increased between 0 and 36 h of oxLDL/nDL treatment. This upregulation was associated with nonapoptotic cell death based on the absence of cleaved caspase-3. Reactive oxygen species (ROS) increased with 12 h oxLDL application and steroidogenic acute regulatory (StAR) protein expression was negligible. In CK(-) cells, the inhibition of TLR4 downregulated LOX-1 and induced apoptosis. We concluded that CK(-) granulosa cells are protected against oxLDL-dependent apoptosis by TLR4, whereas, in CK(+) cells, oxLDL-induced TLR4 activation triggers nonapoptotic cell death. The CK(+) cells might represent immune-like granulosa cells involved in ovarian remodeling processes.

Leptin-deficient (ob/ob) mouse ovaries show fatty degeneration, enhanced apoptosis and decreased expression of steroidogenic acute regulatory enzyme

“…22 A high LC3-II/LC3-I ratio indicates high amount of autophagosomes in granulosa cells. 18 We postulated a lower rate of autophagy in ob/ob mice than in the other groups because of granulosa cells from obese women undergoing in vitro fertilisation therapy display a low LC3-II/LC3-I ratio. 23 Our assumption was confirmed with a weak ratio in the ob/ob group (Figures 4c and d).…”

“…14 --17 They are expressed on endothelial cells, leukocyte subtypes and on granulosa cells from human preovulatory follicles. 15,18 The oxidised lipoproteinsdependent activation of these receptors either triggers apoptosis or survival autophagy in endothelial or granulosa cells. 14,18,19 Ob/ob ovaries could respond to lipid droplet accumulation by upregulation of LOX-1 and/or TLR4 resulting in the cell damage.…”

Autophagy in the endocrine glands

“…Originally, follicular atresia was thought to occur entirely by apoptosis. The discovery of granulosa cell death via oxidised LDL (oxLDL)-dependent lectin-type oxLDL receptor (LOX1)-activated autophagy, however, suggests that autophagic forms of programmed cell death are also involved (Duerrschmidt et al 2006, Serke et al 2009). As obese women have increased levels of oxLDL (Mutlu-Türkoglu et al 2003), and consequently a higher incidence of autophagic granulosa cell death, this pathway could account for a higher rate of infertility in obese women (Duerrschmidt et al 2006).…”

Ovulation as danger signaling event of innate immunity

“…Derived from damaged granulosa/cumulus cells, danger signals are sensed to activate the ovarian INIM system. The promising candidate for danger sensing are the CK + granulosa cells, which regulate TLR4 expression under oxLDL treatment in culture (Serke et al, 2009;Serke et al, 2010). The molecular steps and the cytokine profile generated by the activation cascade in CK + cells are unknown.…”