Low-Density Lipoprotein Receptor-Related Protein 8 (LRP8) Is Upregulated in Granulosa Cells of Bovine Dominant Follicle: Molecular Characterization and Spatio-Temporal Expression Studies

• Published in: Biology of reproduction 2007-03, Vol.76 (3), p.466-475
• Main Authors: Fayad, Tania, Lefebvre, Réjean, Nimpf, Johannes, Silversides, David W, Lussier, Jacques G
• Format: Article
• Language: English
• Subjects: Adaptor Proteins, Signal Transducing - genetics; Adaptor Proteins, Signal Transducing - metabolism; Alternative Splicing; Amino Acid Sequence; Animals; Base Sequence; Biological and medical sciences; Cattle; Cell Adhesion Molecules, Neuronal - genetics; Cell Adhesion Molecules, Neuronal - metabolism; Extracellular Matrix Proteins - genetics; Extracellular Matrix Proteins - metabolism; Female; Fundamental and applied biological sciences. Psychology; Gene Expression; Granulosa Cells - physiology; Hormone metabolism and regulation; Mammalian female genital system; Molecular Sequence Data; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - metabolism; Ovarian Follicle - cytology; Ovarian Follicle - growth & development; Ovulation; Receptors, LDL - genetics; Receptors, LDL - metabolism; Receptors, Lipoprotein - genetics; Receptors, Lipoprotein - metabolism; Sequence Homology, Amino Acid; Serine Endopeptidases - genetics; Serine Endopeptidases - metabolism; Vertebrates: reproduction
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1095/biolreprod.106.057216

The low-density lipoprotein (LDL) receptor-related protein 8 (LRP8) is a member of the LDL receptor family that participates in endocytosis and signal transduction. We cloned the full-length bovine LRP8 cDNA in granulosa cells (GC) of the dominant follicle (DF) as well as several LRP8 mRNA splicing variants, including a variant that contains a proline-rich cytoplasmic insert (A⁷⁵⁹-K⁸¹⁷) that is involved in intracellular signaling. Expression of the A⁷⁵⁹-K⁸¹⁷ variant was analyzed in the GC of follicles at different developmental stages: the small follicle (SF; 2-4 mm), the DF at Day 5 (D5) of the estrus cycle, ovulatory follicles (OF) 24 h after hCG injection, and corpora lutea (CL) at D5. RT-PCR analysis showed that expression was predominant in the GC of DF compared to other follicles and CL (P < 0.0001), whereas the expression of other related receptors, such as LDLR and VLDLR, did not show differences. Temporal analyses of follicular walls from the OF following hCG treatment revealed a decrease in LRP8 mRNA expression starting 12 h post-hCG treatment (P < 0.0001). LRP8 protein was exclusively localized to the GC, with higher levels in the DF than in the SF (P < 0.05). RELN mRNA, which encodes an LRP8 ligand, was highly expressed in the theca of the DF as compared to the OF (P < 0.004), whereas MAPK8IP1 mRNA, which encodes an LRP8 intracellular interacting partner, is expressed in the GC of the DF. These results demonstrate the differential expression patterns of LRP8, RELN, and MAPK8IP1 mRNAs during final follicular growth and ovulation, and suggest that a RELN/LRP8/MAPK8IP1 paracrine interaction regulates follicular growth.