A novel loss-of-function mutation in Npr2 clarifies primary role in female reproduction and reveals a potential therapy for acromesomelic dysplasia, Maroteaux type

Abstract

We discovered a new spontaneous mutant allele of Npr2 named peewee (pwe) that exhibits severe disproportionate dwarfism and female infertility. The pwe phenotype is caused by a four base-pair deletion in exon 3 that generates a premature stop codon at codon 313 (L313X). The Npr2(pwe/pwe) mouse is a model for the human skeletal dysplasia acromesomelic dysplasia, Maroteaux type (AMDM). We conducted a thorough analysis of the female reproductive tract and report that the primary cause of Npr2(pwe/pwe) female infertility is premature oocyte meiotic resumption, while the pituitary and uterus appear to be normal. Npr2 is expressed in chondrocytes and osteoblasts. We determined that the loss of Npr2 causes a reduction in the hypertrophic and proliferative zones of the growth plate, but mineralization of skeletal elements is normal. Mutant tibiae have increased levels of the activated form of ERK1/2, consistent with the idea that natriuretic peptide receptor type 2 (NPR2) signaling inhibits the activation of the MEK/ERK mitogen activated protein kinase pathway. Treatment of fetal tibiae explants with mitogen activated protein kinase 1 and 2 inhibitors U0126 and PD325901 rescues the Npr2(pwe/pwe) growth defect, providing a promising foundation for skeletal dysplasia therapeutics.

Dephosphorylation and inactivation of NPR2 guanylyl cyclase in granulosa cells contributes to the LH-induced decrease in cGMP that causes resumption of meiosis in rat oocytes

“…In particular, bone growth is affected by mutations in Npr2 or the Nppc gene that encodes CNP; increased NPR2 activity results in longer bones, whereas decreased activity results in shorter bones (Chusho et al, 2001;Tamura et al, 2004;Yasoda et al, 2004;Olney, 2006;Miura et al, 2012;Geister et al, 2013). Natriuretic peptide receptors also function in the development of the nervous system (Ter-Avetisyan et al, 2014) and heart (Becker et al, 2014).…”

“…LH acts by lowering the levels of cGMP in the granulosa cells, thus reducing cGMP in the oocyte. Although this regulatory system is best understood in mice (Norris et al, 2009;Vaccari et al, 2009;Zhang et al, 2010;Kawamura et al, 2011;Tsuji et al, 2012;Geister et al, 2013), there is evidence that similar mechanisms operate in other mammals (Törnell et al, 1991;Peng et al, 2013;Hiradate et al, 2014;Zhang et al, 2014), including women (Kawamura et al, 2011;Liu et al, 2014). The LH-induced resumption of the meiotic cell cycle leads into a series of events by which the oocyte matures to become a fertilizable egg (Conti et al, 2012;Clift and Schuh, 2013;Holt et al, 2013;Mehlmann, 2013;Hunzicker-Dunn and Mayo, 2014).…”

“…cGMP is produced in the granulosa cells of mice by natriuretic peptide receptor 2 (NPR2), also known as guanylyl cyclase-B (Zhang et al, 2010;Kawamura et al, 2011;Tsuji et al, 2012;Geister et al, 2013). NPR2 appears to be the only relevant guanylyl cyclase in mouse follicles because follicle-enclosed oocytes in the ovaries of mice with non-functional NPR2 resume meiosis spontaneously (Zhang et al, 2010;Tsuji et al, 2012;Geister et al, 2013) and an inactivating mutation in NPR2 reduces the cGMP content of the follicle to an undetectable level (Geister et al, 2013).…”

“…NPR2 appears to be the only relevant guanylyl cyclase in mouse follicles because follicle-enclosed oocytes in the ovaries of mice with non-functional NPR2 resume meiosis spontaneously (Zhang et al, 2010;Tsuji et al, 2012;Geister et al, 2013) and an inactivating mutation in NPR2 reduces the cGMP content of the follicle to an undetectable level (Geister et al, 2013). Gene expression analysis and enzyme assays have indicated that other guanylyl cyclases are present at levels much lower than those of NPR2 .…”

Bidirectional communication between oocytes and ovarian follicular somatic cells is required for meiotic arrest of mammalian oocytes

“…Treatment of isolated COCs with NPPC promotes elevation of cGMP levels (12,26). Moreover, mutations in either the Npr2 or Nppc genes in mice result in failure to maintain meiotic arrest and precocious resumption of meiosis (12,27,28). Thus, the NPPC/ NPR2 system for generating cGMP in cumulus cells is crucial for the maintenance of meiotic arrest and the coordination of oocyte meiosis with follicular ovulatory mechanisms.…”