The autophagy protein, ATG14 safeguards against unscheduled pyroptosis activation to enable embryo transport during early pregnancy

Recurrent pregnancy loss (RPL), characterized by two or more failed clinical pregnancies, poses a significant challenge to reproductive health. In addition to embryo quality and endometrial function, proper oviduct function is also essential for successful pregnancy establishment. Therefore, structural abnormalities or inflammation resulting from infection in the oviduct may impede the transport of embryos to the endometrium, thereby increasing the risk of miscarriage. However, the precise cellular mechanisms that maintain the structural and functional integrity of the oviduct are not studied yet. Here, we report that autophagy is critical for maintaining the oviduct homeostasis and keeping the inflammation under check to enable embryo transport. Specifically, the loss of the autophagy-related gene, Atg14 in the oviduct causes severe structural abnormalities compromising its cellular plasticity and integrity leading to the retention of embryos. Interestingly, the selective loss of Atg14 in oviduct ciliary epithelial cells did not impact female fertility, highlighting the specificity of ATG14 function in distinct cell types within the oviduct. Mechanistically, loss of Atg14 triggered unscheduled pyroptosis leading to inappropriate embryo retention and impeded embryo transport in the oviduct. Finally, pharmacological activation of pyroptosis in pregnant mice led to an impairment in embryo transport. Together, we found that ATG14 safeguards against unscheduled pyroptosis activation to enable embryo transport from the oviduct to uterus for the successful implantation. Of clinical significance, these findings provide possible insights on the underlying mechanism(s) of early pregnancy loss and might aid in developing novel prevention strategies using autophagy modulators.

The autophagy protein, FIP200 (RB1CC1) mediates progesterone responses governing uterine receptivity and decidualization†

Successful establishment of pregnancy depends on steroid hormone-driven cellular changes in the uterus during the peri-implantation period. To become receptive to embryo implantation, uterine endometrial stromal cells (ESCs) must transdifferentiate into decidual cells that secrete factors necessary for embryo survival and trophoblast invasion. Autophagy is a key homeostatic process vital for cellular homeostasis. Although the uterus undergoes major cellular changes during early pregnancy, the precise role of autophagy in uterine function is unknown. Here, we report that conditional knockout of the autophagy protein FIP200 in the reproductive tract of female mice results in reduced fecundity due to an implantation defect. In the absence of FIP200, aberrant progesterone signaling results in sustained uterine epithelial proliferation and failure of stromal cells to decidualize. Additionally, loss of FIP200 impairs decidualization of human ESCs. We conclude that the autophagy protein FIP200 plays a crucial role in uterine receptivity, decidualization, and fertility. These data establish autophagy as a major cellular pathway required for uterine receptivity and decidualization in both mice and human ESCs.

Fecundity is impaired in a mouse model of osteogenesis imperfecta

Osteogenesis imperfecta (OI), or brittle bone disease, is most often caused by mutations in genes encoding type I collagen or proteins that process it. Women with OI have a small, but significant increase in risk of serious pregnancy complications including uterine rupture. Here, the OI mouse, Col1a2^oim/oim , was used to examine the effects of collagen mutation on establishment and maintenance of pregnancy. Picrosirius birefringence was faint in Col1a2^oim/oim uteri, indicating diminished collagen in the myometrium and endometrium. There was some evidence of increased uterine gland number (p = .055) and size (p = .12) in (p = .055) virgin uteri, though the they were not significantly different than controls. There were no differences in the number of corpora lutea, or the time from pairing to delivery of pups between Col1a2^oim/oim and control dams, suggesting that ovulation and conception occur normally. However, when examined at Gestation Day 6.5 (postimplantation), gestation Day 10.5 (midpregnancy), and Postnatal Days 1-2, Col1a2^oim/oim dams had significantly fewer viable pups than controls overall. In pairwise comparisons, the loss was only significant in the postnatal group, suggesting the gradual loss of pups over time. Overall, the Col1a2^oim/oim mouse data suggest that OI impairs uterine function in pregnancy in a way that affects a small but significant number of fetuses.

Leprdb/+ Dams Protect Wild-type Male Offspring Bone Strength from the Detrimental Effects of a High-Fat Diet

The prevalence of maternal obesity is increasing at an alarming rate and increases the life-long risk of developing cardiometabolic disease in adult offspring. Leptin, an adipokine, is systemically elevated in the obese milieu. We recently showed that maternal hyperleptinemia without obesity improves offspring insulin sensitivity and glucose tolerance while protecting against weight gain on a high-fat, high-sugar (HFD). Here, we investigate the effect of maternal hyperleptinemia on offspring bone by using 2 independent maternal models. First, we compared wild-type (WT) offspring from severely hyperleptinemic Leprdb/+ (DB/+) dams with those from WT dams. In the second model, WT females were implanted with miniosmotic pumps that released either saline (group SAL) or leptin (group LEP; 650ng/hour) and the WT offspring were compared. At 23 weeks of age, a subset of offspring were challenged with a HFD for 8 weeks. When the offspring were 31 weeks of age, bone geometry, strength, and material properties were investigated. The HFD increased trabecular bone volume but decreased both total breaking strength and material strength of femora from the offspring of WT dams. However, male offspring of DB/+ dams were protected from the detrimental effects of a HFD, while offspring of LEP dams were not. Further material analysis revealed a modest decrease in advanced glycation end product accumulation coupled with increased collagen crosslinking in male offspring from DB/+ dams on a HFD. These data suggest that while maternal leptin may protect bone quality from the effects of a HFD, additional factors of the maternal environment controlled by leptin receptor signaling are likely also involved.

The Autophagy Gene Atg16L1 is Necessary for Endometrial Decidualization

Uterine receptivity is critical for establishing and maintaining pregnancy. For the endometrium to become receptive, stromal cells must differentiate into decidual cells capable of secreting factors necessary for embryo survival and placental development. Although there are multiple reports of autophagy induction correlated with endometrial stromal cell (ESC) decidualization, the role of autophagy in decidualization has remained elusive. To determine the role of autophagy in decidualization, we utilized 2 genetic models carrying mutations to the autophagy gene Atg16L1. Although the hypomorphic Atg16L1 mouse was fertile and displayed proper decidualization, conditional knockout in the reproductive tract of female mice reduced fertility by decreasing the implantation rate. In the absence of Atg16L1, ESCs failed to properly decidualize and fewer blastocysts were able to implant. Additionally, small interfering RNA knock down of Atg16L1 was detrimental to the decidualization response of human ESCs. We conclude that Atg16L1 is necessary for decidualization, implantation, and overall fertility in mice. Furthermore, considering its requirement for human endometrial decidualization, these data suggest Atg16L1 may be a potential mediator of implantation success in women.

Osteoblast Malfunction Caused by Cell Stress Response to Procollagen Misfolding in α2(I)-G610C Mouse Model of Osteogenesis Imperfecta

Glycine (Gly) substitutions in collagen Gly-X-Y repeats disrupt folding of type I procollagen triple helix and cause severe bone fragility and malformations (osteogenesis imperfecta [OI]). However, these mutations do not elicit the expected endoplasmic reticulum (ER) stress response, in contrast to other protein-folding diseases. Thus, it has remained unclear whether cell stress and osteoblast malfunction contribute to the bone pathology caused by Gly substitutions. Here we used a mouse with a Gly610 to cysteine (Cys) substitution in the procollagen α2(I) chain to show that misfolded procollagen accumulation in the ER leads to an unusual form of cell stress, which is neither a conventional unfolded protein response (UPR) nor ER overload. Despite pronounced ER dilation, there is no upregulation of binding immunoglobulin protein (BIP) expected in the UPR and no activation of NF-κB signaling expected in the ER overload. Altered expression of ER chaperones αB crystalline and HSP47, phosphorylation of EIF2α, activation of autophagy, upregulation of general stress response protein CHOP, and osteoblast malfunction reveal some other adaptive response to the ER disruption. We show how this response alters differentiation and function of osteoblasts in culture and in vivo. We demonstrate that bone matrix deposition by cultured osteoblasts is rescued by activation of misfolded procollagen autophagy, suggesting a new therapeutic strategy for OI. © 2016 American Society for Bone and Mineral Research.

Myostatin deficiency partially rescues the bone phenotype of osteogenesis imperfecta model mice

Mice with osteogenesis imperfecta (+/oim), a disorder of bone fragility, were bred to mice with muscle over growth to test whether increasing muscle mass genetically would improve bone quality and strength. The results demonstrate that femora from mice carrying both mutations have greater mechanical integrity than their +/oim littermates.

INTRODUCTION

Osteogenesis imperfecta is a heritable connective tissue disorder due primarily to mutations in the type I collagen genes resulting in skeletal deformity and fragility. Currently, there is no cure, and therapeutic strategies encompass the use of antiresorptive pharmaceuticals and surgical bracing, with limited success and significant potential for adverse effects. Bone, a mechanosensing organ, can respond to high mechanical loads by increasing new bone formation and altering bone geometry to withstand increased forces. Skeletal muscle is a major source of physiological loading on bone, and bone strength is proportional to muscle mass.

METHODS

To test the hypothesis that congenic increases in muscle mass in the osteogenesis imperfecta murine model mouse (oim) will improve their compromised bone quality and strength, heterozygous (+/oim) mice were bred to mice deficient in myostatin (+/mstn), a negative regulator of muscle growth. The resulting adult offspring were evaluated for hindlimb muscle mass, and bone microarchitecture, physiochemistry, and biomechanical integrity.

RESULTS

+/oim mice deficient in myostatin (+/mstn +/oim) were generated and demonstrated that myostatin deficiency increased body weight, muscle mass, and biomechanical strength in +/mstn +/oim mice as compared to +/oim mice. Additionally, myostatin deficiency altered the physiochemical properties of the +/oim bone but did not alter bone remodeling.

CONCLUSIONS

Myostatin deficiency partially improved the reduced femoral bone biomechanical strength of adult +/oim mice by increasing muscle mass with concomitant improvements in bone microarchitecture and physiochemical properties.

Hindlimb Skeletal Muscle Function and Skeletal Quality and Strength in +/G610C Mice With and Without Weight-Bearing Exercise

Osteogenesis imperfecta (OI) is a heterogeneous heritable connective tissue disorder associated with reduced bone mineral density and skeletal fragility. Bone is inherently mechanosensitive, with bone strength being proportional to muscle mass and strength. Physically active healthy children accrue more bone than inactive children. Children with type I OI exhibit decreased exercise capacity and muscle strength compared with healthy peers. It is unknown whether this muscle weakness reflects decreased physical activity or a muscle pathology. In this study, we used heterozygous G610C OI model mice (+/G610C), which model both the genotype and phenotype of a large Amish OI kindred, to evaluate hindlimb muscle function and physical activity levels before evaluating the ability of +/G610C mice to undergo a treadmill exercise regimen. We found +/G610C mice hindlimb muscles do not exhibit compromised muscle function, and their activity levels were not reduced relative to wild-type mice. The +/G610C mice were also able to complete an 8-week treadmill regimen. Biomechanical integrity of control and exercised wild-type and +/G610C femora were analyzed by torsional loading to failure. The greatest skeletal gains in response to exercise were observed in stiffness and the shear modulus of elasticity with alterations in collagen content. Analysis of tibial cortical bone by Raman spectroscopy demonstrated similar crystallinity and mineral/matrix ratios regardless of sex, exercise, and genotype. Together, these findings demonstrate +/G610C OI mice have equivalent muscle function, activity levels, and ability to complete a weight-bearing exercise regimen as wild-type mice. The +/G610C mice exhibited increased femoral stiffness and decreased hydroxyproline with exercise, whereas other biomechanical parameters remain unaffected, suggesting a more rigorous exercise regimen or another exercise modality may be required to improve bone quality of OI mice.

Characterization of the MPS I-H knock-in mouse reveals increased femoral biomechanical integrity with compromised material strength and altered bone geometry

Mucopolysaccharidosis type I (MPS I), is an autosomal recessive lysosomal storage disorder caused by a deficiency in the α-L-iduronidase enzyme, resulting in decreased enzymatic activity and accumulation of glycosaminoglycans. The disorder phenotypically manifests with increased urine glycosaminoglycan excretion, facial dysmorphology, neuropathology, cardiac manifestations, and bone deformities. While the development of new treatment strategies have shown promise in attenuating many symptoms associated with the disorder, the bone phenotype remains unresponsive. The aim of this study was to investigate and further characterize the skeletal manifestations of the Idua-W392X knock-in mouse model, which carries a nonsense mutation corresponding to the IDUA-W402X mutation found in Hurler syndrome (MPS I-H) patients. μCT analysis of the microarchitecture demonstrated increased cortical thickness, trabecular number, and trabecular connectivity along with decreased trabecular separation in the tibiae of female homozygous Idua-W392X knock-in (IDUA^−/−) mice, and increased cortical thickness in male IDUA^−/− tibiae. Cortical density, as determined by μCT, and bone mineral density distribution, as determined by quantitative backscattered microscopy, were equivalent in IDUA^−/− and wildtype (Wt) bone. However, tibial porosity was increased in IDUA^−/− cortical bone. Raman spectroscopy results indicated that tibiae from female IDUA^−/− had decreased phosphate to matrix ratios and increased carbonate to phosphate ratios compared to Wt female tibiae, whereas these ratios remained equivalent in male IDUA^−/− and Wt tibiae. Femora demonstrated altered geometry and upon torsional loading to failure analysis, female IDUA^−/− mouse femora exhibited increased torsional ultimate strength, with a decrease in material strength relative to Wt littermates. Taken together, these findings suggest that the IDUA^−/− mutation results in increased bone torsional strength by altering the overall bone geometry and the microarchitecture which may be a compensatory response to increased porosity, reduced bone tensile strength and altered physiochemical composition.