Adipose tissue is a critical regulator of osteoarthritis.

Osteoarthritis (OA), the leading cause of pain and disability worldwide, disproportionally affects individuals with obesity. The mechanisms by which obesity leads to the onset and progression of OA are unclear due to the complex interactions among the metabolic, biomechanical, and inflammatory factors that accompany increased adiposity. We used a murine preclinical model of lipodystrophy (LD) to examine the direct contribution of adipose tissue to OA. Knee joints of LD mice were protected from spontaneous or posttraumatic OA, on either a chow or high-fat diet, despite similar body weight and the presence of systemic inflammation. These findings indicate that adipose tissue itself plays a critical role in the pathophysiology of OA. Susceptibility to posttraumatic OA was reintroduced into LD mice using implantation of a small adipose tissue depot derived from wild-type animals or mouse embryonic fibroblasts that undergo spontaneous adipogenesis, implicating paracrine signaling from fat, rather than body weight, as a mediator of joint degeneration.

Conditional knockout of leptin receptor in the female reproductive tract reduces fertility due to parturition defects in mice.

Leptin is required for fertility, including initiation of estrous cycles. It is therefore challenging to assess the role of leptin signaling during pregnancy. Although neuron-specific transgene approaches suggest that leptin signaling in the central nervous system is most important, experiments with pharmacologic inhibition of leptin in the uterus or global replacement of leptin during pregnancy suggest leptin signaling in the reproductive tract may be required. Here, conditional leptin receptor knockout (Lepr cKO) with a progesterone receptor-driven Cre recombinase was used to examine the importance of leptin signaling in pregnancy. Lepr cKO mice have almost no leptin receptor in uterus or cervix, and slightly reduced leptin receptor levels in corpus luteum. Estrous cycles and progesterone concentrations were not affected by Lepr cKO. Numbers of viable embryos did not differ between primiparous control and Lepr cKO dams on Days 6.5 and 17.5 of pregnancy, despite a slight reduction in the ratio of embryos to corpora lutea, showing that uterine leptin receptor signaling is not required for embryo implantation. Placentas of Lepr cKO dams had normal weight and structure. However, over four parities, Lepr cKO mice produced 22% fewer live pups than controls, and took more time from pairing to delivery by their fourth parity. Abnormal birth outcomes of either dystocia or dead pups occurred in 33% of Lepr cKO deliveries but zero control deliveries, and the average time to deliver each pup after crouching was significantly increased. Thus, leptin receptor signaling in the reproductive tract is required for normal labor and delivery.

Developmental and Transmittable Origins of Obesity-Associated Health Disorders.

The current global obesity pandemic is clearly linked to both the increasing prevalence of, and preference for, foods high in calories, specifically fat and sucrose, and declining levels of daily physical activity. A less commonly discussed possible explanation is that risk of obesity begins in utero as a result of developmental plasticity during early life. This idea fits into the broader Developmental Origins of Health and Diseases (DOHAD) hypothesis, which holds that stressful in utero exposure manifests as disease in adulthood. In this review, we highlight several studies that have revealed the role of epigenetics in multigenerational transmission of developmentally programmed obesity and associated cardiometabolic disease.

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, Col1a2oim/oim , was used to examine the effects of collagen mutation on establishment and maintenance of pregnancy. Picrosirius birefringence was faint in Col1a2oim/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 Col1a2oim/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, Col1a2oim/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 Col1a2oim/oim mouse data suggest that OI impairs uterine function in pregnancy in a way that affects a small but significant number of fetuses.

Decreasing maternal myostatin programs adult offspring bone strength in a mouse model of osteogenesis imperfecta.

During fetal development, the uterine environment can have effects on offspring bone architecture and integrity that persist into adulthood; however, the biochemical and molecular mechanisms remain unknown. Myostatin is a negative regulator of muscle mass. Parental myostatin deficiency (Mstntm1Sjl/+) increases muscle mass in wild-type offspring, suggesting an intrauterine programming effect. Here, we hypothesized that Mstntm1Sjl/+ dams would also confer increased bone strength. In wild-type offspring, maternal myostatin deficiency altered fetal growth and calvarial collagen content of newborn mice and conferred a lasting impact on bone geometry and biomechanical integrity of offspring at 4 mo of age, the age of peak bone mass. Second, we sought to apply maternal myostatin deficiency to a mouse model with osteogenesis imperfecta (Col1a2oim), a heritable connective tissue disorder caused by abnormalities in the structure and/or synthesis of type I collagen. Femora of male Col1a2oim/+ offspring from natural mating of Mstntm1Sjl/+ dams to Col1a2oim/+sires had a 15% increase in torsional ultimate strength, a 29% increase in tensile strength, and a 24% increase in energy to failure compared with age, sex, and genotype-matched offspring from natural mating of Col1a2oim/+ dams to Col1a2oim/+ sires. Finally, increased bone biomechanical strength of Col1a2oim/+ offspring that had been transferred into Mstntm1Sjl/+ dams as blastocysts demonstrated that the effects of maternal myostatin deficiency were conferred by the postimplantation environment. Thus, targeting the gestational environment, and specifically prenatal myostatin pathways, provides a potential therapeutic window and an approach for treating osteogenesis imperfecta.

Maternal high-fat high-sugar diet impairs bone quality and strength but not cartilage in aging mice.

Osteoarthritis (OA) is a prevalent aging disorder of synovial joints and recent work suggests that a parental high-fat diet increases OA severity following joint injury in offspring. We hypothesized that a maternal high-fat high-sugar (HFHS) diet would promote spontaneous osteoarthritis-related cartilage and bone changes in 1-year-old offspring. Female C57BL/6 J mice were placed on either a chow control or HFHS diet for 6 weeks before mating to a chow-fed C57BL/6 J male and maintained on their assigned diets throughout pregnancy and lactation. Male and female offspring were weaned onto a chow diet, raised to 1 year of age, and evaluated for cartilage and bone changes indicative of OA. However, offspring did not show early signs of OA as measured by histological Mankin scoring, mechanical testing of the pericellular matrix, histological synovitis scoring, or subchondral bone thickening as measured by microcomputed Tomography. On the other hand, male offspring from HFHS-fed dams had reduced trabecular bone quality in the tibial metaphysis and decreased cortical thickness. Although maternal HFHS diet did not impact trabecular or cortical bone quality in tibias of female offspring, the radii of these animals had decreased cortical thickness, increased medullary area, and impaired breaking strength compared to those of control-fed dams. Finally, we evaluated bone quality and strength in male and female F2 offspring and found that the grandmaternal diet modestly impacted radial bone geometry but not strength. Together these results suggest that maternal HFHS diet impairs F1 offspring skeletal integrity in a sex and bone site-specific manner.

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, our understanding of the biological processes that preserve the oviductal cellular structure and functional integrity is limited. Here, we report that Atg14-dependent autophagy plays a crucial role in maintaining the cellular integrity of the oviduct by controlling inflammatory responses, thereby supporting efficient embryo transport. Specifically, the conditional depletion of the autophagy-related gene, Atg14 in the oviduct causes severe structural abnormalities compromising its cellular integrity leading to the abnormal 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 via altering the mitochondrial integrity leading to inappropriate embryo retention and impeded embryo transport in the oviduct. Finally, pharmacological activation of pyroptosis in pregnant mice phenocopied the genetically induced defect and caused 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 into the underlying mechanism(s) of early pregnancy loss and might aid in developing novel prevention strategies using autophagy modulators.

Is Obesity a Disease of Stem Cells?

Obesity disrupts physiological homeostasis and alters both systemic and local microenvironments that impact stem cell plasticity and impair regenerative capacity. We present growing evidence that reveals the bidirectionality of obesity-induced stem cell dysfunction and how the molecular changes in stem cells residing in obese environments may accelerate disease severity.

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.

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.

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.