Bone and the Unfolded Protein Response: In Sickness and in Health.

Differentiation and optimal function of osteoblasts and osteoclasts are contingent on synthesis and maintenance of a healthy proteome. Impaired and/or altered secretory capacity of these skeletal cells is a primary driver of most skeletal diseases. The endoplasmic reticulum (ER) orchestrates the folding and maturation of membrane as well as secreted proteins at high rates within a calcium rich and oxidative organellar niche.

Mmp13 deletion in mesenchymal cells increases bone mass and may attenuate the cortical bone loss caused by estrogen deficiency.

The protective effect of estrogens against cortical bone loss is mediated via direct actions on mesenchymal cells, but functional evidence for the mediators of these effects has only recently begun to emerge. We report that the matrix metalloproteinase 13 (MMP13) is the highest up-regulated gene in mesenchymal cells from mice lacking the estrogen receptor alpha (ERα). In sham-operated female mice with conditional Mmp13 deletion in Prrx1 expressing cells (Mmp13), the femur and tibia length was lower as compared to control littermates (Mmp13f.

A decrease in NAD contributes to the loss of osteoprogenitors and bone mass with aging.

Age-related osteoporosis is caused by a deficit in osteoblasts, the cells that secrete bone matrix. The number of osteoblast progenitors also declines with age associated with increased markers of cell senescence. The forkhead box O (FoxO) transcription factors attenuate Wnt/β-catenin signaling and the proliferation of osteoprogenitors, thereby decreasing bone formation.

Osteocyte RANKL is required for cortical bone loss with age and is induced by senescence.

In aging mice, osteoclast number increases in cortical bone but declines in trabecular bone, suggesting that different mechanisms underlie age-associated bone loss in these 2 compartments. Osteocytes produce the osteoclastogenic cytokine RANKL, encoded by Tnfsf11. Tnfsf11 mRNA increases in cortical bone of aged mice, suggesting a mechanism underlying the bone loss.

Estrogens decrease osteoclast number by attenuating mitochondria oxidative phosphorylation and ATP production in early osteoclast precursors.

Loss of estrogens at menopause is a major cause of osteoporosis and increased fracture risk. Estrogens protect against bone loss by decreasing osteoclast number through direct actions on cells of the myeloid lineage. Here, we investigated the molecular mechanism of this effect.

Elevation of the unfolded protein response increases RANKL expression.

Increased production of the osteoclastogenic cytokine RANKL is a common feature of pathologic bone loss, but the underlying cause of this increase is poorly understood. The unfolded protein response (UPR) is activated in response to accumulation of misfolded proteins in the endoplasmic reticulum (ER). Failure to resolve misfolding results in excess UPR signaling that stimulates cytokine production and cell death.

Cxcl12 Deletion in Mesenchymal Cells Increases Bone Turnover and Attenuates the Loss of Cortical Bone Caused by Estrogen Deficiency in Mice.

CXCL12 is abundantly expressed in reticular cells associated with the perivascular niches of the bone marrow (BM) and is indispensable for B lymphopoiesis. Cxcl12 promotes osteoclastogenesis and has been implicated in pathologic bone resorption. We had shown earlier that estrogen receptor α deletion in osteoprogenitors and estrogen deficiency in mice increase Cxcl12 mRNA and protein levels in the BM plasma, respectively.

Delivery of phosphatidylethanolamine blunts stress in hepatoma cells exposed to elevated palmitate by targeting the endoplasmic reticulum.

Genetic obesity increases in liver phosphatidylcholine (PC)/phosphatidylethanolamine (PE) ratio, inducing endoplasmic reticulum (ER) stress without concomitant increase of ER chaperones. Here, it is found that exposing mice to a palm oil-based high fat (HF) diet induced obesity, loss of liver PE, and loss of the ER chaperone Grp78/BiP in pericentral hepatocytes. In Hepa1-6 cells treated with elevated concentration of palmitate to model lipid stress, Grp78/BiP mRNA was increased, indicating onset of stress-induced Unfolded Protein Response (UPR), but Grp78/BiP protein abundance was nevertheless decreased.

Elimination of senescent osteoclast progenitors has no effect on the age-associated loss of bone mass in mice.

Both an increase in osteoclast and a decrease in osteoblast numbers contribute to skeletal aging. Markers of cellular senescence, including expression of the cyclin inhibitor p16, increase with aging in several bone cell populations. The elimination of p16-expressing cells in old mice, using the INK-ATTAC transgene, increases bone mass indicating that senescent cells contribute to skeletal aging.

The Role of FoxOs in Bone Health and Disease.

Recent studies with murine models of cell-specific loss- or gain-of-function of FoxOs have provided novel insights into the function and signaling of these transcription factors on the skeleton. They have revealed that FoxO actions in chondrocytes are critical for normal skeletal development, and FoxO actions in cells of the osteoclast or osteoblast lineage greatly influence bone resorption and formation and, consequently, bone mass. FoxOs also act in osteoblast progenitors to inhibit Wnt signaling and bone formation.

Effect of finishing/polishing techniques and time on surface roughness of esthetic restorative materials.

Background: Surface roughness associated with improper finishing/polishing of restorations can result in plaque accumulation, gingival irritation, surface staining, and poor esthetic of restored teeth. The study aimed to evaluate the efficiency of various finishing and polishing systems and time using various procedures on surface roughness of some esthetic restorative materials.

Materials And Methods: In this study, samples of two composite materials, compomer and glass ionomer cement (GIC) materials, were fabricated.

DNA damage and senescence in osteoprogenitors expressing Osx1 may cause their decrease with age.

Age-related bone loss in mice results from a decrease in bone formation and an increase in cortical bone resorption. The former is accounted by a decrease in the number of postmitotic osteoblasts which synthesize the bone matrix and is thought to be the consequence of age-dependent changes in mesenchymal osteoblast progenitors. However, there are no specific markers for these progenitors, and conclusions rely on results from in vitro cultures of mixed cell populations.

The Effects of Aging and Sex Steroid Deficiency on the Murine Skeleton Are Independent and Mechanistically Distinct.

Old age and sex steroid deficiency are the two most critical factors for the development of osteoporosis. It remains unknown, however, whether the molecular culprits of the two conditions are similar or distinct. We show herein that at 19.

Deletion of FoxO1, 3, and 4 in Osteoblast Progenitors Attenuates the Loss of Cancellous Bone Mass in a Mouse Model of Type 1 Diabetes.

Type 1 diabetes is associated with osteopenia and increased fragility fractures, attributed to reduced bone formation. However, the molecular mechanisms mediating these effects remain unknown. Insulin promotes osteoblast formation and inhibits the activity of the FoxO transcription factors.

Sirtuin1 Suppresses Osteoclastogenesis by Deacetylating FoxOs.

Activation of Sirtuin1 (Sirt1), an nicotinamide adenine dinucleotide oxidized-dependent deacetylase, by natural or synthetic compounds like resveratrol, SRT2104, or SRT3025 attenuates the loss of bone mass caused by ovariectomy, aging, or unloading in mice. Conversely, Sirt1 deletion in osteoclast progenitors increases osteoclast number and bone resorption. Sirt1 deacetylates forkhead box protein (Fox) O1, FoxO3, and FoxO4, and thereby modulates their activity.

The Effects of Androgens on Murine Cortical Bone Do Not Require AR or ERα Signaling in Osteoblasts and Osteoclasts.

In men, androgens are critical for the acquisition and maintenance of bone mass in both the cortical and cancellous bone compartment. Male mice with targeted deletion of the androgen receptor (AR) in mature osteoblasts or osteocytes have lower cancellous bone mass, but no cortical bone phenotype. We have investigated the possibility that the effects of androgens on the cortical compartment result from AR signaling in osteoprogenitors or cells of the osteoclast lineage; or via estrogen receptor alpha (ERα) signaling in either or both of these two cell types upon conversion of testosterone to estradiol.

Sirtuin1 (Sirt1) promotes cortical bone formation by preventing β-catenin sequestration by FoxO transcription factors in osteoblast progenitors.

A decline of the levels and activity of Sirtuin1 (Sirt1), a NAD(+) class III histone deacetylase, with age contributes to the development of several diseases including type 2 diabetes, neurodegeneration, inflammation, and cancer. The anti-aging effects of Sirt1 evidently result from the deacetylation of many transcription factors and co-factors including members of the Forkhead box O (FoxO) family and β-catenin. Wnt/β-catenin is indispensable for osteoblast generation.

FoxO proteins restrain osteoclastogenesis and bone resorption by attenuating H2O2 accumulation.

Besides their cell-damaging effects in the setting of oxidative stress, reactive oxygen species (ROS) play an important role in physiological intracellular signalling by triggering proliferation and survival. FoxO transcription factors counteract ROS generation by upregulating antioxidant enzymes. Here we show that intracellular H2O2 accumulation is a critical and purposeful adaptation for the differentiation and survival of osteoclasts, the bone cells responsible for the resorption of mineralized bone matrix.

FOXOs attenuate bone formation by suppressing Wnt signaling.

Wnt/β-catenin/TCF signaling stimulates bone formation and suppresses adipogenesis. The hallmarks of skeletal involution with age, on the other hand, are decreased bone formation and increased bone marrow adiposity. These changes are associated with increased oxidative stress and decreased growth factor production, which activate members of the FOXO family of transcription factors.

Estrogen receptor-α signaling in osteoblast progenitors stimulates cortical bone accrual.

The detection of estrogen receptor-α (ERα) in osteoblasts and osteoclasts over 20 years ago suggested that direct effects of estrogens on both of these cell types are responsible for their beneficial effects on the skeleton, but the role of ERα in osteoblast lineage cells has remained elusive. In addition, estrogen activation of ERα in osteoclasts can only account for the protective effect of estrogens on the cancellous, but not the cortical, bone compartment that represents 80% of the entire skeleton. Here, we deleted ERα at different stages of differentiation in murine osteoblast lineage cells.

Neurospora crassa fmf-1 encodes the homologue of the Schizosaccharomyces pombe Ste11p regulator of sexual development.

The Neurospora crassa fmf-1 mutation exerts an unusual 'perithecium-dominant' developmental arrest; fmf-1 x fmf-1+ cross becomes arrested in perithecial development regardless of whether the mutant participates in the cross as the male or female parent. We localized fmf-1 to the LG IL genome segment between the centromere-proximal breakpoint of the chromosome segment duplication Dp(IL)39311 and the centromere. By mapping crossovers with respect to RFLP markers in this region we further localized fmf-1 to an approximately 34-kb-genome segment.

Chromosome segment duplications in Neurospora crassa: barren crosses beget fertile science.

Studies on Neurospora chromosome segment duplications (Dps) performed since the publication of Perkins's comprehensive review in 1997 form the focus of this article. We present a brief summary of Perkins's seminal work on chromosome rearrangements, specifically, the identification of insertional and quasiterminal translocations that can segregate Dp progeny when crossed with normal sequence strains (i.e.