The P2X 7 nucleotide receptor (P2X 7 R) is an ATP-gated ion channel expressed in many cell types including osteoblasts and osteocytes. Mice with a null mutation of P2X 7 R have osteopenia in load bearing bones, suggesting that the P2X 7 R may be involved in the skeletal response to mechanical loading. We found the skeletal sensitivity to mechanical loading was reduced by up to 73% in P2X 7 R null (knock-out (KO)) mice. Release of ATP in the primary calvarial osteoblasts occurred within 1 min of onset of fluid shear stress (FSS). After 30 min of FSS, P2X 7 R-mediated pore formation was observed in wild type (WT) cells but not in KO cells. FSS increased prostaglandin (PG) E 2 release in WT cells but did not alter PGE 2 release in KO cells. Studies using MC3T3-E1 osteoblasts and MLO-Y4 osteocytes confirmed that PGE 2 release was suppressed by P2X 7 R blockade, whereas the P2X 7 R agonist BzATP enhanced PGE 2 release. We conclude that ATP signaling through P2X 7 R is necessary for mechanically induced release of prostaglandins by bone cells and subsequent osteogenesis.Mechanical loads applied to bone tissue increase bone formation and improves bone strength (1). Previous studies have suggested that several osteogenic factors, including insulin-like growth factors, transforming growth factor-␤, nitric oxide (NO), and prostaglandins (PGs), 3 mediate mechanically induced bone formation (2-5). PGs in particular have been intensively investigated. Numerous cell culture studies have demonstrated an increased production of PGs in osteoblasts and osteocytes subjected to fluid shear stresses (for review, see Ref. 6). Several PGs have independent anabolic effects on bone tissue. In particular PGE 2 greatly enhances the synthetic activities of osteoblasts (7).In addition to PGs, nucleotides, such as ATP and UTP, are released from cells in response to mechanical stimulation (8 -11), including osteoblasts (12, 13). These nucleotides can act as autocrine and paracrine factors through activation of purinergic (P2) Based on their molecular structure and activated signal pathways, P2 purinergic receptors are divided into two classes: P2X and P2Y (21). The P2X receptors are ligand-gated ion channels that, in general, are nonselective for monovalent cations. However, some of these receptors are also permeable to Ca 2ϩ or even anions. P2Y receptors are G proteinlinked receptors that in many cases are coupled through phospholipase C to the release of Ca 2ϩ from intracellular stores. Seven P2X subtypes and six P2Y subtypes have been identified in mammalian cells (22). The P2X 7 receptor (P2X 7 R) appears to be the most divergent member among P2X family. P2X 7 Rs have the unique ability to form large aqueous pores in the membrane, permeable to hydrophilic molecules as large as 900 Da with prolonged exposure to agonists (21). Activation of P2X 7 Rs stimulates the release of the inflammatory cytokines such as interleukin-1␤ in immune cells (23). P2X 7 R activation also results in cell membrane blebbing (24) and changes in cellular morpholo...

SUMMARY Regulatory T (Treg) cells are essential for maintenance of immune homeostasis. Here we found that hydrogen sulfide (H2S) was required for Foxp3+ Treg cell differentiation and function, and that H2S deficiency led to systemic autoimmune disease. H2S maintained expression of methylcytosine dioxygenases Tet1 and Tet2 by sulfhydrating nuclear transcription factor Y subunit beta (NFYB) to facilitate its binding to Tet1 and Tet2 promoters. Transforming growth factor-β (TGF-β)-activated Smad3 and interleukin-2 (IL-2)-activated Stat5 facilitated Tet1 and Tet2 binding to Foxp3. Tet1 and Tet2 catalyzed conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) in Foxp3 to establish a Treg cell-specific hypomethylation pattern and stable Foxp3 expression. Consequently, Tet1 and Tet2 deletion led to Foxp3 hypermethylation, impaired Treg cell differentiation and function, and autoimmune disease. Thus, H2S promotes Tet1 and Tet2 expression, which are recruited to Foxp3 by TGF-β and IL-2 signaling to maintain Foxp3 demethylation and Treg cell-associated immune homeostasis.

In the human body, 50-70 billion cells die every day, resulting in the generation of a large number of apoptotic bodies. However, the detailed biological role of apoptotic bodies in regulating tissue homeostasis remains unclear. In this study, we used Fas-deficient MRL/lpr and Caspase 3 mice to show that reduction of apoptotic body formation significantly impaired the self-renewal and osteo-/adipo-genic differentiation of bone marrow mesenchymal stem cells (MSCs). Systemic infusion of exogenous apoptotic bodies rescued the MSC impairment and also ameliorated the osteopenia phenotype in MRL/lpr, Caspase 3 and ovariectomized (OVX) mice. Mechanistically, we showed that MSCs were able to engulf apoptotic bodies via integrin αvβ3 and reuse apoptotic body-derived ubiquitin ligase RNF146 and miR-328-3p to inhibit Axin1 and thereby activate the Wnt/β-catenin pathway. Moreover, we used a parabiosis mouse model to reveal that apoptotic bodies participated in the circulation to regulate distant MSCs. This study identifies a previously unknown role of apoptotic bodies in maintaining MSC and bone homeostasis in both physiological and pathological contexts and implies the potential use of apoptotic bodies to treat osteoporosis.

Autophagosomes are double-membrane vesicles generated during autophagy. Biogenesis of the autophagosome requires membrane acquisition from intracellular compartments, the mechanisms of which are unclear. We previously found that a relocation of COPII machinery to the ER-Golgi intermediate compartment (ERGIC) generates ERGIC-derived COPII vesicles which serve as a membrane precursor for the lipidation of LC3, a key membrane component of the autophagosome. Here we employed super-resolution microscopy to show that starvation induces the enlargement of ER-exit sites (ERES) positive for the COPII activator, SEC12, and the remodeled ERES patches along the ERGIC A SEC12 binding protein, CTAGE5, is required for the enlargement of ERES, SEC12 relocation to the ERGIC, and modulates autophagosome biogenesis. Moreover, FIP200, a subunit of the ULK protein kinase complex, facilitates the starvation-induced enlargement of ERES independent of the other subunits of this complex and associates via its C-terminal domain with SEC12. Our data indicate a pathway wherein FIP200 and CTAGE5 facilitate starvation-induced remodeling of the ERES, a prerequisite for the production of COPII vesicles budded from the ERGIC that contribute to autophagosome formation.

These results confirm the findings of previous studies of the effect of rapid maxillary expansion on the maxilla. Additionally, we found that only the cross-sectional area of the upper airway at the posterior nasal spine to basion level significantly gains a moderate increase after rapid maxillary expansion.