The Microbial Metabolite Butyrate Stimulates Bone Formation via T Regulatory Cell-Mediated Regulation of WNT10B Expression.

Nutritional supplementation with probiotics can prevent pathologic bone loss. Here we examined the impact of supplementation with Lactobacillus rhamnosus GG (LGG) on bone homeostasis in eugonadic young mice. Micro-computed tomography revealed that LGG increased trabecular bone volume in mice, which was due to increased bone formation. Butyrate produced in the gut following LGG ingestion, or butyrate fed directly to germ-free mice, induced the expansion of intestinal and bone marrow (BM) regulatory T (Treg) cells. Interaction of BM CD8+ T cells with Treg cells resulted in increased secretion of Wnt10b, a bone anabolic Wnt ligand. Mechanistically, Treg cells promoted the assembly of a NFAT1-SMAD3 transcription complex in CD8+ cells, which drove expression of Wnt10b. Reducing Treg cell numbers, or reconstitution of TCRß-/- mice with CD8+ T cells from Wnt10b-/- mice, prevented butyrate-induced bone formation and bone mass acquisition. Thus, butyrate concentrations regulate bone anabolism via Treg cell-mediated regulation of CD8+ T cell Wnt10b production.

Brain region-specific synaptic function of FUS underlies the FTLD-linked behavioural disinhibition.

Synaptic dysfunction is one of the earliest pathological processes that contribute to the development of many neurological disorders, including Alzheimer's disease and frontotemporal lobar degeneration. However, the synaptic function of many disease-causative genes and their contribution to the pathogenesis of the related diseases remain unclear. In this study, we investigated the synaptic role of fused in sarcoma, an RNA-binding protein linked to frontotemporal lobar degeneration and amyotrophic lateral sclerosis, and its potential pathological role in frontotemporal lobar degeneration using pyramidal neuron-specific conditional knockout mice (FuscKO). We found that FUS regulates the expression of many genes associated with synaptic function in a hippocampal subregion-specific manner, concomitant with the frontotemporal lobar degeneration-linked behavioural disinhibition. Electrophysiological study and molecular pathway analyses further reveal that fused in sarcoma differentially regulates synaptic and neuronal properties in the ventral hippocampus and medial prefrontal cortex, respectively. Moreover, fused in sarcoma selectively modulates the ventral hippocampus-prefrontal cortex projection, which is known to mediate the anxiety-like behaviour. Our findings unveil the brain region- and synapse-specific role of fused in sarcoma, whose impairment might lead to the emotional symptoms associated with frontotemporal lobar degeneration.

An essential function for beta-arrestin 2 in the inhibitory signaling of natural killer cells.

The inhibitory signaling of natural killer (NK) cells is crucial in the regulation of innate immune responses. Here we show that the association of KIR2DL1, an inhibitory receptor of NK cells, with beta-arrestin 2 mediated recruitment of the tyrosine phosphatases SHP-1 and SHP-2 to KIR2DL1 and facilitated 'downstream' inhibitory signaling. Consequently, the cytotoxicity of NK cells was higher in beta-arrestin 2-deficient mice but was inhibited in beta-arrestin 2-transgenic mice. Moreover, beta-arrestin 2-deficient mice were less susceptible than wild-type mice to mouse cytomegalovirus infection, an effect that was abolished by depletion of NK cells. Our findings identify a previously unknown mechanism by which the inhibitory signaling in NK cells is regulated.

Regulatory T cells are expanded by Teriparatide treatment in humans and mediate intermittent PTH-induced bone anabolism in mice.

Teriparatide is a bone anabolic treatment for osteoporosis, modeled in animals by intermittent PTH (iPTH) administration, but the cellular and molecular mechanisms of action of iPTH are largely unknown. Here, we show that Teriparatide and iPTH cause a ~two-threefold increase in the number of regulatory T cells (Tregs) in humans and mice. Attesting in vivo relevance, blockade of the Treg increase in mice prevents the increase in bone formation and trabecular bone volume and structure induced by iPTH Therefore, increasing the number of Tregs is a pivotal mechanism by which iPTH exerts its bone anabolic activity. Increasing Tregs pharmacologically may represent a novel bone anabolic therapy, while iPTH-induced Treg increase may find applications in inflammatory conditions and transplant medicine.

Signaling pathways in aged T cells - a reflection of T cell differentiation, cell senescence and host environment.

With increasing age, the ability of the immune system to protect against new antigenic challenges or to control chronic infections erodes. Decline in thymic function and cumulating antigenic experiences of acute and chronic infections threaten T cell homeostasis, but insufficiently explain the failing immune competence and the increased susceptibility for autoimmunity. Alterations in signaling pathways in the aging T cells account for many of the age-related defects. Signaling threshold calibrations seen with aging frequently built on mechanisms that are operational in T cell development and T cell differentiation or are adaptations to the changing environment in the aging host. Age-related changes in transcription of receptors and signaling molecules shift the balance towards inhibitory pathways, most dominantly seen in CD8 T cells and to a lesser degree in CD4 T cells. Prominent examples are the expression of negative regulatory receptors of the CD28 and the TNF receptor superfamilies as well the expression of various cytoplasmic and nuclear dual-specific phosphatases.

Signal inhibition by the dual-specific phosphatase 4 impairs T cell-dependent B-cell responses with age.

T cell-dependent B-cell responses decline with age, suggesting defective CD4 T-cell function. CD4 memory T cells from individuals older than 65 y displayed increased and sustained transcription of the dual-specific phosphatase 4 (DUSP4) that shortened expression of CD40-ligand (CD40L) and inducible T-cell costimulator (ICOS) (both P < 0.001) and decreased production of IL-4, IL-17A, and IL-21 (all P < 0.001) after in vitro activation. In vivo after influenza vaccination, activated CD4 T cells from elderly individuals had increased DUSP4 transcription (P = 0.002), which inversely correlated with the expression of CD40L (r = 0.65, P = 0.002), ICOS (r = 0.57, P = 0.008), and IL-4 (r = 0.66, P = 0.001). In CD4 KO mice reconstituted with DUSP4 OT-II T cells, DUSP4 had a negative effect on the expansion of antigen-specific B cells (P = 0.003) and the production of ova-specific antibodies (P = 0.03) after immunization. Silencing of DUSP4 in memory CD4 T cells improved CD40L (P < 0.001), IL-4 (P = 0.007), and IL-21 (P = 0.04) expression significantly more in the elderly than young adults. Consequently, the ability of CD4 memory T cells to support B-cell differentiation that was impaired in the elderly (P = 0.004) was restored. Our data suggest that increased DUSP4 expression in activated T cells in the elderly in part accounts for defective adaptive immune responses.

K-RAS GTPase- and B-RAF kinase-mediated T-cell tolerance defects in rheumatoid arthritis.

Autoantibodies to common autoantigens and neoantigens, such as IgG Fc and citrullinated peptides, are immunological hallmarks of rheumatoid arthritis (RA). We examined whether a failure in maintaining tolerance is mediated by defects in T-cell receptor activation threshold settings. RA T cells responded to stimulation with significantly higher ERK phosphorylation (P < 0.001). Gene expression arrays of ERK pathway members suggested a higher expression of KRAS and BRAF, which was confirmed by quantitative PCR (P = 0.003), Western blot, and flow cytometry (P < 0.01). Partial silencing of KRAS and BRAF lowered activation-induced phosphorylated ERK levels (P < 0.01). In individual cells, levels of these signaling molecules correlated with ERK phosphorylation, attesting that their concentrations are functionally important. In confocal studies, B-RAF/K-RAS clustering was increased in RA T cells 2 min after T-cell receptor stimulation (P < 0.001). Overexpression of B-RAF and K-RAS in normal CD4 T cells amplified polyclonal T-cell proliferation and facilitated responses to citrullinated peptides. We propose that increased expression of B-RAF and K-RAS lowers T-cell activation thresholds in RA T cells, enabling responses to autoantigens.

Dietary phosphorus consumption alters T cell populations, cytokine production, and bone volume in mice.

The intake of dietary phosphate far exceeds recommended levels; however, the long-term health consequences remain relatively unknown. Here, the chronic physiological response to sustained elevated and reduced dietary phosphate consumption was investigated in mice. Although serum phosphate levels were brought into homeostatic balance, the prolonged intake of a high-phosphate diet dramatically and negatively impacted bone volume; generated a sustained increase in the phosphate responsive circulating factors FGF23, PTH, osteopontin and osteocalcin; and produced a chronic low-grade inflammatory state in the BM, marked by increased numbers of T cells expressing IL-17a, RANKL, and TNF-α. In contrast, a low-phosphate diet preserved trabecular bone while increasing cortical bone volume over time, and it reduced inflammatory T cell populations. Cell-based studies identified a direct response of T cells to elevated extracellular phosphate. Neutralizing antibodies against proosteoclastic cytokines RANKL, TNF-α, and IL-17a blunted the high-phosphate diet-induced bone loss identifying bone resorption as a regulatory mechanism. Collectively, this study illuminates that habitual consumption of a high-phosphate diet in mice induces chronic inflammation in bone, even in the absence of elevated serum phosphate. Furthermore, the study supports the concept that a reduced phosphate diet may be a simple yet effective strategy to reduce inflammation and improve bone health during aging.

Cyclic Adenosine Monophosphate (cAMP)-Dependent Phosphodiesterase Inhibition Promotes Bone Anabolism Through CD8+ T Cell Wnt-10b Production in Mice.

Cyclic adenosine monophosphate (cAMP)-dependent phosphodiesterase (PDE) inhibitors such as pentoxifylline (PTX) suppress cAMP degradation and promote cAMP-dependent signal transduction. PDE inhibitors increase bone formation and bone mass in preclinical models and are used clinically to treat psoriatic arthritis by targeting inflammatory mediators including activated T cells. T cell activation requires two signals: antigen-dependent CD3-activation, which stimulates cAMP production; and CD28 co-stimulation, which downregulates cAMP-signaling, through PDE activation. PDE-inhibitors consequently suppress T cell activation by disrupting CD28 co-stimulation. Interestingly, we have reported that when CD8+ T cells are activated in the absence of CD28 co-stimulation, they secrete Wnt-10b, a bone anabolic Wnt ligand that promotes bone formation. In the present study, we investigated whether the bone anabolic activity of the PDE-inhibitor PTX, has an immunocentric basis, involving Wnt-10b production by CD8+ T cells. When wild-type (WT) mice were administered PTX, biochemical markers of both bone resorption and formation were significantly increased, with net bone gain in the axial skeleton, as quantified by micro-computed tomography (µCT). By contrast, PTX increased only bone resorption in T cell knockout (KO) mice, causing net bone loss. Reconstituting T cell-deficient mice with WT, but not Wnt-10b knockout (KO) CD8+ T cells, rescued bone formation and prevented bone loss. To study the role of cAMP signaling in Wnt-10b expression, reverse-transcription polymerase chain reaction (RT-PCR) and luciferase-reporter assays were performed using primary T cells. PDE inhibitors intensified Wnt-10b promoter activity and messenger RNA (mRNA) accumulation in CD3 and CD28 activated CD8+ T cells. In contrast, inhibiting the cAMP pathway mediators protein kinase A (PKA) and cAMP response element-binding protein (CREB), suppressed Wnt-10b expression by T cells activated in the absence of CD28 co-stimulation. In conclusion, the data demonstrate a key role for Wnt-10b production by CD8+ T cells in the bone anabolic response to PDE-inhibitors and reveal competing T cell-independent pro-resorptive properties of PTX, which dominate under T cell-deficient conditions. Selective targeting of CD8+ T cells by PDE inhibitors may be a beneficial approach for promoting bone regeneration in osteoporotic conditions. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Epigenetic regulation of killer immunoglobulin-like receptor expression in T cells.

With increasing age, T cells gain expression of killer immunoglobulin-like receptors (KIRs) that transmit negative signals and dampen the immune response. KIR expression is induced in CD4 and CD8 T cells by CpG DNA demethylation suggesting epigenetic control. To define the mechanisms that underlie the age-associated preferential KIR expression in CD8 T cells, we examined KIR2DL3 promoter methylation patterns. With age, CD8 T cells developed a patchy and stochastic promoter demethylation even in cells that did not express the KIR2DL3-encoded CD158b protein; complete demethylation of the minimal KIR2DL3 promoter was characteristic for CD158b-expressing cells. In contrast, the promoter in CD4 T cells was fully methylated irrespective of age. The selectivity for CD8 T cells correlated with lower DNMT1 recruitment to the KIR2DL3 promoter which further diminished with age. In contrast, binding of the polycomb protein EZH2 known to be involved in DNMT1 recruitment was not different. Our data suggest that CD8 T cells endure increasing displacement of DNMT1 from the KIR promoter with age, possibly because of an active histone signature. The ensuing partial demethylation lowers the threshold for transcriptional activation and renders CD8 T cells more susceptible to express KIR, thereby contributing to the immune defect in the elderly.

The gut microbiota is a transmissible determinant of skeletal maturation.

Genetic factors account for the majority of the variance of human bone mass, but the contribution of non-genetic factors remains largely unknown. By utilizing maternal/offspring transmission, cohabitation, or fecal material transplantation (FMT) studies, we investigated the influence of the gut microbiome on skeletal maturation. We show that the gut microbiome is a communicable regulator of bone structure and turnover in mice. In addition, we found that the acquisition of a specific bacterial strain, segmented filamentous bacteria (SFB), a gut microbe that induces intestinal Th17 cell expansion, was sufficient to negatively impact skeletal maturation. These findings have significant translational implications, as the identification of methods or timing of microbiome transfer may lead to the development of bacteriotherapeutic interventions to optimize skeletal maturation in humans. Moreover, the transfer of SFB-like microbes capable of triggering the expansion of human Th17 cells during therapeutic FMT procedures could lead to significant bone loss in fecal material recipients.

Ovariectomy induces bone loss via microbial-dependent trafficking of intestinal TNF+ T cells and Th17 cells.

Estrogen deficiency causes a gut microbiome-dependent expansion of BM Th17 cells and TNF-α-producing T cells. The resulting increased BM levels of IL-17a (IL-17) and TNF stimulate RANKL expression and activity, causing bone loss. However, the origin of BM Th17 cells and TNF+ T cells is unknown. Here, we show that ovariectomy (ovx) expanded intestinal Th17 cells and TNF+ T cells, increased their S1P receptor 1-mediated (S1PR1-mediated) egress from the intestine, and enhanced their subsequent influx into the BM through CXCR3- and CCL20-mediated mechanisms. Demonstrating the functional relevance of T cell trafficking, blockade of Th17 cell and TNF+ T cell egress from the gut or their influx into the BM prevented ovx-induced bone loss. Therefore, intestinal T cells are a proximal target of sex steroid deficiency relevant for bone loss. Blockade of intestinal T cell migration may represent a therapeutic strategy for the treatment of postmenopausal bone loss.

ASK1-JNK signaling cascade mediates Ad-ST13-induced apoptosis in colorectal HCT116 cells.

ST13, a co-factor of heat shock protein, has shown potential antitumor efficacy for colorectal cancer in our previous study. However, the molecular mechanisms governing ST13-induced apoptosis are poorly understood. Here, we demonstrate that Ad-ST13 (ST13 mediated by adenovirus) activates apoptosis signal-regulated kinase (ASK1) and c-Jun N-terminal kinase (JNK) but not p38 (mitogen-activated protein kinase) in human colorectal HCT116 cells. Ad-ST13 also increases extracellular-regulated kinase (ERK) phosphorylation levels, but the change is due to adenovirus replication. Overexpression of ST13 also increases the transcription activity of AP-1. Blocking ASK1-JNK pathway affects Ad-ST13-mediated colorectal cell apoptosis, decreases the release of cytochrome c in cytoplasm and caspase activation. Because ASK1 is known to contain a tetratricopeptide repeat (TPR)-acceptor site and ST13 has TPR domain, we found the interaction between ST13 and ASK1. These results strongly indicate Ad-ST13 triggers colorectal cell apoptosis via ASK1-JNK signaling cascade.

PTH induces bone loss via microbial-dependent expansion of intestinal TNF+ T cells and Th17 cells.

Bone loss is a frequent but not universal complication of hyperparathyroidism. Using antibiotic-treated or germ-free mice, we show that parathyroid hormone (PTH) only caused bone loss in mice whose microbiota was enriched by the Th17 cell-inducing taxa segmented filamentous bacteria (SFB). SFB+ microbiota enabled PTH to expand intestinal TNF+ T and Th17 cells and increase their S1P-receptor-1 mediated egress from the intestine and recruitment to the bone marrow (BM) that causes bone loss. CXCR3-mediated TNF+ T cell homing to the BM upregulated the Th17 chemoattractant CCL20, which recruited Th17 cells to the BM. This study reveals mechanisms for microbiota-mediated gut-bone crosstalk in mice models of hyperparathyroidism that may help predict its clinical course. Targeting the gut microbiota or T cell migration may represent therapeutic strategies for hyperparathyroidism.

Parathyroid hormone-dependent bone formation requires butyrate production by intestinal microbiota.

Parathyroid hormone (PTH) is a critical regulator of skeletal development that promotes both bone formation and bone resorption. Using microbiota depletion by wide-spectrum antibiotics and germ-free (GF) female mice, we showed that the microbiota was required for PTH to stimulate bone formation and increase bone mass. Microbiota depletion lowered butyrate levels, a metabolite responsible for gut-bone communication, while reestablishment of physiologic levels of butyrate restored PTH-induced anabolism. The permissive activity of butyrate was mediated by GPR43 signaling in dendritic cells and by GPR43-independent signaling in T cells. Butyrate was required for PTH to increase the number of bone marrow (BM) regulatory T cells (Tregs). Tregs stimulated production of the osteogenic Wnt ligand Wnt10b by BM CD8+ T cells, which activated Wnt-dependent bone formation. Together, these data highlight the role that butyrate produced by gut luminal microbiota plays in triggering regulatory pathways, which are critical for the anabolic action of PTH in bone.

Molecular identification and functional characterization of a Drosophila dual-specificity phosphatase DMKP-4 which is involved in PGN-induced activation of the JNK pathway.

MAP (Mitogen-activated protein) kinases play an important role in regulating many critical cellular processes. The inactivation of MAP kinases is always accomplished by a family of dual-specificity phosphatases, termed MAPK phosphatases (MKPs). Here, we have identified a novel MKP-like protein, designated DMKP-4, from the Drosophila genome. DMKP-4 is a protein of 387 amino acids, with a dual-specificity phosphatase (DSP) catalytic domain. Recombinant protein DMKP-4 retains intrinsic phosphatase activity against chromogenic substrate pNPP. Overexpression of DMKP-4 inhibited the activation of ERK, JNK and p38 by H(2)O(2), sorbitol and heat shock in HEK293-T cells, and JNK activation in Drosophila S2 cells under PGN stimuli. "Knockdown" of DMKP-4 expression by RNAi significantly enhanced the PGN-stimulated activation of JNK, but not ERK nor p38. Further study revealed that DMKP-4 interacted specifically with JNK via its DSP domain. Mutation of Cys-126 to serine in the DSP domain of DMKP-4 not only eliminated its interaction with JNK, but also markedly reduced its phosphatase activity. Thus, DMKP-4 is a Drosophila homologue of mammalian MKPs, and may play important roles in the regulation of various developmental processes.

IL-17 Receptor Signaling in Osteoblasts/Osteocytes Mediates PTH-Induced Bone Loss and Enhances Osteocytic RANKL Production.

Primary hyperparathyroidism (PHPT) is a condition where elevated PTH levels lead to bone loss, in part through increased production of the osteoclastogenic factor IL-17A, by bone marrow (BM) T-helper 17 (Th17) cells, a subset of helper CD4+ T cells. In animals, PHPT is modeled by continuous PTH treatment (cPTH). In mice, an additional critical action of cPTH is the capacity to increase the production of RANKL by osteocytes. However, a definitive link between IL-17A and osteocytic expression of RANKL has not been made. Here we show that cPTH fails to induce cortical and trabecular bone loss and causes less intense bone resorption in conditional knock-out (IL-17RAΔOCY ) male and female mice lacking the expression of IL-17A receptor (IL-17RA) in dentin matrix protein 1 (DMP1)-8kb-Cre-expressing cells, which include osteocytes and some osteoblasts. Therefore, direct IL-17RA signaling in osteoblasts/osteocytes is required for cPTH to exert its bone catabolic effects. In addition, in vivo, silencing of IL-17RA signaling in in DMP1-8kb-expressing cells blunts the capacity of cPTH to stimulate osteocytic RANKL production, indicating that cPTH augments osteocytic RANKL expression indirectly, via an IL-17A/IL-17RA-mediated mechanism. Thus, osteocytic production of RANKL and T cell production of IL-17A are both critical for the bone catabolic activity of cPTH. © 2018 American Society for Bone and Mineral Research.

Feedback control of MKP-1 expression by p38.

Mitogen-activated protein (MAP) kinases play a critical role in innate immune responses to microbial infection through eliciting the biosynthesis of proinflammatory cytokines. MAP phosphatases (MKP)-1 is an archetypical member of the dual-specificity phosphatase family that deactivates MAP kinases. Induction of MKP-1 has been implicated in attenuating the lipopolysaccharide (LPS) and Peptidoglycan (PGN) responses, but how the expression of the MKP-1 is regulated is still not fully understood. Here, we show that inhibition of p38 MAP kinase by specific inhibitor SB 203580 or RNA interference (RNAi) markedly reduced the expression of MKP-1 in LPS or PGN-treated macrophages, which is correlated with prolonged activation of p38 and JNK. Depletion of MAPKAP kinase 2 (MK2), a downstream substrate of p38, by RNAi also inhibited the expression of MKP-1. The mRNA level of MKP-1 is not affected by inhibition of p38, but the expression of MKP-1 is inhibited by treatment of cycloheximide. Thus, p38 MAPK plays a critical role in mediating expression of MKP-1 at a post-transcriptional level. Furthermore, inhibition of p38 by SB 203580 prevented the expression of MKP-1 in LPS-tolerized macrophages, restored the activation of MAP kinases after LPS restimulation. These results indicate a critical role of p38-MK2-dependent induction of MKP-1 in innate immune responses.

Migration of mouse antibody-secreting hybridoma cells from blood to genital tract and its regulation by sex hormones are associated with the differential expression patterns of adhesion molecules and chemokines in the tract rather than in the antibody-secreting cells.

To understand better the molecular mechanisms of differential migration of antibody-secreting cells (ASCs) into mouse genital tracts, and regulation by sex hormones, surface markers, hormone receptors and adhesion molecules in mouse SG2 and PA4 hybridoma cells, respectively, secreting IgG2b and polymeric IgA antibody were detected by flow cytometry or RT-PCR. Semi-quantitative RT-PCR was also used for measuring mRNA expression of adhesion molecules and chemokines (VCAM-1, ICAM-1, P-selectin, JAM-1 and CXCL12) in genital tracts of various adult mouse groups. The mRNAs of androgen receptor, estrogen receptor beta and CXCR4 were expressed in the ASCs. Sex hormones had no effect on expression of these molecules in ASCs. Except for VCAM-1, mRNA of all examined genes was expressed in normal mouse genital tracts. The mean of relative amounts of ICAM-1 and CXCL12 mRNA in all examined organs of females were higher (2.1- and 1.9-fold) than those in males. After orchiectomy or ovariectomy, the expression of ICAM-1, CXCL12 and P-selectin mRNA in the examined organs increased, except JAM-1 in male and CXCL12 in female. Sex hormone treatment recovered the changes to normal levels of mRNA expression in many examined genital tissues. In combination with our previous work, preferential migration of ASCs into female genital tract and regulation of migration by sex hormones are associated with expression patterns of adhesion molecules and chemokines in genital tract rather than in ASCs.

Regulation of Drosophila p38 activation by specific MAP2 kinase and MAP3 kinase in response to different stimuli.

The p38 mitogen-activated protein kinase (MAPK) signaling pathway plays an important role in cellular responses to inflammatory stimuli and environmental stress. Activation of p38 is mediated through phosphorylation by upstream MAPKK, which in turn is activated by MAPKKK. However, the mechanism of how different upstream MAP2Ks and MAP3Ks specifically contribute to p38 activation in response to different stimuli is still not clearly understood. By using double-stranded RNA-mediated interference (RNAi) in Drosophila cells, we demonstrate that D-MKK3 is a major MAP2K responsible for D-p38 activation by UV, heat shock, NaCl or peptiodglycan (PGN). Stimulation of UV and PGN activates D-p38 through D-MEKK1, heat shock-induced activation of D-p38 signals through both D-MEKK1 and D-ASK1. On the other hand, maximal activation of D-p38 by NaCl requires the expression of four MAP3Ks.