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.

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.

From Osteoimmunology to Osteomicrobiology: How the Microbiota and the Immune System Regulate Bone.

Osteomicrobiology refers to the role of microbiota in bone health and the mechanisms by which the microbiota regulates post-natal skeletal development, bone aging, and pathologic bone loss. Here, we review recent reports linking gut microbiota to changes in bone phenotype. A pro-inflammatory cytokine milieu drives bone resorption in conditions such as sex steroid hormone deficiency. The response of the immune system to activation by the microbiome results in increased circulating osteoclastogenic cytokines in a T cell-dependent mechanism. Additionally, gut microbiota affect bone homeostasis through nutrient absorption, mediation of the IGF-1 pathway, and short chain fatty acid and metabolic products. Manipulation of microbiota through prebiotics or probiotics reduces inflammatory cytokine production, leading to changes in bone density. One mechanism of probiotic action is through upregulating tight junction proteins, increasing the strength of the gut epithelial layer, and leading to less antigen presentation and less activation of intestinal immune cells. Thus, prebiotics or probiotics may represent a future therapeutic avenue for ameliorating the risk of postmenopausal bone loss in humans.

Each member of the poly-r(C)-binding protein 1 (PCBP) family exhibits iron chaperone activity toward ferritin.

The mechanisms through which iron-dependent enzymes receive their metal cofactors are largely unknown. Poly r(C)-binding protein 1 (PCBP1) is an iron chaperone for ferritin; both PCBP1 and its paralog PCBP2 are required for iron delivery to the prolyl hydroxylase that regulates HIF1. Here we show that PCBP2 is also an iron chaperone for ferritin. Co-expression of PCBP2 and human ferritins in yeast activated the iron deficiency response and increased iron deposition into ferritin. Depletion of PCBP2 in Huh7 cells diminished iron incorporation into ferritin. Both PCBP1 and PCBP2 were co-immunoprecipitated with ferritin in HEK293 cells, and expression of both PCBPs was required for ferritin complex formation in cells. PCBP1 and -2 exhibited high affinity binding to ferritin in vitro. Mammalian genomes encode 4 PCBPs, including the minimally expressed PCBPs 3 and 4. Expression of PCBP3 and -4 in yeast activated the iron deficiency response, but only PCBP3 exhibited strong interactions with ferritin. Expression of PCBP1 and ferritin in an iron-sensitive, ccc1 yeast strain intensified the toxic effects of iron, whereas expression of PCBP4 protected the cells from iron toxicity. Thus, PCBP1 and -2 form a complex for iron delivery to ferritin, and all PCBPs may share iron chaperone activity.

A Case of Cribriform-Morular Thyroid Carcinoma Presenting Without Thyroid Nodule.

Cribriform-morular thyroid carcinoma is a rare type of thyroid cancer. It has a strong association with familial adenomatous polyposis (FAP), a hereditary genetic disorder that predisposes individuals to the development of numerous polyps in the colon and rectum. We describe the case of a young female patient who presented with an enlarging goiter, notably without detectable thyroid nodules or masses on ultrasound, who after total thyroidectomy was found to have cribriform-morular thyroid carcinoma. This diagnosis led to genetic testing and diagnosis of FAP syndrome. We demonstrate that this rare thyroid carcinoma may present with nonsuspicious findings on sonographic evaluation while being a valuable harbinger in the diagnosis of FAP syndrome.

Cyclin-dependent kinase 9-cyclin K functions in the replication stress response.

Cyclin-dependent kinase 9 (CDK9) is a well-characterized subunit of the positive transcription elongation factor b complex in which it regulates transcription elongation in cooperation with cyclin T. However, CDK9 also forms a complex with cyclin K, the function of which is less clear. Using a synthetic lethal RNA interference screen in human cells, we identified CDK9 as a component of the replication stress response. Loss of CDK9 activity causes an increase in spontaneous levels of DNA damage signalling in replicating cells and a decreased ability to recover from a transient replication arrest. This activity is restricted to CDK9-cyclin K complexes and is independent of CDK9-cyclin T complex. CDK9 accumulates on chromatin in response to replication stress and limits the amount of single-stranded DNA in cells under stress. Furthermore, we show that CDK9 and cyclin K interact with ataxia telangiectasia and Rad3-related protein and other checkpoint signalling proteins. These results reveal an unexpectedly direct role for CDK9-cyclin K in checkpoint pathways that maintain genome integrity in response to replication stress.

Disseminated Cryptococcosis in An Immunocompetent Host Presenting As Osteomyelitis and Leading to Adrenal Insufficiency.

Disseminated cryptococcosis infection typically occurs in immunocompromised patients, often through pneumonia or meningoencephalitis. Cases in immunocompetent patients are uncommon, and presentation in either bone or adrenal glands are rare. We describe a case of a previously healthy immunocompetent 50-year-old woman who presented with lytic bone lesions followed by meningoencephalitis, dermatologic involvement, and adrenal insufficiency from disseminated cryptococcus. To our knowledge, this is the first case report of an immunocompetent patient with cryptococcus in the combination of blood, bone, skin, central nervous system, and adrenal glands. Clinicians should be aware of atypical presentations of cryptococcal disease. In this review of the literature on cryptococcosis in immunocompetent patients, we find that while rare, cryptococcosis can affect varied organs and should be considered in the differential of infectious diseases.

Relationships between plasma apelin and adiponectin with normal weight obesity, body composition, and cardiorespiratory fitness in working adults.

BACKGROUND: A significant proportion of adults have normal weight obesity (NWO), defined as a normal body mass index (BMI) but disproportionately high body fat percentage. Individuals with NWO may have increased risk of cardiometabolic disorders and lower exercise tolerance, but it is unclear if this obesity phenotype is linked with dysregulated production of adipokines or myokines such as adiponectin and apelin, respectively. METHODS: This cross-sectional, secondary analysis included 177 working adults (mean age 49.6 ± 9.9 yrs, 64% female). Plasma high-molecular weight adiponectin and apelin levels were measured by ELISA. Body composition and fat distribution were assessed using dual energy X-ray absorptiometry. Exercise tolerance (VO2 maximum) was determined by treadmill testing. NWO was defined as a BMI <25 kg/m2 and body fat >30% for women or >23% for men. Participants were categorized as lean, NWO, or overweight-obese. RESULTS: A total of 14.7% of subjects were categorized as lean, 23.7% as having NWO, and 61.6% as having overweight-obesity. Plasma adiponectin levels were elevated in the overweight-obesity group (P < 0.05) compared to the lean and NWO groups, which did not differ from each other (P > 0.05). Adiponectin concentrations were inversely associated with BMI, fat mass, fat mass percent, visceral fat, and trunk to leg fat ratio and positively associated with leg fat mass (all P < 0.001). Plasma apelin levels were similar between the three body composition groups (P < 0.05) and were not significantly associated with any body composition indices. Apelin concentrations were inversely related to VO2 maximum (ß = -0.03 ± 0.01, p = 0.002). CONCLUSION: Plasma adiponectin and apelin levels did not distinguish between lean and NWO groups. Positive relationships with leg fat mass and adiponectin suggest the importance of assessing body composition and fat distribution when studying adipokines and cardiometabolic disorders. Further investigations are needed to understand relationships between exercise, body composition, and apelin secretion.

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.

Plant-based diets and bone health: sorting through the evidence.

PURPOSE OF REVIEW: An increase in awareness of vegetarian and vegan (plant-based) diets has brought forth numerous studies on their effects on health. The study of nutrition-based factors affecting bone health is difficult, given the length of time before clinical effects are evident. Furthermore, population-based studies must account for strong confounding influences as effects may be because of association, not causality. Yet, it is highly plausible that dietary factors affect bone remodeling in multiple ways. Plant-based diets may alter macronutrient and micronutrient balance, may cause differences in prebiotic and probiotic effects on gut microbiota, and may subtly change the inflammatory and immune response. RECENT FINDINGS: Several recent studies have looked at plant-based nutrition and markers of bone health, using measures such as bone turnover markers, bone mineral density, or fracture rates. Although population based and cross-sectional studies can be prone to confounding effects, a majority did not show differences in bone health between vegetarians/vegans and omnivores as long as calcium and vitamin D intake were adequate. A few prospective cohort or longitudinal studies even demonstrate some benefit to a plant-based diet, but this claim remains unproven. SUMMARY: There is no evidence that a plant-based diet, when carefully chosen to maintain adequate calcium and vitamin D levels, has any detrimental effects on bone health. Theoretical findings suggest a long-term plant-based diet may reduce the risk of osteoporosis, through mechanisms that are currently speculative.

Paget's disease of bone: updates for clinicians.

PURPOSE OF REVIEW: To provide clinicians an overview to the diagnosis, treatment, and management of Paget's disease, including recent guideline recommendations, with comparison of the Endocrine Society Clinical Practice Guideline (JCEM 2014) with the new Clinical Guideline review endorsed by the International Osteoporosis Foundation, the American Society of Bone and Mineral Research, the European Calcified Tissues Society, and the United Kingdom Bone Research Society (JBMR 2019). RECENT FINDINGS: Radionuclide bone scans are recommended for assessing the extent of Paget's disease. Bisphosphonates remain the mainstay for therapy with evidence of reducing symptomatic bone pain. One 5 mg intravenous dose of zoledronic acid is the current standard therapy for Paget's disease. SUMMARY: Paget's disease of the bone is characterized by focal increased bone remodeling activity, resulting in sclerotic or lytic lesions and poor bone quality at one or more sites. Patients may be symptomatic with bone pain, or may be asymptomatic, and identified through unexplained elevations in serum alkaline phosphatase. Diagnosis is through plain film imaging, with radionuclide bone scan to determine the extent. A single dose of IV zoledronic acid typically results in extended suppression of bone turnover and amelioration of bone pain. There remains a lack of evidence regarding efficacy of this treatment with regards to other complications of Paget's, but in general, bisphosphonate treatment is recommended.

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.

Advances in treatment of glucocorticoid-induced osteoporosis.

PURPOSE OF REVIEW: The aim of this study is to summarize monitoring, prevention and treatment options of glucocorticoid-induced osteoporosis for patients on chronic glucocorticoid therapy. RECENT FINDINGS: Recent meta-analyses highlight the efficacy of bisphosphonate use in improving bone mineral density and in reducing vertebral fractures in the setting of long-term glucocorticoid use. A new study has now shown that alendronate also reduces the risk of hip fracture in glucocorticoid use. Emerging data indicate that teriparatide and denosumab also reduce the risk of osteoporotic fracture in glucocorticoid-induced osteoporosis. SUMMARY: Glucocorticoid use is a leading cause of secondary osteoporosis; however, patients at risk of glucocorticoid-induced osteoporosis are often not evaluated or treated in a timely manner. Patients on a dose equivalent of 2.5 mg prednisone or greater for 3 months or longer duration should have their fracture risk assessed. Those at moderate or high risk should start bisphosphonate therapy, or if contraindicated, a second-line agent such as teriparatide or denosumab.

Short Communication: Hyperthyroidism in Human Immunodeficiency Virus Patients on Combined Antiretroviral Therapy: Case Series and Literature Review.

We describe an HIV-infected patient initiated on combined antiretroviral therapy (cART) who subsequently developed immune restoration disease (IRD) hyperthyroidism-this case represents one of five such patients seen at our center within the past year. Similar to previous reports of hyperthyroidism due to IRD, all of our patients experienced a rapid early recovery in total CD4 count, but developed symptoms of hyperthyroidism on average 3 years (38 months) after beginning cART, which represents a longer time frame than previously reported. Awareness and recognition of this potential complication of cART, which may occur years after treatment initiation, will allow patients with immune restorative hyperthyroidism to receive timely therapy and avoid the long-term complications associated with undiagnosed thyroid disease.

HIV through the looking glass: insights derived from Hepatitis B.

BACKGROUND: Although higher levels of hepatitis B virus (HBV) replication in HIV-HBV co-infection may relate to liver disease progression, this has not been completely elucidated. We used expression of hepatitis B core antigen (HBcAg) in liver biopsies from HIV-HBV co-infected and HBV mono-infected patients as a marker for HBV replication, and related these findings to clinical and histological parameters. METHODS: Data from 244 HBV patients were compared with 34 HIV-HBV patients. Liver biopsies were scored for inflammation, fibrosis, HBcAg, and hepatitis B surface antigen. Univariate and multivariate analyses were performed. RESULTS: HBcAg, but not hepatitis B surface antigen, staining was stronger in HIV co-infected than in HBV mono-infected. Co-infected and HBV mono-infected had similar alanine aminotransferase, inflammatory and fibrosis scores, and hepatitis B e antigen status. HBcAg staining correlated with HIV after correcting for HBV DNA and hepatitis B e antigen. CD4 counts and HIV RNA level did not correlate with intensity of HBcAg staining. HBV DNA levels were higher in HIV co-infected and correlated with HBcAg staining. CONCLUSIONS: By looking at HBcAg as a reflection of HBV replication in HIV-HBV co-infected with controlled HIV, our findings suggest that these patients may have subtle immune function defects, which could lead to adverse liver disease outcomes.