Bile acids and bilirubin effects on osteoblastic gene profile. Implications in the pathogenesis of osteoporosis in liver diseases

Obesity and lipid metabolism in the development of osteoporosis (Review)

Osteoporosis is a common bone metabolic disease that causes a heavy social burden and seriously threatens life. Improving osteogenic capacity is necessary to correct bone mass loss in the treatment of osteoporosis. Osteoblasts are derived from the differentiation of bone marrow mesenchymal stem cells, a process that opposes adipogenic differentiation. The peroxisome proliferator‑activated receptor γ and Wnt/β‑catenin signaling pathways mediate the mutual regulation of osteogenesis and adipogenesis. Lipid substances play an important role in the occurrence and development of osteoporosis. The content and proportion of lipids modulate the activity of immunocytes, mainly macrophages, and the secretion of inflammatory factors, such as IL‑1, IL‑6 and TNF‑α. These inflammatory effectors increase the activity and promote the differentiation of osteoclasts, which leads to bone imbalance and stronger bone resorption. Obesity also decreases the activity of antioxidases and leads to oxidative stress, thereby inhibiting osteogenesis. The present review starts by examining the bidirectional differentiation of BM‑MSCs, describes in detail the mechanism by which lipids affect bone metabolism, and discusses the regulatory role of inflammation and oxidative stress in this process. The review concludes that a reasonable adjustment of the content and proportion of lipids, and the alleviation of inflammatory storms and oxidative damage induced by lipid imbalances, will improve bone mass and treat osteoporosis.

Microbiota metabolites in bone: Shaping health and Confronting disease

The intricate interplay between the gut microbiota and bone health has become increasingly recognized as a fundamental determinant of skeletal well-being. Microbiota-derived metabolites play a crucial role in dynamic interaction, specifically in bone homeostasis. In this sense, short-chain fatty acids (SCFAs), including acetate, propionate, and butyrate, indirectly promote bone formation by regulating insulin-like growth factor-1 (IGF-1). Trimethylamine N-oxide (TMAO) has been found to increase the expression of osteoblast genes, such as Runt-related transcription factor 2 (RUNX2) and bone morphogenetic protein-2 (BMP2), thus enhancing osteogenic differentiation and bone quality through BMP/SMADs and Wnt signaling pathways. Remarkably, in the context of bone infections, the role of microbiota metabolites in immune modulation and host defense mechanisms potentially affects susceptibility to infections such as osteomyelitis. Furthermore, ongoing research elucidates the precise mechanisms through which microbiota-derived metabolites influence bone cells, such as osteoblasts and osteoclasts. Understanding the multifaceted influence of microbiota metabolites on bone, from regulating homeostasis to modulating susceptibility to infections, has the potential to revolutionize our approach to bone health and disease management. This review offers a comprehensive exploration of this evolving field, providing a holistic perspective on the impact of microbiota metabolites on bone health and diseases.

Bile Acid Network and Vascular Calcification-Associated Diseases: Unraveling the Intricate Connections and Therapeutic Potential

Bile acids play a crucial role in promoting intestinal nutrient absorption and biliary cholesterol excretion, thereby protecting the liver from cholesterol accumulation and bile acid toxicity. Additionally, bile acids can bind to specific nuclear and membrane receptors to regulate energy expenditure and specific functions of particular tissues. Vascular calcification refers to the pathological process of calcium-phosphate deposition in blood vessel walls, which serves as an independent predictor for cardiovascular adverse events. In addition to aging, this pathological change is associated with aging-related diseases such as atherosclerosis, hypertension, chronic kidney disease, diabetes mellitus, and osteoporosis. Emerging evidence suggests a close association between the bile acid network and these aforementioned vascular calcification-associated conditions. Several bile acids have been proven to participate in calcium-phosphate metabolism, affecting the transdifferentiation of vascular smooth muscle cells and thus influencing vascular calcification. Targeting the bile acid network shows potential for ameliorating these diseases and their concomitant vascular calcification by regulating pathways such as energy metabolism, inflammatory response, oxidative stress, and cell differentiation. Here, we present a summary of the metabolism and functions of the bile acid network and aim to provide insights into the current research on the profound connections between the bile acid network and these vascular calcification-associated diseases, as well as the therapeutic potential.

A Rare Case of Primary Sjogren's Syndrome Coexisting With Gilbert Syndrome

Gilbert syndrome (GS) is an autosomal recessive inherited bilirubin metabolism disorder characterized by chronic unconjugated hyperbilirubinemia in the absence of hemolysis and liver disease. Primary Sjogren's syndrome (pSS), mainly occurring in women, is a common connective tissue disease (CTD) wherein bilirubin levels are generally reduced. We report a rare case of pSS coexisting with GS. A 35-year-old female patient presented to our hospital with pSS and chronic unconjugated hyperbilirubinemia, for which low-dose methylprednisolone was ineffective. The patient's liver function test results were normal, serological tests for hepatitis virus were negative, and abdominal ultrasound did not indicate abnormal liver morphology. Bone mineral density determination showed that the Z scores of the left femoral neck and lumbar spine were -1.9 and -2.6, respectively, with T scores of -2.1 and -2.8, respectively. Full-exon sequencing revealed a homozygous TA insertion in the TATA box (A(TA)7TAA) and a heterozygous base substitution from C to A at nucleotide position 686 in exon 1 (c.686C>A) in the uridine glucuronosyltransferase 1A1 (UGT1A1) gene. Therefore, the patient was diagnosed with pSS, GS, and osteoporosis. The dose of methylprednisolone was then reduced and gradually stopped, and treatment for osteoporosis was strengthened. To our knowledge, this is the first report of pSS with GS. It is important to clarify the cause of hyperbilirubinemia in patients with CTD, including pSS, which affects the formulation of correct treatment plans.

BCL-G: 20 years of research on a non-typical protein from the BCL-2 family

Proteins from the BCL-2 family control cell survival and apoptosis in health and disease, and regulate apoptosis-unrelated cellular processes. BCL-Gonad (BCL-G, also known as BCL2-like 14) is a non-typical protein of the family as its long isoform (BCL-G_L) consists of BH2 and BH3 domains without the BH1 motif. BCL-G is predominantly expressed in normal testes and different organs of the gastrointestinal tract. The complexity of regulatory mechanisms of BCL-G expression and post-translational modifications suggests that BCL-G may play distinct roles in different types of cells and disorders. While several genetic alterations of BCL2L14 have been reported, gene deletions and amplifications prevail, which is also confirmed by the analysis of sequencing data for different types of cancer. Although the studies validating the phenotypic consequences of genetic manipulations of BCL-G are limited, the role of BCL-G in apoptosis has been undermined. Recent studies using gene-perturbation approaches have revealed apoptosis-unrelated functions of BCL-G in intracellular trafficking, immunomodulation, and regulation of the mucin scaffolding network. These studies were, however, limited mainly to the role of BCL-G in the gastrointestinal tract. Therefore, further efforts using state-of-the-art methods and various types of cells are required to find out more about BCL-G activities. Deciphering the isoform-specific functions of BCL-G and the BCL-G interactome may result in the designing of novel therapeutic approaches, in which BCL-G activity will be either imitated using small-molecule BH3 mimetics or inhibited to counteract BCL-G upregulation. This review summarizes two decades of research on BCL-G.

Biological properties of the BCL-2 family protein BCL-RAMBO, which regulates apoptosis, mitochondrial fragmentation, and mitophagy

Mitochondria play an essential role in the regulation of cellular stress responses, including cell death. Damaged mitochondria are removed by fission and fusion cycles and mitophagy, which counteract cell death. BCL-2 family proteins possess one to four BCL-2 homology domains and regulate apoptosis signaling at mitochondria. BCL-RAMBO, also known as BCL2-like 13 (BCL2L13), was initially identified as one of the BCL-2 family proteins inducing apoptosis. Mitophagy receptors recruit the ATG8 family proteins MAP1LC3/GABARAP via the MAP1LC3-interacting region (LIR) motif to initiate mitophagy. In addition to apoptosis, BCL-RAMBO has recently been identified as a mitophagy receptor that possesses the LIR motif and regulates mitochondrial fragmentation and mitophagy. In the 20 years since its discovery, many important findings on BCL-RAMBO have been increasingly reported. The biological properties of BCL-RAMBO are reviewed herein.

Gut microbiota and fecal metabolic signatures in rat models of disuse-induced osteoporosis

Background

Assessing the correlation between gut microbiota (GM) and bone homeostasis has increasingly attracted research interest. Meanwhile, GM dysbiosis has been found to be associated with abnormal bone metabolism. However, the function of GM in disuse-induced osteoporosis (DIO) remains poorly understood. In our research, we evaluated the characteristics of GM and fecal metabolomics to explore their potential correlations with DIO pathogenesis.

Methods

DIO rat models and controls (CON) underwent micro-CT, histological analyses, and three-point bending tests; subsequently, bone microstructures and strength were observed. ELISAs were applied for the measurement of the biochemical markers of bone turnover while GM abundance was observed using 16S rDNA sequencing. Metabolomic analyses were used to analyze alterations fecal metabolites. The potential correlations between GM, metabolites, and bone loss were then assessed.

Results

In the DIO group, the abundance of GM was significantly altered compared to that in the CON group. Moreover, DIO significantly altered fecal metabolites. More specifically, an abnormally active pathway associated with bile acid metabolism, as well as differential bacterial genera related to bone/tissue volume (BV/TV), were identified. Lithocholic acid, which is the main secondary bile acid produced by intestinal bacteria, was then found to have a relationship with multiple differential bacterial genera. Alterations in the intestinal flora and metabolites in feces, therefore, may be responsible for DIO-induced bone loss.

Conclusions

The results indicated that changes in the abundance of GM abundance and fecal metabolites were correlated with DIO-induced bone loss, which might provide new insights into the DIO pathogenesis. The detailed regulatory role of GM and metabolites in DIO-induced bone loss needs to be explored further.

Increased concentrations of conjugated bile acids are associated with osteoporosis in PSC patients

Primary sclerosing cholangitis (PSC) is an idiopathic cholestatic liver disease characterized by chronic inflammation and progressive fibrosis of intra- and extrahepatic bile ducts. Osteoporosis is a frequent comorbidity in PSC, and we could previously demonstrate that IL17-dependent activation of bone resorption is the predominant driver of bone loss in PSC. Since we additionally observed an unexpected heterogeneity of bone mineral density in our cohort of 238 PSC patients, the present study focused on a comparative analysis of affected individuals with diagnosed osteoporosis (PSC^OPO, n = 10) or high bone mass (PSC^HBM, n = 7). The two groups were not distinguishable by various baseline characteristics, including liver fibrosis or serum parameters for hepatic function. In contrast, quantification of serum bile acid concentrations identified significant increases in the PSC^OPO group, including glycoursodeoxycholic acid (GUDCA), an exogenous bile acid administered to both patient groups. Although cell culture experiments did not support the hypothesis that an increase in circulating bile levels is a primary cause of PSC-associated osteoporosis, the remarkable differences of endogenous bile acids and GUDCA in the serum of PSC^OPO patients strongly suggest a yet unknown impairment of biliary metabolism and/or hepatic bile acid clearance in this patient subgroup, which is independent of liver fibrosis.

Effects of Icariin on Modulating Gut Microbiota and Regulating Metabolite Alterations to Prevent Bone Loss in Ovariectomized Rat Model

Postmenopausal osteoporosis (PMOP) is an estrogen deficiency-induced bone loss, which has been shown an association with an altered gut microbiota (GM). Gut microbiota-bone axis has been recognized as a crucial mediator for bone homeostasis. Icariin (ICA) is an effective agent to delay bone loss by regulating the bone homeostasis. Thus, we hypothesize that ICA can prevent bone loss by modulating GM and regulating metabolite alterations. The effects of ICA on bone metabolism improvement in ovariectomized (OVX) rats and their relationships with the GM and fecal metabolites were investigated. Micro-computed tomography (micro-CT) and hematoxylin-eosin (HE) staining showed a typical bone boss in OVX group, while ICA or estradiol (E2) administration exhibited positive effects on bone micro-architecture improvement. The GM such as Actinobacteria, Gammaproteobacteria, Erysipelotrichi, Erysipelotrichales, Enterobacteriales, Actinomycetales, Ruminococcus and Oscillospira significantly correlated to serum bone Gla-protein (BGP), receptor activator of nuclear factor-κB (RANK), receptor activator of nuclear factor-κB ligand (RANKL), osteoprotegerin (OPG) and tartrate resistant acid phosphatase (TRACP). Further t-test revealed a substantial variation of the GM and fecal metabolites in different treatments. Among them, Lachnoclostridium, Butyricimonas, Rikenella, Paraprevolla, Adlercreutzia, Enterorhabdus, Anaerovorax, Allobaculum, Elusimicrobium, Lactococcus, Globicatella and Lactobacillus were probably the key microbial communities driving the change of bile acid, amino acid and fatty acid, thereby leading to an improvement of PMOP. The significant up-regulation of L-Saccharopine, 1-Aminocyclohexadieneacid and linoleic acid after ICA administration suggested important contributions of amino acid and fatty acid metabolisms in the prevention and treatment of PMOP. Taken together, our study has provided new perspectives to better understand the effects of ICA on PMOP improvement by regulating GM and the associated fecal metabolites. Our findings contribute to develop ICA as a potential therapy for PMOP.

An Integrated Metabolomic Study of Osteoporosis: Discovery and Quantification of Hyocholic Acids as Candidate Markers

Osteoporosis is becoming a highly prevalent disease in a large proportion of the global aged population. Serum metabolite markers may be important for the treatment and early prevention of osteoporosis. Serum samples from 32 osteoporosis and 32 controls were analyzed by untargeted metabolomics and lipidomic approaches performed on an ultra-high performance liquid chromatography and high-resolution mass spectrometry (UHPLC-HRMS) system. To find systemic disturbance of osteoporosis, weighted gene correlation network analysis (WGCNA) and statistical methods were employed for data-mining. Then, an in-depth targeted method was utilized to determine potential markers from the family of key metabolites. As a result, 1,241 metabolites were identified from untargeted methods and WGCNA indicated that lipids metabolism is deregulated and glycerol phospholipids, sphingolipids, fatty acids, and bile acids (BA) are majorly affected. As key metabolites of lipids metabolism, 66 bile acids were scanned and 49 compounds were quantified by a targeted method. Interestingly, hyocholic acids (HCA) were found to play essential roles during the occurrence of osteoporosis and may be potential markers. These metabolites may be new therapeutic or diagnosis targets for the screening or treatment of osteoporosis. Quantified measurement of potential markers also enables the establishment of diagnostic models for the following translational research in the clinic.

BCL2L13: physiological and pathological meanings

BCL2L13 is a BCL2-like protein. It has been discovered for two decades, now on the way to be a hotspot of research with its physiological and pathological meanings found in recent years. Start with the pro-apoptotic activity, there have been reported consecutively that BCL2L13 could also induce mitochondrial fragmentation, inhibit cell death and promote mitophagy. Similar to BNIP3, BCL2L13 cannot be indiscriminately categorized into pro- or anti-apoptotic proteins. It anchors in the mitochondrial outer membrane, and expresses in various cells and tissues. This article reviews for the first time that BCL2L13 functions in physiological processes, such as growth and development and energy metabolism, and its dysregulation participating in pathological processes, including cancer, bacterial infection, cardiovascular diseases and degenerative diseases, suggesting its important roles in these events.

Bilirubin and bile acids in osteocytes and bone tissue. Potential role in the cholestatic-induced osteoporosis

BACKGROUND AND AIMS

Osteoporosis is a common complication in patients with primary biliary cholangitis. Both bilirubin and lithocholic acid (LCA) result in detrimental effects on osteoblastic cells, and ursodeoxycholic acid (UDCA) counteracts these outcomes. However, there is no information on the consequences of these retained substances of cholestasis and sera from cholestatic patients in osteocytes.

METHODS

The impact of bilirubin, LCA, UDCA and serum from jaundiced patients on viability, differentiation, mineralization and apoptosis has been assessed in MLO-Y4 and MLO-A5 osteocyte cell lines. Effects on gene expression were assessed in these cells and in human bone fragments.

RESULTS

Lithocholic acid 10 μmol/L and bilirubin 50 μmol/L decreased viability in MLO-Y4 and MLO-A5 cells (11% and 53% respectively; P ≤ .01). UDCA alone or combined with LCA or bilirubin increased cell viability. Jaundiced sera decreased cell viability (56%), an effect which was reverted by UDCA. Bilirubin decreased differentiation by 47% in MLO-Y4 (P ≤ .01) and mineralization (87%) after 21 days in MLO-A5 (P ≤ .03). Both bilirubin and LCA increased apoptosis in MLO-Y4, and UDCA diminished the apoptotic effect. Moreover, bilirubin down-regulated RUNX2 and up-regulated RANKL gene expression in bone tissue, MLO-Y4 and MLO-A5 cells, and LCA up-regulated RANKL expression in bone tissue. UDCA 100 μmol/L increased the gene expression of all these genes in bone tissue and MLO-Y4 cells and neutralized the decreased RUNX2 expression induced by bilirubin.

CONCLUSION

Bilirubin and LCA have damaging consequences in osteocytes by decreasing viability, differentiation and mineralization, increasing apoptosis and modifying gene expression, effects that are neutralized by UDCA.

Metabolomic Associations with Serum Bone Turnover Markers

Bone is a dynamic tissue that is in a constant state of remodeling. Bone turnover markers (BTMs), procollagen type I N-terminal propeptide (P1NP) and C-terminal telopeptides of type I collagen (CTX), provide sensitive measures of bone formation and resorption, respectively. This study used ultra-high-resolution metabolomics (HRM) to determine plasma metabolic pathways and targeted metabolites related to the markers of bone resorption and formation in adults. This cross-sectional clinical study included 34 adults (19 females, mean 27.8 years), without reported illnesses, recruited from a US metropolitan area. Serum BTM levels were quantified by an ELISA. Plasma HRM utilized dual-column liquid chromatography and mass spectrometry to identify metabolites and metabolic pathways associated with BTMs. Metabolites significantly associated with P1NP (p < 0.05) were significantly enriched in pathways linked to the TCA cycle, pyruvate metabolism, and metabolism of B vitamins important for energy production (e.g., niacin, thiamin). Other nutrition-related metabolic pathways associated with P1NP were amino acid (proline, arginine, glutamate) and vitamin C metabolism, which are important for collagen formation. Metabolites associated with CTX levels (p < 0.05) were enriched within lipid and fatty acid beta-oxidation metabolic pathways, as well as fat-soluble micronutrient pathways including, vitamin D metabolism, vitamin E metabolism, and bile acid biosynthesis. P1NP and CTX were significantly related to microbiome-related metabolites (p < 0.05). Macronutrient-related pathways including lipid, carbohydrate, and amino acid metabolism, as well as several gut microbiome-derived metabolites were significantly related to BTMs. Future research should compare metabolism BTMs relationships reported here to aging and clinical populations to inform targeted therapeutic interventions.

Long non-coding RNA SNHG15 is a competing endogenous RNA of miR-141-3p that prevents osteoarthritis progression by upregulating BCL2L13 expression

Increasing evidence has demonstrated that the dysregulated expression of long noncoding RNAs (lncRNAs) has important roles in the progression of osteoarthritis (OA), but the function of the lncRNA SNHG15 remains unclear. In the present study, we observed that SNHG15 was downregulated in OA cartilage tissues and IL-1β-induced chondrocytes. The lower expression of SNHG15 was negatively associated with the observed modified Mankin scale scores, extracellular matrix (ECM) degradation and chondrocyte apoptosis. Downregulated expression of SNHG15 increased chondrocyte viability and decreased chondrocyte apoptosis and ECM degradation in vitro and reduced damage to articular cartilage in vivo. Mechanistically, we demonstrated that SNHG15 overexpression promotes the expression of BCL2L13 by sponging miR-141-3p. The higher expression of miR-141-3p was negatively correlated with SNHG15 and BCL2L13 levels in OA cartilage tissues, and a positive correlation was also shown between SNHG15 and BCL2L13 levels. Furthermore, ectopic expression of miR-141-3p or knockdown of BCL2L13 expression could both reduce the effects of SNHG15 on chondrocyte proliferation, apoptosis and ECM degradation. Collectively, these findings reveal that SNHG15 inhibits OA progression by acting as an miR-141-3p sponge to promote BCL2L13 expression, suggesting that knockdown of SNHG15 expression in chondrocytes can be a potential therapeutic strategy to ameliorate OA progression.

The involvement of genes related to bile secretion pathway in rat tooth germ development

Tooth formation is accomplished under strict genetic control procedures. Therefore, exploring the gene network system of tooth development has a very positive practical significance for the study of tooth tissue regeneration and the prevention and treatment of tooth abnormalities. Early bell stage is the initial phase of odontoblast formation and dentin matrix deposition in the process of tooth development. Through RNA sequencing and differential gene analysis of the rat tooth germ samples at cap stage and early bell stage, we found that the bile secretion pathway was the most significant difference signal pathway during the development between cap stage and bell stage, which mainly included ABCC3, AQP4, SLC10A1, SLC2A1, SLC4A4, ADCY5, AQP9, CFTR, ATP1A2, ATP1B1 and ATP1A1, totally 11genes. Immunostaining revealed that SLC2A1, SLC4A4, ADCY5 and ATP1B1were mainly expressed in epithelium in bud stage and inner and outer enamel epithelium during the embryonic phase. In the postnatal 1 and postnatal 7, SLC2A1, SLC4A4 and ABCC3 were highly expressed in ameloblasts and odontoblasts while ADCY5, ATP1B1 and SLC10A1was expressed moderately only in odontoblasts. This finding illustrated that the bile secretion pathway related genes may participate in the development of tooth germ.