Céline Gillet

Oleate Abrogates Palmitate-Induced Lipotoxicity and Proinflammatory Response in Human Bone Marrow-Derived Mesenchymal Stem Cells and Osteoblastic Cells.

Osteoporosis is a metabolic bone disease associated with unequilibrated bone remodeling resulting from decreased bone formation and/or increased bone resorption, leading to progressive bone loss. In osteoporotic patients, low bone mass is associated with an increase of bone marrow fat resulting from accumulation of adipocytes within the bone marrow. Marrow adipocytes are active secretory cells, releasing cytokines, adipokines and free fatty acids (FA) that influence the bone marrow microenvironment and alter the biology of neighboring cells. Therefore, we examined the effect of palmitate (Palm) and oleate (Ole), 2 highly prevalent FA in human organism and diet, on the function and survival of human mesenchymal stem cells (MSC) and MSC-derived osteoblastic cells. The saturated FA Palm exerted a cytotoxic action via initiation of endoplasmic reticulum stress and activation of the nuclear factor κB (NF-κB) and ERK pathways. In addition, Palm induced a proinflammatory response, as determined by the up-regulation of Toll-like receptor 4 expression as well as the increase of IL-6 and IL-8 expression and secretion. Moreover, we showed that MSC-derived osteoblastic cells were more sensitive to lipotoxicity than undifferentiated MSC. The monounsaturated FA Ole fully neutralized Palm-induced lipotoxicity by impairing activation of the pathways triggered by the saturated FA. Moreover, Ole promoted Palm detoxification by fostering its esterification into triglycerides and storage in lipid droplets. Altogether, our data showed that physiological concentrations of Palm and Ole differently modulated cell death and function in bone cells. We therefore propose that FA could influence skeletal health.

D-glucose‑ and 3-O-methyl-D-glucose-induced upregulation of selected genes in rat hepatocytes and INS1E cells: Re‑evaluation of the possible role of hexose phosphorylation

The biochemical events involved in the upregulation of selected glucose‑responsive genes by 3‑O‑methyl‑D‑glucose (3‑MG) remain to be elucidated. The present study mainly aimed to re‑evaluate the possible role of 3‑MG phosphorylation in the upregulation of the thioredoxin interacting protein (TXNIP) and liver pyruvate kinase (LPK) genes in rat hepatocytes and INS1E cells. TXNIP and LPK transcription was assessed in rat liver and INS1E cells exposed to a rise in D‑glucose concentration, 2‑deoxy‑D‑glucose (2‑DG), 3‑MG and, when required, D‑mannoheptulose. The phosphorylation of D‑[U‑14C]glucose and 3‑O‑[14C]methyl‑D‑glucose (14C-labeled 3-MG) was measured in rat liver, INS1E cell and rat pancreatic islet homogenates. The utilization of D‑[5‑3H]glucose by intact INS1E cells was also measured. In rat hepatocytes, a rise in the D‑glucose concentration increased the TXNIP/hypoxanthine‑guanine phosphoribosyl transferase (HPRT) and LPK/HPRT ratios, while 2‑DG and 3‑MG also increased the TXNIP/HPRT ratio, but not the LPK/HPRT ratio. In INS1E cells, the TXNIP/HPRT and LPK/HPRT ratios were increased in response to the addition of D‑glucose, 2‑DG and 3‑MG. Furthermore, D‑mannoheptulose abolished the response to D‑glucose and 2‑DG, but not to 3‑MG, in these cells. Liver cell homogenates catalyzed the phosphorylation of 3‑MG to a modest extent, whilst INS1E and rat pancreatic islet cell homogenates did not. Moreover, 3‑MG marginally decreased D‑glucose phosphorylation in INS1E cell homogenates but not in liver cell homogenates. D‑[5‑3H]glucose utilization by intact INS1E cells was decreased by 2‑DG, but not by 3‑MG. These findings reinforce the view that the upregulation of the TXNIP and LPK genes induced by 3‑MG is not attributable to its phosphorylation or any favorable effect on D‑glucose metabolism.

Osteonecrosis of the Femoral Head: Lipotoxicity Exacerbation in MSC and Modifications of the Bone Marrow Fluid

Osteonecrosis of the femoral head (ON) is a multifactorial bone disease that can evolve to a progressive destruction of the hip joint. Different pathogenic processes have been proposed, among them, an increase of bone marrow (BM) fat resulting from adipocyte accumulation. Marrow adipocytes are active BM residents that influence the microenvironment by releasing cytokines, adipokines, and free fatty acids (FA). We explored the impact of palmitate (Palm) and oleate on function and survival of BM-derived mesenchymal stromal cells (MSC) of osteonecrotic patients (ONMSC) and healthy volunteers. Moreover, we analyzed the FA profile of the serum and the BM supernatant fluid (BMSF). We demonstrated that exposure to the saturated FA Palm favored MSC differentiation through the adipogenic lineage at the expense of the osteoblastic phenotype. Moreover, adipogenesis was intensified in ONMSC. The susceptibility to Palm toxicity was aggravated in ONMSC concomitantly with a greater activation of the proapoptotic extracellular signal-regulated kinase pathway. Moreover, cellular mechanisms implicated in the protection against lipotoxicity, such as stearoyl-coenzyme A desaturase 1 and carnitine palmitoyl transferase 1 expression, were dysregulated in ONMSC. Palm-induced interleukin (IL)-6 and IL-8 secretion was also exacerbated in ONMSC. Our results established that, in the serum, the FA profiles were comparable in ON and healthy subjects. However, both the concentrations and the FA composition were modified in the BMSF of ON patients, highlighting a drastic change of the BM microenvironment in ON patients. Altogether, our work suggests that marrow adipocyte enlargement could affect the process of bone remodeling and, therefore, play a role in the pathogenesis of ON.

Immunocytochemistry of GLUT2, uptake of fluorescent desnitroso-streptozotocin analogs and phosphorylation of D-glucose in INS-1E cells.

The non-invasive imaging of GLUT2-expressing cells remains a challenge. As streptozotocin, and similarly alloxan, may be transported into cells by GLUT2, the major aim of the present study was to assess the possible use of fluorescent desnitroso-streptozotocin analogs for in vitro labeling of GLUT2-expressing cells. INS-1E cells, human embryonic kidney (HEK) cells, rat isolated pancreatic islets, rat hepatic cells, rat exocrine pancreatic cells and tumoral insulin-producing BRIN-BD11 cells were incubated in the presence of two distinct fluorescent desnitroso-streptozotocin analogs, probes A and B. The immunocytochemistry of GLUT2 in INS-1E cells and the phosphorylation of D-glucose by INS-1E cell homogenates were also examined. The uptake of probes A and B (12.0 µM) by INS-1E cells yielded apparent intracellular concentrations approximately one order of magnitude higher than the extracellular concentration. The two probes differed from one another by the absolute values for their respective uptake and time course, but not so by the pattern of their concentration dependency. Comparable results were recorded in HEK cells, rat isolated pancreatic islets and hepatocytes. Vastly different findings were recorded, however, in rat exocrine pancreatic cells, which do not express GLUT2. Moreover, an unusual concentration dependency for the uptake of each probe was observed in tumoral BRIN-BD11 cells. It is proposed that suitable fluorescent desnitroso-streptozotocin analogs may be used to label GLUT2-expressing cells.

Phenotype of Bone Marrow Adipose Tissue: Specificities of the Anatomical Distribution, Secretory Profile, Lipid Content, and Response to Nutritional Status

Purpose of ReviewBone marrow adipose tissue (BMAT) is currently considered as a unique and typical fat depot, able to modulate the metabolism of bone cells that share the same microenvironment, with putative subsequent impact on skeletal health. The aim of the present review is to update knowledge related to the molecular phenotype of the BMAT adipocytes.Recent FindingsAlthough sharing white and brown adipose tissue-like features, BMAT exhibits its own specific properties. It may consist of two sub-populations of adipocytes, ensuring different metabolic functions and presenting distinct lipidomic and genetic profiles. Current evidence highlights the dynamic lipid composition of BMAT, varying according to pathophysiological situations.SummarySince several studies are now demonstrating an alteration of BMAT lipid composition in bone diseases associated with a loss of bone integrity, the investigation of the qualitative aspect of marrow adiposity is currently overtaking its quantitative assessment. A better knowledge of the BMAT lipid content could enlarge the therapeutic potential for bone diseases such as osteoporosis and osteonecrosis.

Non traumatic osteonecrosis of the femoral head is associated with low bone mass

OBJECTIVE Osteoporosis (OP) and osteonecrosis of the femoral head (ONFH) share common clinical and pathophysiological features we sought to determine whether ONFH was associated with an increased prevalence of OP and whether the increased prevalence of OP was related to the stage of ONFH at diagnosis. METHODS We included 243 patients with ONFH and 399 age and sex-matched healthy controls. Data was gathered including demography, risk factors, ARCO staging of ONFH and bone mineral density (BMD). RESULTS Overall, BMD (defined by the T-score) was significantly lower in the ONFH group at both the femoral head (-0.96±1.11) and the lumbar spine (-1.22±1.47) compared to the control group (-0.55±0.97 and -0.73±1.31) (p<0.01). The ONFH group depicted a significantly higher proportion of osteopenia (50.39% vs 40.87%, p=0.027) and of OP (18.78% vs 7.33%, p<0.001) relative to the control group. Stage 1 and 2 ONFH patients (53.86%, p=0.0203; OR=1.54 (95% CI: [1.04; 2.29])) were at a higher risk of osteopenia than the control group (40.88%), but not stages 3 or 4 (48.47%, p=0.2569; OR=1.27 (95% CI: [0.78; 2.06]). Patients with stage 3 or 4 ONFH (25.31%, p<0.001; OR=3.93 (95% CI: [1.63; 10.96])) were at a higher risk of osteoporosis than patients in the stage 1 and 2 ONFH (7.24%), and compared to the control group (7.33%, adj. p-value<0.001; OR=4.89 (95% CI: [2.77; 8.76]). CONCLUSIONS Non-traumatic osteonecrosis of the femoral heads is associated with low bone mineral density. This study showed that fractural stages ONFH were associated with a 5-fold risk of osteoporosis.

Bone and Bone Marrow, Interactions

Bone and bone marrow function closely together, as a single unit, exhibiting functional, and structural interdependences. They form a unique system implicating regulated and coordinated cooperation and interactions that are critical to assure optimal hematopoiesis as well as the maintenance of skeletal integrity.