Gut microbiota-derived propionate mediates the neuroprotective effect of osteocalcin in a mouse model of Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder with no absolute cure. The evidence of the involvement of gut microbiota in PD pathogenesis suggests the need to identify certain molecule(s) derived from the gut microbiota, which has the potential to manage PD. Osteocalcin (OCN), an osteoblast-secreted protein, has been shown to modulate brain function. Thus, it is of interest to investigate whether OCN could exert protective effect on PD and, if yes, whether the underlying mechanism lies in the subsequent changes in gut microbiota.

RESULTS

The intraperitoneal injection of OCN can effectively ameliorate the motor deficits and dopaminergic neuronal loss in a 6-hydroxydopamine-induced PD mouse model. The further antibiotics treatment and fecal microbiota transplantation experiments confirmed that the gut microbiota was required for OCN-induced protection in PD mice. OCN elevated Bacteroidetes and depleted Firmicutes phyla in the gut microbiota of PD mice with elevated potential of microbial propionate production and was confirmed by fecal propionate levels. Two months of orally administered propionate successfully rescued motor deficits and dopaminergic neuronal loss in PD mice. Furthermore, AR420626, the agonist of FFAR3, which is the receptor of propionate, mimicked the neuroprotective effects of propionate and the ablation of enteric neurons blocked the prevention of dopaminergic neuronal loss by propionate in PD mice.

CONCLUSIONS

Together, our results demonstrate that OCN ameliorates motor deficits and dopaminergic neuronal loss in PD mice, modulating gut microbiome and increasing propionate level might be an underlying mechanism responsible for the neuroprotective effects of OCN on PD, and the FFAR3, expressed in enteric nervous system, might be the main action site of propionate. Video abstract.

Maternal oral administration of osteocalcin protects offspring from metabolic impairment in adulthood

OBJECTIVE

Maternal diet during pregnancy has been found to influence the health of offspring. However, strategies for modulation of maternal energy metabolism without an adverse effect on the fetus have remained limited. It was recently shown that oral administration of uncarboxylated osteocalcin (GluOC) improves metabolic status in adult female mice. Whether maternal GluOC administration during gestation might improve the metabolic status of offspring was investigated.

METHODS

Female C57BL/6 mice were fed a normal diet (ND) or high-fat, high-sucrose diet (HFS) and were given saline or GluOC by oral administration during pregnancy. The resulting offspring were in turn assigned to ND- or HFS-fed groups immediately after weaning, and their body weight, glucose metabolism, serum lipid parameters, and level of adipose tissue inflammation were subsequently assessed.

RESULTS

Maternal HFS feeding during gestation had adverse effects on glucose and lipid parameters, body weight, and adipose tissue inflammation in female offspring fed the same diet, and these effects were attenuated by maternal oral GluOC administration.

CONCLUSIONS

Maternal oral administration of GluOC protects HFS-fed female offspring from metabolic disorders induced by maternal obesity.

The effects of muscle contraction and recombinant osteocalcin on insulin sensitivity ex vivo

We tested whether GPRC6A, the putative receptor of undercarboxylated osteocalcin (ucOC), is present in mouse muscle and whether ucOC increases insulin sensitivity following ex vivo muscle contraction. GPPRC6A is expressed in mouse muscle and in the mouse myotubes from a cell line. ucOC potentiated the effect of ex vivo contraction on insulin sensitivity.

INTRODUCTION

Acute exercise increases skeletal muscle insulin sensitivity. In humans, exercise increases circulating ucOC, a hormone that increases insulin sensitivity in rodents. We tested whether GPRC6A, the putative receptor of ucOC, is present in mouse muscle and whether recombinant ucOC increases insulin sensitivity in both C2C12 myotubes and whole mouse muscle following ex vivo muscle contraction.

METHODS

Glucose uptake was examined in C2C12 myotubes that express GPRC6A following treatment with insulin alone or with insulin and increasing ucOC concentrations (0.3, 3, 10 and 30 ng/ml). In addition, glucose uptake, phosphorylated (p-)AKT and p-AS160 were examined ex vivo in extensor digitorum longus (EDL) dissected from C57BL/6J wild-type mice, at rest, following insulin alone, after muscle contraction followed by insulin and after muscle contraction followed by recombinant ucOC then insulin exposure.

RESULTS

We observed protein expression of the likely receptor for ucOC, GPRC6A, in whole muscle sections and differentiated mouse myotubes. We observed reduced GPRC6A expression following siRNA transfection. ucOC significantly increased insulin-stimulated glucose uptake dose-dependently up to 10 ng/ml, in differentiated mouse C2C12 myotubes. Insulin increased EDL glucose uptake (∼30 %, p < 0.05) and p-AKT and p-AKT/AKT compared with rest (all p < 0.05). Contraction prior to insulin increased muscle glucose uptake (∼25 %, p < 0.05), p-AKT, p-AKT/AKT, p-AS160 and p-AS160/AS160 compared with contraction alone (all p < 0.05). ucOC after contraction increased insulin-stimulated muscle glucose uptake (∼12 % p < 0.05) and p-AS160 (<0.05) more than contraction plus insulin alone but without effect on p-AKT. In the absence of insulin and/or of contraction, ucOC had no significant effect on muscle glucose uptake.

CONCLUSIONS

GPRC6A, the likely receptor of osteocalcin (OC), is expressed in mouse muscle. ucOC treatment augments insulin-stimulated skeletal muscle glucose uptake in C2C12 myotubes and following ex vivo muscle contraction. ucOC may partly account for the insulin sensitizing effect of exercise.

Oral administration of osteocalcin improves glucose utilization by stimulating glucagon-like peptide-1 secretion

Uncarboxylated osteocalcin (GluOC), a bone-derived hormone, regulates energy metabolism by stimulating insulin secretion and pancreatic β-cell proliferation. We previously showed that the effect of GluOC on insulin secretion is mediated largely by glucagon-like peptide-1 (GLP-1) secreted from the intestine in response to GluOC exposure. We have now examined the effect of oral administration of GluOC on glucose utilization as well as the fate of such administered GluOC in mice. Long-term intermittent or daily oral administration of GluOC reduced the fasting blood glucose level and improved glucose tolerance in mice without affecting insulin sensitivity. It also increased the fasting serum insulin concentration as well as the β-cell area in the pancreas. A small proportion of orally administered GluOC reached the small intestine and remained there for at least 24h. GluOC also entered the general circulation, and the serum GLP-1 concentration was increased in association with the presence of GluOC in the intestine and systemic circulation. The putative GluOC receptor, GPRC6A was detected in intestinal cells, and was colocalized with GLP-1 in some of these cells. Our results suggest that orally administered GluOC improved glucose handling likely by acting from both the intestinal lumen and the general circulation, with this effect being mediated in part by stimulation of GLP-1 secretion. Oral administration of GluOC warrants further study as a safe and convenient option for the treatment or prevention of metabolic disorders.

Osteocalcin induces growth hormone/insulin-like growth factor-1 system by promoting testosterone synthesis in male mice

Osteocalcin has been shown to enhance testosterone production in men. In the present study, we investigated the effects of osteocalcin on testosterone and on induction of the growth hormone/insulin-like growth factor-1 axis. Osteocalcin injection stimulated growth, which could be inhibited by castration. In addition, osteocalcin induced testosterone secretion in testes both in vivo and in vitro. Using real-time polymerase chain reaction and Western blotting, we showed that growth hormone expression was significantly increased in the pituitary after osteocalcin injection (p<0.05). Growth hormone expression in CLU401 mouse pituitary cells was also significantly stimulated (p<0.05) by osteocalcin-induced MA-10 cells. Osteocalcin injection also promoted hepatic expression of growth hormone receptor and insulin-like growth factor-1 (p<0.05), as demonstrated by real-time polymerase chain reaction and Western blotting. Similarly, osteocalcin-induced MA-10 cells promoted growth hormone receptor and insulin-like growth factor-1 expression in NCTC1469 cells. These results suggest that the growth-stimulating activities of osteocalcin are mediated by testicular testosterone secretion, and thus provide valuable information regarding the regulatory effects of osteocalcin expression on the growth hormone/insulin-like growth factor-1 axis via reproductive activities.

Intermittent injections of osteocalcin improve glucose metabolism and prevent type 2 diabetes in mice

The uncarboxylated form of the osteoblast-specific secreted molecule osteocalcin is a hormone favoring glucose handling and increasing energy expenditure. As a result, the absence of osteocalcin leads to glucose intolerance in mice, while genetically modified mice with an increase in uncarboxylated osteocalcin are protected from type 2 diabetes and obesity. Here, we tested in the mouse the therapeutic potential of intermittent administration of osteocalcin. We found that daily injections of osteocalcin at either 3 or 30 ng/g/day significantly improved glucose tolerance and insulin sensitivity in mice fed a normal diet. This was attributable, in part, to an increase in both β-cell mass and insulin secretion. When mice were fed a high-fat diet (HFD), daily injections of osteocalcin partially restored insulin sensitivity and glucose tolerance. Moreover, mice treated with intermittent osteocalcin injections displayed additional mitochondria in their skeletal muscle, had increased energy expenditure and were protected from diet-induced obesity. Finally, the hepatic steatosis induced by the HFD was completely rescued in mice receiving osteocalcin daily. Overall, these results provide evidence that daily injections of osteocalcin can improve glucose handling and prevent the development of type 2 diabetes.

Effect of an isoflavones-containing red clover preparation and alkaline supplementation on bone metabolism in ovariectomized rats

The aim of this study was to test the combined effect of a quality-controlled red clover extract (RCE) standardized to contain 40% isoflavones by weight (genistein, daidzein, biochanin A, and formononetin present as hydrolyzed aglycones) together with a modified alkaline supplementation on bone metabolic and biomechanical parameters in an experimental model of surgically-induced menopause. Sprague-Dawley female rats were maintained under controlled standard conditions of light and fed with conventional food of standard calcium content and no alfalfa or soybean components. Rats were randomized into four groups: Group A represented normal rats (sham operated) while three other groups were ovariectomized (OVX) and fed for three months as follows: standard food (group B), 6 mg/kg/day food mixed with RCE (Group C), or given 6 mg/kg/day of RCE plus a modified alkaline supplementation (BP) through a nasogastric tube at a dose of 16 mg (group D). The animals were killed 90 days after surgery. As compared to group B, RCE or RCE + BP treatments brought about significantly higher level of estradiol and mitigated the weight loss of the uterus and improved maximum load of the femoral neck. Osteocalcin level showed an over 65% increase in group B but both RCE and RCE + BP treatments prevented such abnormality with a significantly better result in RCE + BP group which virtually normalized such parameter as well as urinary excretion of DPD. Group C and D reduced the over 20% loss of bone mineral density and bone mineral content/body weight ratio observed in untreated post-ovariectomy group. Untreated ovariectomy caused about 48% decrease of cancellous bone mass in the femoral neck while this abnormality was prevented at similar extent by both RCE and RCE + BP treatments. Ovariectomy determined an over 80% increase of bone alkaline phosphatase (BALP) level but both RCE and RCE + BP treatments significantly mitigated such variable. The BALP decrease yielded by the combined RCE + BP treatment was statistically lower than RCE alone. Taken together these data show that red clover preparation in dosages amenable to clinical practice do improve OVX-induced osteoporosis while a mild metabolic alkalosis might further synergize some therapeutic aspects.

Cotargeting tumor and tumor endothelium effectively inhibits the growth of human prostate cancer in adenovirus-mediated antiangiogenesis and oncolysis combination therapy

Tumor-endothelial interaction contributes to local prostate tumor growth and distant metastasis. In this communication, we designed a novel approach to target both cancer cells and their "crosstalk" with surrounding microvascular endothelium in an experimental hormone refractory human prostate cancer model. We evaluated the in vitro and in vivo synergistic and/or additive effects of a combination of conditional oncolytic adenovirus plus an adenoviral-mediated antiangiogenic therapy. In the in vitro study, we demonstrated that human umbilical vein endothelial cells (HUVEC) and human C4-2 androgen-independent (AI) prostate cancer cells, when infected with an antiangiogenic adenoviral (Ad)-Flk1-Fc vector secreting a soluble form of Flk1, showed dramatically inhibited proliferation, migration and tubular formation of HUVEC endothelial cells. C4-2 cells showed maximal growth inhibition when coinfected with Ad-Flk1-Fc and Ad-hOC-E1, a conditional replication-competent Ad vector with viral replication driven by a human osteocalcin (hOC) promoter targeting both prostate cancer epithelial and stromal cells. Using a three-dimensional (3D) coculture model, we found that targeting C4-2 cells with Ad-hOC-E1 markedly decreased tubular formation in HUVEC, as visualized by confocal microscopy. In a subcutaneous C4-2 tumor xenograft model, tumor volume was decreased by 40-60% in animals treated with Ad-Flk1-Fc or Ad-hOC-E1 plus vitamin D3 alone and by 90% in a combined treatment group, compared to untreated animals in an 8-week treatment period. Moreover, three of 10 (30%) pre-established tumors completely regressed when animals received combination therapy. Cotargeting tumor and tumor endothelium could be a promising gene therapy strategy for the treatment of both localized and metastatic human prostate cancer.

[Regulation of bone mineralization by parathyroid hormone]

In randomized clinical trials, parathyroid hormone (PTH) showed potent anabolic effects on the lumbar spine and decreased the risk of incident vertebral fractures dramatically. Although the anabolic effect of PTH on cortical bone in the femoral neck is still unclear, it should be demonstrated in further clinical studies. Concurrent or sequential therapies of PTH and anti-resorptive agents will be one of the major issues of treatment for osteoporosis in the future.

Administration of osteocalcin accelerates orthodontic tooth movement induced by a closed coil spring in rats

The effect of local administration of osteocalcin (OC) on experimental tooth movement was examined in the rat. The maxillary first molar was first moved mesially with an initial tipping force of 30 g with a closed-coil spring anchored to the incisor for 10 days (n = 48). Three experimental groups (n = 8) were injected with purified rat OC at doses of 0.1, 1, and 10 micrograms, respectively. The injection into the palatal bifurcation site of the first molar was repeated daily. The control groups (n = 8) were injected with rat serum albumin (10 micrograms), phosphate buffered saline (PBS), or were not injected. Tooth movement was evaluated daily by measuring the inter-cuspal distance between the first and the second molars on a precise plaster model. The cumulative tooth movement (mm) in the 1-microgram OC-injected groups was significantly more than that in all of the control groups on day 9. The rate of tooth movement (mm/day) showed periodical elevation, with high values on days 1, 4, 7, and 9. Acceleration of tooth movement by OC was significant in the early experimental period. Subsequently, acceleration of early tooth movement by OC was histologically evaluated (n = 40). Each of four animals from the control (PBS, n = 20) and the experimental (1 microgram OC, n = 20) groups was killed daily up to 5 days. A significantly larger number of osteoclasts accumulated on the mesial alveolar bone surface in the 1-microgram OC-injected group on day 3 than that observed in control group. These results suggest that administration of OC accelerates orthodontic tooth movement due to enhancement of osteoclastogenesis on the pressure side, primarily in the early experimental period.

Effects of local administration of osteocalcin on experimental tooth movement

The purpose of this study was to evaluate the effects of local administration of osteocalcin, a major noncollagenous bone matrix protein, on experimental tooth movement in rats. An orthodontic elastic band was inserted between the upper first and second molars, and the first molar was moved mesially. Purified osteocalcin (0 to 10 micrograms) in 20 microliters of phosphate-buffered saline was injected into the region of the root bifurcation of the first molar daily for 4 days. Tooth movement increased significantly following the injections. Histological studies revealed that the injections markedly stimulated the appearance of osteoclasts on the pressured side of the alveolar bone surface. The results suggest that osteocalcin has an additive effect on the rate of orthodontic tooth movement through the enhancement of osteoclastogenesis on the pressured side.

Biological accessibility of calcitonin and osteocalcin marked 125J for rats

Biological accessibility of calcitonin and osteocalcin marked 125J for rast. In this study we estimated the biological accessibility and the degree of biological accessibility of calcitonin in relation to highly specific marker-osteocalcin after a single intraperitoneal administration. We showed mean values of biopharmaceutical parameters for the analysed hormones.