Modulation of nutrient sensing nuclear hormone receptors promotes weight loss through appetite suppression in mice.

AIM: Peroxisome proliferator activated receptors (PPARs) are nuclear receptors involved in glucose and lipid metabolism. Three isoforms of PPARs have been identified with different tissue distribution and biological functions. Although the pharmacology of each receptor is well studied, the physiological effect of simultaneous activation of PPARalpha, gamma and delta is only starting to emerge. We sought to determine the biological effects of a novel PPAR pan activator and elucidate the physiological mechanisms involved. METHODS: Ob/ob, diet-induced obese (DIO) or PPARalpha knockout mice were administered a novel agonist that activates all PPARs to various degrees to determine the effect on body weight, body composition, food intake and energy expenditure. In addition, serum parameters including glucose, insulin, triglycerides and ketone bodies as well as tissue acylcarnitine were evaluated. The effect of the novel agonist on liver and skeletal muscle histopathology was also studied. RESULTS: We report that simultaneous activation of all PPARs resulted in substantial weight loss in ob/ob and DIO mice. Consistent with known PPAR pharmacology, we observed that agonist treatment increased lipid oxidation, although appetite suppression was mainly responsible for the weight loss. Agonist-induced weight loss was completely absent in PPARalpha knockout mice suggesting that PPARalpha pharmacology was the major contributor to weight regulation in mice. CONCLUSIONS: Our work provides evidence that simultaneous activation of PPARalpha, gamma and delta decreases body weight by regulating appetite. These effects of the pan agonist were completely absent in PPARalpha knockout mice, suggesting that PPARalpha pharmacology was the major contributor to weight loss.

Administration of myostatin does not alter fat mass in adult mice.

AIM: Myostatin, a member of the TGF-beta superfamily, is produced by skeletal muscle and acts as a negative regulator of muscle mass. It has also been suggested that low-dose administration of myostatin (2 mug/day) in rodents can reduce fat mass without altering muscle mass. In the current study, we attempted to further explore the effects of myostatin on adipocytes and its potential to reduce fat mass, since myostatin administration could potentially be a useful strategy to treat obesity and its complications in humans. METHODS: Purified myostatin protein was examined for its effects on adipogenesis and lipolysis in differentiated 3T3-L1 adipocytes as well as for effects on fat mass in wild-type, myostatin null and obese mice. RESULTS: While myostatin was capable of inhibiting adipogenesis in 3T3-L1 cells, it did not alter lipolysis in fully differentiated adipocytes. Importantly, pharmacological administration of myostatin over a range of doses (2-120 mug/day) did not affect fat mass in wild-type or genetically obese (ob/ob, db/db) mice, although muscle mass was significantly reduced at the highest myostatin dose. CONCLUSIONS: Our results suggest that myostatin does not reduce adipose stores in adult animals. Contrary to prior indications, pharmacological administration of myostatin does not appear to be an effective strategy to treat obesity in vivo.

Engineered pluripotent mesenchymal cells integrate and differentiate in regenerating bone: a novel cell-mediated gene therapy.

BACKGROUND: Among the approximately 6.5 million fractures suffered in the United States every year, about 15% are difficult to heal. As yet, for most of these difficult cases there is no effective therapy. We have developed a mouse radial segmental defect as a model experimental system for testing the capacity of Genetically Engineered Pluripotent Mesenchymal Cells (GEPMC, C3H10T1/2 clone expressing rhBMP-2), for gene delivery, engraftment, and induction of bone growth in regenerating bone. METHODS: Transfected GEPMC expressing rhBMP-2 were further infected with a vector carrying the lacZ gene, that encodes for beta-galactosidase (beta-gal). In vitro levels of rhBMP-2 expression and function were confirmed by immunohistochemistry, and bioassay. Differentiation was assayed using alkaline phosphatase staining. GEPMC were transplanted in vivo into a radial segmental defect. The main control groups included lacZ clones of WT-C3H10T1/2-LacZ, and CHO-rhBMP-2 cells. New bone formation was measured quantitatively via fluorescent labeling, X-ray analysis and histomorphometry. Engrafted mesenchymal cells were localized in vivo by beta-gal expression, and double immunofluorescence. RESULTS: In vitro, GEPMC expressed rhBMP-2, beta-gal and spontaneously differentiated into osteogenic cells expressing alkaline phosphatase. Detection of transplanted cells revealed engrafted cells that had differentiated into osteoblasts and co-expressed beta-gal and rhBMP-2. Analysis of new bone formation revealed that at four to eight week post-transplantation, GEPMS significantly enhanced segmental defect repair. CONCLUSIONS: Our study shows that cell-mediated gene transfer can be utilized for growth factor delivery to signaling receptors of transplanted cells (autocrine effect) and host mesenchymal cells (paracrine effect) suggesting the ability of GEPMC to engraft, differentiate, and stimulate bone growth. We suggest that our approach should lead to the designing of mesenchymal stem cell based gene therapy strategies for bone lesions as well as other tissues.