Because stem cells are often found to improve repair tissue including heart without evidence of engraftment or differentiation, mechanisms underlying wound healing are still elusive. Several studies have reported that stem cells can fuse with cardiomyocytes either by permanent or partial cell fusion processes. However, the respective physiological impact of these two processes remains unknown in part because of the lack of knowledge of the resulting hybrid cells. To further characterize cell fusion, we cocultured mouse fully differentiated cardiomyocytes with human multipotent adipose-derived stem (hMADS) cells as a model of adult stem cells. We found that heterologous cell fusion promoted cardiomyocyte reprogramming back to a progenitor-like state. The resulting hybrid cells expressed early cardiac commitment and proliferation markers such as GATA-4, myocyte enhancer factor 2C, Nkx2.5, and Ki67 and exhibited a mouse genotype. Interestingly, human bone marrow-derived stem cells shared similar reprogramming properties than hMADS cells but not human fibroblasts, which suggests that these features might be common to multipotent cells. Furthermore, cardiac hybrid cells were preferentially generated by partial rather than permanent cell fusion and that intercellular structures composed of f-actin and microtubule filaments were involved in the process. Finally, we showed that stem cell mitochondria were transferred into cardiomyocytes, persisted in hybrids and were required for somatic cell reprogramming. In conclusion, by providing new insights into previously reported cell fusion processes, our data might contribute to a better understanding of stem cell-mediated regenerative mechanisms and thus, the development of more efficient stem cell-based heart therapies. STEM CELLS 2011; 29:812-824 Disclosure of potential conflicts of interest is found at the end of this article.

Peripheral serotonin, synthesized by tryptophan hydroxylase-1 (TPH 1 ), has been shown to play a key role in several physiological functions. Recently, controversy has emerged about whether peripheral serotonin has any effect on bone density and remodeling. We therefore decided to investigate in detail bone remodeling in growing and mature TPH 1 knockout mice (TPH 1 −/−). Bone resorption in TPH 1 −/− mice, as assessed by biochemical markers and bone histomorphometry, was markedly decreased at both ages. Using bone marrow transplantation, we present evidence that the decrease in bone resorption in TPH 1 −/− mice is cell-autonomous. Cultures from TPH 1 −/− in the presence of macrophage colony-stimulating factor and receptor activator for NF-KB ligand (RANKL) displayed fewer osteoclasts, and the decreased differentiation could be rescued by adding serotonin. Our data also provide evidence that in the presence of RANKL, osteoclast precursors express TPH 1 and synthesize serotonin. Furthermore, pharmacological inhibition of serotonin receptor 1B with SB224289, and of receptor 2A with ketanserin, also reduced the number of osteoclasts. Our findings reveal that serotonin has an important local action in bone, as it can amplify the effect of RANKL on osteoclastogenesis.neuromediator | osteopetrosis B one remodeling is a highly integrated process that continuously renews mineralized tissue throughout the skeleton to assure harmonious growth, maintenance, and repair throughout the lifespan of the individual. It couples the resorption of mineralized bone by osteoclasts and bone formation by osteoblasts. Osteoblasts originate from mesenchymal stem cells (1), and osteoclasts are multinucleated cells derived from a hematopoietic precursor of the monocyte macrophage lineage (2). Dysregulation of osteoclast function or differentiation results in an osteopetrotic phenotype, with a marked increase in bone density. In contrast, increased bone resorption is associated with bone loss in diseases such as osteoporosis, arthritis, and metastatic bone lesions. Molecular communication between osteoblasts and osteoclasts is required to regulate the commitment, proliferation, and differentiation of bone cell precursors. The main osteoclastogenic signals are the receptor activator for NF-KB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF), both of which are cytokines secreted by osteoblasts (3).Serotonin, or 5-hydroxytryptamine (5-HT), mediates a wide range of central functions, such as mood, behavior, sleep, blood pressure, and thermoregulation (4). Peripherally, serotonin is involved mainly in the regulation of vascular and heart functions (5, 6) and in gastrointestinal mobility (7). The diverse actions of 5-HT result from the presence of multiple 5-HT receptors (5-HTRs). These various different receptors have been divided into seven classes (5-HT 1 R to 5-HT 7 R) (8). Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in 5-HT biosynthesis. There are two isoforms of this enzyme: TPH 2 is mainly expressed in brain, and...

Osteopetrosis is a rare genetic disorder characterized by an increase of bone mass due to defective osteoclast function. Patients typically displayed spontaneous fractures, anemia, and in the most severe forms hepatosplenomegaly and compression of cranial facial nerves leading to deafness and blindness. Osteopetrosis comprises a heterogeneous group of diseases as several forms are known with different models of inheritance and severity from asymptomatic to lethal. This review summarizes the genetic and clinical features of osteopetrosis, emphasizing how recent studies of this disease have contributed to understanding the central role of the skeleton in the whole body physiology. In particular, the interplay of bone with the stomach, insulin metabolism, male fertility, the immune system, bone marrow, and fat is described.

The most common outcome of defective dental morphogenesis in human patients is dental agenesis (absence of teeth). This may affect either the primary or permanent dentition and can range from 5 or fewer missing teeth (hypodontia), 6 or more (oligodontia), to complete absence of teeth (anodontia). Both isolated and syndromic dental agenesis have been reported to be associated with a large number of mutated genes. The aim of this review was to analyze the dental phenotypes of syndromic and nonsyndromic dental agenesis linked to gene mutations. A systematic review of the literature focusing on genes ( MSX1, PAX9, AXIN2, PITX2, WNT10A, NEMO, EDA, EDAR, EDARADD, GREMLIN2, LTBP3, LRP6, and SMOC2) known to be involved in dental agenesis was performed and included 101 articles. A meta-analysis was performed using the dental phenotypes of 522 patients. The total number and type of missing teeth were analyzed for each mutated gene. The percentages of missing teeth for each gene were compared to determine correlations between genotypes and phenotypes. Third molar agenesis was included in the clinical phenotype assessment. The findings show that isolated dental agenesis exists as part of a spectrum of syndromes for all the identified genes except PAX9 and that the pattern of dental agenesis can be useful in clinical diagnosis to identify (or narrow) the causative gene mutations. While third molar agenesis was the most frequent type of dental agenesis, affecting 70% of patients, it was described in only 30% of patients with EDA gene mutations. This study shows that the pattern of dental agenesis gives information about the mutated gene and could guide molecular diagnosis for geneticists.

Bidirectional transcription, leading to the expression of an antisense (AS) RNA partially complementary to the protein coding sense (S) RNA, is an emerging subject in mammals and has been associated with various processes such as RNA interference, imprinting and transcription inhibition. Homeobox genes do not escape this bidirectional transcription, raising the possibility that such AS transcription occurs during embryonic development and may be involved in the complexity of regulation of homeobox gene expression. According to the importance of the Msx1 homeobox gene function in craniofacial development, especially in tooth development, the expression and regulation of its recently identified AS transcripts were investigated in vivo in mouse from E9.5 embryo to newborn, and compared with the S transcript and the encoded protein expression pattern and regulation. The spatial and temporal expression patterns of S, AS transcripts and protein are consistent with a role of AS RNA in the regulation of Msx1 expression in timely controlled developmental sites. Epithelial–mesenchymal interactions were shown to control the spatial organization of S and also AS RNA expression during early patterning of incisors and molars in the odontogenic mesenchyme. To conclude, this study clearly identifies the Msx1 AS RNA involvement during tooth development and evidences a new degree of complexity in craniofacial developmental biology: the implication of endogenous AS RNAs.

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Most of kidney stones are made of calcium oxalate crystals. Randall's plaque, an apatite deposit at the tip of the renal papilla is considered to be at the origin of these stones. Hypercalciuria may promote Randall's plaque formation and growth. We analysed whether long-term exposure of Abcc6-/mice (a murine model of Randall's plaque) to vitamin D supplementation, with or without calcium-rich diet, would accelerate the formation of Randall's plaque. Eight groups of mice (including Abcc6-/and wild-type) received vitamin D alone (100,000 UI/Kg every 2 weeks), a calcium-enriched diet alone (calcium gluconate 2g/l in drinking water), both vitamin D supplementation and calcium rich diet, or a standard diet (controls) for 6 months. Kidney calcifications were assessed by 3Dmicro-computed tomography, µ-Fourier transform infrared spectroscopy, field emissionscanning electron microscopy, transmission electron microscopy and Yasue staining. At 6 months, Abcc6-/mice exposed to vitamin D and calcium supplementation developed massive Randall's plaque when compared to control Abcc6-/mice (p<0.01). Wild-type animals did not develop significant calcifications when exposed to vitamin D. Combined administration of vitamin D and calcium accelerates significantly Randall's plaque formation in a murine model. This original model raises concerns about the cumulative risk of vitamin D supplementation and calcium intakes in Randall's plaque formation.

Cherubism is a rare genetic disorder characterized by extensive growth of a bilateral granuloma of the jaws, resulting in facial disfigurement. Cherubism is caused by gain-of-function mutations in the SH3BP2 gene, leading to overactivation of nuclear factor of activated T cells, cytoplasmic 1 (NFATc1)-dependent osteoclastogenesis. Recent findings in human and mouse cherubism have suggested that calcineurin inhibitors might be drug candidates in cherubism medical treatment. A 4-year-old boy with aggressive cherubism was treated with the calcineurin inhibitor tacrolimus for 1 year, and clinical, radiological, and molecular data were obtained. Immunohistologic analysis was performed to compare preoperative and postoperative NFATc1 staining and tartrate resistant acid phosphatase (TRAP) activity. Real-time PCR was performed to analyze the relative expression levels of OPG and RANKL. After tacrolimus therapy, the patient showed significant clinical improvement, including stabilization of jaw size and intraosseous osteogenesis. Immunohistologic analyses on granuloma showed that tacrolimus caused a significant reduction in the number of TRAP-positive osteoclasts and NFATc1 nuclear staining in multinucleated giant cells. Molecular analysis showed that tacrolimus treatment also resulted in increased OPG expression. We present the first case of effective medical therapy in cherubism. Tacrolimus enhanced bone formation by stimulating osteogenesis and inhibiting osteoclastogenesis.