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LRP6 in mesenchymal stem cells is required for bone formation during bone growth and bone remodeling.

ABSTRACT: Lipoprotein receptor-related protein 6 (LRP6) plays a critical role in skeletal development and homeostasis in adults. However, the role of LRP6 in mesenchymal stem cells (MSCs), skeletal stem cells that give rise to osteoblastic lineage, is unknown. In this study, we generated mice lacking LRP6 expression specifically in nestin(+) MSCs by crossing nestin-Cre mice with LRP6(flox) mice and investigated the functional changes of bone marrow MSCs and skeletal alterations. Mice with LRP6 deletion in nestin(+) cells demonstrated reductions in body weight and body length at 1 and 3 months of age. Bone architecture measured by microCT (µCT) showed a significant reduction in bone mass in both trabecular and cortical bone of homozygous and heterozygous LRP6 mutant mice. A dramatic reduction in the numbers of osteoblasts but much less significant reduction in the numbers of osteoclasts was observed in the mutant mice. Osterix(+) osteoprogenitors and osteocalcin(+) osteoblasts significantly reduced at the secondary spongiosa area, but only moderately decreased at the primary spongiosa area in mutant mice. Bone marrow MSCs from the mutant mice showed decreased colony forming, cell viability and cell proliferation. Thus, LRP6 in bone marrow MSCs is essential for their survival and proliferation, and therefore, is a key positive regulator for bone formation during skeletal growth and remodeling.

SUBMITTER: Li C

PROVIDER: S-EPMC4472141 | biostudies-other | 2014

REPOSITORIES: biostudies-other

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Project description:BackgroundDuring bone fracture repair, mesenchymal stem cells (MSC) differentiate into chondrocytes and osteoblasts to form a fracture callus. Our laboratory previously reported that alcohol-exposed rodents with a surgically created tibia fracture display deficient fracture callus formation and diminished signs of endochondral ossification characterized by the absence of chondrocytes and mature hypertrophic chondrocytes, suggesting that alcohol may inhibit MSC differentiation. These findings led to our hypothesis that alcohol exposure inhibits mesenchymal stem cell chondrogenic differentiation within the developing fracture callus.MethodsIn the present study, we utilized a lineage-tracing approach to determine which stage(s) of chondrogenic differentiation are affected by alcohol exposure. We utilized lineage-specific reporter mice to determine the effects of alcohol on MSC and early and late chondrogenic cell frequencies within the fracture callus. In addition, serially sectioned slides were stained immunofluorescently and immunohistochemically and quantified to determine the effect of alcohol on cell proliferation and apoptosis, respectively, within the fracture callus of alcohol-administered rodents.ResultsAlcohol-administered rodents had a reduced fracture callus area at 4, 6, and 9 days postfracture. Alcohol had no effect on apoptosis in the fracture callus at any of the examined timepoints. Alcohol-administered rodents had significantly fewer proliferative cells in the fracture callus at 9 days postfracture, but no effect on cell proliferation was observed at earlier fracture callus timepoints. Alcohol-administered rodents had reduced Collagen2a1- and Collagen10a1-expressing cells in the developing fracture callus, suggesting that alcohol inhibits both early chondrogenic differentiation and later chondrocyte maturation during fracture callus development.ConclusionThe data suggest that alcohol could affect normal fracture healing through the mitigation of MSC chondrogenic differentiation at the callus site.

Project description:There is a critical need to generate functional hepatocytes to aid in liver repair and regeneration upon availability of a renewable, and potentially personalized, source of human hepatocytes (hHEP). Currently, the vast majority of primary hHEP are obtained from human tissue through cadavers. Recent advances in stem cell differentiation have opened up the possibility to obtain fully functional hepatocytes from embryonic or induced pluripotent stem cells, or adult stem cells. With respect to the latter, human bone marrow mesenchymal stromal cells (hBMSCs) can serve as a source of autogenetic and allogenic multipotent stem cells for liver repair and regeneration. A major aspect of hBMSC differentiation is the extracellular matrix (ECM) composition and, in particular, the role of glycosaminoglycans (GAGs) in the differentiation process. In this study, we examine the influence of four distinct culture conditions/protocols (T1-T4) on GAG composition and hepatic markers. ?-Fetoprotein and hepatocyte nuclear factor-4? were expressed continually over 21 days of differentiation, as indicated by real time quantitative PCR analysis, while albumin (ALB) expression did not begin until day 21. Hepatocyte growth factor (HGF) appears to be more effective than activin A in promoting hepatic-like cells through the mesenchymal-epithelial transition, perhaps due to the former binding to the HGF receptor to form a unique complex that diversifies the biological functions of HGF. Of the four protocols tested, uniform hepatocyte-like morphological changes, ALB secretion, and glycogen storage were found to be highest with protocol T2, which involves both early- and late-stage combinations of growth factors. The total GAG profile of the hBMSC ECM is rich in heparan sulfate (HS) and hyaluronan, both of which fluctuate during differentiation. The GAG profile of primary hHEP showed an HS-rich ECM, and thus, it may be possible to guide hBMSC differentiation to more mature hepatocytes by controlling the GAG profile expressed by differentiating cells.

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LRP6 in mesenchymal stem cells is required for bone formation during bone growth and bone remodeling.

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