Osterix represses adipogenesis by negatively regulating PPARγ transcriptional activity

A Multifaceted Giant Protein Microtubule-Actin Cross-Linking Factor 1

Microtubule-actin cross-linking factor 1 (MACF1), also known as actin cross-linking family protein 7 (ACF7), is a giant cytolinker protein with multiple conserved domains that can orchestrate cytoskeletal networks of actin and microtubules. MACF1 is involved in various biological processes, including cell polarity, cell-cell connection, cell proliferation, migration, vesicle transport, signal transduction, and neuronal development. In this review, we updated the physiological and pathological roles of MACF1, highlighting the components and signaling pathways involved. Novel evidence showed that MACF1 is involved in diverse human diseases, including multiple neuronal diseases, congenital myasthenic syndrome, premature ovarian insufficiency, spectraplakinopathy, osteoporosis, proliferative diabetic retinopathy, and various types of cancer. We also reviewed the physiological roles of MACF1, including its involvement in adhesome formation, bone formation, neuronal aging, and tooth development. In addition, MACF1 plays other roles, functioning as a biomarker for the prediction of infections in patients with burns and as a marker for genome selection breeding. These studies reinforce the idea that MACF1 is a bona fide versatile, multifaceted giant protein. Identifying additional MACF1 functions would finally help with the treatment of diseases caused by MACF1 defects.

From tradition to science: Possible mechanisms of ghee in supporting bone and joint health

Ghee, a traditional form of clarified butter, has been used for centuries in Ayurvedic medicine for its numerous health benefits. Recent scientific studies have begun to elucidate the molecular mechanisms by which ghee may support bone and joint health. This review explores the bioactive components of ghee, including short-chain fatty acids (SCFAs), medium-chain fatty acids (MCFAs), and fat-soluble vitamins (A, D, E, K2), and their potential therapeutic effects on bone density, joint lubrication, and inflammation. SCFAs in ghee can potentially improve joint lubrication and reduce inflammation. MCFAs and conjugated linoleic acid (CLA) exhibit anti-inflammatory properties, modulating cytokine production and oxidative stress pathways. Vitamins D and K2 in ghee can play potentially crucial roles in calcium metabolism and bone mineralization, while vitamin A supports immune regulation and cartilage health. This review integrates traditional knowledge with contemporary scientific research, highlighting the potential of ghee as a complementary therapy for conditions such as osteoporosis and arthritis. By understanding the molecular mechanisms involved, future studies can focus on this field to shed a light on different effects of ghee on bone and joint health.

Vitisin A-13-O-β-D-glucoside and Vitisin A from Iris lactea inhibit lipogenesis and promote lipolysis via the PKA/HSL pathway during adipogenic transdifferentiation of C2C12 cells

Oligostilbenes are a group of natural products derived from the polymerization of stilbene monomers. Despite the demonstration of their activities in regulating lipid metabolism, the function of oligostilbenes in the adipogenic transdifferentiation of multipotent myoblast cells remains unknown. Hence, the five oligostilbenes from Iris lactea were tested for their regulatory effects on adipogenic transdifferentiation of C2C12 myoblast cells. As a result, it was shown that Vitisin A-13-O-β-D-glucoside (VitAOG), Vitisin A (VitA) and Hopeaphenol (Hop) can greatly inhibit the adipogenic transdifferentiation of C2C12 cells by reducing lipid accumulation and downregulating the expression of peroxisome proliferator-activated receptor gamma (PPARγ), CCAAT/enhancer binding protein beta (C/EBPβ) and fatty acid binding proteins 4 (FABP4). In contrast, Vitisin D (VitD) and Isohopeaphenol (Isohop) promote adipogenic transdifferentiation of C2C12 cells by increasing lipid accumulation and upregulating the expression of adipogenesis and lipogenesis markers. Further research found that the lipolytic protein levels of adipocyte triglyceride lipase (ATGL) and phosphorylation of hormone-sensitive lipase (HSL) were elevated by VitAOG and VitA. Additionally, VitAOG and VitA maintain lipid homeostasis by improving mitochondrial function. Taken together, our study reveals an effect of oligostilbenes on lipid metabolism in C2C12 cells, and VitAOG and VitA can be regarded as potential candidates for the treatment of obesity and other disorders of lipid metabolism.

Boeravinone B, a natural rotenoid, inhibits osteoclast differentiation through modulating NF-κB, MAPK and PI3K/Akt signaling pathways

Osteoporosis is a major public health concern, which requires novel therapeutic strategies to prevent or mitigate bone loss. Natural compounds have attracted attention as potential therapeutic agents due to their safety and efficacy. In this study, we investigated the regulatory activities of boeravinone B (BOB), a natural rotenoid isolated from the medicinal plant Boerhavia diffusa, on the differentiation of osteoclasts and mesenchymal stem cells (MSCs), the two main cell components responsible for bone remodeling. We found that BOB inhibited osteoclast differentiation and function, as determined by TRAP staining and pit formation assay, with no significant cytotoxicity. Furthermore, our results showing that BOB ameliorates ovariectomyinduced bone loss demonstrated that BOB is also effective in vivo. BOB exerted its inhibitory effects on osteoclastogenesis by downregulating the RANKL/RANK signaling pathways, including NF-κB, MAPK, and PI3K/Akt, resulting in the suppression of osteoclast-specific gene expression. Further experiments revealed that, at least phenomenologically, BOB promotes osteoblast differentiation of bone marrow-derived MSCs but inhibits their differentiation into adipocytes. In conclusion, our study demonstrates that BOB inhibits osteoclastogenesis and promotes osteoblastogenesis in vitro by regulating various signaling pathways. These findings suggest that BOB has potential value as a novel therapeutic agent for the prevention and treatment of osteoporosis. [BMB Reports 2023; 56(10): 545-550].

Boeravinone B, a natural rotenoid, inhibits osteoclast differentiation through modulating NF-κB, MAPK and PI3K/Akt signaling pathways

Osteoporosis is a major public health concern, which requires novel therapeutic strategies to prevent or mitigate bone loss. Natural compounds have attracted attention as potential therapeutic agents due to their safety and efficacy. In this study, we investigated the regulatory activities of boeravinone B (BOB), a natural rotenoid isolated from the medicinal plant Boerhavia diffusa, on the differentiation of osteoclasts and mesenchymal stem cells (MSCs), the two main cell components responsible for bone remodeling. We found that BOB inhibited osteoclast differentiation and function, as determined by TRAP staining and pit formation assay, with no significant cytotoxicity. Furthermore, our results showing that BOB ameliorates ovariectomyinduced bone loss demonstrated that BOB is also effective in vivo. BOB exerted its inhibitory effects on osteoclastogenesis by downregulating the RANKL/RANK signaling pathways, including NF-κB, MAPK, and PI3K/Akt, resulting in the suppression of osteoclast-specific gene expression. Further experiments revealed that, at least phenomenologically, BOB promotes osteoblast differentiation of bone marrow-derived MSCs but inhibits their differentiation into adipocytes. In conclusion, our study demonstrates that BOB inhibits osteoclastogenesis and promotes osteoblastogenesis in vitro by regulating various signaling pathways. These findings suggest that BOB has potential value as a novel therapeutic agent for the prevention and treatment of osteoporosis. [BMB Reports 2023; 56(10): 545-550].

Acute Bone Loss and Infrapatellar Fat Pad Fibrosis in the Knee After an In Vivo ACL Injury in Adolescent Mice

BACKGROUND

Young patients are 6 times more likely than adults to have a primary anterior cruciate ligament (ACL) graft failure. Biological factors (ie, tunnel osteolysis) may account for up to a third of these failures. Previous evaluations of patient ACL explants indicated significant bone loss within the entheseal regions. However, it remains unknown if the degree of bone loss within the ACL insertion regions, wherein ACL grafts are fixated, exceeds that of the femoral and tibial condylar bone.

HYPOTHESIS

Bone loss in the mineralized matrices of the femoral and tibial ACL entheses is distinct from that clinically reported across the whole knee after injury.

STUDY DESIGN

Controlled laboratory study.

METHODS

We developed a clinically relevant in vivo mouse ACL injury model to cross-sectionally track the morphological and physiological postinjury changes within the ACL, femoral and tibial entheses, synovial joint space, and load-bearing epiphyseal cortical and trabecular bone components of the knee joint. Right ACLs of 10-week-old C57BL/6J female mice (N = 75) were injured in vivo with the contralateral ACLs serving as controls. Mice were euthanized at 1, 3, 7, 14, or 28 days after injury (n = 12/cohort). Downstream analyses included volumetric cortical and trabecular bone analyses and histopathologic assessments of the knee joint after injury. Gait analyses across all time points were also performed (n = 15 mice).

RESULTS

The majority of the ACL injuries in mice were partial tears. The femoral and tibial cortical bone volumes were 39% and 32% lower, respectively, at 28 days after injury than those of the uninjured contralateral knees (P < .01). Trabecular bone measures demonstrated little difference between injured and control knees after injury. Across all bone measures, bone loss was similar between the injured knee condyles and ACL entheses. There was also significant inflammatory activity within the knee after injury. By 7 days after injury, synovitis and fibrosis were sigificantly elevated in the injured knee compared with the controls (P < .01), which corresponded with significantly higher osteoclast activity in bone at this time point compared with the controls. This inflammatory response signficantly persisted throughout the duration of the study (P < .01). The hindlimb gait after injury deviated from normal, but mice habitually loaded their injured knee throughout the study.

CONCLUSION

Bone loss was acute and persisted for 4 weeks after injury in mice. However, the authors' hypothesis was not confirmed, as bone quality was not significantly lower in the entheses compared with the condylar bone regions after injury. With relatively normal hindlimb loading but a significant physiological response after injury, bone loss in this model may be driven by inflammation.

CLINICAL RELEVANCE

There is persistent bone resorption and fibrotic tissue development after injury that is not resolved. Inflammatory and catabolic activity may have a significant role in the postinjury decline of bone quality in the knee.

SP7 gene silencing dampens bone marrow stromal cell hypertrophy, but it also dampens chondrogenesis

For bone marrow stromal cells (BMSC) to be useful in cartilage repair their propensity for hypertrophic differentiation must be overcome. A single day of TGF-β1 stimulation activates intrinsic signaling cascades in BMSCs which subsequently drives both chondrogenic and hypertrophic differentiation. TGF-β1 stimulation upregulates SP7, a transcription factor known to contribute to hypertrophic differentiation, and SP7 remains upregulated even if TGF-β1 is subsequently withdrawn from the chondrogenic induction medium. Herein, we stably transduced BMSCs to express an shRNA designed to silence SP7, and assess the capacity of SP7 silencing to mitigate hypertrophy. SP7 silencing dampened both hypertrophic and chondrogenic differentiation processes, resulting in diminished microtissue size, impaired glycosaminoglycan production and reduced chondrogenic and hypertrophic gene expression. Thus, while hypertrophic features were dampened by SP7 silencing, chondrogenic differentation was also compromised. We further investigated the role of SP7 in monolayer osteogenic and adipogenic cultures, finding that SP7 silencing dampened characteristic mineralization and lipid vacuole formation, respectively. Overall, SP7 silencing affects the trilineage differentiation of BMSCs, but is insufficient to decouple BMSC hypertrophy from chondrogenesis. These data highlight the challenge of promoting BMSC chondrogenesis whilst simultaneously reducing hypertrophy in cartilage tissue engineering strategies.

Gene expression profiles for in vitro human stem cell differentiation into osteoblasts and osteoclasts: a systematic review

Background

There have been promising results published regarding the potential of stem cells in regenerative medicine. However, the vast variety of choices of techniques and the lack of a standard approach to analyse human osteoblast and osteoclast differentiation may reduce the utility of stem cells as a tool in medical applications. Therefore, this review aims to systematically evaluate the findings based on stem cell differentiation to define a standard gene expression profile approach.

Methods

This review was performed following the PRISMA guidelines. A systematic search of the study was conducted by retrieving articles from the electronic databases PubMed and Web of Science to identify articles focussed on gene expression and approaches for osteoblast and osteoclast differentiation.

Results

Six articles were included in this review; there were original articles of in vitro human stem cell differentiation into osteoblasts and osteoclasts that involved gene expression profiling. Quantitative polymerase chain reaction (qPCR) was the most used technique for gene expression to detect differentiated human osteoblasts and osteoclasts. A total of 16 genes were found to be related to differentiating osteoblast and osteoclast differentiation.

Conclusion

Qualitative information of gene expression provided by qPCR could become a standard technique to analyse the differentiation of human stem cells into osteoblasts and osteoclasts rather than evaluating relative gene expression. RUNX2 and CTSK could be applied to detect osteoblasts and osteoclasts, respectively, while RANKL could be applied to detect both osteoblasts and osteoclasts. This review provides future researchers with a central source of relevant information on the vast variety of gene expression approaches in analysing the differentiation of human osteoblast and osteoclast cells. In addition, these findings should enable researchers to conduct accurately and efficiently studies involving isolated human stem cell differentiation into osteoblasts and osteoclasts.

Conditional loss of IKKα in Osterix + cells has no effect on bone but leads to age-related loss of peripheral fat

NF-κB has been reported to both promote and inhibit bone formation. To explore its role in osteolineage cells, we conditionally deleted IKKα, an upstream kinase required for non-canonical NF-κB activation, using Osterix (Osx)-Cre. Surprisingly, we found no effect on either cancellous or cortical bone, even following mechanical loading. However, we noted that IKKα conditional knockout (cKO) mice began to lose body weight after 6 months of age with severe reductions in fat mass and lower adipocyte size in geriatric animals. qPCR analysis of adipogenic markers in fat pads of cKO mice indicated no difference in early differentiation, but instead markedly lower leptin with age. We challenged young mice with a high fat diet finding that cKO mice gained less weight and showed improved glucose metabolism. Low levels of recombination at the IKKα locus were detected in fat pads isolated from old cKO mice. To determine whether recombination occurs in adipocytes, we examined fat pads in Osx-Cre;TdT reporter mice; these showed increasing Osx-Cre-mediated expression in peripheral adipocytes from 6 weeks to 18 months. Since Osx-Cre drives recombination in peripheral adipocytes with age, we conclude that fat loss in cKO mice is most likely caused by progressive deficits of IKKα in adipocytes.

Epigenetic Dysregulation of the Homeobox A5 (HOXA5) Gene Associates with Subcutaneous Adipocyte Hypertrophy in Human Obesity

Along with insulin resistance and increased risk of type 2 diabetes (T2D), lean first-degree relatives of T2D subjects (FDR) feature impaired adipogenesis in subcutaneous adipose tissue (SAT) and subcutaneous adipocyte hypertrophy well before diabetes onset. The molecular mechanisms linking these events have only partially been clarified. In the present report, we show that silencing of the transcription factor Homeobox A5 (HOXA5) in human preadipocytes impaired differentiation in mature adipose cells in vitro. The reduced adipogenesis was accompanied by inappropriate WNT-signaling activation. Importantly, in preadipocytes from FDR individuals, HOXA5 expression was attenuated, with hypermethylation of the HOXA5 promoter region found responsible for its downregulation, as revealed by luciferase assay. Both HOXA5 gene expression and DNA methylation were significantly correlated with SAT adipose cell hypertrophy in FDR, whose increased adipocyte size marks impaired adipogenesis. In preadipocytes from FDR, the low HOXA5 expression negatively correlated with enhanced transcription of the WNT signaling downstream genes NFATC1 and WNT2B. In silico evidence indicated that NFATC1 and WNT2B were directly controlled by HOXA5. The HOXA5 promoter region also was hypermethylated in peripheral blood leukocytes from these same FDR individuals, which was further revealed in peripheral blood leukocytes from an independent group of obese subjects. Thus, HOXA5 controlled adipogenesis in humans by suppressing WNT signaling. Altered DNA methylation of the HOXA5 promoter contributed to restricted adipogenesis in the SAT of lean subjects who were FDR of type 2 diabetics and in obese individuals.

Cdc42 in osterix-expressing cells alters osteoblast behavior and myeloid lineage commitment

Osteoblasts are not only responsible for bone formation. They also support hematopoiesis. This requires responding to cues originating from several signaling pathways, a task performed by Rho GTPases. We therefore examined several transgenic mouse models and used inhibitors of Cdc42 in vitro. Deletion of Cdc42 in vivo using the Osterix promoter suppressed osteoblast function, while its deletion in differentiating osteoblasts using the Collagen-α1(I) promoter decreased osteoblast numbers. In both cases, bone mineral density diminished confirming the importance of Cdc42. Evaluation of hematopoiesis revealed that deletion of Cdc42 using the Osterix, but not the Collagen-α1(I) promoter increased the common myeloid progenitors (CMPs) in the bone marrow as well as the erythrocytes and the thrombocytes/platelets in peripheral blood. Causality between Cdc42 loss in early osteoblasts and increased myelopoiesis was confirmed in vitro. Work in vitro supported the conclusion that interleukin-4 mediated the increase in myelopoiesis. Thus, Cdc42 is required for healthy bone through regulation of bone formation in Osterix-expressing osteoblasts and the number of osteoblasts in differentiating osteoblasts. In addition, its expression in early osteoblasts/stromal cells modulates myelopoiesis. This highlights the importance of osteoblasts in regulating hematopoiesis.

An In Vitro and In Vivo Comparison of Osteogenic Differentiation of Human Mesenchymal Stromal/Stem Cells

The use of stem cells in regenerative medicine, including tissue engineering and transplantation, has generated a great deal of enthusiasm. Mesenchymal stromal/stem cells (MSCs) can be isolated from various tissues, most commonly, bone marrow but more recently adipose tissue, dental pulp, and Wharton's jelly, to name a few. MSCs display varying phenotypic profiles and osteogenic differentiating capacity depending and their site of origin. MSCs have been successfully differentiated into osteoblasts both in vitro an in vivo but discrepancies exist when the two are compared: what happens in vitro does not necessarily happen in vivo, and it is therefore important to understand why these differences occur. The osteogenic process is a complex network of transcription factors, stimulators, inhibitors, proteins, etc., and in vivo experiments are helpful in evaluating the various aspects of this osteogenic process without distractions and confounding variables. With that in mind, the results of in vitro experiments need to be carefully considered and interpreted with caution as they do not perfectly replicate the conditions found within living organisms. This is where in vivo experiments help us better understand interactions that might occur in the osteogenic process that cannot be replicated in vitro. Potentially, these differences could also be exploited to develop an optimal MSC cell therapeutic product that can be used for bone disorders. There are many bone disorders, most of which cause a great deal of discomfort. Clinically acceptable protocols could be developed in which MSCs are used to aid in bone regeneration providing relief for patients with chronic pain. The aim of this review is to examine the differences between studies conducted in vitro and in vivo with regard to the osteogenic process to better define the gaps in current osteogenic research. By better understanding osteogenic differentiation, we can better define treatment strategies for various bone disorders.

Targeted Ptpn11 deletion in mice reveals the essential role of SHP2 in osteoblast differentiation and skeletal homeostasis

The maturation and function of osteoblasts (OBs) rely heavily on the reversible phosphorylation of signaling proteins. To date, most of the work in OBs has focused on phosphorylation by tyrosyl kinases, but little has been revealed about dephosphorylation by protein tyrosine phosphatases (PTPases). SHP2 (encoded by PTPN11) is a ubiquitously expressed PTPase. PTPN11 mutations are associated with both bone and cartilage manifestations in patients with Noonan syndrome (NS) and metachondromatosis (MC), although the underlying mechanisms remain elusive. Here, we report that SHP2 deletion in bone gamma-carboxyglutamate protein-expressing (Bglap+) bone cells leads to massive osteopenia in both trabecular and cortical bones due to the failure of bone cell maturation and enhanced osteoclast activity, and its deletion in Bglap+ chondrocytes results in the onset of enchondroma and osteochondroma in aged mice with increased tubular bone length. Mechanistically, SHP2 was found to be required for osteoblastic differentiation by promoting RUNX2/OSTERIX signaling and for the suppression of osteoclastogenesis by inhibiting STAT3-mediated RANKL production by osteoblasts and osteocytes. These findings are likely to explain the compromised skeletal system in NS and MC patients and to inform the development of novel therapeutics to combat skeletal disorders.

Recent Advances of Osterix Transcription Factor in Osteoblast Differentiation and Bone Formation

With increasing life expectations, more and more patients suffer from fractures either induced by intensive sports or other bone-related diseases. The balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption is the basis for maintaining bone health. Osterix (Osx) has long been known to be an essential transcription factor for the osteoblast differentiation and bone mineralization. Emerging evidence suggests that Osx not only plays an important role in intramembranous bone formation, but also affects endochondral ossification by participating in the terminal cartilage differentiation. Given its essentiality in skeletal development and bone formation, Osx has become a new research hotspot in recent years. In this review, we focus on the progress of Osx's function and its regulation in osteoblast differentiation and bone mass. And the potential role of Osx in developing new therapeutic strategies for osteolytic diseases was discussed.

Gene regulatory landscape in osteoblast differentiation

The development of osteoblasts, a bone-forming cell population, occurs in conjunction with development of the skeleton, which creates our physical framework and shapes the body. In the past two decades, genetic studies have uncovered the molecular framework of this process-namely, transcriptional regulators and signaling pathways coordinate the cell fate determination and differentiation of osteoblasts in a spatial and temporal manner. Recently emerging genome-wide studies provide additional layers of understanding of the gene regulatory landscape during osteoblast differentiation, allowing us to gain novel insight into the modes of action of the key regulators, functional interaction among the regulator-bound enhancers, epigenetic regulations, and the complex nature of regulatory inputs. In this review, we summarize current understanding of the transcriptional regulation in osteoblasts, in terms of the gene regulatory landscape.

Epigenetic Control of Mesenchymal Stem Cell Fate Decision via Histone Methyltransferase Ash1l

Previous research indicates that knocking out absent, small, or homeotic-like (Ash1l) in mice, a histone 3 lysine 4 (H3K4) trimethyltransferase, can result in arthritis with more severe cartilage and bone destruction. Research has documented the essential role of Ash1l in stem cell fate decision such as hematopoietic stem cells and the progenitors of keratinocytes. Following up on those insights, our research seeks to document the function of Ash1l in skeletal formation, specifically whether it controls the fate decision of mesenchymal progenitor cells. Our findings indicate that in osteoporotic bones, Ash1l was significantly decreased, indicating a positive correlation between bone mass and the expression of Ash1l. Silencing of Ash1l that had been markedly upregulated in differentiated C3H10T1/2 (C3) cells hampered osteogenesis and chondrogenesis but promoted adipogenesis. Consistently, overexpression of an Ash1l SET domain-containing fragment 3 rather than Ash1lΔN promoted osteogenic and chondrogenic differentiation of C3 cells and simultaneously inhibited adipogenic differentiation. This indicates that the role of Ash1l in regulating the differentiation of C3 cells is linked to its histone methyltransferase activity. Subcutaneous ex vivo transplantation experiments confirmed the role of Ash1l in the promotion of osteogenesis. Further experiments proved that Ash1l can epigenetically affect the expression of essential osteogenic and chondrogenic transcription factors. It exerts this impact via modifications in the enrichment of H3K4me3 on their promoter regions. Considering the promotional action of Ash1l on bone, it could potentially prompt new therapeutic strategy to promote osteogenesis. Stem Cells 2019;37:115-127.

Cysteine-rich protein 61 regulates adipocyte differentiation from mesenchymal stem cells through mammalian target of rapamycin complex 1 and canonical Wnt signaling

Emerging evidence suggests that cysteine-rich protein 61 (CYR61) plays a role in the differentiation and development of chondrocytes, osteoblasts, and osteoclasts; however, little is known about its role in adipogenesis. The current study indicates that the expression level of Cyr61 was altered in primary cultured marrow stromal cells and the established mesenchymal cell line, C3H10T1/2, after adipogenic treatment. Overexpressing Cyr61 repressed C3H10T1/2 and primary marrow stromal cells to differentiate into mature adipocytes. Conversely, inhibition of endogenous Cyr61 induced C3H10T1/2 and primary marrow stromal cells to fully differentiate. Mechanism investigations reveal that knockdown of Cyr61 inhibited the nuclear translocation of β-catenin and decreased nuclear protein levels of β-catenin and transcription factor 7-like 2. Moreover, the silencing of Cyr61 increased protein levels of phosphorylated ribosomal protein S6 kinase B1, mammalian target of rapamycin, eukaryotic translation initiation factor 4E-binding protein 1, and ribosomal protein S6-the major components of mammalian target of rapamycin complex 1 (mTORC1) signaling-in C3H10T1/2 cells. Additional investigations demonstrated that treatment with rapamycin significantly attenuated adipocyte formation that was induced by Cyr61 small interfering RNA (siRNA) transfection. Moreover, Cyr61 siRNA also lost its ability to stimulate adipocyte formation under the background of β-catenin overexpression. Taken together, our study provides evidence that CYR61 regulates adipocyte differentiation via multiple signaling pathways that involve at least the inactivation of mTORC1 signaling and the activation of canonical Wnt signaling.-Yang, Y., Qi, Q., Wang, Y., Shi, Y., Yang, W., Cen, Y., Zhu, E., Li, X., Chen, D., Wang, B. Cysteine-rich protein 61 regulates adipocyte differentiation from mesenchymal stem cells through mammalian target of rapamycin complex 1 and canonical Wnt signaling.

Epigenetic Contribution of High-Mobility Group A Proteins to Stem Cell Properties

High-mobility group A (HMGA) proteins have been examined to understand their participation as structural epigenetic chromatin factors that confer stem-like properties to embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and cancer stem cells (CSCs). The function of HMGA was evaluated in conjunction with that of other epigenetic factors such as histones and microRNAs (miRs), taking into consideration the posttranscriptional modifications (PTMs) of histones (acetylation and methylation) and DNA methylation. HMGA proteins were coordinated or associated with histone and DNA modification and the expression of the factors related to pluripotency. CSCs showed remarkable differences compared with ESCs and iPSCs.

Osteoblast AMP-Activated Protein Kinase Regulates Postnatal Skeletal Development in Male Mice

Studies have shown that AMP-activated protein kinase (AMPK), a crucial regulator of energy homeostasis, plays important roles in osteoblast differentiation and mineralization. However, little is known about in vivo roles of osteoblastic AMPK in bone development. Thus, to investigate in vivo roles of osteoblast AMPK, we conditionally inactivated Ampk in osterix (Osx)-expressing cells by crossing Osx-Cre mice with floxed AMPKα1 to generate mice lacking AMPKα1 in osteoblasts (Ampk-/- mice). Compared with wild-type and Ampk+/- mice, Ampk-/- mice displayed retardation of postnatal bone development, although bone deformity was not observed at birth. Microcomputed tomography showed significant reductions in trabecular bone volume, cortical bone length, and density, as well as increased cortical porosity in femur as well as development defects of skull in 8-week-old Ampk-/- mice. Surprisingly, histomorphometric analysis demonstrated that the number of osteoclasts was significantly increased, although bone formation rate was not altered. Loss of trabecular network connections and mass, as well as shortened growth plates and reduced thickness of cartilage adjacent to the growth plate, was observed in Ampk-/- mice. In primary cultured osteoblasts from calvaria, the expressions of alkaline phosphatase, type 1 collagen, osteocalcin, bone morphogenetic protein 2, Runx2, and osterix were significantly inhibited in Ampk-/- osteoblasts, whereas the expression of receptor activator of nuclear κB ligand (RANKL) and the RANKL/osteoprotegerin ratio were significantly increased. These findings indicate that osteoblastic AMPK plays important roles in bone development in vivo and that deletion of AMPK in osteoblasts decreases osteoblastic differentiation and enhances bone turnover by increasing RANKL expression.