Srebf1a is a key regulator of transcriptional control for adipogenesis

Adipogenesis is regulated by a complex cascade of transcriptional factors, but little is known about the early events that regulate the adipogenic program. Here, we report the role of the srebf1a gene in the differentiation of fibroblastic 3T3-F442A cells. We found that expression of srebf1a depended on GSK3β activity and that GSK3β activity was necessary for C/EBPβ phosphorylation at Thr188. Knockdown of srebf1a inhibited the adipogenic program because it blocked the expression of genes encoding PPARγ2, C/EBPα, SREBP1c and even FABP4, demonstrating that SREBP1a activation is upstream of these three essential adipogenic transcription factors. Kinetic analysis during differentiation illustrated that the order of expression of adipogenic genes was the following: cebpb, srebf1a, pparg2, cebpa, srebp1c and fabp4. Our data suggest that srebf1a acts as an essential link between the GSK3β-C/EBPβ signaling axis and the beginning of the adipogenic transcriptional cascade

Transcriptional regulatory program in wild-type and retinoblastoma gene-deficient mouse embryonic fibroblasts during adipocyte differentiation

<p>Abstract</p> <p>Background</p> <p>Although many molecular regulators of adipogenesis have been identified a comprehensive catalogue of components is still missing. Recent studies showed that the retinoblastoma protein (pRb) was expressed in the cell cycle and late cellular differentiation phase during adipogenesis. To investigate this dual role of pRb in the early and late stages of adipogenesis we used microarrays to perform a comprehensive systems-level analysis of the common transcriptional program of the classic 3T3-L1 preadipocyte cell line, wild-type mouse embryonic fibroblasts (MEFs), and retinoblastoma gene-deficient MEFs (Rb-/- MEFs).</p> <p>Findings</p> <p>Comparative analysis of the expression profiles of 3T3-L1 cells and wild-type MEFs revealed genes involved specifically in early regulation of the adipocyte differentiation as well as secreted factors and signaling molecules regulating the later phase of differentiation. In an attempt to identify transcription factors regulating adipogenesis, bioinformatics analysis of the promoters of coordinately and highly expressed genes was performed. We were able to identify a number of high-confidence target genes for follow-up experimental studies. Additionally, combination of experimental data and computational analyses pinpointed a feedback-loop between Pparg and Foxo1.</p> <p>To analyze the effects of the retinoblastoma protein at the transcriptional level we chose a perturbated system (Rb-/- MEFs) for comparison to the transcriptional program of wild-type MEFs. Gene ontology analysis of 64 deregulated genes showed that the Rb-/- MEF model exhibits a brown(-like) adipocyte phenotype. Additionally, the analysis results indicate a different or additional role for pRb family member involvement in the lineage commitment.</p> <p>Conclusion</p> <p>In this study a number of commonly modulated genes during adipogenesis in 3T3-L1 cells and MEFs, potential transcriptional regulation mechanisms, and differentially regulated targets during adipocyte differentiation of Rb-/- MEFs could be identified. These data and the analysis provide a starting point for further experimental studies to identify target genes for pharmacological intervention and ultimately remodeling of white adipose tissue into brown adipose tissue.</p

Pathogenesis of adolescent idiopathic scoliosis in girls - a double neuro-osseous theory involving disharmony between two nervous systems, somatic and autonomic expressed in the spine and trunk: possible dependency on sympathetic nervous system and hormones with implications for medical therapy

Anthropometric data from three groups of adolescent girls - preoperative adolescent idiopathic scoliosis (AIS), screened for scoliosis and normals were analysed by comparing skeletal data between higher and lower body mass index subsets. Unexpected findings for each of skeletal maturation, asymmetries and overgrowth are not explained by prevailing theories of AIS pathogenesis. A speculative pathogenetic theory for girls is formulated after surveying evidence including: (1) the thoracospinal concept for right thoracic AIS in girls; (2) the new neuroskeletal biology relating the sympathetic nervous system to bone formation/resorption and bone growth; (3) white adipose tissue storing triglycerides and the adiposity hormone leptin which functions as satiety hormone and sentinel of energy balance to the hypothalamus for long-term adiposity; and (4) central leptin resistance in obesity and possibly in healthy females. The new theory states that AIS in girls results from developmental disharmony expressed in spine and trunk between autonomic and somatic nervous systems. The autonomic component of this double neuro-osseous theory for AIS pathogenesis in girls involves selectively increased sensitivity of the hypothalamus to circulating leptin (genetically-determined up-regulation possibly involving inhibitory or sensitizing intracellular molecules, such as SOC3, PTP-1B and SH2B1 respectively), with asymmetry as an adverse response (hormesis); this asymmetry is routed bilaterally via the sympathetic nervous system to the growing axial skeleton where it may initiate the scoliosis deformity (leptin-hypothalamic-sympathetic nervous system concept = LHS concept). In some younger preoperative AIS girls, the hypothalamic up-regulation to circulating leptin also involves the somatotropic (growth hormone/IGF) axis which exaggerates the sympathetically-induced asymmetric skeletal effects and contributes to curve progression, a concept with therapeutic implications. In the somatic nervous system, dysfunction of a postural mechanism involving the CNS body schema fails to control, or may induce, the spinal deformity of AIS in girls (escalator concept). Biomechanical factors affecting ribs and/or vertebrae and spinal cord during growth may localize AIS to the thoracic spine and contribute to sagittal spinal shape alterations. The developmental disharmony in spine and trunk is compounded by any osteopenia, biomechanical spinal growth modulation, disc degeneration and platelet calmodulin dysfunction. Methods for testing the theory are outlined. Implications are discussed for neuroendocrine dysfunctions, osteopontin, sympathoactivation, medical therapy, Rett and Prader-Willi syndromes, infantile idiopathic scoliosis, and human evolution. AIS pathogenesis in girls is predicated on two putative normal mechanisms involved in trunk growth, each acquired in evolution and unique to humans

Tumour necrosis factor-α inhibits adipogenesis via a β-catenin/TCF4(TCF7L2)-dependent pathway

Tumour necrosis factor-α (TNF-α), a proinflammatory cytokine, is a potent negative regulator of adipocyte differentiation. However, the mechanism of TNF-α-mediated antiadipogenesis remains incompletely understood. In this study, we first confirm that TNF-α inhibits adipogenesis of 3T3-L1 preadipocytes by preventing the early induction of the adipogenic transcription factors peroxisome proliferator-activated receptor-γ (PPARγ) and CCAATαenhancer binding protein-α (C/EBPα). This suppression coincides with enhanced expression of several reported mediators of antiadipogenesis that are also targets of the Wnt/ β-catenin/T-cell factor 4 (TCF4) pathway. Indeed, we found that TNF-α enhanced TCF4-dependent transcriptional activity during early antiadipogenesis, and promoted the stabilisation of β-catenin throughout antiadipogenesis. We analysed the effect of TNF-α on adipogenesis in 3T3-L1 cells in which β-catenin/TCF signalling was impaired, either via stable knockdown of β-catenin, or by overexpression of dominant-negative TCF4 (dnTCF4). The knockdown of β-catenin enhanced the adipogenic potential of 3T3-L1 preadipocytes and attenuated TNF-α-induced antiadipogenesis. However, β-catenin knockdown also promoted TNF-α-induced apoptosis in these cells. In contrast, overexpression of dnTCF4 prevented TNF-α-induced antiadipogenesis but showed no apparent effect on cell survival. Finally, we show that TNF-α-induced antiadipogenesis and stabilisation of β-catenin requires a functional death domain of TNF-α receptor 1 (TNFR1). Taken together these data suggest that TNFR1-mediated death domain signals can inhibit adipogenesis via a β-catenin/TCF4-dependent pathway.</p