Branched-chain amino acids (BCAA) are strongly associated with dysregulated glucose and lipid metabolism, but the underlying mechanisms are poorly understood. We report that inhibition of the kinase (BDK) or overexpression of the phosphatase (PPM1K) that regulates branched-chain ketoacid dehydrogenase (BCKDH), the committed step of BCAA catabolism, lowers circulating BCAA, reduces hepatic steatosis, and improves glucose tolerance in the absence of weight loss in Zucker fatty rats. Phosphoproteomics analysis identified ATP-citrate lyase (ACL) as an alternate substrate of BDK and PPM1K. Hepatic overexpression of BDK increased ACL phosphorylation and activated de novo lipogenesis. BDK and PPM1K transcript levels were increased and repressed, respectively, in response to fructose feeding or expression of the ChREBP-β transcription factor. These studies identify BDK and PPM1K as a ChREBP-regulated node that integrates BCAA and lipid metabolism. Moreover, manipulation of the BDK:PPM1K ratio relieves key metabolic disease phenotypes in a genetic model of severe obesity.

Differentiation of functional thyroid epithelia from pluripotent stem cells (PSCs) holds the potential for application in regenerative medicine. However, progress toward this goal is hampered by incomplete understanding of the signaling pathways needed for directed differentiation without forced over-expression of exogenous transgenes. Here we use mouse PSCs to identify key conserved roles for BMP and FGF signaling in regulating thyroid lineage specification from foregut endoderm in mouse and Xenopus. Thyroid progenitors derived from mouse PSCs can be matured into thyroid follicular organoids that provide functional secretion of thyroid hormones in vivo and rescue hypothyroid mice after transplantation. Moreover, by stimulating the same pathways we were also able to derive human thyroid progenitors from normal and disease-specific iPSCs generated from patients with hypothyroidism resulting from NKX2-1 haploinsufficiency. Our studies have therefore uncovered the regulatory mechanisms that underlie early thyroid organogenesis and provide a significant step toward cell-based regenerative therapy for hypothyroidism.

The vitamin D receptor (VDR) and its ligand 1,25-OH 2 -VD 3 (calcitriol) play an essential role in mineral homeostasis in mammals. Interestingly, the VDR is expressed very early in adipogenesis in 3T3-L1 cells, suggesting that the VDR signaling pathway may play a role in adipocyte biology and function. Indeed, it has been known for a number of years that calcitriol is a potent inhibitor of adipogenesis in this model but with no clear mechanism identified. In this study, we have further defined the molecular mechanism by which the unliganded VDR and calcitriol-liganded VDR regulate adipogenesis. In the presence of calcitriol, the VDR blocks adipogenesis by down-regulating both C/EBP␤ mRNA expression and C/EBP␤ nuclear protein levels at a critical stage of differentiation. In addition, calcitriol allows for the up-regulation of the recently described C/EBP␤ corerepressor, ETO, which would further inhibit the action of any remaining C/EBP␤, whose action is required for adipogenesis. In contrast, in the absence of calcitriol, the unliganded VDR appears necessary for lipid accumulation, since knock-down of the VDR using siRNA both delays and prevents this process. Taken together, these data support the notion that the intracellular concentrations of calcitriol can play an important role in either promoting or inhibiting adipogenesis via the VDR and the transcriptional pathways that it targets. Further examination of this hypothesis in vivo may shed new light on the biology of adipogenesis.The regulation of adipogenesis is a key biologic process that is required for both lipid storage and the development of the endocrine adipocyte. Both of these are key processes that determine the morbidity of obesity. Indeed, obesity is the leading risk for the development of Type 2 diabetes as well as an important contributing risk to heart disease and stroke. Thus, further understanding of the biology of adipogenesis might allow for the development of novel targets for new drugs to modify the function of the adipocyte in vivo.The murine 3T3-L1 cell line has provided an ideal model system to understand adipocyte development. This line differentiates from fibroblast preadipocyte precursors to mature adipocytes when presented with a hormonal mixture that activates a number of key signaling pathways. These pathways induce a regulatory cascade beginning with the induction of the CCAAT/enhancer-binding protein ␤ and ␦ isoforms (C/EBP␤ and -␦), 2 which in turn induce C/EBP␣ and the nuclear receptor peroxisome proliferator-activated receptor ␥ (PPAR␥, present as two isoforms, ␥1 and ␥2) (1). Once expressed, C/EBP␣ and PPAR␥ enhance each other's production and are necessary for terminal differentiation (2). In addition, the production of a PPAR␥ ligand is also necessary to allow PPAR␥ to activate target genes to allow for differentiation (3). Whereas PPAR␥ binds the thiazolidinediones, the prostenoid 15-deoxy-⌬ 12-14 -prostaglandin J 2 , some polyunsaturated fatty acids, and phospholipids, such as lysophosphatidic acid, its natural ligand(...