Development of brown and white adipocytes and its regulation by microRNAs and long non-coding RNAs.
Research in the Lodish Laboratory related to Diabetes and Obesity falls into two broad areas: understanding the roles of microRNAs (miRNAs) and long noncoding RNAs (LncRNAs) in the development and pathophysiology of brown and white adipocytes, and defining the mechanisms of insulin resistance and stress responses in adipose cells.
- MicroRNAs in fat cell development and obesity.
Brown adipocytes arise in vivo from a Myf5-positive, bipotential myoblastic progenitor by the action of the Prdm16 (PR domain containing 16) transcription factor. Recently we investigated the role of miRNAs in brown fat adipogenesis and identified a brown fat-enriched miRNA cluster, miR-193b-365, as a key regulator of brown fat development. Blocking miR-193b and/or miR-365 in primary brown preadipocytes dramatically impaired brown adipocyte adipogenesis by enhancing expression of Runx1t1 (runt-related transcription factor 1; translocated to 1) whereas myogenic markers were significantly induced. In contrast, forced expression of miR-193b and/or miR-365 in C2C12 myoblasts blocked the entire program of myogenesis, and, in adipogenic conditions, miR-193b induced myoblasts to differentiate into brown adipocytes. MiR-193b-365 was upregulated by Prdm16 partially through the action of the transcription factor PPARγ. Taken together, these results underlie the importance of tissue enriched miRNAs 193b-365 in regulating lineage specification between brown fat and muscle, and also suggest that these or other miRNAs may have therapeutic potential in inducing expression of brown fat-specific genes. Another miRNA, miR-203 was also enriched in brown fat. We are following up earlier work showing that a knock down of miR-203 results in a block of adipogenesis in primary brown pre-adipocytes. Further, forced expression of miR-203 in C2C12 myoblasts blocked the myogenic program and induced differentiation into adipocytes. We are identifying the mRNA targets of miR-203. Using the CRISPR/Cas system we are generating mice that have a mutated seed sequence in the miR-203 to analyze the effect of miR-203 seed region mutation on the development of white and brown adipose tissue.
- LncRNAs in fat cell development and function.
The global expression patterns and functional contributions of long intergenic noncoding RNA (lincRNA) during adipogenesis have not been explored. We profiled the transcriptome of primary brown and white adipocytes, pre- brown and white adipocytes, and cultured adipocytes and identified 175 lincRNAs that are specifically regulated during both brown and white adipogenesis. Many lincRNAs are adipose-enriched, strongly induced during adipogenesis, and bound at their promoters by key adipogenic transcription factors such as PPARγ and CEBPα. RNAi-mediated loss of function screens identified 9 functional lncRNAs required for adipogenesis; mRNA analyses showed that each of these lncRNAs is essential for normal induction of a discrete set of adipocyte- induced mRNAs and for down regulation of a discrete set of mRNAs expressed in adipocyte progenitor cells. We further focused on one X-linked lincRNA required for proper adipogenesis; both the human and mouse orthologs of this lincRNA contain numerous copies of a conserved 156 bp repeating RNA sequence motif. In collaboration with the Rinn laboratory at Harvard, our data thusfar suggest a model in which lncRNAs such can interface with and modulate nuclear architecture across chromosomes. More generally we have identified numerous lincRNAs that comprise a critical transcriptional regulatory layer that is functionally required for proper differentiation of either or both brown and white adipocytes. We are currently working to understand how several of these noncoding RNAs affect nuclear organization and gene expression and why they are so essential for development of brown and/or white adipocytes.
- Novel kinases important for adipocyte development.
Using primary murine embryonic fibroblasts and mouse splenic B cells stimulated in vitro by hydrogen peroxide, we are investigating whether a kinase important for signal transduction in immune cells also mediates activation of oxidative stress induced pathways, in what subcellular compartment the signaling occurs and what components regulate activation of this kinase.
1. Xie, H., B. Lim, and H. F. Lodish. MicroRNAs Induced during Adipogenesis That Accelerate Fat Cell Development Are Downregulated in Obesity Diabetes 58: 1050-1057 (2009). PMCID: PMC2671055
2. Wong, G.W., S. A. Krawczyk, C. Kitidis-Mitrokostas, G. Ge, E. Spooner, C. Hug, R. Gimeno, and H. F. Lodish. Identification and characterization of CTRP9, a novel secreted glycoprotein from adipose tissue that reduces serum glucose in mice and forms heterotrimers with adiponectin FASEB Journal 23: 241 - 258 (2009). PMCID:
3. Liu, Q., M.-S. Gauthier, L. Sun, N. Ruderman, and H. F. Lodish Activation of AMP-activated protein kinase signaling pathway by adiponectin and insulin in mouse adipocytes. Requirement of acyl-CoA synthetases FATP1 and Acsl1 and association with an elevation in AMP/ATP ratio FASEB Journal 24:4229 - 4239 (2010) PMCID:
4. Sun, L., H. Xie, M. Mori, R. Alexander, B. Yuan, S. Hattangadi, Q. Liu, R. Kahn, and H. Lodish. Mir-193b-365 is essential for brown fat differentiation. Nature Cell Biology. 13:958 - 965. (2011) PMCID: PMC3149720
5. Liu, Q, B. Yuan, K. Lo, H. Patterson, Y. Sun, and H. Lodish Adiponectin regulates expression of hepatic genes critical for glucose and lipid metabolism PNAS 109: 14568 - 14573 (2012). PMCID: PMC3437840
6. Lo, K. A., A. Labadorf, N. J. Kennedy, M. S. Han, Y. S. Yap, B. Matthews, X. Xin, L. Sun, R. J. Davis, H. F. Lodish, and E. Fraenkel. Analysis of In Vitro Insulin-Resistance Models and Their Physiological Relevance to In Vivo Diet-Induced Adipose Insulin Resistance. Cell Reports 5:259-270 (2013) S2211-1247(13)00480-4 [pii] 10.1016/j.celrep.2013.08.039. PMCID: PMC3874466
7. Sun, L., L. Goff, C. Trapnell, R. Alexander, A. Lo, E. Hacisuleyman, M. Savageau, B. Talon-Vega, D. Kelley, D. Hendrickson, B. Yuan, M. Kellis, H. Lodish, and J. Rinn, Long noncoding RNAs regulate adipogenesis. PNAS 110:3387 - 3392 (2013). PMCID:
8. Trajkovski, M., and H. Lodish. MicroRNA networks regulate development of brown adipocytes. Trends Endocrinol Metab 24:442-450 (2013). PMCID: PMC3979327