This career development plan will prepare Dr. Irfan Lodhi to transition to a position as an independent academic investigator in metabolic research. The mentored phase (K99) of this 5 year project will be completed in the laboratory of Dr. Clay Semenkovich at Washington University School of Medicine. The overall objective of this project is to understand the role of lipogenic pathways in the activation of PPARg, a key regulator of adipose tissue development and metabolism. PPARg belongs to the peroxisome proliferator- activated receptor (PPAR) family of ligand-activated nuclear receptors, originally identified based on their ability to be activated by agents that promote peroxisome proliferation. Endogenous pathways of PPARg activation have remained unclear. Previous work suggests that de novo lipogenesis mediated by fatty acid synthase (FAS) is important for endogenous activation of PPARg in adipocytes. A mass spectrometry-based approach identified several FAS-dependent complex lipids as putative endogenous ligands for PPARg. These lipids are made in peroxisomes and require a previously unidentified peroxisomal enzyme named PexRAP for their synthesis. Knockdown of PexRAP in cultured cells impaired PPARg activation and adipogenesis, both of which could be rescued with rosiglitazone, a pharmacological activator of PPARg. Antisense oligonucleotide- mediated knockdown of PexRAP in mice decreased expression of PPARg-dependent genes, reduced fat mass, increased leanness, and improved insulin sensitivity. Additional studies suggested that genes involved in peroxisomal biogenesis increase during adipogenesis and are regulated by PPARg. Together, these studies led to the hypothesis that peroxisome-derived lipids activate PPARg and, reciprocally, PPARg promotes peroxisomal biogenesis, resulting in a feed-forward cycle that drives adipocyte differentiation. The following specific aims are designed to test this hypothesis.
Aim 1 will determine if mice with adipose-specific deletion of PexRAP are protected from diet-induced and genetic forms of obesity and diabetes.
Aim 2 will characterize the molecular mechanism of PexRAP function in adipocytes. Finally, Aim 3 will determine the role of peroxisomal biogenesis in adipocyte differentiation.

Public Health Relevance

Obesity and associated metabolic diseases represent an enormous public health problem. Findings from the studies proposed in this application may lead to novel therapeutic approaches for treatment of these ubiquitous disorders.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Transition Award (R00)
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Special Emphasis Panel (NSS)
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Haft, Carol R
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Washington University
Internal Medicine/Medicine
Schools of Medicine
Saint Louis
United States
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Park, Hongsuk; He, Anyuan; Tan, Min et al. (2018) Peroxisome-derived lipids regulate adipose thermogenesis by mediating cold-induced mitochondrial fission. J Clin Invest :
Dean, John M; Lodhi, Irfan J (2018) Structural and functional roles of ether lipids. Protein Cell 9:196-206
Lodhi, Irfan J; Dean, John M; He, Anyuan et al. (2017) PexRAP Inhibits PRDM16-Mediated Thermogenic Gene Expression. Cell Rep 20:2766-2774
Cipolla, Cynthia M; Lodhi, Irfan J (2017) Peroxisomal Dysfunction in Age-Related Diseases. Trends Endocrinol Metab 28:297-308
Funai, Katsuhiko; Lodhi, Irfan J; Spears, Larry D et al. (2016) Skeletal Muscle Phospholipid Metabolism Regulates Insulin Sensitivity and Contractile Function. Diabetes 65:358-70
Lodhi, Irfan J; Wei, Xiaochao; Yin, Li et al. (2015) Peroxisomal lipid synthesis regulates inflammation by sustaining neutrophil membrane phospholipid composition and viability. Cell Metab 21:51-64
Lodhi, Irfan J; Link, Daniel C; Semenkovich, Clay F (2015) Acute ether lipid deficiency affects neutrophil biology in mice. Cell Metab 21:652-3
Lodhi, Irfan J; Semenkovich, Clay F (2014) Peroxisomes: a nexus for lipid metabolism and cellular signaling. Cell Metab 19:380-92
Hsu, Fong-Fu; Lodhi, Irfan J; Turk, John et al. (2014) Structural distinction of diacyl-, alkylacyl, and alk-1-enylacyl glycerophosphocholines as [M - 15]? ions by multiple-stage linear ion-trap mass spectrometry with electrospray ionization. J Am Soc Mass Spectrom 25:1412-20