Altered regulation of adipogenesis with respect to disease processes

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Davies, Stephanie Jane
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University College Cork
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Dysregulation of adipose tissue metabolism is associated with multiple metabolic disorders. One such disease, known as Dunnigan-type familial partial lipodystrophy (FPLD2) is characterised by defective fat metabolism and storage. FPLD2 is caused by a specific subset of mutations in the LMNA gene. The mechanisms by which LMNA mutations lead to the adipose specific FPLD2 phenotype have yet to be determined. Previous work employed RNA-Seq analysis to assess the effects of wild-type (WT) and mutant (R482W) LMNA on the expression profile of differentiating 3T3-L1 mouse preadipocytes and identified over 200 transcripts whose expression was altered. Four of these genes namely ITM2A, IGFBP5, PTPRQ and WNT6 were selected for detailed investigation using the 3T3-L1 in-vitro adipogenesis model. Preliminary investigations carried out identified a complex endogenous IGFBP5 expression profile in 3T3-L1 differentiation, with IGFBP5 over-expression and knockdown leading to inhibited and enhanced differentiation, respectively. Investigation into the effects of LMNA over-expression on IGFBP5 yielded conflicting results and further analysis is required to elucidate the mechanisms regulating IGFBP5 expression in adipogenesis. In this thesis ITM2A is identified as a novel modulator of adipogenesis and results show that endogenous ITM2A expression is transiently down-regulated during induction of 3T3-L1 differentiation. ITM2A over-expression was seen to moderately inhibit differentiation of 3T3-L1 preadipocytes while shRNA mediated knockdown of ITM2A significantly enhanced 3T3-L1 differentiation. Investigation of PPARγ levels indicate that this enhanced adipogenesis is mediated through the stabilization of the PPARγ protein at specific time points during differentiation. The results demonstrate that ITM2A knockdown is sufficient to rescue the inhibitory effects of LMNA WT and R482W mutant over-expression on 3T3-L1 differentiation and indicate a novel therapeutic approach for FPLD2.
Adipogenesis , Lipodystrophy , FPLD2
Davies, S. J. 2017. Altered regulation of adipogenesis with respect to disease processes. PhD Thesis, University College Cork.