Identification of PPAR gamma phosphorylation mechanisms and the relationship with corepressors recruitment

Author(s)

Thaís Helena Tittanegro

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2018-12-10

Examining board members

Ana Carolina Migliorini Figueira; Francisco de Assis Rocha Neves; Leonardo dos Reis Silveira

• Advisor: Ana Carolina Migliorini Figueira

Abstract

Peroxisome proliferator-activated receptor gamma (PPAR'gamma') is the master regulator of adipogenesis and plays an important role in the regulation of glucose homeostasis and lipid metabolism. However, PPAR'gamma' is the target of thiazolidinediones (TZDs), a set of antidiabetic drugs for type 2 Diabetes Mellitus treatment, being associated with many undesirable side effects. TZDs are PPAR'gamma' full agonists and are able to block the phosphorylation at the S273 site of nuclear receptor through the cyclin-dependent kinase 5 (Cdk5). The phosphorylation results in expression deregulation of a large number of genes leading to insulin resistance. Although this modification of PPAR'gamma' does not alter its adipogenic capacity, it is suggested that other mechanisms, such as the differential recruitment of corepressors (among them, the silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) and nuclear receptor corepressor (NCoR)), may alter gene expression in a phospho-dependent manner, inducing anti-diabetic or pro-adipogenic actions. Therefore, in order to clarify the relationship between repression mechanisms and their preferences for receptor interaction domains (IDs) related to PPAR'gamma' phosphorylation, we found that: (i) receptor phosphorylation may be able to reduce its activity; (ii) receptor phosphorylation does not alter corepressors recruitment; (iii) ID2 of SMRT and NCoR is extremely relevant for the interaction with PPAR'gamma'; (iv) ID1 may be involved with phosphorylation and corepressors recruitment; and (v) the presence of Cdk5 may be able to reduce receptor interaction with NCoR, indicating a dynamic system of competition for the S273 site, since recruitment is altered when ID1 is modified. In addition, we evaluated the gene expression profile of PPAR'gamma' targets. Expression of some of these genes is specifically regulated by S273 phosphorylation or is involved in the adipogenesis process. In an attempt to better understand the existence of other aspects that may result in a differentiated expression of these genes, we explored a crosstalk relationship with LXR'alpha'. LXR'alpha' is a PPAR'gamma' partner in conditions of inflammation and metabolic control, which is also phosphorylated at the S196 site. It was observed that four genes as Selenbp1, Gk, Cd36 and Apod showed differential expression when inhibition of LXR'alpha' and PPAR'gamma' phosphorylation occurs. Through this work, it was possible to generate knowledge about the molecular mechanisms of PPAR'gamma' modulation, creating new possibilities of more specific treatments for metabolic diseases (AU)

• FAPESP's process: 16/13480-9 - Identification of the mechanisms of phosphorylation of PPARy and its relations with the recruitment of corepressors
• Grantee: Thaís Helena Tittanegro
• Support Opportunities: Scholarships in Brazil - Master