The Role of Relaxin Signaling in Adipose Tissue Fibrosis and Function

Metabolic disorders, such as obesity, are associated with adipose tissue hypoxia, inflammation and fibrosis, and impaired lipid uptake, causing ectopic lipid uptake other organs, such as the liver. Furthermore, the secreted adipokine profile changes dramatically, with impaired secretion of antifibrotic factors (e.g. adiponectin), and

elevated release of profibrotic adipokines (e.g. endotrophin, leptin). This alteration in the secretome negatively affects other organs, elevating the risk of metabolic diseases such as diabetes. Therefore, adipose tissue dysfunction is a crucial element in the development and progression of metabolic disease.

Our previous work, focused on the antifibrotic role of the hormone relaxin, established that relaxin, through its receptor RXFP1, reduced established hepatic fibrosis in mice. We discovered that one mechanism for relaxin’s actions is through selective activation of peroxisome proliferator-activated receptor γ (PPARγ). RXFP1-knockout

mice develop age-related fibrosis in many tissues, but no studies had been conducted in adipose tissue. Our recent experiments revealed that RXFP1-knockout mice developed age-related fibrosis in the visceral, subcutaneous and brown adipose tissue, and have increased inflammation and decreased serum adiponectin

levels. Furthermore, we have established for the first time that RXFP1 is expressed by the adipose tissue macrophages. Nothing is known about the mechanisms by which relaxin protects against adipose tissue fibrosis or the impairments in function, or in alterations in adipose tissue secretion. Given the importance of adipose

tissue functioning in the maintenance of metabolism, and the importance of its secretome in affecting other organs, targeting the relaxin pathway represents a novel approach to treating metabolic disease characterized by adipose tissue dysfunction. Our long-term goal is to uncover biochemical mechanisms underlying metabolic disease in order to develop

effective treatments. Our central hypothesis for this proposal is that relaxin regulates both adipose tissue and liver function and thereby promotes normal functioning. This hypothesis is based on the new finding that relaxin plays a role in adipose fibrosis and function, and our previous findings implicating relaxin in liver fibrosis and

regeneration. The rationale for the proposed studies is that understanding the mechanisms for relaxin’s effects in these tissues will lead to development of specific targets for treatment. Our experience in endocrinology and liver disease models, and nanoparticle development, will provide a conducive research environment to

successful completion of the proposed studies. We propose three Specific Aims: 1. Identify the mechanisms for the antifibrotic effects of relaxin in adipose tissue. 2. Determine the effect of the relaxin pathway on the adipose tissue secretome and interorgan signaling to the liver. 3. Develop relaxin receptor-targeting nanoparticles on adipose tissue fibrosis in vivo.

In Aim 1, we will utilize conditional RXFP1 knockout mice with conjugated linoleic or diet-induced obesity models to determine the roles of RXFP1 in different adipose tissue cells and their signaling pathways. In Aim 2, we will conduct proteomics studies to distinguish between secreted factors from conditional RXFP1 knockout

mice. In Aim 3, we will develop adipose tissue-targeting nanoparticles to deliver relaxin and selective PPARγ agonists for treatment of adipose tissue dysfunction. Successful completion of these Aims will provide critical insights into the mechanisms regulating adipose tissue fibrosis and function, and will test a new avenue for

treatment. This would provide the potential to combat the current increase in obesity-related diseases and comorbidities, which is a major issue not only in the population at-large, but particularly in the veteran population.