The results obtained in this project highlight the potential of α-MSH as a future obesity therapy by inducing WAT browning, improving the inflammatory, fibrotic and oxidative profile and by changing cell response mechanisms like ER stress and autophagy.
Specifically:
The effect of intraperitoneal administration alpha-MSH was determined in inguinal subcutaneous (ingWAT), mesenteric (mWAT), epididymal (eWAT) and retroperitoneal (rpWAT) adipose tissue of diet-induced obese (DIO) and standard diet (SD)-fed mice. In DIO mice, alpha-MSH decreases mice body weight, without affecting food intake, and the ingWAT and mWAT mass, promoting a significant rise in the number of smaller adipocytes. Additionally, it was observed an increase in the mass of brown adipose tissue and an improvement on serum lipid profile, insulin resistance and glucose homeostasis. However, SD-fed mice responded differently to alpha-MSH since they did not lose weight and did not change neither the glycaemia nor the plasmatic adiponectin or leptin.
Regarding WAT browning, in ingWAT of DIO mice alpha-MSH increases mRNA expression of browning hallmark genes and mitochondrial respiratory rate. In contradiction, in mWAT, eWAT and rpWAT from HFD-fed mice, alpha-MSH was not able to induce browning. In SD-fed mice, alpha-MSH does not have a browning effect on eWAT and mWAT. However, in rpWAT, alpha-MSH decreased the expression of almost browning markers. Accordingly, the size of larger lipid droplets in rpWAT was increased by alpha-MSH. To have a comprehensive perception of the diet effect on WAT browning, the expression of browning hallmark genes was compared between SD and HFD-fed groups. rpWAT presented a global stimulation of browning-related gene expression when animals were exposed to HFD. Accordingly, in rpWAT islets of multilocular fat cells, indicative of the beige adipocytes, were easily identified.
Treatment with alpha-MSH was able to differentially modulate the expression profile of inflammatory cytokines in SD-fed and DIO animals. Overall, it enhanced TGFb expression in lean mice and increased IL-10 levels in DIO mice. The expression of Marco was significantly decreased and expression of galectin-3, an indicator of macrophage-rich areas, was found augmented only in DIO mice treated with alpha-MSH. Expression of Col6a3 and Mmp3 genes, both related to fibrosis, were significantly reduced with alpha-MSH treatment.
Regarding ER stress response, both PERK expression and spliced Xbp1 levels increased in ingWAT of DIO mice but dropped significantly after treatment with alpha-MSH. Concerning autophagy/lipophagy mechanisms, the melanocortin negatively regulated the expression of lamp-2, p62 and Lpl, but only in DIO mice. So, in ingWAT from HFD-fed mice, fibrosis, oxidative stress, ER stress and autophagy/lipophagy are affected by α-MSH treatment, which translates in a decreased level of carbonylated proteins and oxidized lipids.
These results were compiled into 3 publications:
1-Salazar, M.J., Rodrigues, A.R., Sousa, M., Magalhães J, Neves D, Almeida, H., Gouveia, A.M. (2021) Characterization of α-msh browning effect in diverse mice white adipose tissue depots. Journal of Molecular Endocrinology, 66(1), pp. 23-34
2-Rodrigues AR, Salazar MJ, Rocha-Rodrigues S, Gonçalves IO, Cruz C, Neves D, Almeida H, Magalhães J, Gouveia AM (2019) Peripherally administered melanocortins induce mice fat browning and prevent obesity. Int J Obes (Lond). 43(5):1058-1069
3-Adriana R. Rodrigues, Maria J. Salazar, Alexandra M. Gouveia (2020) Obesity and adipose tissue remodelling in "Recent Advances in Obesity Research: Understanding Obesity - From its Causes to Impact on Life", Bentham publishers- Vol. 1, 55-80
They were also included into 5 congress abstracts, published in national and international journals. They were presented by 12 oral communications (3 were selected as the best oral communication) and by 5 posters in national and international meetings. We organized one Symposium entitled "Plasticity of adipose tissue in obesity" presented in 21º Congresso Português de Obesidade Aveiro, November 24-26 (2017). Salazar MJ, the project fellowship, was selected for funding to participate in EASO New Investigators United Autumn School 2018, Palma Mallorca, Spain. One Master thesis was concluded intitled "Adipose tissue dysfunction in obesity: modulation of cellular stress responses by melanocortins". |
