ABC | Volume 115, Nº1, July 2020

Original Article Decreased Collagen Type I is Associated with Increased Metalloproteinase-2 Activity and Protein Expression of Leptin in the Myocardium of Obese Rats Danielle Cristina Tomaz da Silva-Bertani, 1 D anielle Fernandes Vileigas, 1 Gustavo Augusto Ferreira Mota, 1 Sérgio Luiz Borges de Souza, 1 Loreta Casquel De Tomasi, 1 Dijon Henrique Salomé de Campos, 1 Adriana Fernandes de Deus, 1 Paula Paccielli Freire, 2 C arlos Augusto Barnabe Alves, 2 Carlos Roberto Padovani, 2 Antonio Carlos Cicogna 1 Faculdade de Medicina de Botucatu - Universidade Estadual Paulista (UNESP), 1 Botucatu, SP - Brazil Instituto de Biociências - Universidade Estadual Paulista (UNESP), 2 Botucatu, SP - Brazil Mailing Address: Antonio Carlos Cicogna • Faculdade de Medicina de Botucatu, Universidade Estadual de São Paulo (UNESP) - Avenue Prof. Mário Rubens Guimarães Montenegro, s/n. Postal Code 18618687, Botucatu, SP – Brazil E-mail: ac.cicogna@unesp.br Manuscript received August 13, 2018, revised manuscript June 27, 2019, accepted July 17, 2019 DOI: https://doi.org/10.36660/abc.20180143 Abstract Background: Obesity is a risk factor for medical complications, including the cardiovascular system. There is limited information on collagen in the heart in obesity. Our previous study showed decreased protein levels of myocardial collagen type I in obese rats fed a high-fat diet for 34 weeks. However, the mechanisms responsible for low levels are not fully elucidated. Objective: The purpose of this study was to test the hypothesis that the reduction in collagen type I is associated with increased metalloproteinase-2 (MMP-2) activity, which is linked to elevated leptin in the myocardium of obese rats. Methods: Thirty-day-old male Wistar rats were randomized into two groups, control (standard diet) and obese (high-fat diet), and fed for 34 weeks. The general animal characteristics and metabolic and endocrine profiles were evaluated. Myocardial protein expressions of collagen I, leptin, tissue inhibitors of metalloproteinases (TIMP), and MMP-2 activity were assessed. Pearson correlation was employed to determine the associations between variables. The level of significance was 5%. Results: The obese animals had increased adiposity index compared to control. Comorbidities such as glucose intolerance, hyperinsulinemia, insulin resistance, hyperleptinemia, and hypertension were observed in obese rats. Obesity reduced collagen I, TIMP-1, and TIMP-2, and it increased leptin and MMP-2 in the myocardium. There was a negative correlation between collagen I and MMP-2 and a positive correlation between leptin and MMP-2. Conclusion: The hypothesis was confirmed; the reduction in collagen type I is associated with increased MMP-2 activity and leptin expression in the myocardium of obese rats. (Arq Bras Cardiol. 2020; 115(1):61-70) Keywords: Cardiovascular Diseases/physiopathology; Obesity; Collagen Type 1; Rats; Leptin; Adiposity; Tissue Inhibitor of Metalloproteinases; Metaloproteinase-2. Introduction Obesity is a chronic metabolic disorder characterized by excessive accumulation of adipose tissue. The prevalence of obesity has increased worldwide, representing a major public health problem that affects both developed and developing countries. 1,2 The adipocytes are influenced by several substances, and they secrete numerous peptides that act directly or indirectly on the cardiovascular system. Therefore, adipose tissue is not simply an energy deposit, but also an active endocrine, paracrine and autocrine organ with multiple functions, including the ability to synthesize and release mediators, like leptin, that participate in multiple biological processes, including those that occur in the heart. 3 The heart is composed of myocytes, nerves, vessels, and the extracellular matrix (ECM). The main component of the ECM is collagen, predominantly type I and III, with type I being the most abundant, corresponding to approximately 80% of total myocardial collagen. 4 This protein is produced by fibroblasts and degraded by the family of matrix metalloproteinases (MMP). 5 In a stable condition, it contributes to the maintenance of cardiac architecture and function. 6 Several mechanisms act to ensure that the components of matrix degradation by MMP are precisely controlled, including tissue inhibitors of metalloproteinases (TIMP). 7 Cardiac collagen changes in response to neuro-hormonal and mechanical stimuli, 6,8 due to elevated synthesis and decreased degradation or vice versa. Several studies have analyzed the expression of collagen type I in different tissues in experimental models of obesity. 9-11 There is limited information on the behavior of this type of collagen in the heart in obese animals. Although Carroll et al. 12 have shown elevated myocardial collagen type I in obese 61