Small fragments of hyaluronan are increased in individuals with obesity and contribute to low-grade inflammation through TLR-mediated activation of innate immune cells

• Published in: International Journal of Obesity 2022-11, Vol.46 (11), p.1960-1969
• Main Authors: Romo, Mònica, López-Vicario, Cristina, Pérez-Romero, Noelia, Casulleras, Mireia, Martínez-Puchol, Ana Isabel, Sánchez, Belén, Flores-Costa, Roger, Alcaraz-Quiles, José, Duran-Güell, Marta, Ibarzábal, Ainitze, Espert, Juan José, Clària, Joan, Titos, Esther
• Format: Article
• Language: English
• Subjects: 13; 13/21; 38/39; 38/77; 631/443/319/1642/393; 692/699/2743/393; 82/80; 96/95; Adipose tissue; Body fat; Body mass index; Body size; Cell activation; Cytokines; Damage patterns; Enzyme-linked immunosorbent assay; Epidemiology; Extracellular matrix; Fluorescence; Fragments; Gene expression; Health Promotion and Disease Prevention; Hyaluronan synthase; Hyaluronic acid; Immune system; Immunoassay; Inflammation; Interleukin 8; Internal Medicine; Ion exchange; Ion-exchange chromatography; Leukocytes; Leukocytes (neutrophilic); Low molecular weights; Medicine; Medicine & Public Health; Metabolic Diseases; Molecular weight; Monocyte chemoattractant protein 1; Monocytes; NF-κB protein; Obesity; Peripheral blood mononuclear cells; Phosphorylation; Plasma levels; Proteins; Public Health; Statistical analysis; Toll-like receptors
• ISSN: 0307-0565; 1476-5497
• DOI: 10.1038/s41366-022-01187-z

Background and aim Extracellular matrix (ECM) components released during excessive fat mass expansion are considered potential endogenous danger/alarm signals contributing to innate immune system activation. The aim of the current study was to specifically measure plasma levels of low molecular weight (LMW) hyaluronan (HA) and to evaluate its role as pro-inflammatory damage-associated molecular pattern (DAMP) on leukocyte response in the context of human obesity. Subjects and methods Participants were selected according to their body mass index (BMI, kg/m 2 ) as non-obese (BMI  29.9, n  = 33). Plasma samples were size-dependent fractionated using ion-exchange chromatography to specifically obtain LMW HA fractions that were subsequently quantified by ELISA. Cell incubation experiments with synthetic HA molecules were performed on freshly Ficoll-isolated neutrophils (PMN) and peripheral blood monocytes (PBMC). Leukocyte and adipose tissue gene expression was assessed by real-time PCR and NF-κB activation by western blot. Plasma cytokine levels were measured by fluorescent bead-based (Luminex) immunoassay. Results We observed a statistically significant increase in the circulating levels of HA fragments of LMW in individuals with obesity which were consistent with significant up-regulated expression of the LMW HA synthesizing enzyme hyaluronan synthase-1 (HAS-1) in obese adipose tissue. Gene expression assessment of HA receptors revealed up-regulated levels for TLR2 in both obese PMN and PBMC. Synthetic HA molecules of different sizes were tested on leukocytes from healthy donors. LMW HA fragments (15–40 kDa) and not those from intermediate molecular sizes (75–350 kDa) induced a significant up-regulation of the expression of major pro-inflammatory cytokines such as IL-1β, MCP-1 and IL-8 in PBMC. Importantly, LMW HA was able to induce the phosphorylation of IKK α/β complex supporting its pro-inflammatory role through NF-κB activation. Conclusion Circulating LMW HA molecules are elevated in obesity and may play an important role in triggering low-grade inflammation and the development of metabolic complications.