Macrophage ubiquitin-specific protease 2 modifies insulin sensitivity in obese mice

Abstract

We previously reported that ubiquitin-specific protease (USP) 2 in macrophages down-regulates genes associated with metabolic diseases, suggesting a putative anti-diabetic role for USP2 in macrophages. In this study, we evaluate this role at both cellular and individual levels. Isolated macrophages forcibly expressing Usp2a, a longer splicing variant of USP2, failed to modulate the insulin sensitivity of 3T3-L1 adipocytes. Similarly, macrophage-selective overexpression of Usp2a in mice (Usp2a transgenic mice) had a negligible effect on insulin sensitivity relative to wild type littermates following a three-month high-fat diet. However, Usp2a transgenic mice exhibited fewer M1 macrophages in their mesenteric adipose tissue. Following a six-month high-fat diet, Usp2a transgenic mice exhibited a retarded progression of insulin resistance in their skeletal muscle and liver, and an improvement in insulin sensitivity at an individual level. Although conditioned media from Usp2a-overexpressing macrophages did not directly affect the insulin sensitivity of C2C12 myotubes compared to media from control macrophages, they did increase the insulin sensitivity of C2C12 cells after subsequent conditioning with 3T3-L1 cells. These results indicate that macrophage USP2A hampers obesity-elicited insulin resistance via an adipocyte-dependent mechanism.

Ubiquitin-Specific Protease 2 Modulates the Lipopolysaccharide-Elicited Expression of Proinflammatory Cytokines in Macrophage-like HL-60 Cells

“…To further evaluate the anti-inflammatory properties of USP2A in macrophages, we employed a different macrophage model. We measured cytokine gene expression in macrophages isolated from Tg mice ectopically expressing Usp2a under the control of the FIRE promoter [ 24 , 29 ]. After treatment with LPS (5 μ g/mL) for 4 h, we measured the expression levels of cytokine transcripts in macrophages isolated from Usp2a Tg mice, as well as in littermate control mice.…”

“…In our previous study, Usp2a Tg mice exhibited minimal accumulation of USP2A proteins in their macrophages, although their Usp2a transcript levels had increased dramatically [ 29 ]. Small increases in USP2A protein levels may result in relatively weak expressional changes in metabolic disorder-associated genes in adipose tissue macrophages, followed by gradual changes in insulin sensitivity [ 24 ]. This implies that certain posttranscriptional or posttranslational mechanisms work to keep intracellular USP2 pools at a constant level in isolated macrophages.…”

“…USP2 participates in various cellular events, including circadian rhythm modulation [ 22 ], carcinogenesis [ 23 ], prevention of insulin resistance [ 24 ], and spermatogenesis [ 25 ]. USP2 encodes two splice variants in humans and mice: the longer splice variant USP2A (approximately 69 kDa) and the shorter USP2B (approximately 45 kDa) [ 26 ].…”

Inhibition of ubiquitin‐specific protease 2 causes accumulation of reactive oxygen species, mitochondria dysfunction, and intracellular ATP decrement in C2C12 myoblasts

“…Western blotting analysis was performed as previously described (Saito et al, ). Briefly, total cellular protein was extracted with RIPA buffer (50 mmol/L Tris‐HCl [pH 7.6], 150 mmol/L sodium chloride, 1% Nonidet P‐40, 0.5% sodium deoxycholate, 0.1% SDS, 1 mmol/L EDTA, protease inhibitor cocktail [Roche Life Science, Basel, Switzerland]).…”

“…USP2, a member of the USP family, is widely expressed in organs, with relatively higher expression levels reported in the testis and skeletal muscle (Gousseva and Baker, 2003;Kitamura et al, 2013). It has diverse functions in a wide variety of cells, such as pro-and antiapoptotic effects in cancerous cells (Gewies and Grimm, 2003;Priolo et al, 2006), regulatory roles in cytokine production in macrophages (Zhang et al, 2014;Sun et al, 2016;Kitamura et al, 2017), and modulation of glucose and lipid metabolism (Molusky et al, 2012;Kitamura et al, 2013;Nelson et al, 2016;Saito et al, 2017). In a previous study, dominant negative forms of USP2 were found to interrupt the differentiation of L6 myoblasts into myofibers indicating the involvement of USP2 in myocyte differentiation (Park et al, 2002).…”