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TNF, but not hyperinsulinemia or hyperglycemia, is a key driver of obesity-induced monocytosis revealing that inflammatory monocytes correlate with insulin in obese male mice.

Authors
  • Breznik, Jessica A1, 2, 3
  • Naidoo, Avee1, 2, 3
  • Foley, Kevin P4, 5
  • Schulz, Christian1, 2, 3
  • Lau, Trevor C4, 5
  • Loukov, Dessi1, 2, 3
  • Sloboda, Deborah M4, 5, 6
  • Bowdish, Dawn M E1, 2, 3
  • Schertzer, Jonathan D4, 5
  • 1 Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Canada. , (Canada)
  • 2 McMaster Immunology Research Centre, McMaster University, Hamilton, Canada. , (Canada)
  • 3 Michael G. DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Canada. , (Canada)
  • 4 Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Canada. , (Canada)
  • 5 Farncombe Family Digestive Health Research Institute, McMaster University, Hamilton, Canada. , (Canada)
  • 6 Department of Obstetrics and Gynecology and Pediatrics, McMaster University, Hamilton, Canada. , (Canada)
Type
Published Article
Journal
Physiological Reports
Publisher
Wiley (Physiological Reports)
Publication Date
Dec 01, 2018
Volume
6
Issue
23
Identifiers
DOI: 10.14814/phy2.13937
PMID: 30548217
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Inflammation contributes to obesity-related hyperinsulinemia and insulin resistance, which often precede type 2 diabetes. Inflammation is one way that obesity can promote insulin resistance. It is not clear if the extent of obesity, hyperinsulinemia, or hyperglycemia, underpins changes in cellular immunity during diet-induced obesity. In particular, the requirement for obesity or directionality in the relationship between insulin resistance and monocyte characteristics is poorly defined. Inflammatory cytokines such as tumor necrosis factor (TNF) can contribute to insulin resistance. It is unclear if TNF alters monocytosis or specific markers of cellular immunity in the context of obesity. We measured bone marrow and blood monocyte characteristics in WT and TNF-/- mice that were fed obesogenic, high fat (HF) diets. We also used hyperglycemic Akita mice and mice implanted with insulin pellets in order to determine if glucose or insulin were sufficient to alter monocyte characteristics. We found that diet-induced obesity in male mice increased the total number of monocytes in blood, but not in bone marrow. Immature, inflammatory (Ly6Chigh ) monocytes decreased within the bone marrow and increased within peripheral blood of HF-fed mice. We found that neither hyperinsulinemia nor hyperglycemia was sufficient to induce the observed changes in circulating monocytes in the absence of diet-induced obesity. In obese HF-fed mice, antibiotic treatment lowered insulin and insulin resistance, but did not alter circulating monocyte characteristics. Fewer Ly6Chigh monocytes were present within the blood of HF-fed TNF-/- mice in comparison to HF-fed wild-type (WT) mice. The prevalence of immature Ly6Chigh monocytes in the blood correlated with serum insulin and insulin resistance irrespective of the magnitude of adipocyte or adipose tissue hypertrophy in obese mice. These data suggest that diet-induced obesity instigates a TNF-dependent increase in circulating inflammatory monocytes, which predicts increased blood insulin and insulin resistance independently from markers of adiposity or adipose tissue expansion. © 2018 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

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