Hypothalamic microglia morphology is altered after myocardial infarction in mice; effects of TNF-alpha interference
L. Gouweleeuw1, U.L.M. Eisel1, H. Wajant2, O. Maier3, R.G. Schoemaker1,4
1Department of Neurobiology, GELIFES, University of Groningen, The Netherlands; 2Division of Molecular Internal Medicine, Department of Internal Medicine II, University of Wurzburg; 3Institute of Cell Biology and Immunology, University of Stuttgart, Germany; 4Department of Cardiology, University medical center Groningen, The Netherlands
Background: Repair mechanisms after myocardial infarction (MI) include an inflammatory response that is not restricted to the heart, and may even present itself in the brain as neuroinflammation. Accordingly, in the paraventricular nucleus of the hypothalamus (PVN), increased expression of TNF-alpha has been reported. We investigated whether neuroinflammation after MI, by means of altered microglia morphology, could be affected by interference with TNF-alpha signaling.
Methods: Twelve weeks old male 12-week old c57bl/6 mice were subjected to MI or sham surgery. Subsequently, MI mice were treated with either saline; Etanercept; a TNF-R1 antagonist; or a TNF-R2 agonist. Sham mice received saline injections. Mice were sacrificed 18 days after surgery. The PVN was stained with an anti-Iba1 antibody to visualize microglia. Changes in microglia morphology were obtained from total cell size, cell body area and process area. Sholl analysis provided more detailed information about the processes.
Results: In the PVN, microglia increased in size after MI (MI 4293±163 versus saline 3105±261pixels). All TNF-alpha interference significant increased microglia cell size compared to sham, with most pronounced effect of the TNF-R2 agonist (5583±377 pixels). Effects could be completely attributed to increased process areas as cell body areas did not change. Sholl analysis of microglia of sham and MI mice overlapped, suggesting mainly process thickening, whereas all TNF-alpha intervention groups appeared significantly higher than sham as well as saline MI, indicative for more and/or longer processes.
Conclusion: In conclusion, interference with TNF-alpha signaling in mice propagate changes in hypothalamic microglia morphology after MI. Increased process area suggest alternative activation of microglia in the PVN, while thickening/prolongation of processes may represent different inflammatory states.