¹Hoshi Univ., Pharmacol., Tokyo, Japan, ²Natl. Cancer Ctr. Res. Inst., Cancer Pathophysiol., Tokyo, Japan, ³Natl. Cancer Ctr. Hosp., Pharm., Tokyo, Japan, ⁴Japan Small Animal Medical Center, ICU, Saitama, Japan

Background: Cancer cachexia causes weight loss, loss of appetite, muscle weakness, systemic inflammation, and mental disorders such as depression and anxiety, leading to treatment resistance and a decline in quality of life. On the other hand, it has been reported that glial cells in the brain, together with neurons, contribute to the maintenance of brain function, and that dysfunction of these cells may induce the development of psychiatric symptoms.

Aims & Objectives: In this study, we analyzed timeline changes in hypothalamic microglia during the formation process of cancer cachexia.

Method: We created a mouse model of cachexia by peritoneal dissemination of pancreatic cancer cells (Pan02 cells) and investigated the timeline changes in the expression of several inflammatory mediators and immune checkpoint molecules in hypothalamic microglia 1 week (pre-cachexia stage) and 3 weeks (cachexia stage) later. To characterize microglia in the brain, we isolated CD11b-positive microglia from the hypothalamus of a mouse model of peritoneal dissemination using auto magnetic-activated cell sorting (MACS).

Results: We found a high-level expression of tumor necrosis factor-α (TNFα), interleukin (IL)-1β and IL-6 in hypothalamic CD11b-positive microglia at the pre-cachexia and cachexia stages. On the other hand, an analysis of changes in immune checkpoint receptors over time showed significant decreases in the expression of immune checkpoint receptors programmed death receptor-1 (PD-1) and CD112R, another immune checkpoint receptors, in hypothalamic microglia at the cachexia stage, but not at the pre-cachexia stage. Furthermore, a significant increase in the expression of lipocalin 2 (LCN2), an activator of the hypothalamic-pituitary-adrenal (HPA) axis and a stress-related inflammatory secreted protein, was similarly observed in hypothalamic microglia at the cachexia stage, whereas no change in the mRNA expression of PD-1 and CD112R was found at the pre-cachexia stage. In addition, c-Fos expression in the paraventricular nucleus (PVN) was observed after LCN2 was administered either intracerebroventricularly or into the PVN of the hypothalamus. Furthermore, we found that the cachexia state in tumor-bearing mice were partially improved by suppressing the HPA axis.

Discussion & Conclusions: The results of this study suggest that the breakdown of the inflammatory suppression mechanism in hypothalamic microglia during the progression of cancer pathology further may promote stress-related inflammation in the brain, leading to cachexia-like systemic symptoms accompanied by immune fluctuation.