Depression and anxiety are common neuropsychiatric disorders in modern society, causing severe social problems , . Finding methods to prevent the occurrence of these disorders may be of great clinical importance. There are numerous reports that under stressful conditions, abnormally elevated proinflammatory cytokines in the brain mediate the pathogenesis of behavioral disorders such as depression and anxiety , , and accordingly, suppression of neuroinflammation is considered as a potential strategy to prevent psychological disorders , . In recent studies, we had reported that pretreatment of mice with a low dose of an innate immune system stimulant, such as lipopolysaccharide (LPS), macrophage-colony stimulating factor (M−CSF), and monophosphoryl lipid A (MPL), may prevent the development of depression- or anxiety-like behaviors, associated with a marked attenuation of neuroinflammatory responses , , , suggesting that drugs that stimulate the innate immune response could be used to prevent psychological disorders.
Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a clinically available drug that can cross the blood–brain barrier  and shows neuroprotective effects in a number of central nervous system disorders, such as Parkinson’s disease , , traumatic or spinal brain injury , , , , cerebral ischemia , and Alzheimer’s disease , , . For example, in mouse models of Parkinson’s disease induced by paraquat plus lipopolysaccharide or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), central or systemic administration of GM-CSF has been shown to prevent the loss of dopaminergic neurons in the substantia nigra pars compacta , . Administration of GM-CSF can also provide neuroprotection in a mouse model of traumatic brain injury induced by controlled cortical impact or lateral fluid percussion , . In animal models of spinal cord injury, a single administration of GM-CSF or daily administration of GM-CSF for 5 consecutive days was found to suppress neuronal apoptosis and promote behavioral recovery in the Basso-Beattie-Bresnahan (BBB) locomotor test in the injured spinal cord , . In a rat model of middle cerebral artery occlusion/reperfusion or combined common carotid/distal middle cerebral artery occlusion, intracarotid or intravenous injection of GM-CSF was reported to reduce infarct volume and improve neurological function , and in a mouse model of Alzheimer’s disease, treatment with GM-CSF was found to improve brain amyloidosis and cognitive impairment , . In addition, in a randomized, double-blind, and placebo-controlled trial involving Alzheimer’s disease, researchers found that treatment with GM-CSF can lower plasma markers of neurodegeneration, including total tau and ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) . However, to date, the neuroprotective effect of GM-CSF in the pathogenesis of neuropsychiatric disorders remains unclear.
Since the GM-CSF can stimulate the innate immune cells , , , we hypothesize that pretreatment with GM-CSF before stress exposure may have a prophylactic effect on chronic stress-induced behavioral abnormalities in animals. As expected, our results showed that stimulation of the innate immune system by a single low dose of GM-CSF pre-injection one day before stress exposure prevented depression- and anxiety-like behaviors and neuroinflammatory responses in the brain of mice caused by chronic social defeat stress (CSDS), suggesting that GM-CSF could be a potential drug to prevent behavioral abnormalities induced by chronic stress in mice.
All animal experiments were approved by the Animal Ethics Committee of Nantong University (approval number: 2110836) and were conducted in accordance with the internationally accepted guidelines for the use of animals in toxicology as adopted by the Society of Toxicology in 1999. The six-week-old C57BL6/J mice and the eight-week-old male and female CD1 mice were obtained from Beijing Vital River Laboratory Animal Technology Co., Ltd. (Beijing, China). The CD1 mice have been widely used to
GM-CSF preconditioning prevents CSDS-induced depression-like behaviors in mice
First, we examined the effect of a single GM-CSF pre-injection at a low dose (100μg/kg) on CSDS-induced depression-like behaviors in mice (Fig. 1A). In the SIT, a two-way ANOVA for the time spent in the interaction zone in the absence of the target showed no significant effects for stress exposure (F1,36=0.16, p=0.69), GM-CSF pre-injection (F1,36=0.0006, p=0.98), and the stress×GM-CSF interaction (F1,36=0.17, p=0.68) (Fig. 1B), whereas two-way ANOVA showed significant effects for
Depression is a public psychological problem that represents a severe economic and social burden in modern society , . The development of new strategies that can reduce the morbidity of depression is of great importance for improving people’s mental health. One of the major findings of the present study was that a single GM-CSF pre-injection one day before stress exposure prevented CSDS-induced depression- and anxiety-like behaviors in mice in the SIT, TST, FST, LDT, EMP test, and OFT.
Our results demonstrate a prophylactic effect of GM-CSF pre-injection on CSDS-induced depression- and anxiety-like behaviors by triggering innate immune activation and preventing the progression of neuroinflammatory responses. These findings may help to develop new strategies to prevent chronic stress-related behavioral disorders. It is noteworthy that in the present study we did not investigate the prophylactic effect of GM-CSF on the behavioral abnormalities induced by CSDS in female mice.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
This work was supported by the Natural Science Foundation of China (81974216), the Science and Technology Project of Nantong City (JC2020020), the Six Talent Peaks Project in Jiangsu Province (SWYY-071), and the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province (20KJB310025).
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