The effects of neuroinflammation on oxidative stress and key reproductive neuropeptides in zebrafish

Introduction/Aim:
Infertility is a global health issue affecting both the male and female populations. According to the World Health Organization, half of the individuals diagnosed with infertility were associated with men, which accounts for 7% of the male population worldwide. Reproductive function and fertility are regulated by hormones of the hypothalamic-pituitary-gonadal (HPG) axis. Generally, the hypothalamus secretes the key hypothalamic neuropeptides, including GnRH, GnIH, kisspeptin, spexin and phoenixin. Neuroinflammation has been proven to have several repercussions that affect the immune system and may also lead to biochemical and physiological changes. To date, there is yet a distinct link to be made between neuroinflammation and reproductive function. Thus, this study aims to explore the effect of chronic neuroinflammation on the reproductive axis, specifically in the diencephalon, which consists of the hypothalamus, using zebrafish animal model. We hypothesise that neuroinflammation could potentially affect the expression of specific reproductive neuropeptides in the hypothalamus, impacting the reproductive function.

Methods/Results:
We treated the zebrafish (N=32) with different doses of lipopolysaccharide (LPS) through intraperitoneal injection to induce inflammation. Each group (n=8) were treated with either low dose (1 ug/uL), medium dose (5 ug/uL) or high dose (15 ug/uL) of LPS. Real-time PCR was used to detect changes in the mRNA levels of inflammatory markers and reproductive neuropeptides in the hypothalamus in control and treated fish. It was found that chronic systemic inflammation with high dose significantly increased the expression of pro- and anti-inflammatory markers, including TNFβ (p < 0.001), IL-10 (p < 0.0001) and IL-6 (p < 0.05) in the hypothalamus when compared to the control group. However, there was no significant difference in the expression of IL-1β between all treated groups and control. The expression of reproductive neuropeptide GnRH-3 showed a significant increase in expression at low dose (p < 0.0001), however the expression of spexin-2 in the hypothalamus of zebrafish treated with high dose of LPS was significantly higher (p < 0.0001) compared to that of the control group, and those treated with low dose and medium dose.
Conclusions: 
This study establishes the chronic neuroinflammation in zebrafish model following the five days of systemic inflammation. Neuroinflammation shown to affect reproductive neuropeptide GnRH-3 and Spexin-2 at different doses. Thus, this study implies that neuroinflammation has an affect on the regulation of reproductive neuropeptides.