Leptin

The adipose-derived hormone leptin is known for its ability in controlling energy homeostasis in the body (Lu, 2007). However, newer studies have presented a novel role for leptin in the regulation of mood and emotion. Anxiety and depression are usual in diabetic patients. Diabetes can cause decreased leptin levels in the blood (Ates et al., 2014). Low leptin levels are correlated with depressive behaviors as leptin has antidepressant-like qualities (Lu, 2007). Several studies have suggested mood and cognition are controlled through synaptic changes in the brain because of these aforementioned antidepressant-like actions of leptin (Ge et al., 2018). A 2018 review summarized the role of leptin in neural plasticity as a possible explanation of its antidepressant-like effects (Ge et al., 2018). 

A 2014 study investigated the relationship between diabetes induced anxiety- and depression-like behavior (Ates et al., 2014). How altered leptin and leptin receptor expression levels affected these behaviors in diabetic rats (Ates et al., 2014). Diabetic rats showed increased anxiety-like and depression-like behavior in the study as measured by prefrontal cortex (PFC), blood leptin levels and PFC neuron numbers. They all decreased, and leptin receptor expression and apoptosis were increased (Ates et al., 2014). These results show a decrease of leptin increases leptin receptor expression and can affect PFC neurons, which consequently triggers anxiety- and depression-like behaviors (Ates et al., 2014).

Further, both leptin insufficiency and resistance contribute to alterations of mood. Ghrelin opposes leptin’s effects on appetite and these appetite regulating hormones may have an opposing relationship on mood and stress, as well (Lawson et al., 2012). In fact, a number of studies found that these hormones were connected with different kinds of mood disorders (Zarouna, Wozniak, & Papachristou, 2015). A cross-sectional study suggests leptin could work to help control depressive symptoms (Lawson et al., 2012). 

If leptin could influence neural mechanisms it could consequently be a possible target for new therapeutic approaches to treating anxiety & depression (Ge et al., 2018). This novel role of hormones thought to only control hunger and satiety stands to change the medical view of those associated disorders. The body does not waste its actions and having a hormone that is dual-purposed saves both time and energy. Mother nature is often far cleverer than we give her credit for. 

References

Ates, M., Dayi, A., Kiray, M., Sisman, A. R., Agilkaya, S., Aksu, I., Baykara, B., Buyuk, E., Cetinkaya, C., Cingoz, S., & Uysal, N. (2014). Anxiety- and depression-like behavior are correlated with leptin and leptin receptor expression in prefrontal cortex of streptozotocin-induced diabetic rats. Biotechnic & Histochemistry: Official Publication of the Biological Stain Commission, 89(3), 161–171. https://doi.org/10.3109/10520295.2013.825319

Ge, T., Fan, J., Yang, W., Cui, R., & Li, B. (2018). Leptin in depression: A potential therapeutic target. Cell Death & Disease, 9(11). https://doi.org/10.1038/s41419-018-1129-1

Lawson, E. A., Miller, K. K., Blum, J. I., Meenaghan, E., Misra, M., Eddy, K. T., Herzog, D. B., & Klibanski, A. (2012). Leptin Levels Are Associated With Decreased Depressive Symptoms in Women Across the Weight Spectrum, Independent of Body Fat. Clinical Endocrinology, 76(4), 520–525. https://doi.org/10.1111/j.1365-2265.2011.04182.x

Lu, X.-Y. (2007). The leptin hypothesis of depression: A potential link between mood disorders and obesity? Current Opinion in Pharmacology, 7(6), 648–652. https://doi.org/10.1016/j.coph.2007.10.010

Zarouna, S., Wozniak, G., & Papachristou, A. I. (2015). Mood disorders: A potential link between ghrelin and leptin on human body? World Journal of Experimental Medicine, 5(2), 103–109. https://doi.org/10.5493/wjem.v5.i2.103