SLC30A10 transporter in the digestive system regulates brain manganese under basal conditions while brain SLC30A10 protects against neurotoxicity

Abstract

The essential metal manganese becomes neurotoxic at elevated levels. Yet, the mechanisms by which brain manganese homeostasis is regulated are unclear. Loss-of-function mutations in SLC30A10, a cell surface-localized manganese efflux transporter in the brain and liver, induce familial manganese neurotoxicity. To elucidate the role of SLC30A10 in regulating brain manganese, we compared the phenotypes of whole-body and tissue-specific Slc30a10 knockout mice. Surprisingly, unlike whole-body knockouts, brain manganese levels were unaltered in pan-neuronal/glial Slc30a10 knockouts under basal physiological conditions. Further, although transport into bile is a major route of manganese excretion, manganese levels in the brain, blood, and liver of liver-specific Slc30a10 knockouts were only minimally elevated, suggesting that another organ compensated for loss-of-function in the liver. Additional assays revealed that SLC30A10 was also expressed in the gastrointestinal tract. In differentiated enterocytes, SLC30A10 localized to the apical/luminal domain and transported intracellular manganese to the lumen. Importantly, endoderm-specific knockouts, lacking SLC30A10 in the liver and gastrointestinal tract, had markedly elevated manganese levels in the brain, blood, and liver. Thus, under basal physiological conditions, brain manganese is regulated by activity of SLC30A10 in the liver and gastrointestinal tract, and not the brain or just the liver. Notably, however, brain manganese levels of endoderm-specific knockouts were lower than whole-body knockouts, and only whole-body knockouts exhibited manganese-induced neurobehavioral defects. Moreover, after elevated exposure, pan-neuronal/glial knockouts had higher manganese levels in the basal ganglia and thalamus than controls. Therefore, when manganese levels increase, activity of SLC30A10 in the brain protects against neurotoxicity.

Generation and Validation of Tissue‐Specific Knockout Strains for Toxicology Research

“…The use of knockout mice to study gene function is a staple in toxicology research. Conditional knockout strains, in which gene function is altered in a cell‐ or tissue‐specific manner, are particularly powerful (Taylor et al., ). The Cre‐ loxP system is widely used for generating conditional knockouts (Papaioannou & Behringer, ).…”

“…For example, to understand how loss of the manganese efflux transporter SLC30A10 induces neurological disease, we used the Cre‐ loxP system to generate full‐body and tissue‐specific Slc30a10 knockout mice. Full‐body Slc30a10 knockout mice exhibited extremely elevated manganese in the brain, blood, and liver (Hutchens et al., ; Liu et al., ; Taylor et al., ). These knockouts were also hypothyroid, highlighting a previously unappreciated relationship between manganese toxicity and thyroid function (Hutchens et al., ; Liu et al., ; Taylor et al., ).…”

“…Full‐body Slc30a10 knockout mice exhibited extremely elevated manganese in the brain, blood, and liver (Hutchens et al., ; Liu et al., ; Taylor et al., ). These knockouts were also hypothyroid, highlighting a previously unappreciated relationship between manganese toxicity and thyroid function (Hutchens et al., ; Liu et al., ; Taylor et al., ). Interestingly, brain‐specific Slc30a10 knockouts had no change in brain manganese levels under basal conditions, whereas liver‐ and digestive‐system‐specific knockouts showed moderate and extreme elevations in brain manganese, respectively (Taylor et al., ).…”

“…Interestingly, brain‐specific Slc30a10 knockouts had no change in brain manganese levels under basal conditions, whereas liver‐ and digestive‐system‐specific knockouts showed moderate and extreme elevations in brain manganese, respectively (Taylor et al., ). Comparing the phenotypes of full‐body and tissue‐specific Slc30a10 knockout mice resulted in the unexpected discovery that brain manganese homeostasis is regulated by manganese efflux in the digestive system (Taylor et al., ). This application of the Cre‐ loxP system gave critical insight into the mechanisms of manganese homeostasis and manganese‐induced neurological disease and underlines the power of using tissue‐specific knockouts in research.…”

“…full-body and tissue-specific Slc30a10 knockout mice. Full-body Slc30a10 knockout mice exhibited extremely elevated manganese in the brain, blood, and liver (Hutchens et al, 2017;Liu et al, 2017;Taylor et al, 2019). These knockouts were also hypothyroid, highlighting a previously unappreciated relationship between manganese toxicity and thyroid function (Hutchens et al, 2017;Liu et al, 2017;Taylor et al, 2019).…”