We employed mouse primary ileum organoids to investigate the transcriptional effects of varying 12HBA abundance in BA pools. We identified Slc30a10 as one of the top genes differentially induced by BA pools with varying 12HBA abundance./We found that BA pools, especially those low in 12HBAs, induce cellular manganese efflux and that Slc30a10 induction by BA pools is driven primarily by lithocholic acid signaling via the vitamin D receptor. Administration of lithocholic acid or a vitamin D receptor agonist resulted in increased Slc30a10 expression in mouse ileum epithelia./Another intestinal receptor responsive to certain BAs is the vitamin D receptor (VDR), whose canonical role is to promote calcium and phosphate absorption (29) /We unexpectedly found that varying 12HBA proportions modulates expression of Slc30a10, a manganese efflux transporter critical for whole-body Mn excretion. Cellular Mn levels are tightly regulated, as Mn is essential for numerous cellular processes, yet its excess is toxic (31). /There were 44 genes that were preferentially induced by H10 and M10 compared with H90 and M90, respectively (Fig. 1D). Among these, we noted that several are known transcriptional targets of VDR. These included Cyp24a1, S100g, and Cyp3a11, and we validated these by qPCR (Fig. 1E). This is consistent with the concepts that (i) certain BAs, especially the non- 12HBA LCA and its conjugates, can activate VDR in the micromolar range (10), and (ii) the low-12HBA pools (i.e. H10 and M10) contain more LCA (9 mM, as opposed to 1 mM in the high- 12HBA pools). /We also confirmed that VDR targets Cyp24a1 and S100g were preferentially induced by low-12HBA pools (Fig. S1D). We found that delivery in micelles was not required and that BAs per se were sufficient to induce Fgf15, Fabp6, and S100g (Fig. S1E). Last, to determine whether differential responses to BA pools also occur in human cells, we performed experiments in Caco-2 cells, which are enterocyte-like cells derived from a human epithelial colorectal tumor. We observed that FXR and VDR targets were robustly induced by H10, but not H90 /Among the genes identified to be differentially expressed between BA pools with varying 12HBA abundance, one of the most robust was Slc30a10 (Fig. 1D). This gene encodes a Mn efflux transporter critical for whole-body Mn excretion (34– 41). Humans with mutations in SLC30A10 develop hypermanganesemia, accompanied by parkinsonism and cirrhosis (34, 35, 42–44). /In gut organoids, low-12HBA pools were superior to high- 12HBA pools in inducing Slc30a10 (Fig. 2, A and B). This preferential induction was consistent across multiple independent batches of organoids (Fig. 2, C and D). This differential expression of Slc30a10 was also observed when BA pools were delivered without micelles (Fig. 2E), indicating a direct effect of BAs. We also validated that the H10 pool induces SLC30A10 in human Caco-2 cells (Fig. 2F). /We predicted that the induction of Slc30a10 expression by low-12HBA pools would increase Mn efflux from organoids. To test this, we carried out Mn efflux assays, where we preloaded cells with Mn, washed away unabsorbed Mn, then treated the cells with vehicle or BA pools, and measured Mn levels in efflux media. Organoids treated with H10 had higher Mn in their efflux media compared with organoids treated with vehicle or H90 (Fig. 2G). Consistently, Caco-2 cells receiving H10 also showed higher Mn efflux compared with vehicle- and H90-treated cells (Fig. 2H). Altogether, these data show that BAs, particularly pools low in 12HBAs, induce cellular Mn efflux, consistent with their induction of Slc30a10 / /Recently, SLC30A10 mRNA expression was found to be induced by the VDR agonist 1a,25-dihydroxyvitamin D3 in Caco-2 cells (45) /. Without LCA, H10 induction of Slc30a10 was significantly blunted (Fig. 3A). This pattern was similar to that of VDR targets Cyp24a1 and S100g /