Clostridium scindens: a human gut microbe with a high potential to convert glucocorticoids into androgens

Abstract

Clostridium scindens American Type Culture Collection 35704 is capable of converting primary bile acids to toxic secondary bile acids, as well as converting glucocorticoids to androgens by side-chain cleavage. The molecular structure of the side-chain cleavage product of cortisol produced by C. scindens was determined to be 11β-hydroxyandrost-4-ene-3,17-dione (11β-OHA) by high-resolution mass spectrometry, 1H and 13C NMR spectroscopy, and X-ray crystallography. Using RNA-Seq technology, we identified a cortisol-inducible (∼1,000-fold) operon (desABCD) encoding at least one enzyme involved in anaerobic side-chain cleavage. The desC gene was cloned, overexpressed, purified, and found to encode a 20α-hydroxysteroid dehydrogenase (HSDH). This operon also encodes a putative “transketolase” (desAB) hypothesized to have steroid-17,20-desmolase/oxidase activity, and a possible corticosteroid transporter (desD). RNA-Seq data suggests that the two-carbon side chain of glucocorticords may feed into the pentose-phosphate pathway and are used as a carbon source. The 20α-HSDH is hypothesized to function as a metabolic “rheostat” controlling rates of side-chain cleavage. Phylogenetic analysis suggests this operon is rare in nature and the desC gene evolved from a gene encoding threonine dehydrogenase. The physiological effect of 11β-OHAD on the host or other gut microbes is currently unknown.

Consequences of bile salt biotransformations by intestinal bacteria

“…Interestingly, C. scindens VPI 12708 metabolizes the 11b-hydroxyandrostenedione (11b-OHAD) product, reducing the 17-keto group to a 17a-hydroxy. 70 Previously, we reported that testosterone enhances 7a-dehydroxylating activity in C. hylemonae TN27172 72 ; however, it is unknown what effect 11b-OHAD, and its subsequent gut microbial metabolites has on bile acid 7a-dehydroxylation.…”

The desA and desB genes from Clostridium scindens ATCC 35704 encode steroid-17,20-desmolase

“…In the current study, we report that the desA and desB genes from C. scindens The conversion of cortisol to 11β-hydroxyandrostenedione by C. scindens is an important step in a multi-species gut microbial endocrine pathway that results in the formation of 11β-hydroxyandrogens (9). Previous studies reveal a number of cortisol metabolites following incubation with mixed human or rat fecal bacteria included 3α,11β,17β-trihydroxy-5β-androstane, 3α,11β,17β-trihydroxy-5α-androstane, demonstrating the ability of gut microbes to form 5α-, 17β-reduced metabolites (3,4).…”

“…Utilization of RNA-Seq to identify differentially expressed genes, coupled with biochemical characterization of the recombinant gene products was necessary to determine the nucleic acid sequences encoding this bacteria steroid biotransforming pathway (9).…”

“…The application of genome-wide transcriptomics (RNA-Seq) identified a polycistronic cortisol-inducible operon (desABCD) which included a gene encoding 20α-HSDH (desC) (9). The desA and desB genes are annotated as Nterminal and C-terminal transketolases, respectively.…”

“…Transketolase catalyzes the TPPdependent transfer of glycol aldehyde to an aldose acceptor. Comparison of the transketolation reaction to that of steroid-17,20-desmolase suggests an analogous reaction, and that desAB encodes a novel steroid transketolase (9). C. cadavaris and Butyricicoccus desmolans were shown previously to generate 20β-dihydrocortisol as well by guest, on May 12, 2018 www.jlr.org Downloaded from 6 were extracted from the resulting cell pellet using the QIAprep Spin Miniprep kit (Qiagen, Valencia, CA).…”