Diet Differentially Impacts Gastrointestinal Integrity, Fecal β‐glucuronidase Activity, and Longitudinal Fecal Microbial Communities of C57BL/6J Mice in Response to Ovariectomy‐Induced Obesity
Authors: Liu Tzu‐Wen , Nelson Erik R. , Wallig Matthew A. , Bhatt Aadra P. , Pellock Samuel J. , Lin Ching‐Yen , Redinbo Matthew R. , Swanson Kelly S. 
Published: November 2023

Obesity affects 65% of post‐menopausal women and is linked to the onset of metabolic dysfunction. Loss of ovarian hormone production is thought to be the cause of menopause‐associated obesity; however, the mechanisms are not fully understood. We previously demonstrated that ovariectomy (OVX) altered the composition of cecal microbiota of mice fed a low‐fat (LFD) but not a high‐fat diet (HFD). To determine how and when OVX affected the gut microbiota in these mice, we examined longitudinal fecal samples for assessment of microbial communities and activity of β‐glucuronidase, an enzyme involved in enterohepatic estrogen recycling.METHODS10‐wk‐old female C57BL/6J mice were purchased and ad libitum fed either a LFD (10% kcal from fat) or HFD (60% kcal from fat) for 2 wk. Mice then underwent either OVX or sham (SHM) surgery at 12 wk of age, resulting in 4 treatment groups (n=10/group): 1) SHM/LFD; 2) OVX/LFD; 3) SHM/HFD; 4) OVX/HFD. Mice were fed their allotted diets for 12 wk and then euthanized at 24 wk of age. Serum was collected at the end of study for measurement of lipopolysaccharide‐binding protein (LPSBP) concentrations. Fecal pellets were collected before the surgery was performed (baseline) and 4‐, 8‐, and 12‐wk post‐surgery. Bacterial β‐glucuronidase activity was assessed in fecal samples collected at 12‐wk post‐surgery. DNA from all fecal samples were extracted, followed by 16S rRNA gene‐based amplicon Illumina MiSeq sequencing and analysis using QIIME 1.9.1. The longitudinal changes of fecal microbiota were analyzed using ZIBR package in R.RESULTSOVX/HFD mice were markedly heavier (P<0.05) than SHM/HFD mice while OVX/LFD and SHM/LFD mice did not differ in body weight and adiposity. OVX/HFD mice had greater (P<0.05) serum LPSBP concentrations than OVX/LFD mice, but did not differ from SHM groups, suggesting that ovarian hormone production protected GI integrity against HFD insults. Fecal β‐glucuronidase activity was greater (P<0.05) in the SHM/HFD group compared to SHM/LFD, but neither was different from the OVX groups. Principal coordinates analysis (PCoA) of weighted UniFrac distances of the longitudinal fecal microbiota revealed a distinct separation (P<0.05) between diets. Differential clustering between SHM and OVX mice occurred soon after ovariectomy; however, this was only observed in those fed LFD but not HFD. The relative abundance of Clostridium and an undefined genus in family Clostridiaceae were greater in OVX/HFD mice at wk4 compared to SHM/HFD, indicating a response due to the loss of ovarian hormone production.CONCLUSIONLoss of ovarian hormone production impacts the susceptibility of HFD‐related GI disruption. Changes in the fecal microbial community occurred early during the progression of ovariectomy‐induced obesity, although differential clustering due to ovariectomy was only observed when fed LFD.