Male c57bl 6 mice

Donor mice: Eleven‐ to twelve‐week‐old C57Bl/6 male ob/ob mice (Charles River, L'Arbresle, France) or 20‐week‐old C57Bl/6 male mice (Charles River, L'Arbresle, France) fed a 60% HFD (Serino et al, 2007) served as donor mice. Then, the caecum content of these mice served as transplant and was suspended in sterile reduced PBS (N₂ gas and thioglycolic acid, Sigma Aldrich, St. Louis, MO). Non‐antibiotic treated 6‐week‐old conventional C57Bl/6 male mice (Charles River, L'Arbresle, France) served as recipient mice and were gavaged with 200 μl of either sterile reduced PBS (Conv + PBS) or 200 μl at 200 mg/ml caecum suspension of dysbiotic gut microbiota from either ob/ob mice (Conv + OM(ob)) or from HFD‐induced obese mice (Conv + OM(HFD)) once per week, for 2 weeks (“OM” stands for obese microbiota). The caecum content from 3 to 6 mice per group of donors was pooled and provided to recipient mice at the same concentration of 200 mg/ml. Note that the unmatched age for donor mice in protocol #2 is related to the fact that the major point we wanted to investigate herein is the putative metabolic effect of transferring a dysbiotic gut microbiota; therefore, we did not intend to compare donors of protocol #2 against each other.

Young (2.5-4 month old) C57BL/6 male mice were obtained from Charles River Laboratories and aged (19-22 month old) C57BL/6 male mice were obtained through the National Institute on Aging rodent colony. All mice were housed in a climate controlled environment with 12:12 light:dark cycle and fed standard rodent chow and water ad libitum. All procedures were approved by the University of Connecticut Medical School IACUC (protocol 100705) and carried out in accordance with these regulations. All mice underwent gross pathological examination at time of sacrifice and animals with obvious pathology were excluded from the study.

Young (4–8 months) C57Bl/6 male mice were purchased from Charles River, and old (26–28 months) C57Bl/6 male mice were obtained from the National Institute on Aging rodent colony. Mice were fed normal rodent chow ad libitum for the duration of the study. After a 2‐week acclimation period, the young and old mice were divided into two subgroups: control animals (YC, OC) continued on normal drinking water and the other animals (YNMN, ONMN) received nicotinamide mononucleotide (NMN; Sigma‐Aldrich Corp., St. Louis, MO, USA) in the drinking water (target dose of 300 mg kg⁻¹ day⁻¹) for 8 weeks. Body mass and water intake were monitored three times per week, and NMN concentration in the drinking water was adjusted to account for water intake. All mice were housed in an animal care facility at the University of Colorado Boulder on a 12‐hour: 12‐hour light–dark cycle. All animal procedures conformed to the Guide to the Care and Use of Laboratory Animals (NIH publication n. 85‐23, revised 1996) and were approved by the UCB Animal Care and Use Committee.