Sweet Taste Receptor Deficient Mice Have Decreased Adiposity and Increased Bone Mass

Functional expression of sweet taste receptors (T1R2 and T1R3) has been reported in numerous metabolic tissues, including the gut, pancreas, and, more recently, in adipose tissue. It has been suggested that sweet taste receptors in these non-gustatory tissues may play a role in systemic energy balance and metabolism. Smaller adipose depots have been reported in T1R3 knockout mice on a high carbohydrate diet, and sweet taste receptors have been reported to regulate adipogenesis in vitro. To assess the potential contribution of sweet taste receptors to adipose tissue biology, we investigated the adipose tissue phenotypes of T1R2 and T1R3 knockout mice. Here we provide data to demonstrate that when fed an obesogenic diet, both T1R2 and T1R3 knockout mice have reduced adiposity and smaller adipocytes. Although a mild glucose intolerance was observed with T1R3 deficiency, other metabolic variables analyzed were similar between genotypes. In addition, food intake, respiratory quotient, oxygen consumption, and physical activity were unchanged in T1R2 knockout mice. Although T1R2 deficiency did not affect adipocyte number in peripheral adipose depots, the number of bone marrow adipocytes is significantly reduced in these knockout animals. Finally, we present data demonstrating that T1R2 and T1R3 knockout mice have increased cortical bone mass and trabecular remodeling. This report identifies novel functions for sweet taste receptors in the regulation of adipose and bone biology, and suggests that in these contexts, T1R2 and T1R3 are either dependent on each other for activity or have common independent effects in vivo

Twin arginine translocation, ammonia incorporation, and polyamine biosynthesis are crucial for Proteus mirabilis fitness during bloodstream infection.

The Gram-negative bacterium Proteus mirabilis is a common cause of catheter-associated urinary tract infections (CAUTI), which can progress to secondary bacteremia. While numerous studies have investigated experimental infection with P. mirabilis in the urinary tract, little is known about pathogenesis in the bloodstream. This study identifies the genes that are important for survival in the bloodstream using a whole-genome transposon insertion-site sequencing (Tn-Seq) approach. A library of 50,000 transposon mutants was utilized to assess the relative contribution of each non-essential gene in the P. mirabilis HI4320 genome to fitness in the livers and spleens of mice at 24 hours following tail vein inoculation compared to growth in RPMI, heat-inactivated (HI) naïve serum, and HI acute phase serum. 138 genes were identified as ex vivo fitness factors in serum, which were primarily involved in amino acid transport and metabolism, and 143 genes were identified as infection-specific in vivo fitness factors for both spleen and liver colonization. Infection-specific fitness factors included genes involved in twin arginine translocation, ammonia incorporation, and polyamine biosynthesis. Mutants in sixteen genes were constructed to validate both the ex vivo and in vivo results of the transposon screen, and 12/16 (75%) exhibited the predicted phenotype. Our studies indicate a role for the twin arginine translocation (tatAC) system in motility, translocation of potential virulence factors, and fitness within the bloodstream. We also demonstrate the interplay between two nitrogen assimilation pathways in the bloodstream, providing evidence that the GS-GOGAT system may be preferentially utilized. Furthermore, we show that a dual-function arginine decarboxylase (speA) is important for fitness within the bloodstream due to its role in putrescine biosynthesis rather than its contribution to maintenance of membrane potential. This study therefore provides insight into pathways needed for fitness within the bloodstream, which may guide strategies to reduce bacteremia-associated mortality

Enterococcus faecalis Polymicrobial Interactions Facilitate Biofilm Formation, Antibiotic Recalcitrance, and Persistent Colonization of the Catheterized Urinary Tract

Indwelling urinary catheters are common in health care settings and can lead to catheter-associated urinary tract infection (CAUTI). Long-term catheterization causes polymicrobial colonization of the catheter and urine, for which the clinical significance is poorly understood. Through prospective assessment of catheter urine colonization, we identified Enterococcus faecalis and Proteus mirabilis as the most prevalent and persistent co-colonizers. Clinical isolates of both species successfully co-colonized in a murine model of CAUTI, and they were observed to co-localize on catheter biofilms during infection. We further demonstrate that P. mirabilis preferentially adheres to E. faecalis during biofilm formation, and that contact-dependent interactions between E. faecalis and P. mirabilis facilitate establishment of a robust biofilm architecture that enhances antimicrobial resistance for both species. E. faecalis may therefore act as a pioneer species on urinary catheters, establishing an ideal surface for persistent colonization by more traditional pathogens such as P. mirabilis

The molecular and metabolic program by which white adipocytes adapt to cool physiologic temperatures.

Although visceral adipocytes located within the body's central core are maintained at approximately 37°C, adipocytes within bone marrow, subcutaneous, and dermal depots are found primarily within the peripheral shell and generally exist at cooler temperatures. Responses of brown and beige/brite adipocytes to cold stress are well studied; however, comparatively little is known about mechanisms by which white adipocytes adapt to temperatures below 37°C. Here, we report that adaptation of cultured adipocytes to 31°C, the temperature at which distal marrow adipose tissues and subcutaneous adipose tissues often reside, increases anabolic and catabolic lipid metabolism, and elevates oxygen consumption. Cool adipocytes rely less on glucose and more on pyruvate, glutamine, and, especially, fatty acids as energy sources. Exposure of cultured adipocytes and gluteal white adipose tissue (WAT) to cool temperatures activates a shared program of gene expression. Cool temperatures induce stearoyl-CoA desaturase-1 (SCD1) expression and monounsaturated lipid levels in cultured adipocytes and distal bone marrow adipose tissues (BMATs), and SCD1 activity is required for acquisition of maximal oxygen consumption at 31°C

Glucose tolerance is mildly impaired and insulin sensitivity is similar between WT and T1R3 KO mice.

<p>A) Fasted glucose of WT (n = 6) and T1R3 KO (n = 9) mice. B) IP GTT in WT (n = 6) and T1R3 KO (n = 9) mice on Western Diet for 23 weeks. Time course following glucose injection (left panel) and AUC (right panel). C) Serum insulin 30 min following glucose injection during IP GTT. D) Intraperitoneal insulin tolerance test (left panel) in WT (n = 6) and T1R3 KO (n = 8) mice on Western diet for 23.5 weeks. Quantification of AUC (right panel). E) Random fed glucose from WT (n = 6) and T1R3 KO (n = 9) mice on Western Diet for 24 weeks. F. Random fed NEFA from WT (n = 6) and T1R3 KO (n = 9) mice on Western Diet for 24 weeks. G. Serum NEFA from WT (n = 6) and T1R3 KO (n = 9) mice on Western Diet for 23 weeks, fasted for 16 h. For each panel, data are expressed as mean plus S.D. Significance was determined using an unpaired Student’s t-test. P <0.01 indicated with ##.</p

T1R2 KO mice have reduced adiposity on Western Diet.

<p>A) Body weight in WT (n = 9) and T1R2 KO (n = 9) mice on Western Diet for 14 weeks. B) Fat as percent of body weight or C) as mass. D) Lean mass as percent of body weight or E) as mass in WT and T1R2 KO animals. F) Adipose depot and liver weights following Western diet feeding. Data are expressed as mean and S.D. Significance was determined using an unpaired Student’s t-test. <i>P</i> <0.05 indicated with #.</p

T1R2 KO mice do not have detectable changes in energy balance or glucose homeostasis.

<p>A) Blood glucose from WT (n = 9) and T1R2 KO (n = 9) animals on Western Diet for 10 weeks following a 16 h fast. B) IP GTT in WT (n = 9) and T1R2 KO (n = 9) mice following 10 weeks on Western Diet C) Serum insulin in WT (n = 9) and T1R2 KO (n = 9) animals 30 min following glucose injections of IP GTT. D) Random fed glucose from WT (n = 9) and T1R2 KO (n = 9) animals following 14 weeks on Western Diet. E) Non-esterified fatty acids measured from serum of WT (n = 9) and T1R2 KO (n = 9) mice following 14 weeks on Western Diet. F) Non-esterified fatty acids measured from serum of WT (n = 9) and T1R2 KO (n = 9) mice on Western Diet for 10 weeks following a 16 h fast. G) Respiratory Quotient (RQ) and H) total activity were measured on WT (n = 9) and T1R2 KO (n = 9) mice in Comprehensive Laboratory Animal Monitoring System (CLAMS) cages after 3 weeks on Western Diet. I) Food intake in WT (n = 9) and T1R2 KO (n = 9) animals on Western Diet measured over 5 weeks. Data are expressed as mean plus S.D</p

T1R3 KO animals demonstrate trabecular remodeling and increased cortical bone.

<p>WT (n = 7) and T1R3 KO (n = 8) mice were placed on Western Diet for 24 weeks. Trabecular (A) and cortical (B,C) parameters were evaluated in the femur by µCT. Significance was determined using an unpaired Student’s t-test. <i>P</i> <0.05 indicated with #, <i>P</i> <0.01 indicated with ##, and <i>P</i> <0.005 indicated with ###. Data are expressed as mean plus S.D.</p