Obesity is associated with altered gene expression in human tastebuds

TITLE: Obesity is associated with altered gene expression in human tastebuds

CITATION & LINK: IntJ Obes. 2019; 43:1475-1484

AUTHORS: Nicholas Archer, Jan Shaw, Maeva Cochet-Broch, et al (4)

REVIEWER: Robyn Flipse, MS, MA, RDN

Objective

• To assess if there are underlying fundamental differences in the physiology of taste tissue between lean and obese individuals using analysis of gene expression in fungiform papillae.

Background

• Taste and orosensory signalling are important in the cephalic phase response which impacts nutrient intake, satiety, and termination of food consumption.
• Results of research comparing taste acuity in lean and obese individuals is mixed.
• Both increased and decreased taste acuity has been found in those with obesity, or no association at all.
• Studies in individuals before and after weight loss or bariatric surgery trend towards increased taste acuity following both.
• Tastebuds are a collection of 50-100 taste cells and are composed of four different cell populations that have distinct functions or roles in taste perception.
  • Type I and III cells are associated with salt and sour taste, respectively
  • Type II cells are responsible for sweet, bitter, and umami taste detection

Methods

• A cross-sectional design was used to analyze the transcriptomic profile (RNA-seq) of human fungiform taste papillae biopsied from 23 lean (mean BMI 22.1) and 13 obese (mean BMI37.2) Caucasian females (age 18-55) to identify differences in gene expression.
• Fungiform taste papillae were quantified by counting the density of papillae on the tongue and biopsies were performed after a 2-hour morning fast.
• Samples were separated into three equal groups accounting for obesity status, age group, and the doctor performing the biopsy.
• RNA extract was converted into sequencing libraries using an input of 700 nanograms RNA per sample yielding 2.9 billion reads from the 36 participants.
• Data analysis was completed in R (a language for statistical computing) using the R package for differential gene and transcript expression analysis of RNA-seq experiments.

Findings

• Taste receptor genes were present in all samples and there was no difference observed in the density of fungiform taste papillae between the two groups.
• Obesity status was the key factor influencing variability in gene expression between individuals, with no evidence for an age-related influence.
• A total of 62 genes showed significantly different expression levels between the lean and obese participants with a consistent reduction in the expression of taste-related genes in the obese group.
  • The reduction in type II taste cell genes seen in the obese group is consistent with findings in animal studies.

Conclusions

• The gene expression of the human fungiform papillae is distinctly different between lean and obese people.
• The majority of the taste genes showing expression differences between lean and obese were type II taste cells.
• Type I and III taste cells showed similar expression level between lean and obese groups.

Points to Consider

• Chronic inflammatory processes in obese individuals may account for some of the variability in fungiform papillae profiles seen in the lean and obese groups.
• A reduction in type II taste cells in obese individuals may provide evidence of a link between taste and obesity.
• Taste cells turnover every 7-24 days raising the possibility of preferentially influencing type II taste cells to reverse back to a lean profile.

Robyn Flipse, MS, MA, RDN is a registered dietitian, cultural anthropologist and scientific advisor to the Calorie Control Council, whose 30+ year career includes maintaining a busy nutrition counseling practice, teaching food and nutrition courses at the university level, and authoring 2 popular diet books and numerous articles and blogs on health and fitness. Her ability to make sense out of confusing and sometimes controversial nutrition news has made her a frequent guest on major media outlets, including CNBC, FOX News and USA Today. Her passion is communicating practical nutrition information that empowers people to make the best food decisions they can in their everyday diets. Reach her on Twitter @EverydayRD and check out her blog The Everyday RD.