Circadian clock gene expression in human buccal cells: potential use as a biomarker for circadian rhythm disorders.

Abstract

A lack of diurnal variation in blood pressure is a risk factor for end‐organ disease. Time‐of‐day‐dependent oscillations in biological processes are mediated by a number of oscillating transcription factors, collectively termed the “molecular clock,” that control transcription of various regulators of physiological function. In particular, the genetic disruption of BMAL1 is known to impair blood pressure rhythms in mice. The goal of this feasibility study was to determine if human buccal cell BMAL1 mRNA is expressed in a time‐of‐day‐dependent manner. Following IRB approval, we recruited 11 healthy, adult volunteers (7 females, 4 males; 23‐50 years old) who were not on any medications, and had normal sleep patterns. Volunteers were instructed to swab for buccal cells at 6 AM, 12 noon, 6 PM, and 10 PM for three consecutive days and to return the swabs after the third day for RNA extraction and subsequent analysis by qRT‐PCR. We consistently obtained greater than 1 μg of total RNA in all buccal samples from all participants. BMAL1 mRNA displayed a reproducible rhythmic pattern in 9 of the 11 volunteers over the 3 day period (e.g. Day 1, 6 AM 2248±413, 12 PM 1149±336, 6 PM 715±211,10 PM 904±385 copy number/μg total RNA). These data suggest that human buccal cells exhibit rhythms in the circadian “molecular clock,” and may prove useful as a biomarker for determining mechanisms of circadian rhythm disorders such as nocturnal hypertension.