Association between phase shifts, expression levels, and amplitudes in peripheral circadian clocks

Data analyses examining the relationship between circadian phase shifts and amplitudes are scarce. The aim of this data analysis was to explore the association between the phase shifts of gene expression, their amplitudes, and daily levels as a result of a given treatment under ad libitum or restricted feeding (RF) conditions. Two hundred forty data sets of gene expression (clock and metabolic genes) from various tissues and treatments were statistically analyzed. The data revealed a significant association between phase delays and increased amplitudes. Moreover, upon subgroup analyses, separating the RF from the non-RF groups, phase delays were significantly correlated with increased amplitudes and phase advances with decreased amplitudes. This picture was also achieved when clock genes, but not metabolic genes, were analyzed. In contrast, under RF, increased amplitude of metabolic genes correlated with phase advances. Moreover, phase advances under RF led to increased average daily levels in clock genes, but not in metabolic genes. In summary, these data demonstrated statistically significant association between phase shifts, daily levels, and amplitudes in circadian gene expression in peripheral tissues under timed versus ad libitum feeding conditions.