Quantitative Peptidomics
for Discovery of Circadian-Related
Peptides from the Rat Suprachiasmatic Nucleus
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Abstract
In mammals the suprachiasmatic nucleus (SCN), the master
circadian
clock, is sensitive to light input via the optic chiasm and synchronizes
many daily biological rhythms. Here we explore variations in the expression
levels of neuropeptides present in the SCN of rats using a label-free
quantification approach that is based on integrating peak intensities
between daytime, Zeitgeber time (ZT) 6, and nighttime, ZT 18. From
nine analyses comparing the levels between these two time points,
10 endogenous peptides derived from eight prohormones exhibited significant
differences in their expression levels (adjusted <i>p</i>-value <0.05). Of these, seven peptides derived from six prohormones,
including GRP, PACAP, and CART, exhibited ≥30% increases at
ZT 18, and the VGRPEWWMDYQ peptide derived from proenkephalin
A showed a >50% increase at nighttime. Several endogenous peptides
showing statistically significant changes in this study have not been
previously reported to alter their levels as a function of time of
day, nor have they been implicated in prior functional SCN studies.
This information on peptide expression changes serves as a resource
for discovering unknown peptide regulators that affect circadian rhythms
in the SCN