3 research outputs found
Functional Peptidomics: Stimulus- and Time-of-Day-Specific Peptide Release in the Mammalian Circadian Clock
Daily oscillations
of brain and body states are under complex temporal
modulation by environmental light and the hypothalamic suprachiasmatic
nucleus (SCN), the master circadian clock. To better understand mediators
of differential temporal modulation, we characterize neuropeptide
releasate profiles by nonselective capture of secreted neuropeptides
in an optic nerve horizontal SCN brain slice model. Releasates are
collected following electrophysiological stimulation of the optic
nerve/retinohypothalamic tract under conditions that alter the phase
of the SCN activity state. Secreted neuropeptides are identified by
intact mass via matrix-assisted laser desorption/ionization time-of-flight
mass spectrometry (MALDI-TOF MS). We found time-of-day-specific suites
of peptides released downstream of optic nerve stimulation. Peptide
release was modified differentially with respect to time-of-day by
stimulus parameters and by inhibitors of glutamatergic or PACAPergic
neurotransmission. The results suggest that SCN physiology is modulated
by differential peptide release of both known and unexpected peptides
that communicate time-of-day-specific photic signals via previously
unreported neuropeptide signatures
Quantitative Peptidomics for Discovery of Circadian-Related Peptides from the Rat Suprachiasmatic Nucleus
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 VGRPEÂWWMDYQ 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
Comparing Label-Free Quantitative Peptidomics Approaches to Characterize Diurnal Variation of Peptides in the Rat Suprachiasmatic Nucleus
Mammalian
circadian rhythm is maintained by the suprachiasmatic nucleus (SCN)
via an intricate set of neuropeptides and other signaling molecules.
In this work, peptidomic analyses from two times of day were examined
to characterize variation in SCN peptides using three different label-free
quantitation approaches: spectral count, spectra index and SIEVE.
Of the 448 identified peptides, 207 peptides were analyzed by two
label-free methods, spectral count and spectral index. There were
24 peptides with significant (adjusted <i>p</i>-value <
0.01) differential peptide abundances between daytime and nighttime,
including multiple peptides derived from secretogranin II, cocaine
and amphetamine regulated transcript, and proprotein convertase subtilisin/kexin
type 1 inhibitor. Interestingly, more peptides were analyzable and
had significantly different abundances between the two time points
using the spectral count and spectral index methods than with a prior
analysis using the SIEVE method with the same data. The results of
this study reveal the importance of using the appropriate data analysis
approaches for label-free relative quantitation of peptides. The detection
of significant changes in so rich a set of neuropeptides reflects
the dynamic nature of the SCN and the number of influences such as
feeding behavior on circadian rhythm. Using spectral count and spectral
index, peptide level changes are correlated to time of day, suggesting
their key role in circadian function