The formation of a fuzzy complex in the negative arm regulates the robustness of the circadian clock.

The circadian clock times cellular processes to the day/night cycle via a Transcription-Translation negative Feedback Loop (TTFL). However, a mechanistic understanding of the negative arm in both the timing of the TTFL and its control of output is lacking. We posited that the formation of negative-arm protein complexes was fundamental to clock regulation stemming from the negative arm. Using a modified peptide microarray approach termed Linear motif discovery using rational design (LOCATE), we characterized the interaction of the disordered negative-arm clock protein FREQUENCY to its partner protein FREQUENCY-Interacting RNA helicase. LOCATE identified a specific Short Linear Motif (SLiM) and interaction hotspot as well as positively charged islands that mediate electrostatic interactions, suggesting a model where negative arm proteins form a fuzzy complex essential for clock timing and robustness. Further analysis revealed that the positively charged islands were an evolutionarily conserved feature in higher eukaryotes and contributed to proper clock function.

The Resonance and Adaptation of Neurospora crassa Circadian and Conidiation Rhyth ms to Short Light-Dark Cycles

Circadian clocks control the physiological and behavioral rhythms to adapt to the environment with a period of ~24 h. However, the influences and mechanisms of the extreme light/dark cycles on the circadian clock remain unclear. We showed that, in Neurospora crassa, both the growth and the microconidia production contribute to adaptation in LD12:12 (12 h light/12 h dark, periodically). Mathematical modeling and experiments demonstrate that in short LD cycles, the expression of the core clock protein FREQUENCY was entrained to the LD cycles when LD > 3:3 while it free ran when T ≤ LD3:3. The conidial rhythmicity can resonate with a series of different LD conditions. Moreover, we demonstrate that the existence of unknown blue light photoreceptor(s) and the circadian clock might promote the conidiation rhythms that resonate with the environment. The ubiquitin E3 ligase FWD-1 and the previously described CRY-dependent oscillator system were implicated in regulating conidiation under short LD conditions. These findings shed new light on the resonance of Neurospora circadian clock and conidiation rhythms to short LD cycles, which may benefit the understandings of both the basic regulatory aspects of circadian clock and the adaptation of physiological rhythms to the extreme conditions.

Recent Advances in Chronotherapy Targeting Respiratory Diseases

Respiratory diseases contribute to a significant percentage of mortality and morbidity worldwide. The circadian rhythm is a natural biological process where our bodily functions align with the 24 h oscillation (sleep–wake cycle) process and are controlled by the circadian clock protein/gene. Disruption of the circadian rhythm could alter normal lung function. Chronotherapy is a type of therapy provided at specific time intervals based on an individual’s circadian rhythm. This would allow the drug to show optimum action, and thereby modulate its pharmacokinetics to lessen unwanted or unintended effects. In this review, we deliberated on the recent advances employed in chrono-targeted therapeutics for chronic respiratory diseases.

The Circadian Clock Protein BMAL1 Acts as a Metabolic Sensor In Macrophages to Control the Production of Pro IL-1β

The transcription factor BMAL1 is a clock protein that generates daily or circadian rhythms in physiological functions including the inflammatory response of macrophages. Intracellular metabolic pathways direct the macrophage inflammatory response, however whether the clock is impacting intracellular metabolism to direct this response is unclear. Specific metabolic reprogramming of macrophages controls the production of the potent pro-inflammatory cytokine IL-1β. We now describe that the macrophage molecular clock, through Bmal1, regulates the uptake of glucose, its flux through glycolysis and the Krebs cycle, including the production of the metabolite succinate to drive Il-1β production. We further demonstrate that BMAL1 modulates the level and localisation of the glycolytic enzyme PKM2, which in turn activates STAT3 to further drive Il-1β mRNA expression. Overall, this work demonstrates that BMAL1 is a key metabolic sensor in macrophages, and its deficiency leads to a metabolic shift of enhanced glycolysis and mitochondrial respiration, leading to a heightened pro-inflammatory state. These data provide insight into the control of macrophage driven inflammation by the molecular clock, and the potential for time-based therapeutics against a range of chronic inflammatory diseases.

Elucidation of Master Allostery Essential for Circadian Clock Oscillation in Cyanobacteria

Spatio-temporal allostery is the source of complex but ordered biological phenomena. To identify the structural basis for allostery that drives the cyanobacterial circadian clock, we crystallized the clock protein KaiC in four distinct states, which cover a whole cycle of phosphor–transfer events at Ser431 and Thr432. The minimal set of allosteric events required for oscillatory nature is a bidirectional coupling between the coil-to-helix transition of the Ser431-dependent phospho-switch in the C-terminal domain of KaiC and ADP release from its N-terminal domain during ATPase cycle. An engineered KaiC–protein oscillator consisting of a minimal set of the identified master allosteric events exhibited mono-phosphorylation cycle of Ser431 with a temperature-compensated circadian period, providing design principles for simple post-translational biochemical circadian oscillators.One Sentence SummaryCoupling between a phospho-switch and KaiC ATPase-dependent nucleotide exchange drives the cyanobacterial circadian clock.

L-3,4-Dihydroxyphenylalanine Recovers Circadian Rhythm Disturbances in the Rat Models of Parkinson's Disease by Regulating the D1R-ERK1/2-mTOR Pathway

Objective: Patients with Parkinson's disease (PD) frequently experience disruptions in the 24-h daily profile of both behavioral and biological markers. However, whether L-3,4-dihydroxyphenylalanine (L-dopa) influences these markers associated with circadian rhythm or not is still an open question. This study aims to explore the L-dopa effects on the rhythmic expression of core clock proteins [brain and muscle Arnt-like protein-1 (BMAL1) and circadian locomotor cycle kaput (CLOCK)], in the striatum of the rat model of PD and its underlying molecular mechanisms.Methods: Unilateral 6-hydroxydopamine (6-OHDA)-lesioned rat models were used in this study. L-dopa administrations were adopted to investigate the changes of circadian rhythm in PD. The behavioral tests and the measurements of the blood pressure (BP) and temperature were evaluated. The striatum was collected at intervals of 4 h. Western blot was used to examine the expressions of clock protein and the molecular protein of the D1R-ERK1/2-mTOR pathway. The rhythmic expressions of symptom parameters and circadian proteins were analyzed using the Cosinor model and/or the coefficient of variability (CV) that was used to describe the variability of the 24-h rhythm.Results: The circadian rhythms of BP and temperature were disrupted in 6-OHDA-lesioned PD rats compared with the sham group, while this process was reversed mildly by L-dopa treatment. The expressions of BMAL1 and CLOCK protein were rhythmic fluctuated without significant phase alterations when 6-OHDA or L-dopa was applied. Furthermore, the expressions of striatal BMAL1 protein in the 6-OHDA-lesioned group were significantly lower than those in the sham group at 04:00, 08:00, and 12:00, and the CLOCK protein was decreased at 04:00, 08:00, 12:00, 16:00, and 20:00 (all p < 0.05). The CV of the expressions of both BMAL1 and CLOCK was decreased in the 6-OHDA group; this process was reversed by L-dopa. Moreover, the CV of BMAL1 and CLOCK was elevated in the L-dopa rats. The phosphorylation levels of ERK1/2, S6K1, and 4E-BP1 in 6-OHDA-lesioned striatum were increased by L-dopa or D1 receptor agonist SKF38393 (p < 0.05, respectively), not by the combination of L-dopa and D1 receptor antagonist SCH23390, which was similar to the expressions of BMAL1 and CLOCK.Conclusion: L-dopa recovers the circadian rhythm disturbances in PD rats by regulating the D1R-ERK1/2-mTOR pathway.