Cell-type specific investigation of molecular rhythms in the prefrontal cortex

Circadian rhythms are ~24-hour rhythms in physiological processes that are generated by a transcriptional-translational feedback loop called the molecular clock. The molecular clock then generates rhythmic expression of downstream targets, including up to 43% of protein coding genes in mice. Recently, studies have shown that molecular rhythms are extensively altered in the prefrontal cortex (PFC) of individuals with psychiatric diseases; however, the contribution of cell-type specific rhythms remains unknown. Using RNA sequencing, we examine translatomic rhythms in two cell types in the mouse PFC, parvalbumin (PV) and pyramidal cells, both of which have been heavily implicated in schizophrenia. We further assess the consequences of molecular clock dysfunction on PV cell properties as well as on psychiatric disease relevant behavior. Finally, we expand our analysis to compare transcriptomic rhythms between the mouse PFC and two psychiatric disease relevant subregions of the PFC in humans. We find that while the molecular clock oscillates in synchrony between PV and pyramidal cells, nearly twice as many transcripts are rhythmic in pyramidal cells than in PV cells. Moreover, rhythmic transcripts in pyramidal cells show broad overlap between sexes while rhythmic transcripts in PV cells are largely distinct between sexes, consistent with the observed sex-specific diurnal changes in PV cell electrophysiological properties. Interestingly, processes associated with mitochondrial function are highly enriched for rhythmic transcripts in PV cells from males. Furthermore, disruption of the molecular clock leads to reduced PV expression and increased excitability of PV cells, as well as deficits in cognitive flexibility. In our cross-species analysis, we find that while rhythms in core v molecular clock components are conserved across species in the PFC, the difference in peak times between the mouse PFC and human PFC subregions differs by sex. Nevertheless, overall transcriptomic rhythms are largely unique between the mouse PFC and human PFC. As up to 80% of drug targets show rhythms in gene expression, this work provides critical insight into cross species translation of preclinical findings. Moreover, our cell-type specific findings suggest that there are sex and cell-type specific vulnerabilities to circadian rhythm disruption, which may have implications for psychiatric diseases such as schizophrenia.