Brum, P. O. | bioRxiv Science

bioRxiv2026

PER2- and state-dependent transcriptional programs gate neural stem cell proliferation with niche-specific circadian autonomy

Adult neural stem cells (NSCs) in the mouse brain are predominantly quiescent, with activation tightly regulated to balance neurogenesis and stem cell maintenance. Circadian clocks temporally organize core cellular processes, potentially gating NSC activation. We examined adult NSC temporal dynamics across the day and observed rhythmic expression of core circadian clock components BMAL1 and PER2 in both mammalian niches, the subgranular zone (SGZ) of the dentate gyrus and the subventricular zone (SVZ). While cell cultures derived from both niches show BMAL1 and PER2 protein, only SGZ-derived NSCs exhibit synchronized self-sustained core clock oscillations across the population. Comparative analyses of WT and Per2 knockout NSCs revealed state-specific, circadian clock-dependent oscillatory transcriptional programs. This identified ASCL1 and CCND1 as candidate regulators of cell-cycle coordination, with daytime accumulation preceding a nighttime S-phase peak. The temporal control of S-phase entry in NSCs was abolished in Per2 knockout mice. Together, our findings reveal state-specific, PER2-dependent circadian regulation of adult NSCs in both neurogenic niches, and a specific dependence on external stimuli for synchronization in the SVZ.

cell biology↗

bioRxiv2026

Metformin modulates autophagy in heterozygous and CRISPR-edited TSC2 primary fibroblasts

BackgroundTuberous Sclerosis Complex (TSC) is a genetic disorder caused by variants in TSC1 or TSC2, leading to mTORC1 hyperactivation and autophagy suppression. Although TSC tumorigenesis typically follows a "two-hit" model, the role of TSC2 haploinsufficiency in autophagy regulation remains unclear. We evaluated autophagy markers in haploinsufficient and gene-edited TSC2 primary cells and investigated the role of metformin in modulating autophagy levels. MethodsPrimary fibroblast cultures were obtained from one healthy individual and three from patients carrying heterozygous germline TSC2 variants: the pathogenic variants c.1008T>G and c.4375C>T.A variant of uncertain significance (VUS) c.724A>T. CRISPR/Cas9-RNP editing was used to model loss of heterozygosity (LOH) in cell pools carrying each variant. Cultures were treated with rapamycin, HBSS, metformin, bafilomycin A1, or vehicle controls, and autophagy was assessed by autolysosomes formation by flow cytometry (acridine orange) and autophagosomes immunofluorescence (LC3 and p-S6K). ResultsIn wild-type cells, only HBSS increased autophagy-positive (acridine orange-positive) cells versus control (15.6% vs. 7.5%; p=0.003). In heterozygous pathogenic cells, rapamycin and metformin increased autophagic cells: c.1008T>G (16.2%, p=0.006; 17.6%, p=0.002) and c.4375C>T (12.5%, p=0.003; 13.3%, p=0.001), versus DMSO controls (9.2% and 7.1%, respectively). VUS c.724A>T cells, with rapamycin increasing autophagic cells (9.74% vs. 6.5%; p=0.0152). In CRISPR-edited cells, all treatments increased the number of autophagic cells compared to the heterozygous cells: c.1008T>G (rapamycin 27.1% vs. 16.7%, p<0.001; metformin 27.2% vs. 17.6%, p<0.001) and c.4375C>T (rapamycin 21.3% vs. 13.1%, p=0.0021; metformin 21.5% vs. 13.6%, p=0.0029). Editing also restored metformin responsiveness in VUS cells (12.5% vs. 8.4%; p=0.0055). Immunochemistry confirmed increased total LC3II and decreased p-S6K across treated cells compared to the control (DMSO). ConclusionThese findings demonstrate that TSC2 haploinsufficiency functionally impairs autophagy prior to second-hit loss. Metformin effectively restores autophagy with phenotypical changes of mTORC1 blockade, highlighting an accessible translational strategy to restore and induce autophagy in TSC cells.

molecular biology↗