Associations of chronotype and social jetlag with eating jetlag and their changes among German students during the first COVID-19 lockdown. The Chronotype and Nutrition study.

Due to their biologically later chronotype, young students are vulnerable to a discrepant sleeping pattern between work- and free days, coined social jetlag (SJL). This study examined whether a later chronotype and/or a larger SJL are related to an analogous discrepancy in meal timing defined as eating jetlag (EJL) and whether chronotype and/or changes in SJL during the first COVID-19 related lockdown in Germany associated with changes in EJL. Baseline data were collected from September 2019-January 2020 among 317 students (58% females) aged 18-25 years of which a total of 156 students (67% females) completed an online follow-up survey in June-July 2020 (1st lockdown). Data were collected on daily routines, timing of meals/snacks, and physical activity. Chronotype was determined using the Munich ChronoType Questionnaire; SJL and EJL correspond to the difference in the daily midpoint of sleep/eating duration between work- and free days. Multivariable linear regression revealed that students with a later chronotype or a larger SJL experienced a larger EJL (padjusted = 0.0124 and padjusted<0.0001). A later chronotype at baseline and reductions in SJL during lockdown associated with concurrent reductions in EJL (padjusted = 0.027 and padjusted<0.0001). In conclusion, students with a later chronotype exhibit a more erratic meal pattern, which associates with SJL. During lockdown, flexible daily schedules allowed students to align the meal timing with their inner clock.

Characterization of group X phospholipase A(2) as the major enzyme secreted by human keratinocytes and its regulation by the phorbol ester TPA.

HaCaT as well as human primary keratinocytes constitutively expressed mRNA of the human secreted phospholipase A(2) subtype groups X, V, IIA, and IID. A similar expression pattern was also found in human skin biopsies. Protein analysis showed that under serum-free conditions only group X secreted phospholipase A(2) is secreted into cell culture supernatants of HaCaT as well as human primary keratinocytes, whereas the other secreted phospholipases A(2) were not detectable at protein level. HaCaT keratinocytes constitutively released secreted phospholipase A(2) activity into the cell culture supernatant, being reflected by a constant release of fatty acids. The phorbol ester 12-O-tetradecanoylphorbol-13-acetate, which is a potent inducer of inflammation in skin, drastically reduced the mRNA level of group X secreted phospholipase A(2) and other secreted phospholipase A(2) subtypes as well as secreted phospholipase A(2) activity in cell culture supernatants. This suggests that inhibition of secreted phospholipase A(2) expression and activity as well as of fatty acid release by 12-O-tetradecanoylphorbol-13-acetate treatment might be a critical step impairing the integrity of the epidermis during phorbol-ester-induced pathologic processes in skin. The results show that group X secreted phospholipase A(2) represents the major secreted phospholipase A(2) subtype in human keratinocytes and thus may indicate a physiologic role for this enzyme in epidermis in vivo.