Amandine Chaix

Tumor protein 53-induced nuclear protein 1 expression is repressed by miR-155, and its restoration inhibits pancreatic tumor development

Pancreatic cancer is a disease with an extremely poor prognosis. Tumor protein 53-induced nuclear protein 1 (TP53INP1) is a proapoptotic stress-induced p53 target gene. In this article, we show by immunohistochemical analysis that TP53INP1 expression is dramatically reduced in pancreatic ductal adenocarcinoma (PDAC) and this decrease occurs early during pancreatic cancer development. TP53INP1 reexpression in the pancreatic cancer-derived cell line MiaPaCa2 strongly reduced its capacity to form s.c., i.p., and intrapancreatic tumors in nude mice. This anti-tumoral capacity is, at least in part, due to the induction of caspase 3-mediated apoptosis. In addition, TP53INP1−/− mouse embryonic fibroblasts (MEFs) transformed with a retrovirus expressing E1A/rasV12 oncoproteins developed bigger tumors than TP53INP1+/+ transformed MEFs or TP53INP1−/− transformed MEFs with restored TP53INP1 expression. Finally, TP53INP1 expression is repressed by the oncogenic micro RNA miR-155, which is overexpressed in PDAC cells. TP53INP1 is a previously unknown miR-155 target presenting anti-tumoral activity.

Time-Restricted Feeding Is a Preventative and Therapeutic Intervention against Diverse Nutritional Challenges

Because current therapeutics for obesity are limited and only offer modest improvements, novel interventions are needed. Preventing obesity with time-restricted feeding (TRF; 8-9 hr food access in the active phase) is promising, yet its therapeutic applicability against preexisting obesity, diverse dietary conditions, and less stringent eating patterns is unknown. Here we tested TRF in mice under diverse nutritional challenges. We show that TRF attenuated metabolic diseases arising from a variety of obesogenic diets, and that benefits were proportional to the fasting duration. Furthermore, protective effects were maintained even when TRF was temporarily interrupted by ad libitum access to food during weekends, a regimen particularly relevant to human lifestyle. Finally, TRF stabilized and reversed the progression of metabolic diseases in mice with preexisting obesity and type II diabetes. We establish clinically relevant parameters of TRF for preventing and treating obesity and metabolic disorders, including type II diabetes, hepatic steatosis, and hypercholesterolemia.

Diet and Feeding Pattern Affect the Diurnal Dynamics of the Gut Microbiome

The gut microbiome and daily feeding/fasting cycle influence host metabolism and contribute to obesity and metabolic diseases. However, fundamental characteristics of this relationship between the feeding/fasting cycle and the gut microbiome are unknown. Our studies show that the gut microbiome is highly dynamic, exhibiting daily cyclical fluctuations in composition. Diet-induced obesity dampens the daily feeding/fasting rhythm and diminishes many of these cyclical fluctuations. Time-restricted feeding (TRF), in which feeding is consolidated to the nocturnal phase, partially restores these cyclical fluctuations. Furthermore, TRF, which protects against obesity and metabolic diseases, affects bacteria shown to influence host metabolism. Cyclical changes in the gut microbiome from feeding/fasting rhythms contribute to the diversity of gut microflora and likely represent a mechanism by which the gut microbiome affects host metabolism. Thus, feeding pattern and time of harvest, in addition to diet, are important parameters when assessing the microbiomes contribution to host metabolism.

Local circadian clock gates cell cycle progression of transient amplifying cells during regenerative hair cycling

Significance Here, we show that cell autonomous circadian clock optimizes physiological regeneration of hair follicles by synchronizing mitotic progression in transient amplifying hair-matrix cells. The daily mitotic rhythm makes hairs grow faster in the morning than in the evening. Also, because of high sensitivity of mitotic cells to radiation, significantly greater hair loss occurs in the morning than in the evening following exposure to the same dose of γ-radiation. These results provide a roadmap for developing new radiation therapy protocols, when radiation cytotoxicity can be either minimized or maximized by timing its delivery throughout the course of the day. Regenerative cycling of hair follicles offers an unique opportunity to explore the role of circadian clock in physiological tissue regeneration. We focused on the role of circadian clock in actively proliferating transient amplifying cells, as opposed to quiescent stem cells. We identified two key sites of peripheral circadian clock activity specific to regenerating anagen hair follicles, namely epithelial matrix and mesenchymal dermal papilla. We showed that peripheral circadian clock in epithelial matrix cells generates prominent daily mitotic rhythm. As a consequence of this mitotic rhythmicity, hairs grow faster in the morning than in the evening. Because cells are the most susceptible to DNA damage during mitosis, this cycle leads to a remarkable time-of-day–dependent sensitivity of growing hair follicles to genotoxic stress. Same doses of γ-radiation caused dramatic hair loss in wild-type mice when administered in the morning, during mitotic peak, compared with the evening, when hair loss is minimal. This diurnal radioprotective effect becomes lost in circadian mutants, consistent with asynchronous mitoses in their hair follicles. Clock coordinates cell cycle progression with genotoxic stress responses by synchronizing Cdc2/Cyclin B-mediated G2/M checkpoint. Our results uncover diurnal mitotic gating as the essential protective mechanism in highly proliferative hair follicles and offer strategies for minimizing or maximizing cytotoxicity of radiation therapies.

Daily Eating Patterns and Their Impact on Health and Disease

Cyclical expression of cell-autonomous circadian clock components and key metabolic regulators coordinate often discordant and distant cellular processes for efficient metabolism. Perturbation of these cycles, either by genetic manipulation, disruption of light/dark cycles, or, most relevant to the human population, via eating patterns, contributes to obesity and dysmetabolism. Time-restricted feeding (TRF), during which time of access to food is restricted to a few hours, without caloric restriction, supports robust metabolic cycles and protects against nutritional challenges that predispose to obesity and dysmetabolism. The mechanism by which TRF imparts its benefits is not fully understood but likely involves entrainment of metabolically active organs through gut signaling. Understanding the relationship of feeding pattern and metabolism could yield novel therapies for the obesity pandemic.

The circadian coordination of cell biology.

Chaix et al. review how cells generate circadian oscillations and how circadian clocks control cell biology.

The effects of time-restricted feeding on lipid metabolism and adiposity

Maintaining natural feeding rhythms with time-restricted feeding (TRF), without altering nutritional intake, prevents and reverses diet-induced obesity (DIO) and its associated metabolic disorders in mice. TRF has a direct effect on animal adiposity, causes an alteration of adipokine signaling, and diminishes white adipose tissue inflammation. Many genes involved in lipid metabolism are normally circadian, but their expression is perturbed with DIO; TRF restores their cyclical expression. One mechanism through which TRF could affect host metabolism is by altering the gut microbiome. Changes in the gut microbiome are coupled with an altered stool bile acid profile. Hence, TRF could affect lipid metabolism by altering bile acid signaling. TRF introduces many new possibilities in treating obesity and its associated metabolic disorders. However, further studies are needed to show whether these physiological findings in mice translate to humans.