Coronaviral ORF6 protein mediates inter-organelle contacts and modulates host cell lipid flux for virus production.

Lipid droplets (LDs) form inter-organelle contacts with the endoplasmic reticulum (ER) that promote their biogenesis, while LD contacts with mitochondria enhance ß-oxidation of contained fatty acids. Viruses have been shown to take advantage of lipid droplets to promote viral production, but it remains unclear whether they also modulate the interactions between LDs and other organelles. Here, we showed that coronavirus ORF6 protein targets LDs and is localized to the mitochondria-LD and ER-LD contact sites, where it regulates LD biogenesis and lipolysis. At the molecular level, we find that ORF6 inserts into the LD lipid monolayer via its two amphipathic helices. ORF6 further interacts with ER membrane proteins BAP31 and USE1 to mediate ER-LDs contact formation. Additionally, ORF6 interacts with the SAM complex in the mitochondrial outer membrane to link mitochondria to LDs. In doing so, ORF6 promotes cellular lipolysis and LD biogenesis to reprogram host cell lipid flux and facilitate viral production.

Prostaglandin E2 accelerated recovery of chemotherapy-induced intestinal damage by increasing expression of cyclin D.

Intestinal stem cells (ISCs) play a crucial role in maintaining intestinal homeostasis upon chemotherapy and radiotherapy. It has been documented that prostaglandin E2 (PGE2) treatment improved hematopoietic stem cell function in vitro and in vivo, while the relationship between PGE2 and intestinal stem cells remains unclear. Presently, mice were exposed to PGE1, dmPGE2 and indomethacin. Numbers and function of ISCs were assessed by analyzing Olfm4+ ISCs. Intestinal protection of dmPGE2 was investigated on a 5-fluorouracil (5FU)-induced intestinal damage mouse model. The results showed that dmPGE2 treatment, but not PGE1, increased numbers of Olfm4+ ISCs in dose- and time-dependent manners. Indomethacin treatment decreased numbers of Olfm4+ ISCs. The beneficial effects of short-term dmPGE2 treatment on intestine were supported in a 5FU-induced intestinal damage model. Our data showed that 5FU treatment significantly decreased numbers of Olfm4+ ISCs and goblet cells in intestine, which could be ameliorated by dmPGE2 treatment. dmPGE2 treatment accelerated the recovery of 5FU-induced ISC injury via increasing expression of cyclin D1 and D2 in intestine. Furthermore, dmPGE2 treatment-induced expression of cyclin D1 and D2 might be mediated by up-regulation of FOXM1 expression in intestine. These findings feature PGE2 as an effective protector against chemotherapy-induced intestinal damage.

Polyinosinic-polycytidylic acid accelerates intestinal stem cell proliferation via modulating Myc expression.

It is well known that exposure of double-stranded RNA (dsRNA) to intestine immediately induces villus damage with severe diarrhea, which is mediated by toll-like receptor 3 signaling activation. However, the role of intestinal stem cells (ISCs) remains obscure during the pathology. In the present study, polyinosinic-polycytidylic acid (poly[I:C]), mimicking viral dsRNA, was used to establish intestinal damage model. Mice were acutely and chronically exposed to poly(I:C), and ISCs in jejunum were analyzed. The results showed that the height of villus was shorter 48 hr after acute poly(I:C) exposure compared with that of controls, while chronic poly(I:C) treatment increased both villus height and crypt depth in jejunum compared with control animals. The numbers of ISCs in jejunum were significantly increased after acute and chronic poly(I:C) exposure. Poly (I:C)-stimulated ISCs have stronger capacities to differentiate into intestine endocrine cells. Mechanistically, poly(I:C) treatment increased expression of Stat1 and Axin2 in the intestinal crypt, which was along with increased expression of Myc, Bcl2, and ISC proliferation. These findings suggest that dsRNA exposure could induce ISC proliferation to ameliorate dsRNA-induced intestinal injury.

Isoprenaline protects intestinal stem cells from chemotherapy-induced damage.

BACKGROUND AND PURPOSE: Damage to intestinal epithelial cells and mucosa limits the effectiveness of several anti-cancer chemotherapeutic agents but the underlying mechanism (s) remain unknown. Little is known of how enteric nervous system regulates proliferation, differentiation, impairment, and regeneration of intestinal stem cells. Here we have investigated the effects of isoprenaline on the damaged intestinal stem cells induced by chemotherapeutic treatments in mice. EXPERIMENTAL APPROACH: The effects of inhibiting sympathetic and parasympathetic nerves on intestinal stem cells were examined in male C57BL/6J mice. Protection by isoprenaline of intestinal stem cells was assessed in the presence or absence of 5-fluorouracil (5FU) or cisplatin. Cellular apoptosis, cell cycle, PI3K/Akt signalling, and NF-κB signalling in intestinal stem cells were mechanistically evaluated. KEY RESULTS: The sympathetic nerve inhibitor 6-OHDA decreased the number and function of intestinal stem cells. 5FU or cisplatin treatment damaged both intestinal stem cells and sympathetic nerves. Notably, isoprenaline accelerated the recovery of intestinal stem cells after 5FU or cisplatin treatment. This protective effect of isoprenaline on damaged intestinal stem cells was mediated by ß2 -adrenoceptors. The benefits of isoprenaline were mainly mediated by inhibiting cellular apoptosis induced by 5FU treatment, which might contribute to fine-tuning regulating NF-κB signalling pathway by isoprenaline administration. CONCLUSIONS AND IMPLICATIONS: Treatment with isoprenaline is a new approach to ameliorate the damage to intestinal stem cells following exposure to cancer chemotherapeutic agents.

Transient Inhibition of mTORC1 Signaling Ameliorates Irradiation-Induced Liver Damage.

Recurrent liver cancer after surgery is often treated with radiotherapy, which induces liver damage. It has been documented that activation of the TGF-ß and NF-κB signaling pathways plays important roles in irradiation-induced liver pathologies. However, the significance of mTOR signaling remains undefined after irradiation exposure. In the present study, we investigated the effects of inhibiting mTORC1 signaling on irradiated livers. Male C57BL/6J mice were acutely exposed to 8.0 Gy of X-ray total body irradiation and subsequently treated with rapamycin. The effects of rapamycin treatment on irradiated livers were examined at days 1, 3, and 7 after exposure. The results showed that 8.0 Gy of irradiation resulted in hepatocyte edema, hemorrhage, and sinusoidal congestion along with a decrease of ALB expression. Exposure of mice to irradiation significantly activated the mTORC1 signaling pathway determined by pS6 and p-mTOR expression via western blot and immunostaining. Transient inhibition of mTORC1 signaling by rapamycin treatment consistently accelerated liver recovery from irradiation, which was evidenced by decreasing sinusoidal congestion and increasing ALB expression after irradiation. The protective role of rapamycin on irradiated livers might be mediated by decreasing cellular apoptosis and increasing autophagy. These data suggest that transient inhibition of mTORC1 signaling by rapamycin protects livers against irradiation-induced damage.

Inhibition of mTORC1 signaling protects kidney from irradiation-induced toxicity via accelerating recovery of renal stem-like cells.

BACKGROUND: Irradiation-induced kidney damage is inevitable during radiotherapeutic practice, which limits effective radiotherapy doses on tumor treatment. In the present study, the role of mTOR complex 1 (mTORC1) signaling was investigated in irradiation-induced renal injuries. METHODS: Mice were exposed to 8.0-Gy X-ray of total body irradiation and subsequently treated with rapamycin. Changes of renal morphology were assessed by hematoxylin and eosin staining. Expression of pS6 and CD133 was detected via immunostaining. Cellular apoptosis and proliferation were measured by TUNEL, caspase-3 and BrdU staining. Activation of mTORC1, TGF-ß and NF-κB signaling pathways was determined through western blot analysis. RESULTS: Our data displayed that irradiation disrupted the structures of renal corpuscles and tubules and decreased the density of CD133+ renal stem-like cells, which were related with increasing cellular apoptosis and decreasing cell proliferation post exposure. Activation of mTORC1, TGF-ß and NF-κB signaling pathways was determined in irradiated renal tissues, which were inhibited by rapamycin treatment. Application of rapamycin after irradiation decreased cellular apoptosis and increased autophagy and cell proliferation in renal tissues. The density of CD133+ renal stem-like cells was significantly increased in irradiated kidneys after rapamycin treatment. The morphology of irradiated renal corpuscles and tubules was gradually recovered upon rapamycin treatment. CONCLUSIONS: These findings indicate that inhibition of mTORC1 signaling by rapamycin ameliorates irradiation-induced renal toxicity mediated by decreasing cellular apoptosis and increasing CD133+ renal stem-like cells.