Aspartate Alleviates Colonic Epithelial Damage by Regulating Intestinal Stem Cell Proliferation and Differentiation via Mitochondrial Dynamics

Aspartate in tumor microenvironment and beyond: Metabolic interactions and therapeutic perspectives

Aspartate is a proteinogenic non-essential amino acid with several essential functions in proliferating cells. It is mostly produced in a cell autonomous manner from oxalacetate via glutamate oxalacetate transaminases 1 or 2 (GOT1 or GOT2), but in some cases it can also be salvaged from the microenvironment via transporters such as SLC1A3 or by macropinocytosis. In this review we provide an overview of biosynthetic pathways that produce aspartate endogenously during proliferation. We discuss conditions that favor aspartate uptake as well as possible sources of exogenous aspartate in the microenvironment of tumors and bone marrow, where most available data have been generated. We highlight metabolic fates of aspartate, its various functions, and possible approaches to target aspartate metabolism for cancer therapy.

Berberine enhances the function of intestinal stem cells in healthy and radiation-injured mice

Intestinal stem cells (ISCs) are pivotal for the maintenance and regeneration of the intestinal epithelium. Berberine (BBR) exhibits diverse biological activities, but it remains unclear whether BBR can modulate ISCs' function. Therefore, we investigated the effects of BBR on ISCs in healthy and radiation-injured mice and explored the potential underlying mechanisms involved. The results showed that BBR significantly increased the length of the small intestines, the height of the villi, and the depth and density of the crypts, promoted the proliferation of cryptal epithelial cells and increased the number of OLFM4+ ISCs and goblet cells. Crypts from the BBR-treated mice were more capable of growing into enteroids than those from untreated mice. BBR alleviated WAI-induced intestinal injury. BBR suppressed the apoptosis of crypt epithelial cells, increased the quantity of goblet cells, and increased the quantity of OLFM4+ ISCs and tdTomato+ progenies of ISCs after 8 Gy WAI-induced injury. Mechanistically, BBR treatment caused a significant increase in the quantity of p-S6, p-STAT3 and p-ERK1/2 positive cryptal epithelial cells under physiological conditions and after WAI-induced injury. In conclusion, BBR is capable of enhancing the function of ISCs either physiologically or after radiation-induced injury, indicating that BBR has potential value in the treatment of radiation-induced intestinal injury.

Dietary α-Ketoglutarate Alleviates Escherichia coli LPS-Induced Intestinal Barrier Injury by Modulating the Endoplasmic Reticulum-Mitochondrial System Pathway in Piglets

BACKGROUND

α-Ketoglutarate (AKG) plays a pivotal role in mitigating inflammation and enhancing intestinal health.

OBJECTIVES

This study aimed to investigate whether AKG could protect against lipopolysaccharide (LPS)-induced intestinal injury by alleviating disorders in mitochondria-associated endoplasmic reticulum (MAM) membranes, dysfunctional mitochondrial dynamics, and endoplasmic reticulum (ER) stress in a piglet model.

METHODS

Twenty-four piglets were subjected to a 2 × 2 factorial design with dietary factors (basal diet or 1% AKG diet) and LPS treatment (LPS or saline). After 21 d of consuming either the basal diet or AKG diet, piglets received injections of LPS or saline. The experiment was divided into 4 treatment groups [control (CON) group: basal diet + saline; LPS group: basal diet +LPS; AKG group: AKG diet + saline; and AKG_LPS group: AKG + LPS], each consisting of 6 piglets.

RESULTS

The results demonstrated that compared with the CON group, AKG enhanced jejunal morphology, antioxidant capacity, and the messenger RNA and protein expression of tight junction proteins. Moreover, it has shown a reduction in serum diamine oxidase activity and D-lactic acid content in piglets. In addition, fewer disorders in the ER-mitochondrial system were reflected by AKG, as evidenced by AKG regulating the expression of key molecules of mitochondrial dynamics (mitochondrial calcium uniporter, optic atrophy 1, fission 1, and dynamin-related protein 1), ER stress [activating transcription factor (ATF) 4, ATF 6, CCAAT/enhancer binding protein homologous protein, eukaryotic initiation factor 2α, glucose-regulated protein (GRP) 78, and protein kinase R-like ER kinase], and MAM membranes [mitofusin (Mfn)-1, Mfn-2, GRP 75, and voltage-dependent anion channel-1].

CONCLUSIONS

Dietary AKG can prevent mitochondrial dynamic dysfunction, ER stress, and MAM membrane disorder, ultimately alleviating LPS-induced intestinal damage in piglets.

Oleanolic acid alleviate intestinal inflammation by inhibiting Takeda G-coupled protein receptor (TGR) 5 mediated cell apoptosis

Oleanolic acid (OA) is a bioactive compound present in plant-based foods known for its beneficial impact on gastrointestinal health, specifically in alleviating diarrhea. Nonetheless, the underlying mechanisms by which OA mitigates gut epithelial damage have yet to be elucidated. In this study, OA significantly markedly ameliorated adverse effects induced by Dextran Sulfate Sodium (DSS), including weight loss and epithelial morphological damage in a murine model. Remarkably, compared to normal mice, standalone administration of OA had no discernible impact on the animals. Concurrently, we identified a significant up-regulation in the expression levels of TGR5 and BAX in the intestines of DSS-exposed mice, coupled with a decline in Bcl2 expression. Correlation analyses revealed a robust association between TGR5 and BAX expression. Oral administration of OA efficaciously counteracted these alterations. To probe the role of TGR5 in cellular apoptosis, further, a lentivirus transfection approach was utilized to induce TGR5 overexpression in intestinal epithelial cells (IPEC-J2). RNA sequencing indicated that TGR5 overexpression significantly influenced biological processes, particularly in modulating cellular activation and intercellular adhesion, in contrast to the control group cells. Functional assays substantiated that TGR5 overexpression compromised cell viability and accelerated apoptosis. Notably, OA treatment in TGR5-overexpressed cells restored cell viability, suppressed TGR5 and BAX expression, and augmented Bcl2 expression. In sum, our data suggest that OA mitigates intestinal epithelial apoptosis and bolsters cellular proliferation by downregulating TGR5. This research provides valuable insights into the prospective utility of OA as a functional food supplement or adjunctive therapeutic agent for enhancing gastrointestinal health.

Modulation of stem cell fate in intestinal homeostasis, injury and repair

The mammalian intestinal epithelium constitutes the largest barrier against the external environment and makes flexible responses to various types of stimuli. Epithelial cells are fast-renewed to counteract constant damage and disrupted barrier function to maintain their integrity. The homeostatic repair and regeneration of the intestinal epithelium are governed by the Lgr5⁺ intestinal stem cells (ISCs) located at the base of crypts, which fuel rapid renewal and give rise to the different epithelial cell types. Protracted biological and physicochemical stress may challenge epithelial integrity and the function of ISCs. The field of ISCs is thus of interest for complete mucosal healing, given its relevance to diseases of intestinal injury and inflammation such as inflammatory bowel diseases. Here, we review the current understanding of the signals and mechanisms that control homeostasis and regeneration of the intestinal epithelium. We focus on recent insights into the intrinsic and extrinsic elements involved in the process of intestinal homeostasis, injury, and repair, which fine-tune the balance between self-renewal and cell fate specification in ISCs. Deciphering the regulatory machinery that modulates stem cell fate would aid in the development of novel therapeutics that facilitate mucosal healing and restore epithelial barrier function.