ClC-c regulates the proliferation of intestinal stem cells via the EGFR signalling pathway in Drosophila.

OBJECTIVES: Adult stem cells uphold a delicate balance between quiescent and active states, which is crucial for tissue homeostasis. Whereas many signalling pathways that regulate epithelial stem cells have been reported, many regulators remain unidentified. MATERIALS AND METHODS: Flies were used to generate tissue-specific gene knockdown and gene knockout. qRT-PCR was used to assess the relative mRNA levels. Immunofluorescence was used to determine protein localization and expression patterns. Clonal analyses were used to observe the phenotype. RNA-seq was used to screen downstream mechanisms. RESULTS: Here, we report a member of the chloride channel family, ClC-c, which is specifically expressed in Drosophila intestinal stem/progenitor cells and regulates intestinal stem cell (ISC) proliferation under physiological conditions and upon tissue damage. Mechanistically, we found that the ISC loss induced by the depletion of ClC-c in intestinal stem/progenitor cells is due to inhibition of the EGFR signalling pathway. CONCLUSION: Our findings reveal an ISC-specific function of ClC-c in regulating stem cell maintenance and proliferation, thereby providing new insights into the functional links among the chloride channel family, ISC proliferation and tissue homeostasis.

Aging-related upregulation of the homeobox gene caudal represses intestinal stem cell differentiation in Drosophila.

The differentiation efficiency of adult stem cells undergoes a significant decline in aged animals, which is closely related to the decline in organ function and age-associated diseases. However, the underlying mechanisms that ultimately lead to this observed decline of the differentiation efficiency of stem cells remain largely unclear. This study investigated Drosophila midguts and identified an obvious upregulation of caudal (cad), which encodes a homeobox transcription factor. This factor is traditionally known as a central regulator of embryonic anterior-posterior body axis patterning. This study reports that depletion of cad in intestinal stem/progenitor cells promotes quiescent intestinal stem cells (ISCs) to become activate and produce enterocytes in the midgut under normal gut homeostasis conditions. However, overexpression of cad results in the failure of ISC differentiation and intestinal epithelial regeneration after injury. Moreover, this study suggests that cad prevents intestinal stem/progenitor cell differentiation by modulating the Janus kinase/signal transducers and activators of the transcription pathway and Sox21a-GATAe signaling cascade. Importantly, the reduction of cad expression in intestinal stem/progenitor cells restrained age-associated gut hyperplasia in Drosophila. This study identified a function of the homeobox gene cad in the modulation of adult stem cell differentiation and suggested a potential gene target for the treatment of age-related diseases induced by age-related stem cell dysfunction.

Taurine represses age-associated gut hyperplasia in Drosophila via counteracting endoplasmic reticulum stress.

As they age, adult stem cells become more prone to functional decline, which is responsible for aging-associated tissue degeneration and diseases. One goal of aging research is to identify drugs that can repair age-associated tissue degeneration. Multiple organ development-related signaling pathways have recently been demonstrated to have functions in tissue homeostasis and aging process. Therefore, in this study, we tested several chemicals that are essential for organ development to assess their ability to delay intestinal stem cell (ISC) aging and promote gut function in adult Drosophila. We found that taurine, a free amino acid that supports neurological development and tissue metabolism in humans, represses ISC hyperproliferation and restrains the intestinal functional decline seen in aged animals. We found that taurine represses age-associated ISC hyperproliferation through a mechanism that eliminated endoplasmic reticulum (ER) stress by upregulation of the target genes of unfolded protein response in the ER (UPRER ) and inhibiting the c-Jun N-terminal kinase (JNK) signaling. Our findings show that taurine plays a critical role in delaying the aging process in stem cells and suggest that it may be used as a natural compound for the treatment of age-associated, or damage-induced intestinal dysfunction in humans.

Lipoic acid rejuvenates aged intestinal stem cells by preventing age-associated endosome reduction.

The age-associated decline of adult stem cell function is closely related to the decline in tissue function and age-related diseases. However, the underlying mechanisms that ultimately lead to the observed functional decline of stem cells still remain largely unexplored. This study investigated Drosophila midguts and found a continuous downregulation of lipoic acid synthase, which encodes the key enzyme for the endogenous synthesis of alpha-lipoic acid (ALA), upon aging. Importantly, orally administration of ALA significantly reversed the age-associated hyperproliferation of intestinal stem cells (ISCs) and the observed decline of intestinal function, thus extending the lifespan of Drosophila. This study reports that ALA reverses age-associated ISC dysfunction by promoting the activation of the endocytosis-autophagy network, which decreases in aged ISCs. Moreover, this study suggests that ALA may be used as a safe and effective anti-aging compound for the treatment of ISC-dysfunction-related diseases and for the promotion of healthy aging in humans.

Peroxisome Elevation Induces Stem Cell Differentiation and Intestinal Epithelial Repair.

Epithelial-repair-dependent mucosal healing (MH) is associated with a more favorable prognosis for patients with inflammatory bowel disease (IBD). MH is accomplished via repair and regeneration of the intestinal epithelium. However, the mechanism underlying MH is ill defined. We found a striking upregulation of peroxisomes in the injured crypts of IBD patients. By increasing peroxisome levels in Drosophila midguts, we found that peroxisome elevation enhanced RAB7-dependent late endosome maturation, which then promoted stem and/or progenitor-cell differentiation via modulation of Janus Kinase (JAK) and Signal Transducer and Activator of Transcription (STAT)-SOX21A signaling. This in turn enhanced ISC-mediated regeneration. Importantly, RAB7 and SOX21 were upregulated in the crypts of IBD patients. Moreover, administration of drugs that increased peroxisome levels reversed the symptoms of dextran sulfate sodium (DSS)-induced colitis in mice. This study demonstrates a peroxisome-mediated epithelial repair mechanism, which opens a therapeutic avenue for the enhancement of MH in IBD patients.