Upregulation of complement C1q reflects mucosal regeneration in a mouse model of colitis

Revisiting the relationship between complement and ulcerative colitis

Ulcerative colitis (UC) is an inflammatory bowel disorder (IBD) characterized by relapsing chronic inflammation of the colon that causes continuous mucosal inflammation. The global incidence of UC is steadily increasing. Immune mechanisms are involved in the pathogenesis of UC, of which complement is shown to play a critical role by inducing local chronic inflammatory responses that promote tissue damage. However, the function of various complement components in the development of UC is complex and even paradoxical. Some components (e.g. C1q, CD46, CD55, CD59, and C6) are shown to safeguard the intestinal barrier and reduce intestinal inflammation, while others (e.g. C3, C5, C5a) can exacerbate intestinal damage and accelerate the development of UC. The complement system was originally thought to function primarily in an extracellular mode; however, recent evidence indicates that it can also act intracellularly as the complosome. The current study provides an overview of current studies on complement and its role in the development of UC. While there are few studies that describe how intracellular complement contributes to UC, we discuss potential future directions based on related publications. We also highlight novel methods that target complement for IBD treatment.

Paeoniflorin prevents aberrant proliferation and differentiation of intestinal stem cells by controlling C1q release from macrophages in chronic colitis

The pathological features of inflammatory bowel disease necessitate therapeutic strategies aimed at restoring intestinal mucosal barrier function in addition to controlling inflammation. Paeoniflorin, a bioactive herbal constituent isolated from the root of Paeonia albiflora Pall, has been reported to protect against acute colitis in mice. However, the direct molecular target of paeoniflorin in preventing colitis remains elusive. Here, we evaluated the therapeutical effects of Paeoniflorin using IL-10^-/- chronic colitis model, and explored the precise mechanism of action involved. Our results demonstrated that intragastric administration of Paeoniflorin significantly ameliorated inflammatory response and restored the aberrant intestinal proliferation and differentiation in IL-10^-/-colitis mice. By utilizing a chemical biology approach, we identified C1qa, a crucial component of C1q, is the direct target of Paeoniflorin. Binding of Paeoniflorin to C1qa prevented the cleavage of C1q on macrophages, resulting in the aggregation of surface membrane-anchored C1q and the diminished C1q secretion. The excessive surface membrane-anchored C1q significantly enhanced the phagocytic capability of macrophages and promoted the elimination of infiltrated bacteria and inflammatory cells in mouse colon. The reduced C1q secretion conferred by Paeoniflorin dampened Wnt/β-catenin signaling activation, thereby rectifying the aberrant proliferation and differentiation of intestinal stem cells (ISCs). In summary, our study demonstrates that Paeoniflorin can orchestrate mucosal healing and intestinal inflammation elimination through C1q-bridged macrophage-ISCs crosstalk, highlighting a novel strategy to treat chronic colitis by restoring mucosal homeostasis via targeting C1q.

Interleukin-22 Deficiency Contributes to Dextran Sulfate Sodium-Induced Inflammation in Japanese Medaka, Oryzias latipes

Mucosal tissue forms the first line of defense against pathogenic microorganisms. Cellular damage in the mucosal epithelium may induce the interleukin (IL)-22-related activation of many immune cells, which are essential for maintaining the mucosal epithelial barrier. A previous study on mucosal immunity elucidated that mammalian IL-22 contributes to mucus and antimicrobial peptides (AMPs) production and anti-apoptotic function. IL-22 has been identified in several teleost species and is also induced in response to bacterial infections. However, the roles of IL-22 in teleost immunity and mucus homeostasis are poorly understood. In this study, Japanese medaka (Oryzias latipes) was used as a model fish. The medaka il22, il22 receptor A1 (il22ra1), and il22 binding protein (il22bp) were cloned and characterized. The expression of medaka il22, il22ra1, and il22bp in various tissues was measured using qPCR. These genes were expressed at high levels in the mucosal tissues of the intestines, gills, and skin. The localization of il22 and il22bp mRNA in the gills and intestines was confirmed by in situ hybridizations. Herein, we established IL-22-knockout (KO) medaka using the CRISPR/Cas9 system. In the IL-22-KO medaka, a 4-bp deletion caused a frameshift in il22. To investigate the genes subject to IL-22-dependent regulation, we compared the transcripts of larval medaka between wild-type (WT) and IL-22-KO medaka using RNA-seq and qPCR analyses. The comparison was performed not only in the naïve state but also in the dextran sulfate sodium (DSS)-exposed state. At the transcriptional level, 368 genes, including immune genes, such as those encoding AMPs and cytokines, were significantly downregulated in IL-22-KO medaka compared that in WT medaka in naïve states. Gene ontology analysis revealed that upon DSS stimulation, genes associated with cell death, acute inflammatory response, cell proliferation, and others were upregulated in WT medaka. Furthermore, in DSS-stimulated IL-22-KO medaka, wound healing was delayed, the number of apoptotic cells increased, and the number of goblet cells in the intestinal epithelium decreased. These results suggested that in medaka, IL-22 is important for maintaining intestinal homeostasis, and the disruption of the IL-22 pathway is associated with the exacerbation of inflammatory pathology, as observed for mammalian IL-22.