Cyclin-dependent kinases (CDKs) are key players in cell cycle regulation. So far, more than ten CDKs have been described. Their direct interaction with cyclins allow progression through G1 phase, transitions to S and G2 phase and finally through mitosis (M). While CDK activation is important in cell renewal, its aberrant expression can lead to the development of malignant tumor cells. Dysregulations in CDK pathways are often encountered in various types of cancer, including all gastrointestinal (GI) tract tumors. This prompted the development of CDK inhibitors as novel therapies for cancer. Currently, CDK inhibitors such as CDK4/6 inhibitors are used in pre-clinical studies for cancer treatment. In this review, we will focus on the therapeutic role of various CDK inhibitors in colorectal cancer, with a special focus on the CDK4/6 inhibitors.

Immune cell activity is a major factor for disease progression in inflammatory bowel diseases (IBD). Classifying the type and functional state of immune cells is therefore crucial in clinical diagnostics of IBD. Label-free optical technologies exploiting NADH and FAD autofluorescence, such as multiphoton microscopy, have been used to describe tissue morphology in healthy and inflamed colon samples. Nevertheless, a strategy for the identification of single immune cell subtypes within the tissue is yet to be developed. This work aims to initiate an understanding of autofluorescence changes depending on immune cell type and activation state. For this, NADH and FAD autofluorescence signals of different murine immune cell subtypes under native conditions, as well as upon in vitro stimulation and cell death, have been evaluated. Autofluorescence was assessed using flow cytometry and multiphoton microscopy. Our results reveal significantly increased NADH and FAD signals in innate immune cells compared to adaptive immune cells. This allowed identification of relative amounts of neutrophils and CD4+ T cells in mixed cell suspensions, by using NADH signals as a differentiation marker. Furthermore, in vitro stimulation significantly increased NADH and FAD autofluorescence in adaptive immune cells and macrophages. Cell death induced a significant drop in NADH autofluorescence, while FAD signals were hardly affected. Taken together, these results demonstrate the value of autofluorescence as a tool to characterize immune cells in different functional states, paving the way to the label-free clinical classification of IBD in the future.

T cells are crucial for the antitumor response against colorectal cancer (CRC). T-cell reactivity to CRC is nevertheless limited by T-cell exhaustion. However, molecular mechanisms regulating T-cell exhaustion are only poorly understood. We investigated the functional role of cyclin-dependent kinase 1a (Cdkn1a or p21) in cluster of differentiation (CD) 4⁺ T cells using murine CRC models. Furthermore, we evaluated the expression of p21 in patients with stage I to IV CRC. In vitro coculture models were used to understand the effector function of p21-deficient CD4⁺ T cells. We observed that the activation of cell cycle regulator p21 is crucial for CD4⁺ T-cell cytotoxic function and that p21 deficiency in type 1 helper T cells (Th1) leads to increased tumor growth in murine CRC. Similarly, low p21 expression in CD4⁺ T cells infiltrated into tumors of CRC patients is associated with reduced cancer-related survival. In mouse models of CRC, p21-deficient Th1 cells show signs of exhaustion, where an accumulation of effector/effector memory T cells and CD27/CD28 loss are predominant. Immune reconstitution of tumor-bearing Rag1^-/- mice using ex vivo-treated p21-deficient T cells with palbociclib, an inhibitor of cyclin-dependent kinase 4/6, restored cytotoxic function and prevented exhaustion of p21-deficient CD4⁺ T cells as a possible concept for future immunotherapy of human disease. Our data reveal the importance of p21 in controlling the cell cycle and preventing exhaustion of Th1 cells. Furthermore, we unveil the therapeutic potential of cyclin-dependent kinase inhibitors such as palbociclib to reduce T-cell exhaustion for future treatment of patients with colorectal cancer.

Colorectal cancer (CRC) continues to be one of the most frequently diagnosed types of cancers in the world. CRC is considered to affect mostly elderly patients, and the number of diagnosed cases increases with age. Even though general screening improves outcomes, the overall survival and recurrence-free CRC rates in aged individuals are highly dependent on their history of comorbidities. Furthermore, aging is also known to alter the immune system, and especially the adaptive immune T cells. Many studies have emphasized the importance of T cell responses to CRC. Therefore, understanding how age-related changes affect the outcome in CRC patients is crucial. This review focuses on what is so far known about age-related T cell dysfunction in elderly patients with colorectal cancer and how aged T cells can mediate its development. Last, this study describes the advances in basic animal models that have potential to be used to elucidate the role of aged T cells in CRC.

Intestinal immune homeostasis relies on intestinal epithelial cells (IECs), which provide an efficient barrier, and warrant a state of tolerance between the microbiome and the mucosal immune system. Thus, proper epithelial microbial sensing and handling of microbes is key to preventing excessive immunity, such as seen in patients with inflammatory bowel disease (IBD). To date, the molecular underpinnings of these processes remain incompletely understood. This study identifies TIFA as a driver of intestinal inflammation and an epithelial signaling hub between the microbiome and mucosal immune cells. TIFA was constitutively expressed in crypt epithelial cells and was highly induced in the intestine of mice and IBD patients with intestinal inflammation. We further identified IL-22 signaling via STAT3 as key mechanism driving TIFA expression in IECs. At the molecular level, we demonstrate that TIFA expression is essential for IEC responsiveness to the bacterial metabolite ADP-heptose. Most importantly, ADP-heptose-induced TIFA signaling orchestrates an inflammatory cellular response in the epithelium, with NF-κB and inflammasome activation, and high levels of chemokine production. Finally, mice lacking TIFA were protected from intestinal inflammation when subjected to a model of experimental colitis. In conclusion, our study implicates that targeting TIFA may be a strategy for future IBD therapy.

Background: Atrial fibrillation (AF) is the most common cardiac arrhythmia with a massive burden on global health. The prevalence of AF increases dramatically with age and can be up to 18% in patients older than 80 years. Telomeres, which are short, repeated DNA sequences at the end of chromosomes, are known to act as a biological aging marker. In this study, we investigated the relation of telomere shortening and AF in the context of atrial remodeling. Furthermore, we assessed changes in the gene expression profiles of patients with AF according to telomere length (TL) and left atrial fibrosis. Methods: We included 72 patients undergoing catheter ablation for AF. Bipolar voltage maps were obtained to determine left atrial low voltage areas as a surrogate for atrial fibrosis. TL was quantified and correlated to low voltage areas. 3′ mRNA sequencing was performed for gene expression profiling. Clonal hematopoiesis of indeterminate potential was assessed by next generation sequencing. Telomerase reverse transcriptase knockout ( Tert ^−/− ) and telomerase RNA component knockout ( Terc ^−/− ) mice were used to investigate the mechanistic impact of telomere shortening on atrial remodeling. Results: Patients with advanced left atrial fibrosis had shorter telomeres compared with patients with healthy left atria. Furthermore, there was a strong correlation between the extent of left atrial low voltage areas, TL, and outcome after catheter ablation of AF. 24 months after ablation, only 26.5% of patients with advanced fibrosis and short TL were in sinus rhythm compared with 62.5% of patients with no/low fibrosis and long TL. Gene expression profiles and clonal hematopoiesis of indeterminate potential frequency differed in patients with AF with short and long telomeres. Finally, atrial tissue of mouse models with shortened telomeres showed marked left atrial fibrosis and over‐expression of fibrosis‐related genes. Conclusions: Telomere shortening is correlated with left atrial remodeling. Shorter telomeres are associated with a series of molecular events which could eventually lead to cardiac fibrosis and perpetuate AF.