B cell senescence promotes age-related changes in oral microbiota.

In recent years, there has been increasing attention towards understanding the relationship between age-related alterations in the oral microbiota and age-associated diseases, with reports emphasizing the significance of maintaining a balanced oral microbiota for host health. However, the precise mechanisms underlying age-related changes in the oral microbiota remain elusive. We recently reported that cellular senescence of ileal germinal center (GC) B cells, triggered by the persistent presence of commensal bacteria, results in diminished IgA production with aging and subsequent alterations in the gut microbiota. Consequently, we hypothesize that a similar phenomenon may occur in the oral cavity, potentially contributing to age-related changes in the oral microbiota. Examination of p16-luc mice, wherein the expression of the senescent cell marker p16INK4a can be visualized, raised under specific pathogen-free (SPF) or germ-free (GF) conditions, indicated that, unlike ileal GC B cells, the accumulation of senescent cells in GC B cells of cervical lymph nodes increases with age regardless of the presence of commensal bacteria. Furthermore, longitudinal studies utilizing the same individual mice throughout their lifespan revealed concurrent age-related alterations in the composition of the oral microbiota and a decline in salivary IgA secretion. Further investigation involving Rag1-/- mice transplanted with B cells from wild-type or p16INK4a and p21Waf1/Cip1 -double knockout mice unveiled that B cell senescence leads to reduced IgA secretion and alteration of the oral microbiota. These findings advance our understanding of the mechanism of age-associated changes in the oral microbiota and open up possibilities of their control.

Cellular senescence in white matter microglia is induced during ageing in mice and exacerbates the neuroinflammatory phenotype.

Cellular senescence, a state of irreversible cell-cycle arrest caused by a variety of cellular stresses, is critically involved in age-related tissue dysfunction in various organs. However, the features of cells in the central nervous system that undergo senescence and their role in neural impairment are not well understood as yet. Here, through comprehensive investigations utilising single-cell transcriptome analysis and various mouse models, we show that microglia, particularly in the white matter, undergo cellular senescence in the brain and spinal cord during ageing and in disease models involving demyelination. Microglial senescence is predominantly detected in disease-associated microglia, which appear in ageing and neurodegenerative diseases. We also find that commensal bacteria promote the accumulation of senescent microglia and disease-associated microglia during ageing. Furthermore, knockout of p16INK4a, a key senescence inducer, ameliorates the neuroinflammatory phenotype in damaged spinal cords in mice. These results advance our understanding of the role of cellular senescence in the central nervous system and open up possibilities for the treatment of age-related neural disorders.

Bacterial induction of B cell senescence promotes age-related changes in the gut microbiota.

The elucidation of the mechanisms of ageing and the identification of methods to control it have long been anticipated. Recently, two factors associated with ageing-the accumulation of senescent cells and the change in the composition of gut microbiota-have been shown to play key roles in ageing. However, little is known about how these phenomena occur and are related during ageing. Here we show that the persistent presence of commensal bacteria gradually induces cellular senescence in gut germinal centre B cells. Importantly, this reduces both the production and diversity of immunoglobulin A (IgA) antibodies that target gut bacteria, thereby changing the composition of gut microbiota in aged mice. These results have revealed the existence of IgA-mediated crosstalk between the gut microbiota and cellular senescence and thus extend our understanding of the mechanism of gut microbiota changes with age, opening up possibilities for their control.

Gut bacteria identified in colorectal cancer patients promote tumourigenesis via butyrate secretion.

Emerging evidence is revealing that alterations in gut microbiota are associated with colorectal cancer (CRC). However, very little is currently known about whether and how gut microbiota alterations are causally associated with CRC development. Here we show that 12 faecal bacterial taxa are enriched in CRC patients in two independent cohort studies. Among them, 2 Porphyromonas species are capable of inducing cellular senescence, an oncogenic stress response, through the secretion of the bacterial metabolite, butyrate. Notably, the invasion of these bacteria is observed in the CRC tissues, coinciding with the elevation of butyrate levels and signs of senescence-associated inflammatory phenotypes. Moreover, although the administration of these bacteria into ApcΔ14/+ mice accelerate the onset of colorectal tumours, this is not the case when bacterial butyrate-synthesis genes are disrupted. These results suggest a causal relationship between Porphyromonas species overgrowth and colorectal tumourigenesis which may be due to butyrate-induced senescence.

Is distal pancreatectomy with en-bloc celiac axis resection effective for patients with locally advanced pancreatic ductal adenocarcinoma? -Multicenter surgical group study.

OBJECTIVES: We retrospectively investigated the operative outcomes of patients who underwent distal pancreatectomy (DP) for invasive pancreatic ductal adenocarcinoma (PDAC) located at the body and tail. METHODS: Data from 395 patients with PDAC who underwent DP with margin-negative resection (R0 or R1) were collected from seven high-volume centers in Japan from 2001 to 2012. Among them, 72 patients underwent DP with en-bloc celiac axis resection (DP-CAR). The remaining 323 patients underwent conventional DP with splenectomy (DP-S). To determine the efficacy of DP-CAR, clinicopathological data were compared between the DP-CAR and the DP-S groups. RESULTS: The DP-S group consisted mainly of patients with resectable disease (93%), and conversely, all patients in the DP-CAR group had borderline resectable or unresectable disease. The overall morbidity was significantly higher in the DP-CAR group than in the DP-S group (63% vs 47%, respectively; P = 0.017). The median survival time (MST) of the DP-CAR group was significantly shorter than that of the DP-S group (17.5 vs 28.6 months, respectively; P = 0.004). However, the MST of patients in the DP-CAR group (n = 61, 85%) who received adjuvant therapy was significantly longer than that of patients in the DP-S group (n = 65, 20%) who underwent R1 resection (21.9 vs 16.7 months, respectively; P = 0.024). CONCLUSION: DP-CAR followed by adjuvant chemotherapy provided an acceptable overall survival rate in patients with highly advanced PDAC, but should be performed with great caution because of high morbidity. Patients with a high risk of positive surgical margins with DP-S may be candidates for DP-CAR.