P16 I NK 4a Deletion Ameliorates Damage of Intestinal Epithelial Barrier and Microbial Dysbiosis in a Stress-Induced Premature Senescence Model of Bmi-1 Deficiency

Bmi-1 Epigenetically Orchestrates Osteogenic and Adipogenic Differentiation of Bone Marrow Mesenchymal Stem Cells to Delay Bone Aging

With the increase in the aging population, senile osteoporosis (SOP) has become a major global public health concern. Here, it is found that Prx1 and Bmi-1 co-localized in trabecular bone, bone marrow cavity, endosteum, and periosteum. Prx1-driven Bmi-1 knockout in bone-marrow mesenchymal stem cells (BMSCs) reduced bone mass and increased bone marrow adiposity by inhibiting osteoblastic bone formation, promoting osteoclastic bone resorption, downregulating the proliferation and osteogenic differentiation of BMSCs, and upregulating the adipogenic differentiation of BMSCs. However, Prx1-driven Bmi-1 overexpression showed a contrasting phenotype to Prx1-driven Bmi-1 knockout in BMSCs. Regarding mechanism, Bmi-1-RING1B bound to DNMT3A and promoted its ubiquitination and inhibited DNA methylation of Runx2 at the region from 45047012 to 45047313 bp, thus promoting the osteogenic differentiation of BMSCs. Moreover, Bmi-1-EZH2 repressed the transcription of Cebpa by promoting H3K27 trimethylation at the promoter region -1605 to -1596 bp, thus inhibiting the adipogenic differentiation of BMSCs. It is also found that Prx1-driven Bmi-1 overexpression rescued the SOP induced by Prx1-driven Bmi-1 knockout in BMSCs. Thus, Bmi-1 functioned as a hub protein in the epigenetic regulation of BMSCs differentiation to delay bone aging. The Prx1-driven Bmi-1 overexpression in BMSCs can be used as an approach for the translational therapy of SOP.

The existence of senescent cells in conjunctival epithelium from elderly individuals

PURPOSE

The ocular surface microenvironment changes with aging. However, it remains unclear if cellular senescence influences the ocular surface. We investigated the presence of p16INK4a-expressing senescent cells in healthy human conjunctiva.

STUDY DESIGN

Clinical and experimental.

METHODS

Healthy conjunctival tissue samples were obtained from middle-aged and elderly subjects. RT-qPCR was performed to assess the expression of senescence markers CDKN2A (p16INK4a) and CDKN1A (p21CIP1/WAF1) and immunostaining was performed to examine the expression of the senescence marker p16INK4a, stem cell markers Ki67 and p63, tight-junction marker ZO-1.

RESULTS

Our study involved 19 conjunctival tissue samples (10 elderly and 9 middle-aged), mean age [elderly: 75.8 ± 3.7 years (72-81), middle-aged: 52.7 ± 7 years (38-59)], sex (elderly: 3 men, 7 women; middle-aged: 3 men, 6 women). The expression of p16INK4a was significantly increased at the RNA level in the elderly compared to middle-aged (p < 0.05). Positivity rate of p16INK4a was significantly elevated in the elderly (15.0 ± 7.8%) compared to middle-aged (0.2 ± 0.6%) (p < 0.05). Positivity rate of Ki67and p63 was significantly reduced in the elderly (1.7 ± 1.7% and 16.5 ± 9.5%) compared to middle-aged (3.9 ± 1.8% and 24.7 ± 5.7%) (p < 0.05). ZO-1 expression was reduced in tissue samples showing p16INK4a-positivity but retained in tissue samples in which p16INK4a was undetectable.

CONCLUSIONS

Senescent cells accumulate with age in the conjunctival epithelium, accompanied by a decrease in Ki67, p63 and ZO-1 expressing cells.

Soluble Epoxide Hydrolase Contributes to Cell Senescence and ER Stress in Aging Mice Colon

Aging, which is characterized by enhanced cell senescence and functional decline of tissues, is a major risk factor for many chronic diseases. Accumulating evidence shows that age-related dysfunction in the colon leads to disorders in multiple organs and systemic inflammation. However, the detailed pathological mechanisms and endogenous regulators underlying colon aging are still largely unknown. Here, we report that the expression and activity of the soluble epoxide hydrolase (sEH) enzyme are increased in the colon of aged mice. Importantly, genetic knockout of sEH attenuated the age-related upregulation of senescent markers p21, p16, Tp53, and β-galactosidase in the colon. Moreover, sEH deficiency alleviated aging-associated endoplasmic reticulum (ER) stress in the colon by reducing both the upstream regulators Perk and Ire1 as well as the downstream pro-apoptotic effectors Chop and Gadd34. Furthermore, treatment with sEH-derived linoleic acid metabolites, dihydroxy-octadecenoic acids (DiHOMEs), decreased cell viability and increased ER stress in human colon CCD-18Co cells in vitro. Together, these results support that the sEH is a key regulator of the aging colon, which highlights its potential application as a therapeutic target for reducing or treating age-related diseases in the colon.

p16INK4a Plays Critical Role in Exacerbating Inflammaging in High Fat Diet Induced Skin

BACKGROUND

Long term high fat diets (HFD) promote skin aging pathogenesis, but detailed mechanisms remain unclear especially for inflammaging, which has recently emerged as a pathway correlating aging and age-related disease with inflammation. p16INK4a (hereafter termed p16) inhibits the cell cycle, with p16 deletion significantly inhibiting inflammaging. We observed that HFD-induced p16 overexpression in the skin. Therefore, we investigated if p16 exacerbated inflammaging in HFD-induced skin and also if p16 deletion exerted protective effects against this process.

METHODS

Eight-week-old double knockout (KO) ApoE-/-p16-/- mice and ApoE-/- littermates were fed HFD for 12 weeks and their skin phenotypes were analyzed. We measured skin fibrosis, senescence-associated secretory phenotype (SASP) levels, and integrin-inflammasome pathway activation using histopathological, RNA-sequencing (RNA-seq), bioinformatics analysis, and molecular techniques.

RESULTS

We found that HFD contributed to inflammaging in the skin by activating the NLRP3 inflammasome pathway, increasing inflammatory infiltration, and promoting apoptosis by balancing expression between proapoptotic and antiapoptotic molecules. p16 knockout, when compared with the ApoE-/- phenotype, inhibited skin fibrosis by ameliorating inflammatory infiltration and proinflammatory factor expression (Interleukin-1β (IL-1β), Interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α)), and also alleviated inflammaging skin progress induced by HFD in the ApoE-/- mouse model. RNA-seq showed that p16 KO mice inhibited both integrin-inflammasome and NF-κB proinflammatory pathway activation.

CONCLUSIONS

p16 deletion or p16 positive cell clearance could be a novel strategy preventing long term HFD-induced skin aging.