PM2.5 exposure inhibits osteoblast differentiation by increasing the ubiquitination and degradation of Smad4.

Increasing epidemiological evidence has shown that PM2.5 exposure is significantly associated with the occurrence of osteoporosis. It has been well demonstrated that PM2.5 exposure enhanced the differentiation and function of osteoclasts by indirectly causing chronic inflammation, while the mechanism in osteoblasts remains unclear. In our study, toxic effects were evaluated by direct exposure of 20-80 µg/ml PM2.5 to MC3T3-E1 cells and BMSCs. The results showed that PM2.5 exposure did not affect cell viability via proliferation and apoptosis, but significantly inhibited osteoblast differentiation in a dose-dependent manner. Osteogenic transcription factors Runx2 and Sp7 and other biomarkers Alp and Ocn decreased after PM2.5 exposure. RNA-seq revealed TGF-ß signaling was involved in PM2.5 exposure inhibited osteoblast differentiation, which led to P-Smad1/5 and P-Smad2 reduction in the nucleus by increasing the ubiquitination and degradation of Smad4. At last, the inflammation response increased in MC3T3-E1 cells with PM2.5 exposure. Moreover, the mRNA levels of Mmp9 increased in bone marrow-derived macrophage cells treated with the conditional medium collected from MC3T3-E1 cells exposed to PM2.5. Overall, these results indicated that PM2.5 exposure inhibits osteoblast differentiation and concurrently increases the maturation of osteoclasts. Our study provides in-depth mechanistic insights into the direct impact of PM2.5 exposure on osteoblast, which would indicate the unrecognized role of PM2.5 on osteoporosis.

Effects of chronic low-level lead (Pb) exposure on cognitive function and hippocampal neuronal ferroptosis: An integrative approach using bioinformatics analysis, machine learning, and experimental validation.

Lead (Pb), a pervasive and ancient toxic heavy metal, continues to pose significant neurological health risks, particularly in regions such as Southeast Asia. While previous research has primarily focused on the adverse effects of acute, high-level lead exposure on neurological systems, studies on the impacts of chronic, low-level exposure are less extensive, especially regarding the precise mechanisms linking ferroptosis - a novel type of neuron cell death - with cognitive impairment. This study aims to explore the potential effects of chronic low-level lead exposure on cognitive function and hippocampal neuronal ferroptosis. This research represents the first comprehensive investigation into the impact of chronic low-level lead exposure on hippocampal neuronal ferroptosis, spanning clinical settings, bioinformatic analyses, and experimental validation. Our findings reveal significant alterations in the expression of genes associated with iron metabolism and Nrf2-dependent ferroptosis following lead exposure, as evidenced by comparing gene expression in the peripheral blood of lead-acid battery workers and workers without lead exposure. Furthermore, our in vitro and in vivo experimental results strongly suggest that lead exposure may precipitate cognitive dysfunction and induce hippocampal neuronal ferroptosis. In conclusion, our study indicates that chronic low-level lead exposure may activate microglia, leading to the promotion of ferroptosis in hippocampal neurons.

Atf7ip Inhibits Osteoblast Differentiation via Negative Regulation of the Sp7 Transcription Factor.

Epigenetic modifications are critical for cell differentiation and growth. As a regulator of H3K9 methylation, Setdb1 is implicated in osteoblast proliferation and differentiation. The activity and nucleus localization of Setdb1 are regulated by its binding partner, Atf7ip. However, whether Atf7ip is involved in the regulation of osteoblast differentiation remains largely unclear. In the present study, we found that Atf7ip expression was upregulated during the osteogenesis of primary bone marrow stromal cells and MC3T3-E1 cells, and was induced in PTH-treated cells. The overexpression of Atf7ip impaired osteoblast differentiation in MC3T3-E1 cells regardless of PTH treatment, as measured by the expression of osteoblast differentiation markers, Alp-positive cells, Alp activity, and calcium deposition. Conversely, the depletion of Atf7ip in MC3T3-E1 cells promoted osteoblast differentiation. Compared with the control mice, animals with Atf7ip deletion in the osteoblasts (Oc-Cre;Atf7ipf/f) showed more bone formation and a significant increase in the bone trabeculae microarchitecture, as reflected by µ-CT and bone histomorphometry. Mechanistically, Atf7ip contributed to the nucleus localization of Setdb1 in MC3T3-E1, but did not affect Setdb1 expression. Atf7ip negatively regulated Sp7 expression, and through specific siRNA, Sp7 knockdown attenuated the enhancing role of Atf7ip deletion in osteoblast differentiation. Through these data, we identified Atf7ip as a novel negative regulator of osteogenesis, possibly via its epigenetic regulation of Sp7 expression, and demonstrated that Atf7ip inhibition is a potential therapeutic measure for enhancing bone formation.

Salubrinal-mediated activation of eIF2α signaling improves oxidative stress-induced BMSCs senescence and senile osteoporosis.

Bone cells of various lineages become senescent in bone microenvironment. Senotherapies that clear the senescent bone cells improve bone microarchitecture of aged bones. However, the mechanisms underlie for the formation and maintenance of senescent bone cells are largely unknown. Here, we focus on the relationship between endoplasmic reticulum stress (ER stress)-activated unfolded protein response (UPR) signaling and cellular senescence of bone marrow mesenchymal stem cells (BMSCs). The PKR-like endoplasmic reticulum kinase (PERK)-eukaryotic initiation factor 2 α(eIF2α) signaling branch was specifically activated and tightly regulated in senescent BMSCs induced by hydrogen peroxide (H2O2). However, blocking PERK-eIF2α signaling with AMG'44 could not reverse the cellular senescence phenotype of senescent BMSCs. Treated the senescent cells with salubrinal, an inhibitor for dephosphorylation of eIF2α, decreased SA-ß-Gal positive cells and the expression of markers for cellular senescence. Moreover, salubrinal enhanced the apoptosis of senescent BMSCs and upregulated expression of Chop and BIM. Furthermore, salubrinal treatment significantly improved the osteogenesis capacity of senescent BMSCs as reflected by the increase of Alp, Runx2 and Osteocalcin, the formation of Alp-positive staining cells and matrix mineralization. Salubrinal administration results in significant recovery in the bone microarchitecture of senile SAMP6 mice. Taken together, our data reveal an undefined role of PERK-eIF2α signaling in the maintenance of cellular senescent phenotype in BMSCs. The activation of eIF2α signaling with salubrinal is helpful for the clearance of senescent BMSCs and the improvement of bone integrity of aged mice.