PPARγ activation suppresses chondrocyte ferroptosis through mitophagy in osteoarthritis

Abstract Background Osteoarthritis (OA) is a prevalent disease plaguing the elderly. Recently, chondrocyte ferroptosis has been demonstrated to promote the progression of OA. Peroxisome proliferator-activated receptor-γ (PPARγ) is an important factor in maintaining cartilage health. However, the relationship between PPARγ and chondrocyte ferroptosis in OA and its mechanism is completely unclear. Methods We established a surgically induced knee OA rat model to investigate PPARγ and chondrocyte ferroptosis in OA. Rat knee specimens were collected for Safranin O/Fast Green staining and immunohistochemical staining after administered orally placebo or pioglitazone (PPARγ agonist) for 4 weeks. We used RSL3 to establish a chondrocyte ferroptosis model cultured in vitro to study the role of PPARγ activation toward ferroptosis, mitochondrial function, and PTEN-induced putative kinase 1 (Pink1)/Parkin-dependent mitophagy. GW9662 (PPARγ antagonist), Mdivi-1 (mitophagy inhibitor), and chloroquine (mitophagy inhibitor) were employed to investigate the mechanism of PPARγ-Pink1/Parkin-dependent mitophagy in the inhibition of ferroptosis. Results We found that PPARγ activation by pioglitazone attenuated not only OA but also inhibited the expression of the ferroptosis marker acyl-CoA synthetase long-chain family member 4 (ACSL4) at the same time in rats. Furthermore, in vivo and in vitro data indicated that PPARγ activation restored Pink1/Parkin-dependent mitophagy, improved mitochondrial function, inhibited chondrocyte ferroptosis, and delayed the progression of OA. Conclusions The present study demonstrated that PPARγ activation attenuates OA by inhibiting chondrocyte ferroptosis, and this chondroprotective effect was achieved by promoting the Pink1/Parkin-dependent mitophagy pathway

Rosiglitazone Ameliorates Spinal Cord Injury via Inhibiting Mitophagy and Inflammation of Neural Stem Cells

Background. Neurodegenerative diseases, such as Alzheimer’s disease, and traumatic brain and spinal cord injury (SCI) are prevalent in clinical practice. Inhibition of hyperactive inflammation and proliferation of endogenous neural stem cells (NSCs) is a promising treatment strategy for SCI. Our previous studies demonstrated the beneficial effects of rosiglitazone (Rosi) on SCI, but its roles in inflammation inhibition and proliferation of NSCs are unknown. Methods. SCI in a rat model was established, and the effects of Rosi on motor functions were assessed. The effects of Rosi on NSC proliferation and the underlying mechanisms were explored in details. Results. We showed that Rosi ameliorated impairment of moto functions in SCI rats, inhibited inflammation, and promoted proliferation of NSCs in vivo. Rosi increased ATP production through enhancing glycolysis but not oxidative phosphorylation. Rosi reduced mitophagy by downregulating PTEN-induced putative kinase 1 (PINK1) transcription to promote NSC proliferation, which was effectively reversed by an overexpression of PINK1 in vitro. Through KEGG analysis and experimental validations, we discovered that Rosi reduced the expression of forkhead box protein O1 (FOXO1) which was a critical transcription factor of PINK1. Three FOXO1 consensus sequences (FCSs) were found in the first intron of the PINK1 gene, which could be potentially binding to FOXO1. The proximal FCS (chr 5: 156680169–156680185) from the translation start site exerted a more significant influence on PINK1 transcription than the other two FCSs. The overexpression of FOXO1 entirely relieved the inhibition of PINK1 transcription in the presence of Rosi. Conclusions. Besides inflammation inhibition, Rosi suppressed mitophagy by reducing FOXO1 to decrease the transcription of PINK1, which played a pivotal role in accelerating the NSC proliferation

SCP2 mediates the transport of lipid hydroperoxides to mitochondria in chondrocyte ferroptosis

Abstract Sterol carrier protein 2 (SCP2) is highly expressed in human osteoarthritis (OA) cartilage, accompanied by ferroptosis hallmarks, especially the accumulation of lipid hydroperoxides (LPO). However, the role of SCP2 in chondrocyte ferroptosis remains unexplored. Here, we identify that SCP2 transports cytoplasmic LPO to mitochondria in RSL3-induced chondrocyte ferroptosis, resulting in mitochondrial membrane damage and release of reactive oxygen species (ROS). The localization of SCP2 on mitochondria is associated with mitochondrial membrane potential, but independent of microtubules transport or voltage-dependent anion channel. Moreover, SCP2 promotes lysosomal LPO increase and lysosomal membrane damage through elevating ROS. However, SCP2 is not directly involved in the cell membrane rupture caused by RSL3. Inhibition of SCP2 markedly protects mitochondria and reduces LPO levels, attenuating chondrocyte ferroptosis in vitro and alleviating the progression of OA in rats. Our study demonstrates that SCP2 mediates the transport of cytoplasmic LPO to mitochondria and the spread of intracellular LPO, accelerating chondrocyte ferroptosis

Ambient PM2.5 exposure exacerbates severity of allergic asthma in previously sensitized mice

<div><p></p><p><i>Objective</i>: Epidemiological studies have shown that elevated concentrations of ambient particulate matter (aerodynamic diameter ≤2.5 μm; PM2.5) correlates with increased incidence of asthma. The aim of this study was to determine whether PM2.5 participates in the exacerbation of asthma. <i>Methods</i>: Effects of 1, 10 and 100 μg PM2.5 instilled intratracheally in ovalbumin (OVA)-sensitized or asthmatic mice were compared. <i>Results</i>: PM2.5 exposure in the OVA-sensitized and especially asthmatic groups increased Mch responsiveness in a dose-dependent manner. In OVA-sensitized groups, exposure to 1 μg of PM2.5 caused no detectable lung inflammation, while 10 and 100 μg of PM2.5 resulted in a slightly increased trend in numbers of neutrophils and macrophages. Compared with the asthmatic control group, both 10 and 100 μg of PM2.5 provoked a significant increase in eosnophils and neutrophils whereas only 100 μg of PM2.5 noticeably enhanced lymphocytes. In asthmatic groups, administration of 100 μg of PM2.5 greatly increased levels of the pro-inflammatory cytokine TNF-α and Th2-related cytokines IL-4 and IL-10 in bronchoalveolar lavage fluid, but it decreased Th1-related INF-γ. In addition, 10 and 100 μg of PM2.5 exacerbated inflammatory infiltration, goblet cell metaplasia and lung ultrastructure lesions in asthmatic mice. <i>Conclusions</i>: Our results suggested that acute exposure of PM2.5 could synergize with allergens in the subsequent challenge to aggravate the severity of asthma in sensitized mice, possibly by promoting a Th2-biased immune response.</p></div

MITF-siRNA Formulation Is a Safe and Effective Therapy for Human Melasma

It is unclear whether siRNA-based agents can be a safe and effective therapy for diseases. In this study, we demonstrate that microphthalmia-associated transcription factor–siRNA (MITF-siR)-silenced MITF gene expression effectively induced a significant reduction in tyrosinase (TYR), tyrosinase-related protein 1, and melanocortin 1 receptor (MC1R) levels. The siRNAs caused obvious inhibition of melanin synthesis and melanoma cell apoptosis. Using a novel type of transdermal peptide, we developed the formulation of an MITF-siR cream. Results demonstrated that hyperpigmented facial lesions of siRNA-treated subjects were significantly lighter after 12 weeks of therapy than before treatment (P < 0.001); overall improvement was first noted after 4 weeks of siRNA treatment. At the end of treatment, clinical and colorimetric evaluations demonstrated a 90.4% lightening of the siRNA-treated lesions toward normal skin color. The relative melanin contents in the lesions and adjacent normal skin were decreased by 26% and 7.4%, respectively, after treatment with the MITF-siR formulation. Topical application of siRNA formulation significantly lightens brown facial hypermelanosis and lightens normal skin in Asian individuals. This treatment represents a safe and effective therapy for melasma, suggesting that siRNA-based agents could be developed for treating other diseases such as melanoma