Acidic pH environment induces autophagy in osteoblasts

Abstract

Osteoblasts (OBs) play an important role in bone fracture healing, yet the extreme adverse microenvironment in fracture sites has a negative impact on the survival of OBs. Therefore, it is important to study how OBs behave in the complex fracture microenvironment. Studies have shown that autophagy plays a pivotal role in maintaining cellular homeostasis and defending the cell against adverse microenvironments. In this study we found the induction of autophagy in OBs at femoral bone fracture sites, which may be a result of ischemia, oxidative stress and hypoxia within the local area. At fracture sites a low pH environment also developed. Until now it has been unclear whether the induction of autophagy in osteoblasts is triggered by the acidic pH environment. Therefore, we cultured OBs in vitro in media of different pH values, and found both autophagy and apoptosis increased in OBs in acidic conditions. However, when autophagy inhibitor chloroquine (CQ) was used, apoptosis increased significantly compared with that without CQ. Thus indicating that inhibition of autophagy may promote apoptosis in OBs in an acidic environment, which may provide a new therapeutic strategy to decrease cell apoptosis in OBs through the use of drugs that modulate the autophagic state.

FOXO3 Inhibits Human Gastric Adenocarcinoma (AGS) Cell Growth by Promoting Autophagy in an Acidic Microenvironment

“…Such acidic microenvironments induce malignant progression [6]. It has been shown that acidic pH promotes local invasive growth and metastasis.…”

“…The fixed cells were treated with 5% BSA for 30 min and stained with DAPI for 6 min, after which the coverslips were air-dried and mounted in Gel Tol. mRFP-GFP-LC3 fluorescence was observed under a fluorescence microscope, as previously described [6,21,22]. We counted the numbers of mRFP-GFP-LC3 punctae in three independent visual fields.…”

“…The membranes were incubated with HRP-conjugated secondary antibodies (1:10000 dilution, CST) for approximately 1 h at room temperature. Antibody staining was subsequently visualized by chemiluminescence [6,[18][19][20].…”

Platelet Rich Fibrin (PRF) and Its Related Products: Biomolecular Characterization of the Liquid Fibrinogen

“…Thus, considering that we measured the BMP-2 release in physiological conditions, and that we left the samples on the bench to analyze the release of factors at T0, T7, and T14 without adding any substances, apart from EDTA, this could explain the low production of BMP-2 observed in our study. However, since the development of an acidic tissue environment is common in wound healing sites [37], the use of the liquid fibrinogen, for instance at implant sites, may enhance the repair processes as the low pH contributes to stimulate the release of BMP-2. During bone healing, the pH becomes neutral and finally alkaline, thus stimulating alkaline phosphatase and osteocalcin [36].…”

Precise lysosome pH indicator based on self-decomposable nanoparticles

“…The acidic pH of lysosomes maintained by the vacuolar-type H+-ATPase (v-ATPase) [2] that pumps protons from the cytoplasm into the lysosomal lumen was to keep the activity of ~ 60 types of hydrolytic enzymes [3]. Moreover, recent literature reports revealed that acidic pH of lysosomes are closely related to the autophagy [4], so that well known of the precise lysosomes pH changes will give more information on the autophagy process and status. Based on our studies and literature review, amine positive charged nanoparticle endocytosis will probably increase the pH change in endo/lysosomes, such as primary and secondary amine PEG decorated nanoparticles or some hydrophilic decoration on the particle surface [5,6].…”