Peroxisomes in Different Skeletal Cell Types during Intramembranous and Endochondral Ossification and Their Regulation during Osteoblast Differentiation by Distinct Peroxisome Proliferator-Activated Receptors

Abstract

Ossification defects leading to craniofacial dysmorphism or rhizomelia are typical phenotypes in patients and corresponding knockout mouse models with distinct peroxisomal disorders. Despite these obvious skeletal pathologies, to date no careful analysis exists on the distribution and function of peroxisomes in skeletal tissues and their alterations during ossification. Therefore, we analyzed the peroxisomal compartment in different cell types of mouse cartilage and bone as well as in primary cultures of calvarial osteoblasts. The peroxisome number and metabolism strongly increased in chondrocytes during endochondral ossification from the reserve to the hypertrophic zone, whereas in bone, metabolically active osteoblasts contained a higher numerical abundance of this organelle than osteocytes. The high abundance of peroxisomes in these skeletal cell types is reflected by high levels of Pex11β gene expression. During culture, calvarial pre-osteoblasts differentiated into secretory osteoblasts accompanied by peroxisome proliferation and increased levels of peroxisomal genes and proteins. Since many peroxisomal genes contain a PPAR-responsive element, we analyzed the gene expression of PPARɑ/ß/ɣ in calvarial osteoblasts and MC3T3-E1 cells, revealing higher levels for PPARß than for PPARɑ and PPARɣ. Treatment with different PPAR agonists and antagonists not only changed the peroxisomal compartment and associated gene expression, but also induced complex alterations of the gene expression patterns of the other PPAR family members. Studies in M3CT3-E1 cells showed that the PPARß agonist GW0742 activated the PPRE-mediated luciferase expression and up-regulated peroxisomal gene transcription (Pex11, Pex13, Pex14, Acox1 and Cat), whereas the PPARß antagonist GSK0660 led to repression of the PPRE and a decrease of the corresponding mRNA levels. In the same way, treatment of calvarial osteoblasts with GW0742 increased in peroxisome number and related gene expression and accelerated osteoblast differentiation. Taken together, our results suggest that PPARß regulates the numerical abundance and metabolic function of peroxisomes via Pex11ß in parallel to osteoblast differentiation.

PPARα-mediated peroxisome induction compensates PPARγ-deficiency in bronchiolar club cells

“…This finding was corroborated by the qRT-PCR analysis of microdissected bronchiolar airway epithelial samples and siRNA-mediated PPARγ knockdown in C22 cells presented in this study. Similar results were also observed in the primary Osteoblasts that were treated with PPARγ antagonist, GW9662 increased PEX13p protein abundance [ 18 ].…”

Silencing of HJURP induces dysregulation of cell cycle and ROS metabolism in bladder cancer cells via PPARγ-SIRT1 feedback loop

“…Another interesting phenomenon we observed was that in the HJURP - siRNA -treated BCa cells, protein level of PPARγ was strongly upregulated, whereas the ratio of p-SIRT1/t-SIRT1 were considerably downregulated, as well as its substrate acetylated p53 was increased (Figure 4 ). Since PPARγ-SIRT1 feedback loop could play a key role in the regulation of antioxidant response, apoptosis and cell cycle 26 , 28 , 31 , 33 , thus we treated the BCa cells with PPARγ-antagonist GW9662 to deactivate PPARγ protein 25 and RSV to activate SIRT1 56 . With the treatment of GW9662 and RSV, we noticed a significantly recovery of proliferation inhibition as well as scavenge of ROS status in HJURP - siRNA -treated BCa cells and a recovery of induced Catalase (Figure 4 ), one of the most important antioxidant enzymes for degradation of hydrogen peroxide 34 .…”

“…Activation/deactivation of PPARs could affect genes related to cellular metabolism, proliferation, lipid peroxidation and stress response including reactive oxygen species (ROS) 22 . In addition, manipulating of PPAR activity by either agonist or antagonist has been considered as a potential treatment for metabolic diseases and cancer including BCa 23 - 25 . The nuclear receptor PPARγ, a key member of the PPAR family and involving in cell cycle regulation 26 , 27 , could bind to the promoter region of SIRT1 to inhibit the transcription 28 .…”

Simvastatin induces cell cycle arrest and inhibits proliferation of bladder cancer cells via PPARγ signalling pathway

“…For instance, PPARs increase the transcription level of genes for fatty acid oxidation24 and peroxisomal β-oxidation enzymes, which might be important regulators for the homeostasis of the lipid ligands binding to nuclear receptors2526. Many reports suggested PPARs modulation in cancer cells by either agonist or antagonist may be a potential treatment for metabolic diseases and cancer including BCa272829. Among those, the PPARγ pathway is particularly critical for the cancer stem cell properties of ErbB2-positive breast cancer cells3031, and has been reported to inhibit of ErbB activity in human breast cancer cells32.…”