The role of peroxisome proliferator-activated receptor-beta/delta in epidermal growth factor-induced HaCaT cell proliferation

miR-24-3p obstructs the proliferation and migration of HSFs after thermal injury by targeting PPAR-β and positively regulated by NF-κB

Thermal injury repair is a complex process during which the maintenance of the proliferation and migration of human skin fibroblasts (HSFs) exert a crucial role. MicroRNAs have been proven to exert an essential function in repairing skin burns. This study delves into the regulatory effects of miR-24-3p on the migration and proliferation of HSFs that have sustained a thermal injury; thereby, providing deeper insight into thermal injury repair pathogenesis. The PPAR-β protein expression level progressively increased in a time-dependent manner on the 12^th , 24^th , and 48^th hour following the thermal injury of the HSFs. The knockdown of PPAR-β markedly suppressed the proliferation of and migration of HSF. Following thermal injury, the knockdown also promoted the inflammatory cytokine IL-6, TNF-, PTGS-2, and P65 expression. PPAR-β contrastingly exhibited an opposite trend. A targeted relationship between PPAR-β and miR-24-3p was predicted and verified. miR-24-3p inhibited thermal injured-HSFs proliferation and migration and facilitated inflammatory cytokine expression through the regulation of PPAR-β. p65 directly targeted the transcriptional precursor of miR-24 and promoted miR-24 expression. A negative correlation between miR-24-3p expression level and PPAR-β expression level in rats burnt dermal tissues was observed. Our findings reveal that miR-24-3p is conducive to rehabilitating the denatured dermis, which may be beneficial in providing effective therapy of skin burns.

Sudachitin, a polymethoxyflavone from Citrus sudachi, induces apoptosis via the regulation of MAPK pathways in human keratinocyte HaCaT cells

Although we recently reported that sudachitin (5,7,4'-trihydroxy-6,8,3'-trimethoxyflavone), a polymethoxyflavone isolated from the peel of Citrus sudachi, can induce apoptosis in human keratinocyte HaCaT cells, the mechanism underlying its action remains unclear. In this study, we explored the mechanisms underlying sudachitin-induced apoptosis in HaCaT cells. Sudachitin activated p38MAPK and inhibited ERK1/2, whereas another polymethoxyflavone, nobiletin (5,6,7,8,3',4'-hexamethoxyflavone), activated ERK1/2. The p38MAPK inhibitor SB203580 significantly attenuated sudachitin-induced heat shock protein 27 phosphorylation, downstream of p38MAPK, and subsequent apoptosis, indicating that sudachitin induces apoptosis via the p38MAPK pathway. Additionally, sudachitin inhibited serum- and EGF-stimulated Raf-1-ERK1/2 activation, and blocked EGF-induced cell migration and proliferation in HaCaT cells. These results suggest that small structural differences in polymethoxyflavones can induce different cellular responses by altering the regulation of MAPK activities and that sudachitin may be a potential candidate for developing new drugs for skin diseases such as psoriasis.

Nucleolin enhances the proliferation and migration of heat-denatured human dermal fibroblasts

Denatured dermis, a part of dermis in burned skin, has the ability to restore its normal morphology and functions after their surrounding microenvironment is improved. However, the cellular and molecular mechanisms by which the denatured dermis could improve wound healing are still unclear. This study aimed to investigate the role of nucleolin during the recovery of heat-denatured human dermal fibroblasts. Nucleolin mRNA and protein expression were significantly increased time-dependently during the recovery of heat-denatured human dermal fibroblasts (52 °C, 30 seconds). Heat-denaturation promoted a time-dependent cell proliferation, migration, chemotaxis, and scratched wound healing during the recovery of human dermal fibroblasts. These effects were prevented by knockdown of nucleolin expression with small interference RNA (siRNA), whereas overexpression of nucleolin enhanced cell proliferation, migration, and chemotaxis of human dermal fibroblasts with heat-denaturation. In addition, the expression of transforming growth factor-beta 1(TGF-β1) was significantly increased during the recovery of heat-denatured dermis and human dermal fibroblasts. TGF-β1 expression was up-regulated by nucleolin in human dermal fibroblasts. The results suggest that nucleolin expression is up-regulated, and play an important role in promoting cell proliferation, migration, and chemotaxis of human dermal fibroblasts during the recovery of heat-denatured dermis with a mechanism probably related to TGF-β1.

PPARβ/δ and PPARγ maintain undifferentiated phenotypes of mouse adult neural precursor cells from the subventricular zone

The subventricular zone (SVZ) is one of the main niches of neural stem cells in the adult mammalian brain. Stem and precursor cells in this region are the source for neurogenesis and oligodendrogesis, mainly in the olfactory bulb and corpus callosum, respectively. The identification of the molecular components regulating the decision of these cells to differentiate or maintain an undifferentiated state is important in order to understand the modulation of neurogenic processes in physiological and pathological conditions. PPARs are a group of transcription factors, activated by lipid ligands, with important functions in cellular differentiation and proliferation in several tissues. In this work, we demonstrate that mouse adult neural precursor cells (NPCs), in situ and in vitro, express PPARβ/δ and PPARγ. Pharmacological activation of both PPARs isoforms induces proliferation and maintenance of the undifferentiated phenotype. Congruently, inhibition of PPARβ/δ and PPARγ results in a decrease of proliferation and loss of the undifferentiated phenotype. Interestingly, PPARγ regulates the level of EGFR in adult NPCs, concurrent with it is function described in embryonic NPCs. Furthermore, we describe for the first time that PPARβ/δ regulates SOX2 level in adult NPCs, probably through a direct transcriptional regulation, as we identified two putative PPAR response elements in the promoter region of Sox2. EGFR and SOX2 are key players in neural stem/precursor cells self-renewal. Finally, rosiglitazone, a PPARγ ligand, increases PPARβ/δ level, suggesting a possible cooperation between these two PPARs in the control of cell fate behavior. Our work contributes to the understanding of the molecular mechanisms associated to neural cell fate decision and places PPARβ/δ and PPARγ as interesting new targets of modulation of mammalian brain homeostasis.

Targeting peroxisome proliferator-activated receptor-β/δ in colon cancer: how to aim?

Peroxisome proliferator-activated receptor-β/δ (PPARδ) is a ubiquitously expressed, ligand-activated transcriptional factor that performs diverse critical functions in normal cells (e.g., fatty acid metabolism, obesity, apoptosis, and inflammation). Various studies in humans have found that PPARδ is upregulated in primary colorectal cancers; however, these findings have been challenged by those of other reports. Similarly, various in vitro and in vivo mechanistic pre-clinical models have yielded data demonstrating that PPARδ promotes colonic tumorigenesis, but other models have yielded data that contradicts this notion. Definitive studies are therefore needed to establish the exact role of PPARδ in human colorectal tumorigenesis and to provide a theoretical basis for PPARδ therapeutic targeting.

Peroxisome proliferator-activated receptor delta agonists attenuated the C-reactive protein-induced pro-inflammation in cardiomyocytes and H9c2 cardiomyoblasts

C-reactive protein (CRP) has emerged as a new marker for cardiovascular diseases. Activation of peroxisome proliferator-activated receptor delta (PPARdelta) plays beneficial roles in cardiac disorders. However, the relationship between CRP and PPARdelta in cardiac cells remains unclear. This study focused on the underlying molecular mechanisms of CRP and PPARdeltaagonists. Cardiomyocytes and cardiomyoblast cell line (H9c2) were used in different groups: Untreated; 15 microg/ml CRP with or without 1 microM PPARdelta agonists (L-165041). CRP increased PPARdelta and interleukin-6 expression in cardiomyocytes and H9c2 cardiomyoblasts. NF-kappaB inducing kinase (NIK) and NF-kappaB pathway also activated by CRP stimulation. These changes could be inhibited by L-165041 through p38MAPK and c-JNK pathways. However, transfection with siRNA of CD32 CRP receptor did not decrease CRP signaling or reverse the effects of L-165041 in CRP-treated cardiomyocytes and H9c2. Pretreatment with L-165041 attenuated apoptosis induced by hypoxia with or without CRP in H9c2 cardiomyoblasts. CRP up-regulated PPARdelta expression in cardiomyocytes and H9c2. L-165041 attenuated CRP-induced pro-inflammatory signaling through p38MAPK and c-JNK in H9c2 cardiomyoblasts. However, PPARdelta activation attenuated CRP-induced NF-kappaB pathway may be independent of CD32. These results may provide new evidence of PPARdelta beneficial effects for inflammatory cardiomyopathy.

ATP-binding domain of heat shock protein 70 is essential for its effects on the inhibition of the release of the second mitochondria-derived activator of caspase and apoptosis in C2C12 cells

Hydrogen peroxide (H(2)O(2)) is a well known oxidative stress inducer causing apoptosis of many cells. Previously, we have shown that heat shock pretreatment blocked the release of the second mitochondria-derived activator of caspase (Smac) to the cytosol and inhibited apoptosis of C2C12 myoblast cells in response to H(2)O(2). The present study aimed to elucidate the underlying mechanism by over-expressing a major stress-inducible protein, heat shock protein (HSP) 70, and characterizing the resulting cellular changes. We demonstrate that HSP70 over-expression markedly inhibited the release of Smac and prevented the activation of caspases-9 and -3 and apoptosis in C2C12 cells under H(2)O(2) treatment. However, no direct interaction between HSP70 and Smac was observed by co-immunoprecipitation. Mutational analysis demonstrated that the ATP-binding domain of HSP70, rather than the peptide-binding domain, was essential for these observed HSP functions. Taken together, our results provide evidence supporting the role of HSP70 in the protection of C2C12 cells from H(2)O(2)-induced and Smac-promoted apoptosis by preventing the release of Smac from mitochondria, thereby inhibiting activation of caspases-9 and -3. This mechanism of HSP70 action is dependent on its ATP-binding domain but independent of its interaction with Smac protein.

PPARδ activity in cardiovascular diseases: A potential pharmacological target

Activation of peroxisome proliferator-activated receptors (PPARs), and particularly of PPARα and PPARγ, using selective agonists, is currently used in the treatment of metabolic diseases such as hypertriglyceridemia and type 2 diabetes mellitus. PPARα and PPARγ anti-inflammatory, antiproliferative and antiangiogenic properties in cardiovascular cells were extensively clarified in a variety of in vitro and in vivo models. In contrast, the role of PPARδ in cardiovascular system is poorly understood. Prostacyclin, the predominant prostanoid released by vascular cells, is a putative endogenous agonist for PPARδ, but only recently PPARδ selective synthetic agonists were found, improving studies about the physiological and pathophysiological roles of PPARδ activation. Recent reports suggest that the PPARδ activation may play a pivotal role to regulate inflammation, apoptosis, and cell proliferation, suggesting that this transcriptional factor could become an interesting pharmacological target to regulate cardiovascular cell apoptosis, proliferation, inflammation, and metabolism.