Beyond energy provider: multifunction of lipid droplets in embryonic development

Since the discovery, lipid droplets (LDs) have been recognized to be sites of cellular energy reserves, providing energy when necessary to sustain cellular life activities. Many studies have reported large numbers of LDs in eggs and early embryos from insects to mammals. The questions of how LDs are formed, what role they play, and what their significance is for embryonic development have been attracting the attention of researchers. Studies in recent years have revealed that in addition to providing energy for embryonic development, LDs in eggs and embryos also function to resist lipotoxicity, resist oxidative stress, inhibit bacterial infection, and provide lipid and membrane components for embryonic development. Removal of LDs from fertilized eggs or early embryos artificially leads to embryonic developmental arrest and defects. This paper reviews recent studies to explain the role and effect mechanisms of LDs in the embryonic development of several species and the genes involved in the regulation. The review contributes to understanding the embryonic development mechanism and provides new insight for the diagnosis and treatment of diseases related to embryonic developmental abnormalities.

Involvement of mechano-sensitive Piezo1 channel in the differentiation of brown adipocytes

Brown adipocytes expend energy via heat production and are a potential target for the prevention of obesity and related metabolic disorders. Piezo1 is a Ca2+-permeable non-selective cation channel activated by mechanical stimuli. Piezo1 is reported to be involved in mechano-sensation in non-sensory tissues. However, the expression and roles of Piezo1 in brown adipocytes have not been well clarified. Here, we generated a brown adipocyte line derived from UCP1-mRFP1 transgenic mice and showed that Piezo1 is expressed in pre-adipocytes. Application of Yoda-1, a Piezo1 agonist, suppressed brown adipocyte differentiation, and this suppression was significantly attenuated by treatment with a Piezo1 antagonist and by Piezo1 knockdown. Furthermore, the suppression of brown adipocyte differentiation by Yoda-1 was abolished by co-treatment with a calcineurin inhibitor. Thus, these results suggest that activation of Piezo1 suppresses brown adipocyte differentiation via the calcineurin pathway.

Exposure to Stearate Activates the IRE1α/XBP-1 Pathway in 3T3-L1 Adipocytes

In the endoplasmic reticulum (ER), accumulation of abnormal proteins with malformed higher-order structures activates signaling pathways (inositol-requiring enzyme 1α (IRE1α)/X-box binding protein 1 (XBP-1) pathway, protein kinase RNA-activated-like endoplasmic reticulum kinase (PERK)/CCAAT/enhancer binding protein-homologous protein (CHOP) pathway and activating transcription factor 6α (ATF6α) pathway) that result in a cellular response suppressing the production of abnormal proteins or inducing apoptosis. These responses are collectively known as the unfolded protein response (UPR). Recently, it has been suggested that the UPR induced by saturated fatty acids in hepatocytes and pancreatic β cells is involved in the development of metabolic diseases such as diabetes. The effect of palmitate, a saturated fatty acid, on the UPR has also been investigated in adipocytes, which are associated with the development of metabolic disorders, but the results were inconclusive. Therefore, as the major saturated fatty acids present in the daily diet are palmitate and stearate, we examined the effects of these saturated fatty acids on UPR in adipocytes. Here, we show that saturated fatty acids caused limited activation of the UPR in adipocytes. Exposure to stearate for several hours elevated the ratio of spliced XBP-1 mRNA, and this effect was stronger than that of palmitate. Moreover, the phosphorylation level of IRE1α, upstream of XBP-1 and expression levels of its downstream targets such as DNAJB9 and Pdia6 were elevated in 3T3-L1 adipocytes exposed to stearate. On the other hand, stearate did not affect the phosphorylation of PERK, its activation of CHOP, or the cleavage of ATF6α. Thus, in adipocytes, exposure to stearate activates the UPR via the IRE1α/XBP-1 pathway, but not the PERK/CHOP and ATF6α pathway.

Histone H3 methyltransferase Ezh2 promotes white adipocytes but inhibits brown and beige adipocyte differentiation in mice

Obesity is a disease characterized by imbalance between energy intake and expenditure, excessive energy store in white adipocytes, but brown and beige adipocytes consume energy to relieve obesity. In this study, we want to explore the role of the histone H3 methyltransferase Ezh2 in the differentiation of white, brown and beige adipocytes with Ezh2 conditional knockout mice (Ezh2flox/floxPrx1-cre) and mouse embryonic fibroblasts (MEFs). The results showed that Ezh2-deficient mice have a leaner phenotype and less white adipose tissues. The morphological changes in the adipose tissue included smaller white adipose tissue depots, white adipocytes with smaller diameter, smaller lipid droplets inside the brown adipocytes and more beige adipocytes in the Ezh2-deficient mice compared with the control. The differentiation markers of white adipocytes in Ezh2 knockout mice decreased; Ucp1 and other browning markers increased in brown and beige adipocytes. The Ezh2 knockout mice could better tolerate cold stimulation, and they can also resist obesity and insulin resistance induced by a high-fat diet. The Ezh2 inhibitor GSK126 could inhibit the differentiation of MEFs into white adipocytes but promote their differentiation into brown/beige adipocytes. The H3K27me3 demethylase Jmjd3/UTX inhibitor GSKJ4 inhibited MEFs' differentiation into brown/beige adipocytes. These results showed that Ezh2 promotes the differentiation of white adipocytes and inhibits the differentiation of brown and beige adipocytes in vivo and in vitro through its methylase activity and this may represent new knowledge for obesity therapeutic strategy.

Gestational diabetes mellitus is associated with decreased adipose and placenta peroxisome proliferator-activator receptor γ expression in a Chinese population

Peroxisome proliferator-activated receptors γ (PPARγ) is a member of nuclear receptor superfamily, and studies have demonstrated that dysregulation of PPARγ was associated with gestational diabetes mellitus (GDM), which is one of the most common metabolic abnormalities occurring during pregnancy. However, the results regarding the associations between PPARγ and GDM were conflicting among different studies. The present study aimed to determine the expression of PPARγ in adipose and placenta from GDM women in a Chinese population and to further explore the role of PPARγ in GDM women. The adipose and placenta tissues were isolated from GDM women and healthy pregnant women at term. The mRNA and protein expressions of PPARγ in adipose and placenta tissues were determined by qRT-PCR and western blot, respectively. Univariate correlation analysis was used to analyze the relationship between PPARγ expression and clinical characteristics of patients. The levels of tryglycerides and HbA1c were significantly higher, while the levels of low density lipoprotein (LDL) cholesterol, adiponectin and insulin were significantly lower in the GDM women than that in the healthy pregnant women. The mRNA and protein expression of PPARγ in both adipose and placenta from GDM women were significantly lower than that from healthy pregnant women. PPARγ mRNA expression in both adipose and placenta positively correlated with LDL cholesterol and adiponectin levels, and negatively correlated with tryglycerides and glucose levels at 0 h, 1 h and 2 h of 75 g oral glucose tolerance test. In summary, our results suggest that PPARγ may be a key modulator in the development of GDM, due to the roles of PPARγ in glucose homeostasis and adipose tissue development and function.