Diffusion-enhanced characterization of 3D chromatin structure reveals its linkage to gene regulatory networks and the interactome.

The interactome networks at the DNA, RNA, and protein levels are crucial for cellular functions, and the diverse variations of these networks are heavily involved in the establishment of different cell states. We have developed a diffusion-based method, Hi-C to geometry (CTG), to obtain reliable geometric information on the chromatin from Hi-C data. CTG produces a consistent and reproducible framework for the 3D genomic structure and provides a reliable and quantitative understanding of the alterations of genomic structures under different cellular conditions. The genomic structure yielded by CTG serves as an architectural blueprint of the dynamic gene regulatory network, based on which cell-specific correspondence between gene-gene and corresponding protein-protein physical interactions, as well as transcription correlation, is revealed. We also find that gene fusion events are significantly enriched between genes of short CTG distances and are thus close in 3D space. These findings indicate that 3D chromatin structure is at least partially correlated with downstream processes such as transcription, gene regulation, and even regulatory networking through affecting protein-protein interactions.

Characterization of network hierarchy reflects cell state specificity in genome organization.

Dynamic chromatin structure acts as the regulator of transcription program in crucial processes including cancer and cell development, but a unified framework for characterizing chromatin structural evolution remains to be established. Here, we performed graph inferences on Hi-C data sets and derived the chromatin contact networks. We discovered significant decreases in information transmission efficiencies in chromatin of colorectal cancer (CRC) and T-cell acute lymphoblastic leukemia (T-ALL) compared to corresponding normal controls through graph statistics. Using network embedding in the Poincaré disk, the hierarchy depths of chromatin from CRC and T-ALL patients were found to be significantly shallower compared to their normal controls. A reverse trend of change in chromatin structure was observed during early embryo development. We found tissue-specific conservation of hierarchy order in chromatin contact networks. Our findings reveal the top-down hierarchy of chromatin organization, which is significantly attenuated in cancer.

Multi-scale gene regulation mechanism: Spatiotemporal transmission of genetic information.

Gene expression is regulated by many factors, including transcription factors, chromatin three-dimensional topology, modifications of DNA and histone proteins, and non-coding RNAs. The execution of these complex mechanisms requires an effectively coordinated regulation system. In this review, we emphasize that the multi-scale heterogeneous DNA sequence plays a fundamental and important role for gene expression activity and usage of different means of epigenetic regulation. We illustrate here that the chromatin structure organization provides a stage for spatiotemporal regulation between different genes or gene modules and to realize their downstream functional cooperation. Such a perspective expands our understanding of the central dogma: In addition to one-dimensional sequence information, inter-gene interactions can also be transferred from DNA and RNA to protein levels.

Expression regulation of genes is linked to their CpG density distributions around transcription start sites.

The CpG dinucleotide and its methylation behaviors play vital roles in gene regulation. Previous studies have divided genes into several categories based on the CpG intensity around transcription starting sites and found that housekeeping genes tend to possess high CpG density, whereas tissue-specific genes are generally characterized by low CpG density. In this study, we investigated how the CpG density distribution of a gene affects its transcription and regulation pattern. Based on the CpG density distribution around transcription starting site, by means of a semi-supervised neural network we designed, which took data augmentation into account, we divided the human genes into three categories, and genes within each cluster shared similar CpG density distribution. Not only sequence properties, these different clusters exhibited distinctly different structural features, regulatory mechanisms, correlation patterns between the expression level and CpG/TpG density, and expression and epigenetic mark variations during tumorigenesis. For instance, the activation of cluster 3 genes relies more on 3D genome reorganization, compared with cluster 1 and 2 genes, whereas cluster 2 genes showed the strongest correlation between gene expression and H3K27me3. Genes exhibiting uncoupled correlation between gene regulation and histone modifications are mainly in cluster 3. These results emphasized that the usage of epigenetic marks in gene regulation is partially rooted in the sequence property of genes such as their CpG density distribution and explained to some extent why the relation between epigenetic marks and gene expression is controversial.

[Effect of polycystin2 on differentiation and maturation of osteoblasts promoted by low-frequency pulsed electromagnetic fields].

It is known that low-frequency pulsed electromagnetic fields (PEMFs) can promote the differentiation and maturation of rat calvarial osteoblasts (ROBs) cultured in vitro. However, the mechanism that how ROBs perceive the physical signals of PEMFs and initiate osteogenic differentiation remains unknown. In this study, we investigated the relationship between the promotion of osteogenic differentiation of ROBs by 0.6 mT 50 Hz PEMFs and the presence of polycystin2 (PC2) located on the primary cilia on the surface of ROBs. First, immunofluorescence staining was used to study whether PC2 is located in the primary cilia of ROBs, and then the changes of PC2 protein expression in ROBs upon treatment with PEMFs for different time were detected by Western blotting. Subsequently, we detected the expression of PC2 protein by Western blotting and the effect of PEMFs on the activity of alkaline phosphatase (ALP), as well as the expression of Runx-2, Bmp-2, Col-1 and Osx proteins and genes related to bone formation after pretreating ROBs with amiloride HCl (AMI), a PC2 blocker. Moreover, we detected the expression of genes related to bone formation after inhibiting the expression of PC2 in ROBs using RNA interference. The results showed that PC2 was localized on the primary cilia of ROBs, and PEMFs treatment increased the expression of PC2 protein. When PC2 was blocked by AMI, PEMFs could no longer increase PC2 protein expression and ALP activity, and the promotion effect of PEMFs on osteogenic related protein and gene expression was also offset. After inhibiting the expression of PC2 using RNA interference, PEMFs can no longer increase the expression of genes related to bone formation. The results showed that PC2, located on the surface of primary cilia of osteoblasts, plays an indispensable role in perceiving and transmitting the physical signals from PEMFs, and the promotion of osteogenic differentiation of ROBs by PEMFs depends on the existence of PC2. This study may help to elucidate the mechanism underlying the promotion of bone formation and osteoporosis treatment in low-frequency PEMFs.

Hierarchical dinucleotide distribution in genome along evolution and its effect on chromatin packing.

Dinucleotide densities and their distribution patterns vary significantly among species. Previous studies revealed that CpG is susceptible to methylation, enriched at topologically associating domain boundaries and its distribution along the genome correlates with chromatin compartmentalization. However, the multi-scale organizations of CpG in the linear genome, their role in chromatin organization, and how they change along the evolution are only partially understood. By comparing the CpG distribution at different genomic length scales, we quantify the difference between the CpG distributions of different species and evaluate how the hierarchical uneven CpG distribution appears in evolution. The clustering of species based on the CpG distribution is consistent with the phylogenetic tree. Interestingly, we found the CpG distribution and chromatin structure to be correlated in many different length scales, especially for mammals and avians, consistent with the mosaic CpG distribution in the genomes of these species.

Highly hemocompatible zwitterionic micelles stabilized by reversible cross-linkage for anti-cancer drug delivery.

Both blood stability and intelligent-responsiveness after reaching the drug-targeting site are very important features to make desirable nano-drug vehicles (NDVs). Here, a highly nonfouling cross-linked micelle based on a copolymer composed of carboxybetaine methacrylate (CBMA) as hydrophilic segment and 2-(methacryloyloxy)ethyl lipoate (MAEL) as hydrophobic and cross-linked segment is reported. Furthermore, a simple method to evaluate the hemocompatibility of NDVs through examining the activation of a blood-clotting protein (fibrinogen) was introduced. The micelles can encapsulate anticancer drug doxorubicin (DOX) conveniently and release DOX quickly in response to an intracellular reductive environment. With the advantages of excellent stability in fibrinogen (1 mg/mL) PBS solution and 50% fetal bovine serum (FBS), and accelerated intracellular drug release, the biocompatible zwitterionic micelles stabilized by reversible cross-linkage might be a promising drug carrier for cancer chemotherapy.

[Tissue distribution of 1,3-diphenyl-1,3-propanedione in mice].

OBJECTIVE: To investigate tissue distribution characteristics of 1,3-diphenyl-1,3-propanedione (DPPD) in mice. METHODS: Male ICR mice were dosed with DPPD 500 mg/kg via oral gavage, and the tissue samples of the heart, liver, spleen, lungs, kidneys and muscle of each mouse were collected as scheduled. At each time point, the concentrations of DPPD in the mouse tissues were measured by high performance liquid chromatography (HPLC) method. The main pharmacokinetic parameters were calculated by Thermo Kinetica 4.4.1 software. RESULTS: DPPD was absorbed rapidly after oral administration. The concentrations of DPPD in the liver and in the kidney were higher, respectively (liver: AUC(tot)=41.92 µg×h/g, kidney: AUC(tot)=40.40 µg×h/g). The drug concentrations showed a rapid distribution in the liver and lungs (T(max)=0.32 h and 0.33 h respectively) after oral administration, but in the muscle the maximum was 3.85 h. The maximum concentration of DPPD was in the liver (C(max)=31.20 µg/g), which was also the highest tissue concentration of all the subjects. DPPD could be detected at the low concentration within 24 h in all the tissues involved. CONCLUSION: DPPD distributed unevenly in various tissues. In the liver, kidney and muscle, the amount of the drug concentration was larger, and was lower in the lungs and spleen.

Protective effects of 5-methoxypsoralen against acetaminophen-induced hepatotoxicity in mice.

AIM: To investigate the hepatic protective effects of 5-methoxypsoralen (5-MOP) and to learn if 5-MOP causes hepatotoxicity at protective doses. METHODS: C57BL/6J mice were administrated orally with 5-MOP at doses of 12.5, 25 and 50 mg/kg body weight respectively every morning for 4 d before given acetaminophen (APAP) subcutaneously at a dose of 500 mg/kg. The 5-MOP alone group was treated with 5-MOP orally at a dose of 50 mg/kg body weight for 4 d without APAP. Twenty-four hours after APAP administration, blood samples of mice were analyzed for serum enzyme alanine transaminase (ALT), aspartate transaminase (AST), lactate dehydrogenase (LDH) levels, and malondialdehyde (MDA), reduced glutathione (GSH) and oxidized glutathione (GSSG) of liver tissues were measured and histopathologic changes of the liver were observed. RESULTS: Compared with the vehicle control group, the serum levels (IU/L) of ALT, AST and LDH were all increased significantly in APAP group (8355 ± 3940 vs 30 ± 21, P < 0.05; 6482 ± 4018 vs 146 ± 58, P < 0.05; 24627 ± 10975 vs 1504 ± 410, P < 0.05). Compared with APAP group, the serum ALT levels (IU/L) (1674 ± 1810 vs 8355 ± 3940, P < 0.05; 54 ± 39 vs 8355 ± 3940, P < 0.05; 19 ± 9 vs 8355 ± 3940, P < 0.05), AST levels (IU/L) (729 ± 685 vs 6482 ± 4108, P < 0.05; 187 ± 149 vs 6482 ± 4108, P < 0.05; 141 ± 12 vs 6482 ± 4108, P < 0.05) and LDH levels (IU/L) (7220 ± 6317 vs 24 627 ± 10 975, P < 0.05; 1618 ± 719 vs 24 627 ± 10 975, P < 0.05; 1394 ± 469 vs 24 627 ± 10 975, P < 0.05) were all decreased drastically in the three-dosage 5-MOP pretreatment groups. Pretreatment of 5-MOP could attenuate histopathologic changes induced by APAP, including hepatocellular necrosis and infiltration of inflammatory cells, and the effect was dose-dependent. MDA levels (nmol/mg) were decreased by 5-MOP in a dose-dependent manner (0.98 ± 0.45 vs 2.15 ± 1.07, P > 0.05; 0.59 ± 0.07 vs 2.15 ± 1.07, P < 0.05; 0.47 ± 0.06 vs 2.15 ± 1.07, P < 0.05). The pretreatment of 5-MOP could also increase the GSH/GSSG ratio (3.834 ± 0.340 vs 3.306 ± 0.282, P > 0.05; 5.330 ± 0.421 vs 3.306 ± 0.282, P < 0.05; 6.180 ± 0.212 vs 3.306 ± 0.282, P < 0.05). In the group treated with 5-MOP but without APAP, the serum enzyme levels, the liver histopathologic manifestation, and the values of MDA and GSH/GSSG ratio were all normal. CONCLUSION: 5-MOP can effectively protect C57BL/6J mice from APAP-induced hepatotoxicity and possesses an antioxidative activity, and does not cause liver injury at the protective doses.

Protective effects of 2,4-dihydroxybenzophenone against acetaminophen-induced hepatotoxicity in mice.

AIM: To examine the effects of 2,4-dihydroxybenzophenone (BP-1), a benzophenone derivative used as an ultraviolet light absorbent, on acetaminophen (APAP)-induced hepatotoxicity in C57BL/6J mice. METHODS: Mice were administered orally with BP-1 at doses of 200, 400 and 800 mg/kg body weight respectively every morning for 4 d before a hepatotoxic dose of APAP (350 mg/kg body weight) was given subcutaneously. Twenty four hours after APAP intoxication, the serum enzyme including serum alaine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH) were measured and liver histopathologic changes were examined. RESULTS: BP-1 administration dramatically reduced serum ALT, AST and LDH levels. Liver histopathological examination showed that BP-1 administration antagonized APAP-induced liver pathological damage in a dose-dependent manner. Further tests showed that APAP-induced hepatic lipid peroxidation was reduced significantly by BP-1 pretreatment, and glutathione depletion was ameliorated obviously. CONCLUSION: BP-1 can effectively protect C57BL/6J mice from APAP-induced hepatotoxicity, and reduction of oxidative stress might be part of the protection mechanism.

Dual-response nanocarrier based on graft copolymers with hydrazone bond linkages for improved drug delivery.

Core-shell micelles with biodegradability, thermo- and pH-response were successfully demonstrated by poly(2-oxepane-1,5-dione-co-epsilon-caprolactone) (P(OPD-co-CL)) grafted with hydrophilic segments of amine-terminated poly(N-isopropylacrylamide) (At-PNIPAM). To compare with the graft copolymer, P(OPD-co-CL) block PNIPAM polymer was also prepared. The micelles with core-shell structure were formed with both graft and block copolymers by self-assembly in aqueous solutions, of which PNIPAM shell is thermo-response. Furthermore, P(OPD-co-CL)-g-PNIPAM also showed pH-sensitivity, which was attributed to the acid-cleavable property of the hydrazone bond. The low critical micelle concentrations (CMCs) of graft polymers and block polymers were 6.7 mg/L and 14.3mg/L, respectively, which indicated the formation of stable micelles. Both drug-free and drug-loaded micelles were in uniformly spherical shape observed by transmission electron microscopy (TEM). The sizes of the drug-free and drug-loaded micelles prepared from graft polymer were 123.5 nm and 146.5 nm, respectively, and the sizes of those prepared from block polymer were 197.5 nm and 211.5 nm, respectively. The lower critical solution temperature (LCST) for the graft polymer was 34.3 degrees C, while that for the block polymer was 28.1 degrees C, demonstrating a thermo-response. The graft polymeric micelles exhibited thermo-triggered decelerated release at pH 7.4, and pH-triggered accelerated release at 25 degrees C in vitro release test, indicating that the graft polymeric micelles could be a promising site-specific drug delivery system for enhancing the bioavailability of the drug in targeted pathological areas.