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Jinhan He

Publications and source records attributed to Jinhan He.

4 recordsLinked to original sources

Advances in solid-state NMR methods for studying RNA structures and dynamics.

Ribonucleic acid (RNA) structures and dynamics play a crucial role in elucidating RNA functions and facilitating the design of drugs targeting RNA and RNA-protein complexes. However, obtaining RNA structures using conventional biophysical techniques, such as X-ray crystallography and solution nuclear magnetic resonance (NMR), presents challenges due to the inherent flexibility and susceptibility to degradation of RNA. In recent years, solid-state NMR (SSNMR) has rapidly emerged as a promising alternative technique for characterizing RNA structure and dynamics. SSNMR has several distinct advantages, including flexibility in sample states, the ability to capture dynamic features of RNA in solid form, and suitability to character RNAs in various sizes. Recent decade witnessed the growth of 1H-detected SSNMR methods on RNA, which targeted elucidating RNA topology and base pair dynamics in solid state. They have been applied to determine the topology of RNA segment in human immunodeficiency virus (HIV) genome and the base pair dynamics of riboswitch RNA. These advancements have expanded the utility of SSNMR techniques within the RNA research field. This review provides a comprehensive discussion of recent progress in 1H-detected SSNMR investigations into RNA structure and dynamics. We focus on the established 1H-detected SSNMR methods, sample preparation protocols, and the implementation of rapid data acquisition approaches.

Dynamics↗

Heat shock protein 70 is translocated to lipid droplets in rat adipocytes upon heat stimulation.

In mammalian cells, lipid storage droplets contain a triacylglycerol and cholesterol ester core surrounded by a phospholipid monolayer into which a number of proteins are imbedded. These proteins are thought to be involved in modulating the formation and metabolic functions of the lipid droplet. In this study, we show that heat stress upregulates several heat shock proteins (Hsps), including Hsp27, Hsp60, Hsp70, Hsp90, and Grp78, in primary and differentiated adipocytes. Immunostaining and immunoblotting data indicate that among the Hsps examined, only Hsp70 is induced to redirect to the lipid droplet surface in heat-stressed adipocytes. The thermal induction of Hsp70 translocation to lipid droplet does not typically happen in a temperature- or time-dependent manner and occurs abruptly at 30-40 min and rapidly achieves a steady state within 60 min after 40 degrees C stress of adipocytes. Though Hsp70 is co-localized with perilipin on the lipid droplets in stressed adipocytes, immunoprecipitation experiments suggest that Hsp70 does not directly interact with perilipin. Alkaline treatments indicate that Hsp70 associates with the droplet surface through non-hydrophobic interactions. We speculate that Hsp70 might noncovalently associate with monolayer microdomains of the lipid droplet in a manner similar to its interaction with lipid bilayer moieties composed of specific fatty acids. As an acute and specific cellular response to the heat stimulation, accumulation of Hsp70 on adipocytes lipid droplets might be involved in stabilizing the droplet monolayer, transferring nascent proteins to the lipid droplets, or chaperoning denatured proteins on the droplet for subsequent refolding.

Adipocytes↗

Calyculin and okadaic acid promote perilipin phosphorylation and increase lipolysis in primary rat adipocytes.

Lipolysis is primarily regulated by protein kinase A (PKA), which phosphorylates perilipin and hormone-sensitive lipase (HSL), and causes translocation of HSL from cytosol to lipid droplets in adipocytes. Perilipin coats lipid droplet surface and assumes to prevent lipase access to triacylglycerols, thus inhibiting basal lipolysis; phosphorylated perilipin facilitates lipolysis on PKA activation. Here, we induced lipolysis in primary rat adipocytes by inhibiting protein serine/threonine phosphatase with specific inhibitors, okadaic acid and calyculin. The incubation with calyculin promotes incorporation of 32Pi into perilipins, thus, confirming that perilipin is hyperphosphorylated. The lipolysis response to calyculin is gradually accompanied by increased accumulation of phosphorylated perilipin A in a concentration- and time-responsive manner. When perilipin phosphorylation is abrogated by the addition of N-ethylmaleimide, lipolysis ceases. Different from a considerable translocation of HSL upon PKA activation with isoproterenol, calyculin does not alter HSL redistribution in primary or differentiated adipocytes, as confirmed by both immunostaining and immunoblotting. Thus, we suggest that inhibition of the phosphatase by calyculin activates lipolysis via promoting perilipin phosphorylation rather than eliciting HSL translocation in adipocytes. Further, we show that when the endogenous phosphatase is inhibited by calyculin, simultaneous PKA activation with isoproterenol converts most of the perilipin to the hyperphosphorylated species, and induces enhanced lipolysis. Apparently, as PKA phosphorylates perilipin and stimulates lipolysis, the phosphatase acts to dephosphorylate perilipin and attenuate lipolysis. This suggests a two-step strategy governed by a kinase and a phosphatase to modulate the steady state of perilipin phosphorylation and hence the lipolysis response to hormonal stimulation.

Adipocytes↗

Metformin reduces lipolysis in primary rat adipocytes stimulated by tumor necrosis factor-alpha or isoproterenol.

In patients with type 2 non-insulin-dependent diabetes mellitus (NIDDM), the biguanide, metformin, exerts its antihyperglycemic effect by improving insulin sensitivity, which is associated with decreased level of circulating free fatty acids (FFA). The flux of FFA and glycerol from adipose tissue to the blood stream primarily depends on the lipolysis of triacylglycerols in the adipocytes. Adipocyte lipolysis is physiologically stimulated by catecholamine hormones. Tumor necrosis factor-alpha (TNF-alpha), a cytokine largely expressed in adipose tissue, stimulates chronic lipolysis, which may be associated with increased systemic FFA and insulin resistance in obesity and NIDDM. In this study, we examined the role of metformin in inhibiting lipolytic action upon various lipolytic stimulations in primary rat adipocytes. Treatment with metformin attenuated TNF-alpha-mediated lipolysis by suppressing phosphorylation of extracellular signal-related kinase 1/2 and reversing the downregulation of perilipin protein in TNF-alpha-stimulated adipocytes. The acute lipolytic response to adrenergic stimulation of isoproterenol was also restricted by metformin. A high concentration of glucose in the adipocyte culture promoted the basal rate of glycerol release and significantly enhanced the lipolytic action stimulated by either TNF-alpha or isoproterenol. Metformin not only inhibits the basal lipolysis simulated by high glucose, but also suppresses the high glucose-enhanced lipolysis response to TNF-alpha or isoproterenol. The antilipolytic action in adipocytes could be the mechanism by which cellular action by metformin reduces systemic FFA concentration and thus improves insulin sensitivity in obese patients and the hyperglycemic conditions of NIDDM.

Adipocytes↗