Ganglioside deficiency in hypothalamic POMC neurons promotes body weight gain.

BACKGROUND: Glucosylceramide synthase (GCS; gene: UDP-glucose:ceramide glucosyltransferase (Ugcg))-derived gangliosides comprise a specific class of lipids in the plasma membrane that modulate the activity of transmembrane receptors. GCS deletion in hypothalamic arcuate nucleus (Arc) neurons leads to prominent obesity. However, it has not yet been studied how ganglioside depletion affects individual Arc neuronal subpopulations. The current study investigates the effects of GCS deletion specifically in anorexigenic pro-opiomelanocortin (POMC) neurons. Additionally, we investigate insulin receptor (IR) signaling and phosphatidylinositol-(3,4,5)-trisphosphate (PIP3) binding to ATP-dependent K+ (KATP) channels of GCS-deficient POMC neurons. MATERIALS AND METHODS: We generated Ugcgf/f-Pomc-Cre mice with ganglioside deficiency in POMC neurons. Moreover, the CRISPR (clustered regulatory interspaced short palindromic repeats)/Cas9 technology was used to inhibit GCS-dependent ganglioside biosynthesis in cultured mouse POMC neurons, yielding UgcgΔ-mHypoA-POMC cells that were used to study mechanistic aspects in further detail. Proximity ligation assays (PLAs) visualized interactions between gangliosides, IR, and KATP channel subunit sulfonylurea receptor-1 (SUR-1), as well as intracellular IR substrate 2 (IRS-2) phosphorylation and PIP3. RESULTS: Chow-fed Ugcgf/f-Pomc-Cre mice showed a moderate but significant increase in body weight gain and they failed to display an increase of anorexigenic neuropeptide expression during the fasting-to-re-feeding transition. IR, IRS-2, p85, and overall insulin-evoked IR and IRS-2 phosphorylation were elevated in ganglioside-depleted UgcgΔ-mHypoA-POMC neurons. A PLA demonstrated that more insulin-evoked complex formation occurred between PIP3 and SUR-1 in ganglioside-deficient POMC neurons in vitro and in vivo. CONCLUSION: Our work suggests that GCS deletion in POMC neurons promotes body weight gain. Gangliosides are required for an appropriate adaptation of anorexigenic neuropeptide expression in the Arc during the fasting-to-re-feeding transition. Moreover, gangliosides might modulate KATP channel activity by restraining PIP3 binding to the KATP channel subunit SUR-1. Increased PIP3/SUR-1 interactions in ganglioside-deficient neurons could in turn potentially lead to electrical silencing. This work highlights that gangliosides in POMC neurons of the hypothalamic Arc are important regulators of body weight.

Modeling terahertz emission from the target rear side during intense laser-solid interactions.

Relativistic laser-solid target interaction is a powerful source of terahertz radiation where broadband terahertz radiation is emitted from the front and rear surfaces of the target. Even though several experimental works have reported the generation of subpicosecond duration gigawatt peak power terahertz pulses from the target rear surface, the underlying physical process behind their origin is still an open question. Here we discuss a numerical model that can accurately reproduce several aspects of the experimental results. The model is based on the charged particle dynamics at the target rear surface and the evolution of the charge separation field. We identify the major contributors that are responsible for broadband terahertz emission from the rear surface of the target.

Spatiotemporal visualization of the terahertz emission during high-power laser-matter interaction.

Single-cycle pulses with multimillion volts per centimeter field strengths and spectra in the terahertz (THz) band have attracted great interest due to their ability to coherently manipulate molecular orientations and electron spins resonantly and nonresonantly. The tremendous progress made in the development of compact and powerful terahertz sources have identified intense laser-thin foil interaction as a potential candidate for high-power broadband terahertz radiation. They are micrometers in size and deliver radially polarized terahertz pulses with millijoule energy and gigawatt peak power. Although several works have been carried out to investigate the terahertz generation process, their origin and angular distribution are still debated. We present here an indisputable study on their spatiotemporal characteristics and elaborate the underlying physical processes via recording the three-dimensional beam profile along with transient dynamics. These results are substructured with the quantitative visualization of the charge particle spectra.

Characterization of 700 µJ T rays generated during high-power laser solid interaction.

Laser-produced solid density plasmas are well-known as table-top sources of electromagnetic radiation. Recent studies have shown that energetic broadband terahertz pulses (T rays) can also be generated from laser-driven compact ion accelerators. Here we report the measurement of record-breaking T-Ray pulses with energies no less than 0.7 mJ. The terahertz spectrum has been characterized for frequencies ranging from 0.1-133 THz. The dependence of T-Ray yield on incident laser energy is linear and shows no tendencies of saturation. The noncollinear emission pattern and the high yield reveal that the T rays are generated by the transient field at the rear surface of the solid target.

Observation of gigawatt-class THz pulses from a compact laser-driven particle accelerator.

We report the observation of subpicosecond terahertz (T-ray) pulses with energies ≥460 µJ from a laser-driven ion accelerator, thus rendering the peak power of the source higher even than that of state-of-the-art synchrotrons. Experiments were performed with intense laser pulses (up to 5×10(19) W/cm(2)) to irradiate thin metal foil targets. Ion spectra measured simultaneously showed a square law dependence of the T-ray yield on particle number. Two-dimensional particle-in-cell simulations show the presence of transient currents at the target rear surface which could be responsible for the strong T-ray emission.

Harmonic generation from relativistic plasma surfaces in ultrasteep plasma density gradients.

Harmonic generation in the limit of ultrasteep density gradients is studied experimentally. Observations reveal that, while the efficient generation of high order harmonics from relativistic surfaces requires steep plasma density scale lengths (L(p)/λ < 1), the absolute efficiency of the harmonics declines for the steepest plasma density scale length L(p)→0, thus demonstrating that near-steplike density gradients can be achieved for interactions using high-contrast high-intensity laser pulses. Absolute photon yields are obtained using a calibrated detection system. The efficiency of harmonics reflected from the laser driven plasma surface via the relativistic oscillating mirror was estimated to be in the range of 10(-4)-10(-6) of the laser pulse energy for photon energies ranging from 20-40 eV, with the best results being obtained for an intermediate density scale length.

Locked nucleic acid-based in situ hybridisation reveals miR-7a as a hypothalamus-enriched microRNA with a distinct expression pattern.

MicroRNAs (miRNAs) are short (∼22 nucleotides) noncoding RNA molecules that post-transcriptionally repress the expression of protein-coding genes by binding to 3'-untranslated regions of the target mRNAs. To identify miRNAs selectively expressed within the hypothalamus, a part of the brain that controls vital bodily functions, we employed locked nucleic acid (LNA)-fluorescent in situ hybridisation (FISH). The expression pattern of the mature miRNAs miR-7a, miR-7b, miR-137 and miR-153 in mouse brain tissue sections was investigated. Although all studied miRNAs were present in the hypothalamus, miR-7a, was the only miRNA found to be enriched in the hypothalamus, with low or no expression in other parts of the central nervous system (CNS). Within the hypothalamus, strong miR-7a expression was distinct and restricted to some hypothalamic nuclei and adjacent areas. miR-7a expression was particularly prominent in the subfornical organ, as well as the suprachiasmatic, paraventricular, periventricular, supraoptic, dorsomedial and arcuate nuclei. Identical expression patterns for miR-7a were seen in mouse and rat hypothalamus. By combining LNA-FISH with immunohistochemistry, it was shown that miR-7a was preferentially present in small orexigenic neuropeptide Y/agouti-related protein-containing-neurones located in the ventromedial aspect of the arcuate nucleus but not in large pro-opiomelanocortin/cocaine- and amphetamine-regulated transcript-containing anorexigenic neurones of the ventrolateral part of the arcuate nucleus. The limited and distinct expression of miR-7a in the CNS suggests that miR-7a has a role in post-transcriptional regulation in hypothalamic neurones. Particularly strong expression of miR-7a in neurones located in the ventromedial division of the arcuate nucleus, a subregion with a weak blood-brain barrier, raises the possibility that miR-7a is influenced by circulating hormones and is a regulator of the genes involved in body weight control.

Selective regulation of steroid receptor expression in MCF-7 breast cancer cells by a novel member of the heregulin family.

A 52 kDa heregulin secreted by estrogen receptor (ER)-negative human breast cancer cells induced rapid growth of ER-positive MCF-7 breast cancer cells with a stimulatory effect observed at 10(-11)M. This heregulin down-regulated the message for ER in MCF-7 cells within 24 hours after stimulation. Similarly the ER protein was down-regulated within 24 to 48 hours after stimulation of cells. However, this down-regulation occurred without activation of the ER, since the progesterone receptor (PR) level of cells stimulated with the 52 kDa heregulin did not increase over the time period measured. As a control, estradiol down-regulated and activated ER as shown by a pronounced increase in PR content of MCF-7 cells. This finding indicates an important role of this heregulin in the down-regulation of ER in estrogen-dependent human breast cancer cells.