Shane Miller

Ablation of ALCAT1 mitigates hypertrophic cardiomyopathy through effects on oxidative stress and mitophagy.

ABSTRACT Oxidative stress causes mitochondrial dysfunction and heart failure through unknown mechanisms. Cardiolipin (CL), a mitochondrial membrane phospholipid required for oxidative phosphorylation, plays a pivotal role in cardiac function. The onset of age-related heart diseases is characterized by aberrant CL acyl composition that is highly sensitive to oxidative damage, leading to CL peroxidation and mitochondrial dysfunction. Here we report a key role of ALCAT1, a lysocardiolipin acyltransferase that catalyzes the synthesis of CL with a high peroxidation index, in mitochondrial dysfunction associated with hypertrophic cardiomyopathy. We show that ALCAT1 expression was potently upregulated by the onset of hyperthyroid cardiomyopathy, leading to oxidative stress and mitochondrial dysfunction. Accordingly, overexpression of ALCAT1 in H9c2 cardiac cells caused severe oxidative stress, lipid peroxidation, and mitochondrial DNA (mtDNA) depletion. Conversely, ablation of ALCAT1 prevented the onset of T4-induced cardiomyopathy and cardiac dysfunction. ALCAT1 deficiency also mitigated oxidative stress, insulin resistance, and mitochondrial dysfunction by improving mitochondrial quality control through upregulation of PINK1, a mitochondrial GTPase required for mitochondrial autophagy. Together, these findings implicate a key role of ALCAT1 as the missing link between oxidative stress and mitochondrial dysfunction in the etiology of age-related heart diseases.

Relevance of tenascin-C and matrix metalloproteinases in vascular abnormalities in murine hypoplastic lungs.

Background: Tenascin-C (TN-C), an extracellular matrix glycoprotein, is crucial to cell-migration, proliferation, apoptosis and remodeling of tissues, with a potential role in pathobiology of pulmonary hypertension. Matrix metallopro-teinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) are crucial to the integrity of the extracellular matrix. TN-C and MMPs are counter-regulatory molecules, which influence the vascular integrity through modulations of elastin. We have a murine model of pulmonary hypoplasia with coexistent diaphragmatic hernia, vascular abnormalities and excessive arterial smooth muscle cell (SMC) proliferation. Objectives: Our objective was to investigate modulations of TN-C and MMPs in hypoplastic lungs and their possible contribution to the observed pulmonary vascular abnormalities. Methods: We addressed our objectives by pursing immunoblotting and immunohistochemistry and zymography/reverse zymography to assess the alterations in activities of MMPs and their inhibitors. Results: We observed significant down-regulation of MMP-9 activity in hypoplastic lungs at the later fetal developmental stages, whereas MMP-2 activity assessed by gelatin zymography remained unaltered. Reverse zymography revealed up-regulation of activities of TIMP-1, -2, -3 and -4 in hypoplastic lungs during later fetal development, with pronounced increases in TIMP-3 and -4 activities. Furthermore, immunoblot analyses and immunohistochemistry revealed that TN-C protein was down-regulated in developing hypoplastic lungs, compared to normal lungs. Conclusions: (1)TN-C is known to inhibit vascular SMC proliferation. But, decrease in TN-C in hypoplastic lungs may support the observed arterial SMC proliferation. (2) Our studies showed that in hypoplastic lungs the SMC apoptosis is not affected, thus suggesting that SMC proliferation and apoptosis may be two separate processes in pulmonary hypoplasia with coexistent diaphragmatic hernia. Together, our data showed an imbalance in the extracellular matrix proteins, which may contribute to the pulmonary vascular abnormalities.

Silicon immersion gratings for very high-resolution infrared spectroscopy

In our group, development of large format silicon immersion gratings with sizes up to 4 inches in diameter is a routine practice. The first silicon anamorphic immersion grating has an 80x50 mm2 etched grating area, a 63.5° blazed angle and a 5.4 l/mm groove density (or 185 μm period) on a 30mm thick silicon substrate. The groove density is about 4 times coarser than any existing commercial echelle grating, allowing a complete coverage of a cross-dispersed echelle spectrum on a 1k x 1k IR array at R = 220,000 in the K band. The optical measurements show the grating has a high quality wavefront and surface. The rms wavefront error is 0.125 waves and the integrated scattered light is ~1% at 0.6328 nm. A silicon immersion grating with an 85x50 mm2 etched area, a 54.7° blazed angle and 16.1 l/mm groove density on a 40 mm thickness allows for complete wavelength coverage of 1.2-2.4 μm on a 2kx2k IR array. We are in the middle of processing a silicon disk with a 6 inch diameter and 2.5 inch thickness to make a large format silicon immersion grating for the Gemini next generation Advanced Cryogenic Echelle Spectrograph (ACES) and space applications.

Development of silicon grisms and immersion gratings for high-resolution infrared spectroscopy

We report new results on silicon grism and immersion grating development using photolithography and anisotropic chemical etching techniques, which include process recipe finding, prototype grism fabrication, lab performance evaluation and initial scientific observations. The very high refractive index of silicon (n=3.4) enables much higher dispersion power for silicon-based gratings than conventional gratings, e.g. a silicon immersion grating can offer a factor of 3.4 times the dispersion of a conventional immersion grating. Good transmission in the infrared (IR) allows silicon-based gratings to operate in the broad IR wavelength regions (~1- 10 micrometers and far-IR), which make them attractive for both ground and space-based spectroscopic observations. Coarser gratings can be fabricated with these new techniques rather than conventional techniques, allowing observations at very high dispersion orders for larger simultaneous wavelength coverage. We have found new etching techniques for fabricating high quality silicon grisms with low wavefront distortion, low scattered light and high efficiency. Particularly, a new etching process using tetramethyl ammonium hydroxide (TMAH) is significantly simplifying the fabrication process on large, thick silicon substrates, while providing comparable grating quality to our traditional potassium hydroxide (KOH) process. This technique is being used for fabricating inch size silicon grisms for several IR instruments and is planned to be used for fabricating ~ 4 inch size silicon immersion gratings later. We have obtained complete K band spectra of a total of 6 T Tauri and Ae/Be stars and their close companions at a spectral resolution of R ~ 5000 using a silicon echelle grism with a 5 mm pupil diameter at the Lick 3m telescope. These results represent the first scientific observations conducted by the high-resolution silicon grisms, and demonstrate the extremely high dispersing power of silicon- based gratings. The future of silicon-based grating applications in ground and space-based IR instruments is promising. Silicon immersion gratings will make very high-resolution spectroscopy (R>100,000) feasible with compact instruments for implementation on large telescopes. Silicon grisms will offer an efficient way to implement low-cost medium to high resolution IR spectroscopy (R~ 1000-50000) through the conversion of existing cameras into spectrometers by locating a grism in the instruments pupil location.

Breakthroughs in Silicon Grism and Immersion Grating Technology at Penn State

Fabrication of silicon grisms up to 2 inches in dimension has become a routine process at Penn State thanks to newly developed techniques in chemical etching, lithography and post-processing. The newly etched silicon grisms have typical rms surface roughness of ~ 9 nm with the best reaching 0.9 nm, significantly lower than our previous attempts (~ 20-30 nm). The wavefront quality of the etched gratings is high. Typical wavefront error is ~ 0.035 wave at 0.6328 micron, indicating diffraction-limited performance in the entire infrared wavelengths (1.2-10 microns) where silicon has excellent transmission. These processes have also significantly eliminated visible defects due to grating mask breaks during chemical etching. For the best grisms, we have less than 1 defect per cm2. The measured total integrated scatter is less than 1% at 0.6328 micron, indicating similar or lower scatter in the IR when grisms are operated in transmission. These new generation grisms are being evaluated with our Penn State near IR Imager and Spectrograph (PIRIS) in cryogenic temperature. We are applying the new techniques in etching an 80x40 mm2 grating on 30 mm thick substrate to make an anamorphic silicon immersion grating, which can provide a diffraction-limited spectral resolution of R = 220,000 at 2.2 micron. We plan to put this immersion grating in a modified PIRIS to measure magnetic field strength using the Fe I line at 1.56 micron among hundreds of nearby solar type stars to investigate the probability of the Maunder Minimum using the Mt. Wilson 100inch with adaptive optics in 2003.

Development of an extremely coherent single-mode fiber bundle array for high-contrast imaging of extrasolar planets with visible Terrestrial Planet Finder

We report results from development of a prototype extremely coherent single mode fiber optic array for the TPF visible nulling interferometer. This device is used to negate the effects of residual stellar leakage (scattering) due to imperfections in the TPF telescope optics and the visible nulling interferometer optical train. This prototype consists of 10 X 10 single mode fibers, V-groove arrays, two lenslet arrays (one at the front end and the other at the back end) and auxiliary mechanical components. This first development will pave a clear path for making a final coherent fiber array with ~ 1000 fibers. The final array, once fully functional, should be able to improve image contrast by another ~ 3 orders of magnitude after 6-7 orders of magnitude star light subtraction using the visible nulling interferometer to allow detection of earth-like planets as close as 0.1 arcseconds around stars at ~ 10 pc in space with a 4m size TPF. This concept combines all the advantages of a nulling interferometer with the simplicity of a modest size and modest optical quality single aperture telescope, which allows tremendous reduction of the total cost and simplicity of the operation of a visible TPF over other TPF approaches. This fiber array can also be used in the visible coronagraph for rejecting scattered light.

Adaptive optics high-resolution IR spectroscopy with silicon grisms and immersion gratings

The breakthrough of silicon immersion grating technology at Penn State has the ability to revolutionize high-resolution infrared spectroscopy when it is coupled with adaptive optics at large ground-based telescopes. Fabrication of high quality silicon grism and immersion gratings up to 2 inches in dimension, less than 1% integrated scattered light, and diffraction-limited performance becomes a routine process thanks to newly developed techniques. Silicon immersion gratings with etched dimensions of ~ 4 inches are being developed at Penn State. These immersion gratings will be able to provide a diffraction-limited spectral resolution of R = 300,000 at 2.2 micron, or 130,000 at 4.6 micron. Prototype silicon grisms have been successfully used in initial scientific observations at the Lick 3m telescope with adaptive optics. Complete K band spectra of a total of 6 T Tauri and Ae/Be stars and their close companions at a spectral resolution of R ~ 3000 were obtained. This resolving power was achieved by using a silicon echelle grism with a 5 mm pupil diameter in an IR camera. These results represent the first scientific observations conducted by the high-resolution silicon grisms, and demonstrate the extremely high dispersing power of silicon-based gratings. New discoveries from this high spatial and spectral resolution IR spectroscopy will be reported. The future of silicon-based grating applications in ground-based AO IR instruments is promising. Silicon immersion gratings will make very high-resolution spectroscopy (R > 100,000) feasible with compact instruments for implementation on large telescopes. Silicon grisms will offer an efficient way to implement low-cost medium to high resolution IR spectroscopy (R ~ 1000-50000) through the conversion of existing cameras into spectrometers by locating a grism in the instruments pupil location.

Silicon anamorphic gratings for IR high-resolution spectroscopy with future giant telescopes

Future 30m telescopes provide enormous challenges for IR high resolution spectrograph design. The spectrograph collimated beam size will reach ~ 400 mm in order to reach R ~ 25,000 under 0.4 arcsec seeing-limited images. This beam size will push an IR spectrograph volume larger than that of the giant optical echelle spectrograph at 10m telescopes, e.g. the Keck HIRES is 6×6×4 m3 (Vogt et al. 1994). The cost would be enormous considering the entire instrument must be cooled to cryogenic temperatures to be feasible. Here we propose a new kind of IR spectrometer using silicon anamorphic immersion gratings as the main disperser. By operating silicon immersion gratings in an anamorphic immersion mode, the increase in spectral resolving power can be up to a factor of n2 or ~12 times at Brewster’s angle (Dekker 1987). Hence, to reach the same spectral resolution, the collimated beam size is reduced to ~33mm in diameter, which makes the design of the instrument relatively easy. The recent breakthrough in silicon immersion grating technology at Penn State has allowed us to routinely fabricate high quality silicon grisms and immersion gratings with sizes of up to 2 inches, <1% integrated scattered light, and diffraction-limited performance thanks to newly developed techniques. Silicon anamorphic immersion gratings with etched dimensions of ~4 inches are being developed at Penn State. The first grating will be available for testing in late 2002. Currently, industry can supply up to 12 inch diameter silicon ingots. We plan to develop a new tool to handle this large grating size in our state-of-the-art nanofabrication facility. A silicon anamorphic grating of this size can provide a seeing-limited (0.4 arcsec) spectral resolution of R ~ 30,000 or diffraction-limited spectral resolution of R ~ 750,000 at 2.2 microns. In this paper, technical issues related to the design of an anamorphic grating spectrograph are discussed.

New-generation IR instrument components ready for NGST

At Penn State, two new instrument component technologies, namely silicon gratings and gaussian-shaped pupil masks, have been developed and are ready for producing high quality components for all three NGST IR instruments. Fabrication of silicon grisms with sizes up to 2 inches in dimension has become a routine process at Penn State thanks to newly developed techniques in chemical etching, lithography, and post-processing. The newly etched silicon grisms have a typical rms surface roughness of ~ 9 nm with the lowest of 0.9 nm, significantly lower than our previous ones (~ 20-30 nm) and have ~ 0.035 wave wavefront distortion at 0.6328 μm, indicating diffraction-limited performance in the entire infrared wavelengths (1.2 -10 μm) where silicon has excellent transmission. These processes have also significantly eliminated visible defects due to grating mask break during chemical etching. For the best grisms, we have less than 1 defect per cm2. The measured total integrated scatter is less than 1% at 0.6238 mm, indicating similar or lower scatter in the IR when grisms are operated in transmission. Silicon grisms and silicon immersion gratings will both boost spectral resolving power by more than 3 times for NGST near-IR MOS and mid-IR camera and spectrograph without pushing current instrument design. The higher dispersed spectra can be selected either by a filter or a low resolution grism cross-disperser. Our current grating techniques allow us to make gratings with a groove period from a few microns to more than 100 microns. For the first order grism, the theoretical grating efficiency is beyond 80% with a single layer of AR coating. The immersion gratings will have similar grating efficiency. Based on our previous measurements of a silicon echelle grism, this kind of grism can provide ~ 60% efficiency when they are operated in high orders. We have also developed Gaussian-shaped pupil masks for high contrast imaging with the NGST IR cameras. Depending on its final mirror configuration, this kind of mask can offer 10-6 contrast imaging as close as 5 lambda/D to a bright point source. The advantage of using this mask instead of a conventional graded Lyot coronagraph is that it is much easier to implement by simply inserting it at a pupil location to reach deep null. Therefore, the observing efficiency can be significantly improved. A prototype of this kind of mask has been tested at the Mt. Wilson 100inch telescope with adaptive optics and demonstrates 10-3-10-4 contrast at ~ 5 λ/D at the initial observations. The contrast level is comparable to an IR coronagraph in the same IR instrument, but is about one order of magnitude worse than the scattered light levels caused by the mirror surface. We have also studied other mask coronagraph designs for high contrast imaging. The hybrid and band-limited designs show great promise for further improving image contrast. The NGST IR cameras with new coronagraph designs will allow high contrast imaging for extra-solar planets and substellar companions around nearby stars.

High-resolution IR spectroscopic surveys for protoplanetary systems with silicon immersion gratings

The breakthrough of silicon immersion grating technology at Penn State has the ability to revolutionize high-resolution infrared spectroscopy at large ground-based telescopes. Fabrication of high quality silicon grisms and immersion gratings up to 2 inches in dimension has become a routine process thanks to newly developed techniques. Silicon immersion gratings with etched dimensions of ~ 4 inches are being developed at Penn State. This immersion grating will be able to provide diffraction-limited spectral resolution of R = 300,000 at 2.2 micron, or 130,000 at 4.6 micron. To take full advantage of this high dispersing device for high resolution IR spectroscopy at high efficiency, high order adaptive optics is required to fully correct wavefronts distorted by atmospheric turbulence, to reach Strehl ratio of at least ~50%. IR spectroscopy with R > 100,000 opens up new possibilities in investigating the total mass and location of protoplanets through observing absorption lines from the CO fundamental bands at 4.6 microns and other molecular bands formed in the dynamic gaps created by protoplanets. It can also be used to study the density, temperature and composition of the environment where planets form. Large aperture telescopes with low thermal background are essential for ground-based observations to have enough sensitivity for observing thousands of nearby T Tauri stars to study planet formation. The results of protoplanet mass and location distribution will be compared to those of planets obtained from Doppler radial velocity surveys to investigate whether orbital migration and dynamical scattering play a significant role in planet formation and evolution. Future perspectives for developing silicon immersion gratings with sizes larger than 4 inches will also be discussed.