Prototyping of MODIS LAI and FPAR Algorithm with LASUR and LANDSAT Data

This paper describes results from prototyping of the moderate resolution imaging spectroradiometer (MODIS) radiative transfer-based synergistic algorithm for the estimation of global leaf area index (LAI) and fraction of photosynthetically active radiation (FPAR) absorbed by vegetation using land surface reflectances (LASUR) and Landsat data. The algorithm uses multispectral surface reflectances and a land cover classification map as input data to retrieve global LAI and FPAR fields. The authors\u27 objectives are to evaluate its performance as a function of spatial resolution and uncertainties in surface reflectances and the land cover map. They analyzed reasons the algorithm can or cannot retrieve a value of LAI/FPAR from the reflectance data and justified the use of more complex algorithms, instead of NDVI-based methods. The algorithm was tested to investigate the effects of vegetation misclassification on LAI/FPAR retrievals. Misclassification between distinct biomes can fatally impact the quality of the retrieval, while the impact of misclassification between spectrally similar biomes is negligible. Comparisons of results from the coarse and fine resolution retrievals show that the algorithm is dependent on the spatial resolution of the data. By evaluating the data density distribution function, they can adjust the algorithm for data resolution and utilize the algorithm with data from other sensors

Detection of snow change using polarimetric TerraSAR-X time-series (Svalbard, Norway)

Due to recent climate change conditions, i.e. increasing temperatures and changing precipitation patterns, arctic snow cover dynamics exhibit strong changes in terms of extent and duration. Arctic amplification processes and impacts are well documented expected to strengthen in coming decades. In this context, innovative observation methods are helpful for a better comprehension of the spatial variability of snow properties relevant for climate research and hydrological applications. Microwave remote sensing provides exceptional spatial and temporal performance in terms of all-weather application and target penetration. Time-series of Synthetic Active Radar images (SAR) are becoming more accessible at different frequencies and polarimetry has demonstrated a significant advantage for detecting changes in different media. Concerning arctic snow monitoring, SAR sensors can offer continuous time-series during the polar night and with cloud cover, providing a consequent advantage in regard of optical sensors. The aim of this study is dedicated to the spatial and temporal variability of snow in the Ny-Ålesund area on the BrØgger peninsula, Svalbard (N 78°55’ / E 11° 55’) using a high temporal TerraSAR-X Stripmap time series from November 2018 to June 2022, providing four consecutive winter datasets. The dual-cross polarized (HH/VV) SAR data were acquired from two different orbits (ascending and descending) with high incidence angles (36° to 39°) increasing snow volume backscattering and reducing topographic constraints. Additionally, a high spatial resolution Digital Elevation Model (NPI 5-m), consistent in-situ measurements of meteorological data, and snow profiles including lowlands and glaciers sites are available. Polarimetric processing is based on the Kennaugh matrix decomposition, co-polar phase coherence (CCOH) and co-polar phase difference (CPD). The Kennaugh matrix elements K0, K3, K4, and K7 are the total intensity, phase ratio, intensity ratio, and shift between HH and VV phase center, respectively. Their interpretation allows analyzing the structure of the snowpack linked to the near real time of in-situ measurements (snow profiles). The X-band signal is strongly influenced by the snow stratigraphy: internal ice layers reduce or block the penetration of the signal into the snow pack. The best R2 correlation performances between estimated and measured snow heights are ranging from 0.50 to 0.80 for dry snow conditions. Therefore, the use of the X-band for regular snow height estimations remains limited under these conditions. Conversely, this study shows the benefit of TerraSAR-X thanks to the Kennaugh matrix elements analysis. A focus is set (i) on the K0 element corresponding to the total power (Span), and (ii) on the Copolar Phase Difference (CPD, Leinss 2016) between VV and HH polarization: ɸ CPD = ɸ VV - ɸ HH. Our results indicate that the CPD values are related to the snow metamorphism: positive values correspond to dry snow (horizontal structures), negative values indicate recrystallization processes (vertical structures)

Combining in situ observations and remote sensing data to determine the spatial extent of rain-on-snow events on the Brøgger peninsula

Climate change is particularly impacting the Arctic, where the temperature increase is stronger than the global mean due to Arctic Amplification. Long-term observations at sites such as Ny-Alesund on the Brøgger’s peninsula in Svalbard allow understanding meteorological changes taking place in the Arctic. In the last decades, Ny Alesund was affected by a large increase of winter temperatures leading to occasional periods of positive temperatures lasting few days. As a result, the number of rainfall events also increased, contributing to an early degradation of the snowpack on the Brogger peninsula. Meteorological measurements such as at Ny Alesund allow to quantify the temporal variability of these “rain on snow” (ROS) events at specific points. The goal of this study is (i) to spatialize recent ROS events on the Brøgger peninsula during the period 2019-2022 using remote sensing radar data and (ii) to characterize the atmospheric origin of these events using anomalies of 500 hPa height or the identification of cyclonic systems. We use SAR satellite images from each event, mainly TSX and RCM images provided by German and Canadian Space Agencies. We processed the images with a thresholding method in order to find the spatial elevation limits between wet and dry snow after the events. PlanetScope optical images are used for snow extent validation. During the ROS episodes, the snow remains generally dry upstream of the glaciers, while at lower altitudes the snow on the peninsula is systematically wet. These ROS episodes are associated to cyclonic systems originated from the Northern Atlantic Ocean, and to a strong Z500 gradient from high pressure centered in Norway and low pressure centered in Greenland. These results are important to better characterize the origins and the spatial variability of ROS events and to evaluate the impact of these specific events on glaciers, permafrost, or ecology

Identification of LRP-1 as an endocytosis and recycling receptor for B1-integrin in thyroid cancer cells

International audienceLRP-1 is a large endocytic receptor mediating the clearance of various molecules from the extracellular matrix. LRP-1 was reported to control focal adhesion turnover to optimize the adhesion-deadhesion balance to support invasion. To better understand how LRP-1 coordinates cell-extracellular matrix interface, we explored its ability to regulate cell surface integrins in thyroid carcinomas. Using an antibody approach, we demonstrated that β1-integrin levels were increased at the plasma membrane under LRP1 silencing or upon RAP treatment, used as LRP-1 antagonist. Our data revealed that LRP-1 binds with both inactive and active β1-integrin conformations and identified the extracellular ligand-binding domains II or IV of LRP-1 as sufficient to bind β1-integrin. Using a recombinant β1-integrin, we demonstrated that LRP-1 acts as a regulator of β1-integrin intracellular traffic. Moreover, RAP or LRP-1 blocking antibodies decreased up to 36% the number of β1-integrin-containing endosomes. LRP-1 blockade did not significantly affect the levels of β1-integrin-containing lysosomes while decreasing localization of β1-integrin within Rab-11 positive vesicles. Overall, we identified an original molecular process in which LRP-1 acts as a main regulator of β1-integrin internalization and recycling in thyroid cancer cells

Low-density lipoprotein receptor-related protein-1 mediates endocytic clearance of tissue inhibitor of metalloproteinases-1 and promotes its cytokine-like activities.

Tissue inhibitor of metalloproteinases-1 (TIMP-1) regulates the extracellular matrix turnover by inhibiting the proteolytic activity of matrix metalloproteinases (MMPs). TIMP-1 also displays MMP-independent activities that influence the behavior of various cell types including neuronal plasticity, but the underlying molecular mechanisms remain mostly unknown. The trans-membrane receptor low-density lipoprotein receptor-related protein-1 (LRP-1) consists of a large extracellular chain with distinct ligand-binding domains that interact with numerous ligands including TIMP-2 and TIMP-3 and a short transmembrane chain with intracellular motifs that allow endocytosis and confer signaling properties to LRP-1. We addressed TIMP-1 interaction with recombinant ligand-binding domains of LRP-1 expressed by CHO cells for endocytosis study, or linked onto sensor chips for surface plasmon resonance analysis. Primary cortical neurons bound and internalized endogenous TIMP-1 through a mechanism mediated by LRP-1. This resulted in inhibition of neurite outgrowth and increased growth cone volume. Using a mutated inactive TIMP-1 variant we showed that TIMP-1 effect on neurone morphology was independent of its MMP inhibitory activity. We conclude that TIMP-1 is a new ligand of LRP-1 and we highlight a new example of its MMP-independent, cytokine-like functions

Domains II and IV of the extracellular α-chain of LRP-1 are required to bind and promote TIMP-1 endocytosis in CHO cells.

<p><b>A.</b> Schematic representation of LRP-1-derived minireceptors carrying no-ligand-binding cluster (SPCT), extracellular binding-domain II (DII) or extracellular binding-domain IV (DIV). Each construct contains a HA tag at the amino-terminus of the α-chain. <b>B.</b> Transfected CHO cells stably express HA-tagged SPCT (SPCT), HA-tagged mini LRP-II (DII), or HA-tagged mini LRP-IV (DIV). Nontransfected cells served as control (CTRL). Biotinylation of cell-surface proteins was performed, followed by an immunoblot (IB) analysis using anti-HA tag. Bands correspond to the expected molecular weights of SPCT (106 kDa; arrowhead), DII (153 kDa; star), and DIV (164 kDa; double star). <b>C.</b> CHO cells overexpressing HA-tagged LRP-1-derived minireceptors (SPCT, DII, DIV) or not (CTRL) were transiently transfected with RFP-tagged TIMP-1 for 24 hours. Cell-surface proteins were subjected to immunoprecipitation (IP) assay with either anti-HA tag (left panel) or an anti-RFP tag (right panel). Then, immunoblot (IB) analysis was conducted using both anti-LRP-1 β-chain (5A6) and anti-RFP tag. <b>D.</b> Representative sensorgrams for TIMP-1 interacting with DII (left panel) and DIV (right panel). A set of concentrations (5–80 nM) of TIMP-1 or EGF was sequentially injected over immobilized Fc-DII and Fc-DIV. The solid black lines represent the specific binding of TIMP-1 obtained after double-subtraction of the signal obtained on the control flow cell and a blank run. The dotted black lines represent the fit of the data with a kinetic titration 1∶1 interaction model. The grey lines represent the specific binding of EGF obtained after double-subtraction of the signal obtained on the control flow cell and a blank run. Arrows indicate the beginning of each injection. The data illustrated are representative of three independent experiments. <b>E.</b> Binding and internalization of exogenous fluorescent TIMP-1 (fluo-TIMP-1) by CHO cells overexpressing minireceptor SPCT (left), DII (middle) or DIV (right). Binding was assessed by incubating fluo-TIMP-1 (10 nM) at 4°C for 2 hours. Cells were then transferred to 37°C for additional 2 h to allow internalization. All incubations were performed with or without RAP (500 nM), an antagonist of LRP-1-mediated binding and consequently, endocytosis. Fluorescence intensity was quantified by spectrophotometry and expressed as arbitrary units (A.U.). Values below 10 A.U. are considered to be nonspecific. Images in <b>B–D</b> are representative of results obtained in 3 independent experiments. Values in <b>E</b> represent the means ± s.e.m. of 3 independent experiments. NS, not significant; * <i>p</i><0.05, as compared to untreated cells.</p

TIMP-1 binding to LRP-1 increases growth cone volume.

<p><b>A.</b> Cortical neurons from mouse embryos were treated after 24-L-lysine-coated coverslips for 30 min with TIMP-1 (10 nM), RAP (500 nM) or blocking LRP-1 polyclonal antibodies (R2629) or a combination of TIMP-1+RAP and TIMP-1+R2629. Untreated cells served as a control (CTRL). Neurons were incubated with Alexa Fluor 568-phalloidin to label F-actin structures and analyzed by confocal microscopy. <b>B.</b> 3D-quantification of growth cone volume was performed using the AMIRA software and expressed as percent of untreated neurons (CTRL). Images in <b>A</b> are representative of results obtained in 3 independent experiments. Values in <b>B</b> represent the means ± s.e.m. of 3 independent experiments. NS, not significant; ** <i>p</i><0.01. Scale bar: 5 µm.</p