Cryo-EM structures elucidate the multiligand receptor nature of megalin.

Megalin (low-density lipoprotein receptor-related protein 2) is a giant glycoprotein of about 600 kDa, mediating the endocytosis of more than 60 ligands, including those of proteins, peptides, and drug compounds [S. Goto, M. Hosojima, H. Kabasawa, A. Saito, Int. J. Biochem. Cell Biol. 157, 106393 (2023)]. It is expressed predominantly in renal proximal tubule epithelial cells, as well as in the brain, lungs, eyes, inner ear, thyroid gland, and placenta. Megalin is also known to mediate the endocytosis of toxic compounds, particularly those that cause renal and hearing disorders [Y. Hori et al., J. Am. Soc. Nephrol. 28, 1783-1791 (2017)]. Genetic megalin deficiency causes Donnai-Barrow syndrome/facio-oculo-acoustico-renal syndrome in humans. However, it is not known how megalin interacts with such a wide variety of ligands and plays pathological roles in various organs. In this study, we elucidated the dimeric architecture of megalin, purified from rat kidneys, using cryoelectron microscopy. The maps revealed the densities of endogenous ligands bound to various regions throughout the dimer, elucidating the multiligand receptor nature of megalin. We also determined the structure of megalin in complex with receptor-associated protein, a molecular chaperone for megalin. The results will facilitate further studies on the pathophysiology of megalin-dependent multiligand endocytic pathways in multiple organs and will also be useful for the development of megalin-targeted drugs for renal and hearing disorders, Alzheimer's disease [B. V. Zlokovic et al., Proc. Natl. Acad. Sci. U.S.A. 93, 4229-4234 (1996)], and other illnesses.

Megalin-related mechanism of hemolysis-induced acute kidney injury and the therapeutic strategy.

Hemolysis-induced acute kidney injury (AKI) is attributed to heme-mediated proximal tubule epithelial cell (PTEC) injury and tubular cast formation due to intratubular protein condensation. Megalin is a multiligand endocytic receptor for proteins, peptides, and drugs in PTECs and mediates the uptake of free hemoglobin and the heme-scavenging protein α1-microglobulin. However, understanding of how megalin is involved in the development of hemolysis-induced AKI remains elusive. Here, we investigated the megalin-related pathogenesis of hemolysis-induced AKI and a therapeutic strategy using cilastatin, a megalin blocker. A phenylhydrazine-induced hemolysis model developed in kidney-specific mosaic megalin knockout (MegKO) mice confirmed megalin-dependent PTEC injury revealed by the co-expression of kidney injury molecule-1 (KIM-1). In the hemolysis model in kidney-specific conditional MegKO mice, the uptake of hemoglobin and α1-microglobulin as well as KIM-1 expression in PTECs was suppressed, but tubular cast formation was augmented, likely due to the nonselective inhibition of protein reabsorption in PTECs. Quartz crystal microbalance analysis revealed that cilastatin suppressed the binding of megalin with hemoglobin and α1-microglobulin. Cilastatin also inhibited the specific uptake of fluorescent hemoglobin by megalin-expressing rat yolk sac tumor-derived L2 cells. In a mouse model of hemolysis-induced AKI, repeated cilastatin administration suppressed PTEC injury by inhibiting the uptake of hemoglobin and α1-microglobulin and also prevented cast formation. Hemopexin, another heme-scavenging protein, was also found to be a novel ligand of megalin, and its binding to megalin and uptake by PTECs in the hemolysis model were suppressed by cilastatin. Mass spectrometry-based semiquantitative analysis of urinary proteins in cilastatin-treated C57BL/6J mice indicated that cilastatin suppressed the reabsorption of a limited number of megalin ligands in PTECs, including α1-microglobulin and hemopexin. Collectively, cilastatin-mediated selective megalin blockade is an effective therapeutic strategy to prevent both heme-mediated PTEC injury and cast formation in hemolysis-induced AKI. © 2024 The Pathological Society of Great Britain and Ireland.

Megalin is involved in angiotensinogen-induced, angiotensin II-mediated ERK1/2 signaling to activate Na + -H + exchanger 3 in proximal tubules.

BACKGROUND: Kidney angiotensin (Ang) II is produced mainly from liver-derived, glomerular-filtered angiotensinogen (AGT). Podocyte injury has been reported to increase the kidney Ang II content and induce Na + retention depending on the function of megalin, a proximal tubular endocytosis receptor. However, how megalin regulates the renal content and action of Ang II remains elusive. METHODS: We used a mass spectrometry-based, parallel reaction-monitoring assay to quantitate Ang II in plasma, urine, and kidney homogenate of kidney-specific conditional megalin knockout (MegKO) and control (Ctl) mice. We also evaluated the pathophysiological changes in both mouse genotypes under the basal condition and under the condition of increased glomerular filtration of AGT induced by administration of recombinant mouse AGT (rec-mAGT). RESULTS: Under the basal condition, plasma and kidney Ang II levels were comparable in the two mouse groups. Ang II was detected abundantly in fresh spot urine in conditional MegKO mice. Megalin was also found to mediate the uptake of intravenously administered fluorescent Ang II by PTECs. Administration of rec-mAGT increased kidney Ang II, exerted renal extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, activated proximal tubular Na + -H + exchanger 3 (NHE3), and decreased urinary Na + excretion in Ctl mice, whereas these changes were suppressed but urinary Ang II was increased in conditional MegKO mice. CONCLUSION: Increased glomerular filtration of AGT is likely to augment Ang II production in the proximal tubular lumen. Thus, megalin-dependent Ang II uptake should be involved in the ERK1/2 signaling that activates proximal tubular NHE3 in vivo , thereby causing Na + retention.

Adult ALCAPA: from histological picture to clinical features.

BACKGROUND: Anomalous left coronary artery from the pulmonary artery (ALCAPA) is a rare congenital coronary anomaly that results in high mortality if left untreated. Our aim was to extend our knowledge of the histological, angiographic, and clinical characteristics of ALCAPA in order to deepen our understanding of this rare entity. CASE PRESENTATION: We were involved in the assessment, treatment, and pathological evaluation of two adult ALCAPA patients who were rescued from ventricular fibrillation and then surgically treated to establish a dual coronary artery system. Histological studies indicated various chronic ischemic changes in the myocardium, patchy fibrosis, and severely thickened arteriolar walls in both ventricles. The first patient is alive and well 11.5 years after surgical correction without any implantable cardioverter defibrillator (ICD) activations. The second patient required re-do surgery 9 months after the initial operation but subsequently died. Histologically, chronic ischemic alteration of the myocardium and thickened arteriolar walls persisted even after surgical correction, and coronary angiography (CAG) showed an extremely slow flow phenomenon even after surgical correction in both patients. The average postoperative opacification rate in the first case was 7.36 + 1.12 (n = 2) in the RCA, 3.81 + 0.51 (n = 3) in the left anterior descending (LAD) artery, and 4.08 + 0.27 (n = 4) in the left circumflex (LCx) artery. The slow flow phenomenon may represent persistent high arteriolar resistance in both ventricles. CONCLUSIONS: Seldom reported or new findings in adult ALCAPA were identified in two cases. More frequent diagnosis of adult ALCAPA can be expected because of the widespread availability of resuscitation and more advanced diagnostic modalities. Accumulation of pathological and clinical findings and confirmation of the long-term follow-up results after treatment may contribute to expanding our knowledge of this rare entity and establishing optimal treatment.

Two adult cases of Bland-White-Garland syndrome with lethal arrhythmia due to coronary steal phenomenon during physical or mental stress.

We experienced two adult cases of anomalous origin of the left coronary artery from the pulmonary artery, so-called Bland-White-Garland (BWG) syndrome, that presented with ventricular tachycardia (VT) and ventricular fibrillation during exertion in daily life. They presented to our hospital with syncope due to VT, and recovered following application of an automated external defibrillator with cardiopulmonary resuscitation. We diagnosed BWG syndrome by multi-detector computed tomography angiography and coronary angiography. We analyzed the mechanisms of lethal arrhythmias in relation to myocardial ischemia on exertion. Coronary flow modification and implantable cardioverter defibrillator implantation were performed in order to prevent future lethal arrhythmia due to myocardial ischemia. It is important to be aware of congenital heart disease in ordinary cases. .

Quantum key distribution over 120 km using ultrahigh purity single-photon source and superconducting single-photon detectors.

Advances in single-photon sources (SPSs) and single-photon detectors (SPDs) promise unique applications in the field of quantum information technology. In this paper, we report long-distance quantum key distribution (QKD) by using state-of-the-art devices: a quantum-dot SPS (QD SPS) emitting a photon in the telecom band of 1.5 µm and a superconducting nanowire SPD (SNSPD). At the distance of 100 km, we obtained the maximal secure key rate of 27.6 bps without using decoy states, which is at least threefold larger than the rate obtained in the previously reported 50-km-long QKD experiment. We also succeeded in transmitting secure keys at the rate of 0.307 bps over 120 km. This is the longest QKD distance yet reported by using known true SPSs. The ultralow multiphoton emissions of our SPS and ultralow dark count of the SNSPD contributed to this result. The experimental results demonstrate the potential applicability of QD SPSs to practical telecom QKD networks.

High quality-factor Si/SiO(2)-InP hybrid micropillar cavities with submicrometer diameter for 1.55-µm telecommunication band.

We theoretically demonstrate high quality(Q)-factor micropillar cavities at 1.55-µm wavelength based on Si/SiO(2)-InP hybrid structure. An adiabatic design in distributed Bragg reflectors (DBRs) improves Q-factor for upto 3 orders of magnitude, while reducing the diameter to sub-micrometer. A moderate Q-factor of ~3000 and a Purcell factor of ~200 are realized by only 2 taper segments and fewer conventional DBR pairs, enabling single photon generation at GHz rate. As the taper segment number is increased, Q-factor can be boosted to ~10(5)-10(6), enabling coherent exchange between the emitter and the optical mode at 1.55 µm, which is applicable in quantum information networks.

Design of Si/SiO2 micropillar cavities for Purcell-enhanced single photon emission at 1.55 µm from InAs/InP quantum dots.

Numerical simulations were carried out on micropillar cavities consisting of Si/SiO2 distributed Bragg reflectors (DBRs) with an InP spacer layer. Owing to a large refractive index contrast of ~2 in DBRs, cavities with just 4/6.5 top/bottom DBR pairs that give a low pillar height (~4.5 µm), have noticeable Purcell-enhancement effect in the 1.55-µm band. With careful designs on cavities with diameters of ~2.30 µm, a quality factor of up to 3300, a nominal Purcell factor of up to 110, and an output efficiency of ~60% are obtainable. These results ensure improvement of operation frequency and enhancement of photon indistinguishability for 1.55-µm single photon sources based on InAs/InP quantum dots.

Usefulness of right ventricular tissue Doppler imaging for diagnosis of right ventricular myocardial infarction.

BACKGROUND: Right ventricular myocardial infarction (RVMI) is a complication of acute inferior myocardial infarction and sometimes causes severe hemodynamic disturbance. It is therefore important to promptly detect RVMI and assess the severity of right ventricular (RV) dysfunction. Tissue Doppler imaging (TDI) is a useful method to assess left ventricular function and RV function. In this study, we investigated the possibility of diagnosing RVMI using tricuspid annular velocity determined by TDI. METHODS: Thirty consecutive patients with first acute inferior myocardial infarction were studied. The diagnosis of RVMI was based on an ST-segment elevation of at least 0.1 mV in lead V4R. The patients were classified into 12 patients with RVMI (the RVMI group) and 18 patients without RVMI (non-RVMI group). All patients underwent two-dimensional echocardiography, pulsed Doppler and TDI, and coronary angiography within 48 h after onset of myocardial infarction. Tricuspid inflow velocity was recorded by pulsed Doppler and early diastolic tricuspid inflow velocity (TVE) was measured. Peak early diastolic velocity of the tricuspid annulus (TVe') at the RV free wall was recorded using TDI. The ratio of TVE to TVe' (TVE/TVe') was calculated. RESULTS: TVe' was significantly lower in the RVMI group compared to that in the non-RVMI group (5.9 ± 1.3 vs. 9.1 ± 3.1; p = 0.0025). On the basis of a TVe' cutoff value of less than 8.3 cm/s, RVMI was diagnosed with 100 % sensitivity and 61 % specificity. CONCLUSIONS: The early diastolic tricuspid annular velocity determined by TDI is a noninvasive and sensitive index for diagnosing RVMI.

Observation of electrostatically released DNA from gold electrodes with controlled threshold voltages.

DNA oligo-nucleotides, localized at Au metal electrodes in aqueous solution, are found to be released when applying a negative bias voltage to the electrode. The release was confirmed by monitoring the intensity of the fluorescence of cyanine dyes (Cy3) linked to the 5' end of the DNA. The threshold voltage of the release changes depending on the kind of linker added to the DNA 3'-terminal. The amount of released DNA depends on the duration of the voltage pulse. Using this technique, we can retain DNA at Au electrodes or Au needles, and release the desired amount of DNA at a precise location in a target. The results suggest that DNA injection into living cells is possible with this method.