Morphometric Analysis of the Thymic Epithelial Cell (TEC) Network Using Integrated and Orthogonal Digital Pathology Approaches.

The thymus, a central primary lymphoid organ of the immune system, plays a key role in T cell development. Surprisingly, the thymus is quite neglected with regards to standardized pathology approaches and practices for assessing structure and function. Most studies use multispectral flow cytometry to define the dynamic composition of the thymus at the cell population level, but they are limited by lack of contextual insight. This knowledge gap hinders our understanding of various thymic conditions and pathologies, particularly how they affect thymic architecture, and subsequently, immune competence. Here, we introduce a digital pathology pipeline to address these challenges. Our approach can be coupled to analytical algorithms and utilizes rationalized morphometric assessments of thymic tissue, ranging from tissue-wide down to microanatomical and ultrastructural levels. This pipeline enables the quantitative assessment of putative changes and adaptations of thymic structure to stimuli, offering valuable insights into the pathophysiology of thymic disorders. This versatile pipeline can be applied to a wide range of conditions that may directly or indirectly affect thymic structure, ranging from various cytotoxic stimuli inducing acute thymic involution to autoimmune diseases, such as myasthenia gravis. Here, we demonstrate applicability of the method in a mouse model of age-dependent thymic involution, both by confirming established knowledge, and by providing novel insights on intrathymic remodeling in the aged thymus. Our orthogonal pipeline, with its high versatility and depth of analysis, promises to be a valuable and practical toolset for both basic and translational immunology laboratories investigating thymic function and disease.

mTORC2-NDRG1-CDC42 axis couples fasting to mitochondrial fission.

Fasting triggers diverse physiological adaptations including increases in circulating fatty acids and mitochondrial respiration to facilitate organismal survival. The mechanisms driving mitochondrial adaptations and respiratory sufficiency during fasting remain incompletely understood. Here we show that fasting or lipid availability stimulates mTORC2 activity. Activation of mTORC2 and phosphorylation of its downstream target NDRG1 at serine 336 sustains mitochondrial fission and respiratory sufficiency. Time-lapse imaging shows that NDRG1, but not the phosphorylation-deficient NDRG1Ser336Ala mutant, engages with mitochondria to facilitate fission in control cells, as well as in those lacking DRP1. Using proteomics, a small interfering RNA screen, and epistasis experiments, we show that mTORC2-phosphorylated NDRG1 cooperates with small GTPase CDC42 and effectors and regulators of CDC42 to orchestrate fission. Accordingly, RictorKO, NDRG1Ser336Ala mutants and Cdc42-deficient cells each display mitochondrial phenotypes reminiscent of fission failure. During nutrient surplus, mTOR complexes perform anabolic functions; however, paradoxical reactivation of mTORC2 during fasting unexpectedly drives mitochondrial fission and respiration.

Alzheimer's-Associated Upregulation of Mitochondria-Associated ER Membranes After Traumatic Brain Injury.

Traumatic brain injury (TBI) can lead to neurodegenerative diseases such as Alzheimer's disease (AD) through mechanisms that remain incompletely characterized. Similar to AD, TBI models present with cellular metabolic alterations and modulated cleavage of amyloid precursor protein (APP). Specifically, AD and TBI tissues display increases in amyloid-ß as well as its precursor, the APP C-terminal fragment of 99 a.a. (C99). Our recent data in cell models of AD indicate that C99, due to its affinity for cholesterol, induces the formation of transient lipid raft domains in the ER known as mitochondria-associated endoplasmic reticulum (ER) membranes ("MAM" domains). The formation of these domains recruits and activates specific lipid metabolic enzymes that regulate cellular cholesterol trafficking and sphingolipid turnover. Increased C99 levels in AD cell models promote MAM formation and significantly modulate cellular lipid homeostasis. Here, these phenotypes were recapitulated in the controlled cortical impact (CCI) model of TBI in adult mice. Specifically, the injured cortex and hippocampus displayed significant increases in C99 and MAM activity, as measured by phospholipid synthesis, sphingomyelinase activity and cholesterol turnover. In addition, our cell type-specific lipidomics analyses revealed significant changes in microglial lipid composition that are consistent with the observed alterations in MAM-resident enzymes. Altogether, we propose that alterations in the regulation of MAM and relevant lipid metabolic pathways could contribute to the epidemiological connection between TBI and AD.

Mechanistic Insights of Empagliflozin in Nondiabetic Patients With HFrEF: From the EMPA-TROPISM Study.

OBJECTIVES: The goal of this study was to evaluate the effect of empagliflozin, in addition to optimal medical treatment, on epicardial adipose tissue (EAT), interstitial myocardial fibrosis, and aortic stiffness in nondiabetic patients with heart failure with reduced ejection fraction (HFrEF). BACKGROUND: Several randomized clinical trials have established the benefits of the inhibitors of the sodium-glucose cotransporter-2 receptor (SGLT2-i) in HFrEF, independent of their hypoglycemic effects. The mechanisms of the benefits of SGLT2-i in HFrEF have not been well defined. METHODS: This study was a secondary analysis of patients enrolled in the EMPA-TROPISM [ATRU-4] (Are the cardiac benefits of Empagliflozin independent of its hypoglycemic activity?) clinical trial. It was a double-blind, placebo-controlled randomized clinical trial investigating the effect of empagliflozin in nondiabetic patients with HFrEF. Patients underwent cardiac magnetic resonance at baseline and after 6 months. Interstitial myocardial fibrosis was calculated by using T1 mapping (extracellular volume). Aortic stiffness was calculated by using pulsed wave velocity, and EAT was measured from the cine sequences. RESULTS: Empagliflozin is associated with significant reductions in EAT volume (-5.14 mL; 95% CI: -8.36 to -1.92) compared with placebo (-0.75 mL; 95% CI: -3.57 to 2.06; P < 0.05); this finding was paralleled by reductions in subcutaneous adipose tissue area (-5.33 cm2 [95% CI: -12.61 to 1.95] vs 9.13 cm2 [95% CI: -2.72 to 20.99]; P < 0.05). Empagliflozin-treated patients reported a reduction in extracellular volume (-1.25% [±0.56 95% CI] vs 0.24% [±0.57 95% CI]; (P < 0.01)]; specifically, empagliflozin reduced both matrix volume (-7.24 mL [95% CI: -11.59 to -2.91] vs 0.70 mL [95% CI: -0.89 to 2.29]; P < 0.001) and cardiomyocyte volume (-11.08 mL [95% CI: -19.62 to -2.55] vs 0.80 mL [95% CI: -1.96 to 3.55]; P < 0.05). Pulsed wave velocity was also significantly reduced in the empagliflozin group (-0.58 cm/s [95% CI: -0.92 to -0.25] vs 0.60 cm/s [95% CI: 0.14 to 1.06]; P < 0.01). Using proteomics, empagliflozin was associated with a significant reduction in inflammatory biomarkers. CONCLUSIONS: Empagliflozin significantly improved adiposity, interstitial myocardial fibrosis, aortic stiffness, and inflammatory markers in nondiabetic patients with HFrEF. These results shed new light on the mechanisms of action of the benefits of SGLT2-i. (Are the "Cardiac Benefits" of Empagliflozin Independent of Its Hypoglycemic Activity [ATRU-4] [EMPA-TROPISM]; NCT03485222).

Defective Mitochondrial Dynamics Underlie Manganese-Induced Neurotoxicity.

Perturbations in mitochondrial dynamics have been observed in most neurodegenerative diseases. Here, we focus on manganese (Mn)-induced Parkinsonism-like neurodegeneration, a disorder associated with the preferential of Mn in the basal ganglia where the mitochondria are considered an early target. Despite the extensive characterization of the clinical presentation of manganism, the mechanism by which Mn mediated mitochondrial toxicity is unclear. In this study we hypothesized whether Mn exposure alters mitochondrial activity, including axonal transport of mitochondria and mitochondrial dynamics, morphology, and network. Using primary neuron cultures exposed to 100 µM Mn (which is considered the threshold of Mn toxicity in vitro) and intraperitoneal injections of MnCl2 (25mg/kg) in rat, we observed that Mn increased mitochondrial fission mediated by phosphorylation of dynamin-related protein-1 at serine 616 (p-s616-DRP1) and decreased mitochondrial fusion proteins (MFN1 and MFN2) leading to mitochondrial fragmentation, defects in mitochondrial respiratory capacity, and mitochondrial ultrastructural damage in vivo and in vitro. Furthermore, Mn exposure impaired mitochondrial trafficking by decreasing dynactin (DCTN1) and kinesin-1 (KIF5B) motor proteins and increasing destabilization of the cytoskeleton at protein and gene levels. In addition, mitochondrial communication may also be altered by Mn exposure, increasing the length of nanotunnels to reach out distal mitochondria. These findings revealed an unrecognized role of Mn in dysregulation of mitochondrial dynamics providing a potential explanation of early hallmarks of the disorder, as well as a possible common pathway with neurological disorders arising upon chronic Mn exposure.

Randomized Trial of Empagliflozin in Nondiabetic Patients With Heart Failure and Reduced Ejection Fraction.

BACKGROUND: Large clinical trials established the benefits of sodium-glucose cotransporter 2 inhibitors in patients with diabetes and with heart failure with reduced ejection fraction (HFrEF). The early and significant improvement in clinical outcomes is likely explained by effects beyond a reduction in hyperglycemia. OBJECTIVES: The purpose of this study was to assess the effect of empagliflozin on left ventricular (LV) function and volumes, functional capacity, and quality of life (QoL) in nondiabetic HFrEF patients. METHODS: In this double-blind, placebo-controlled trial, nondiabetic HFrEF patients (n = 84) were randomized to empagliflozin 10 mg daily or placebo for 6 months. The primary endpoint was change in LV end-diastolic and -systolic volume assessed by cardiac magnetic resonance. Secondary endpoints included changes in LV mass, LV ejection fraction, peak oxygen consumption in the cardiopulmonary exercise test, 6-min walk test, and quality of life. RESULTS: Empagliflozin was associated with a significant reduction of LV end-diastolic volume (-25.1 ± 26.0 ml vs. -1.5 ± 25.4 ml for empagliflozin vs. placebo, respectively; p < 0.001) and LV end-systolic volume (-26.6 ± 20.5 ml vs. -0.5 ± 21.9 ml for empagliflozin vs. placebo; p < 0.001). Empagliflozin was associated with reductions in LV mass (-17.8 ± 31.9 g vs. 4.1 ± 13.4 g, for empagliflozin vs. placebo, respectively; p < 0.001) and LV sphericity, and improvements in LV ejection fraction (6.0 ± 4.2 vs. -0.1 ± 3.9; p < 0.001). Patients who received empagliflozin had significant improvements in peak O2 consumption (1.1 ± 2.6 ml/min/kg vs. -0.5 ± 1.9 ml/min/kg for empagliflozin vs. placebo, respectively; p = 0.017), oxygen uptake efficiency slope (111 ± 267 vs. -145 ± 318; p < 0.001), as well as in 6-min walk test (81 ± 64 m vs. -35 ± 68 m; p < 0.001) and quality of life (Kansas City Cardiomyopathy Questionnaire-12: 21 ± 18 vs. 2 ± 15; p < 0.001). CONCLUSIONS: Empagliflozin administration to nondiabetic HFrEF patients significantly improves LV volumes, LV mass, LV systolic function, functional capacity, and quality of life when compared with placebo. Our observations strongly support a role for sodium-glucose cotransporter 2 inhibitors in the treatment of HFrEF patients independently of their glycemic status. (Are the "Cardiac Benefits" of Empagliflozin Independent of Its Hypoglycemic Activity? [ATRU-4] [EMPA-TROPISM]; NCT03485222).

HIV Nef and Antiretroviral Therapy Have an Inhibitory Effect on Autophagy in Human Astrocytes that May Contribute to HIV-Associated Neurocognitive Disorders.

A significant number of people living with HIV (PLWH) develop HIV-associated neurocognitive disorders (HAND) despite highly effective antiretroviral therapy (ART). Dysregulated macroautophagy (autophagy) is implicated in HAND pathogenesis. The viral protein Nef, expressed even with suppressive ART, and certain antiretrovirals affect autophagy in non-CNS cells. Astrocytes, vital for CNS microenvironment homeostasis and neuronal health, require autophagy for their own homeostasis. We hypothesized that extracellular Nef and/or ART impact astrocyte autophagy, thus contributing to HAND. We studied in-bulk and selective autophagic flux in primary human astrocytes treated with extracellular Nef and/or a combination of tenofovir+emtricitabine+raltegravir (ART) using Western blotting, a tandem fluorescent LC3 reporter, and transmission electron microscopy/morphometry. We show that after 24 h treatment, Nef and ART decrease autophagosomes through different mechanisms. While Nef accelerates autophagosome degradation without inducing autophagosome formation, ART inhibits autophagosome formation. Combination Nef+ART further depletes autophagosomes by inducing both abnormalities. Additionally, extracellular Nef and/or ART inhibit lysosomal degradation of p62, indicating Nef and/or ART affect in-bulk and selective autophagy differently. Dysregulation of both autophagic processes is maintained after 7 days of Nef and/or ART treatment. Persistent autophagy dysregulation due to chronic Nef and/or ART exposure may ultimately result in astrocyte and neuronal dysfunction, contributing to HAND.

An Ultrastructural Study of the Extruded Polar Tube of Anncaliia algerae (Microsporidia).

All microsporidia share a unique, extracellular spore stage, containing the infective sporoplasm and the apparatus for initiating infection. The polar filament/polar tube when exiting the spore transports the sporoplasm through it into a host cell. While universal, these structures and processes have been enigmatic. This study utilized several types of microscopy, describing and extending our understanding of these structures and their functions. Cryogenically preserved polar tubes vary in diameter from 155 to over 200 nm, noticeably larger than fixed-sectioned or negatively stained samples. The polar tube surface is pleated and covered with fine fibrillar material that projects from the surface and is organized in clusters or tufts. These fibrils may be the sites of glycoproteins providing protection and aiding infectivity. The polar tube surface is ridged with 5-6 nm spacing between ridges, enabling the polar tube to rapidly increase its diameter to facilitate the passage of the various cargo including cylinders, sacs or vesicles filled with particulate material and the intact sporoplasm containing a diplokaryon. The lumen of the tube is lined with a membrane that facilitates this passage. Careful examination of the terminus of the tube indicates that it has a closed tip where the membranes for the terminal sac are located.

Phenotypic Modulation of Skeletal Muscle Fibers in LPIN1-Deficient Lipodystrophic ( fld) Mice.

Lipin-1 ( Lpin1)-deficient lipodystrophic mice have scant and immature adipocytes and develop transient fatty liver early in life. Unlike normal mice, these mice cannot rely on stored triglycerides to generate adenosine triphosphate (ATP) from the ß-oxidation of fatty acids during periods of fasting. To compensate, these mice store much higher amounts of glycogen in skeletal muscle and liver than wild-type mice in order to support energy needs during periods of fasting. Our studies demonstrated that there are phenotypic changes in skeletal muscle fibers that reflect an adaptation to this unique metabolic situation. The phenotype of skeletal muscle (soleus, gastrocnemius, plantaris, and extensor digitorum longus [EDL]) from Lpin1-/- was evaluated using various methods including immunohistochemistry for myosin heavy chains (Myh) 1, 2, 2a, 2b, and 2x; enzyme histochemistry for myosin ATPase, cytochrome-c oxidase (COX), and succinyl dehydrogenase (SDH); periodic acid-Schiff; and transmission electron microscopy. Fiber-type changes in the soleus muscle of Lpin1-/- mice were prominent and included decreased Myh1 expression with concomitant increases in Myh2 expression and myosin-ATPase activity; this change was associated with an increase in the presence of Myh1/2a or Myh1/2x hybrid fibers. Alterations in mitochondrial enzyme activity (COX and SDH) were apparent in the myofibers in the soleus, gastrocnemius, plantaris, and EDL muscles. Electron microscopy revealed increases in the subsarcolemmal mitochondrial mass in the muscles of Lpin1-/- mice. These data demonstrate that lipin-1 deficiency results in phenotypic fiber-specific modulation of skeletal muscle necessary for compensatory fuel utilization adaptations in lipodystrophy.

Increased localization of APP-C99 in mitochondria-associated ER membranes causes mitochondrial dysfunction in Alzheimer disease.

In the amyloidogenic pathway associated with Alzheimer disease (AD), the amyloid precursor protein (APP) is cleaved by ß-secretase to generate a 99-aa C-terminal fragment (C99) that is then cleaved by γ-secretase to generate the ß-amyloid (Aß) found in senile plaques. In previous reports, we and others have shown that γ-secretase activity is enriched in mitochondria-associated endoplasmic reticulum (ER) membranes (MAM) and that ER-mitochondrial connectivity and MAM function are upregulated in AD We now show that C99, in addition to its localization in endosomes, can also be found in MAM, where it is normally processed rapidly by γ-secretase. In cell models of AD, however, the concentration of unprocessed C99 increases in MAM regions, resulting in elevated sphingolipid turnover and an altered lipid composition of both MAM and mitochondrial membranes. In turn, this change in mitochondrial membrane composition interferes with the proper assembly and activity of mitochondrial respiratory supercomplexes, thereby likely contributing to the bioenergetic defects characteristic of AD.

CLEM Methods for Studying Primary Cilia.

CLEM (correlated light and electron microscope) imaging is a highly useful technique for examining primary cilia. With CLEM, it is possible to determine the distribution of tagged proteins along the ciliary membrane and axoneme with high precision. Scanning electron microscopy (SEM) permits measurement of ciliary length and orientation in relation to nearby cellular structures in a 3D image; in optimal cases, this can be combined with superresolution microscopy of selected ciliary components as they enter or leave the cilium. This chapter discusses CLEM methods. In the method described in detail, samples are completely processed for sequential fluorescence and SEM observation. This method is ideal for robust antibody localization and minimizes image manipulation in correlating the fluorescent and SEM images. Alternative methods prepare samples for fluorescence imaging followed by processing for SEM then observation in the SEM. This method is ideal for optimal fluorescence imaging, particularly live cell imaging.

Cecal volvulus in giant ventral hernia.

INTRODUCTION: Colonic volvulus is the third leading cause of the colonic obstruction with cecal volvulus accounting for approximately 40% of all colonic volvulus. Lack of peritonealization of the right colon, adhesions from prior surgery, colonic atony, and distal colonic obstruction are potential risks factors for the development of cecal volvulus. PRERSENTATION OF THE CASE: 63 year old male with history of multiple prior intraabdominal surgeries and recurrent ventral hernia. Presented with colon perforation, as a result of cecal volvulus, which was contained in a giant ventral hernia. Diagnosis of cecal volvulus was suspected based on preoperative imaging studies, and confirmed in the OR. Patient underwent damage control procedure with subsequent challenging abdominal wall closure. DISCUSSION: Axial cecal volvulus and cecal bascule are representing two types of cecal volvulus. Both of these types require a mobile cecum and presence of right colon to occur. It is generally accepted, that mobile cecum is a congenital condition, but in certain situations, particularly after prior intraabdominal surgeries, cecum may lose fixation points and potentially become vulnerable to twisting. This patient with long history of large recurrent ventral hernia had mobile cecum inside the hernia sac and developed cecal volvulus. CONCLUSION: We present a unique case of cecal volvulus in giant ventral hernia after multiple prior intraabdominal surgeries. Challenges in management of this exceptionally difficult patient were discussed. Large ventral hernia with mobile cecum inside hernia sac is a risk factor for cecal volvulus.

Value of CMR for the differential diagnosis of cardiac masses.

OBJECTIVES: The goal of this study was to evaluate the diagnostic value of CMR features for the differential diagnosis of cardiac masses. BACKGROUND: Differentiation of cardiac tumors and thrombi and differentiation of benign from malignant cardiac neoplasms is often challenging but important in clinical practice. Studies assessing the value of cardiac magnetic resonance (CMR) in this regard are scarce. METHODS: We reviewed the CMR scans of patients with a definite cardiac thrombus or tumor. Mass characteristics on cine, T1-weighted turbo spin echo (T1w-TSE) and T2-weighted turbo spin echo (T2w-TSE), contrast first-pass perfusion (FPP), post-contrast inversion time (TI) scout, and late gadolinium enhancement (LGE) sequences were analyzed. RESULTS: There were 84 thrombi, 17 benign tumors, and 25 malignant tumors in 116 patients. Morphologically, thrombi were smaller (median area 1.6 vs. 8.5 cm(2); p < 0.0001), more homogeneous (99% vs. 46%; p < 0.0001), and less mobile (13% vs. 33%; p = 0.007) than tumors. Hyperintensity compared with normal myocardium on T2w-TSE, FPP, and LGE were more common in tumors than in thrombi (85% vs. 42%, 70% vs. 4%, and 71% vs. 5%, respectively; all p < 0.0001). A pattern of hyperintensity/isointensity (compared with normal myocardium) with short TI and hypointensity with long TI was very frequent in thrombi (94%), rare in tumors (2%), and had the highest accuracy (95%) for the differentiation of both entities. Regarding the characterization of neoplastic masses, malignant tumors were larger (median area 11.9 vs. 6.3 cm(2); p = 0.006) and more frequently exhibited FPP (84% vs. 47%; p = 0.03) and LGE (92% vs. 41%; p = 0.001). The ability of CMR features to distinguish benign from malignant neoplasms was moderate, with LGE showing the highest accuracy (79%). CONCLUSIONS: CMR features demonstrated excellent accuracy for the differentiation of cardiac thrombi from tumors and can be helpful for the distinction of benign versus malignant neoplasms.

Molecular analysis of chromium and cobalt-related toxicity.

Occupational and environmental exposure to Co and Cr has been previously linked to a wide array of inflammatory and degenerative conditions and cancer. Recently, significant health concerns have been raised by the high levels of Cr and Co ions and corrosion products released by biomedical implants. Herein, we set to analyze the biological responses associated with Co and Cr toxicity. Histological, ultrastructural, and elemental analysis, performed on Cr and Co exposed patients reveal the presence of corrosion products, metallic wear debris and metal ions at varying concentrations. Metallic ions and corrosion products were also generated in vitro following macrophage phagocytosis of metal alloys. Ex vivo redox proteomic mapped several oxidatively damaged proteins by Cr(III) and Co(II)-induced Fenton reaction. Importantly, a positive correlation between the tissue amounts of Cr(III) and Co(II) ions and tissue oxidative damage was observed. Immobilized- Cr(III) and Co(II) affinity chromatography indicated that metal ions can also directly bind to several metallo and non-metalloproteins and, as demonstrated for aldolase and catalase, induce loss of their biological function. Altogether, our analysis reveals several biological mechanisms leading to tissue damage, necrosis, and inflammation in patients with Cr and Co-associated adverse local tissue reactions.

Imaging the alphavirus exit pathway.

UNLABELLED: Alphaviruses are small enveloped RNA viruses with highly organized structures that exclude host cell proteins. They contain an internal nucleocapsid and an external lattice of the viral E2 and E1 transmembrane proteins. Alphaviruses bud from the plasma membrane (PM), but the process and dynamics of alphavirus assembly and budding are poorly understood. Here we generated Sindbis viruses (SINVs) with fluorescent protein labels on the E2 envelope protein and exploited them to characterize virus assembly and budding in living cells. During virus infection, E2 became enriched in localized patches on the PM and in filopodium-like extensions. These E2-labeled patches and extensions contained all of the viral structural proteins. Correlative light and electron microscopy studies established that the patches and extensions colocalized with virus budding structures, while light microscopy showed that they excluded a freely diffusing PM marker protein. Exclusion required the interaction of the E2 protein with the capsid protein, a critical step in virus budding, and was associated with the immobilization of the envelope proteins on the cell surface. Virus infection induced two distinct types of extensions: tubulin-negative extensions that were ∼2 to 4 µm in length and excluded the PM marker, and tubulin-positive extensions that were >10 µm long, contained the PM marker, and could transfer virus particles to noninfected cells. Tubulin-positive extensions were selectively reduced in cells infected with a nonbudding SINV mutant. Together, our data support a model in which alphavirus infection induces reorganization of the PM and cytoskeleton, leading to virus budding from specialized sites. IMPORTANCE: Alphaviruses are important and widely distributed human pathogens for which vaccines and antiviral therapies are urgently needed. These small highly organized viruses bud from the host cell PM. Virus assembly and budding are critical but little understood steps in the alphavirus life cycle. We developed alphaviruses with fluorescent protein tags on one of the viral membrane (envelope) proteins and used a variety of microscopy techniques to follow the envelope protein and a host cell PM protein during budding. We showed that alphavirus infection induced the formation of patches and extensions on the PM where the envelope proteins accumulate. These sites excluded other PM proteins and correlated with virus budding structures. Exclusion of PM proteins required specific interactions of the viral envelope proteins with the internal capsid protein. Together, our data indicate that alphaviruses extensively reorganize the cell surface and cytoskeleton to promote their assembly and budding.

CEP162 is an axoneme-recognition protein promoting ciliary transition zone assembly at the cilia base.

The transition zone is a specialized compartment found at the base of cilia, adjacent to the centriole distal end, where axonemal microtubules are heavily crosslinked to the surrounding membrane to form a barrier that gates the ciliary compartment. A number of ciliopathy molecules have been found to associate with the transition zone, but factors that directly recognize axonemal microtubules to specify transition zone assembly at the cilia base remain unclear. Here, through quantitative centrosome proteomics, we identify an axoneme-associated protein, CEP162 (KIAA1009), tethered specifically at centriole distal ends to promote transition zone assembly. CEP162 interacts with core transition zone components, and mediates their association with microtubules. Loss of CEP162 arrests ciliogenesis at the stage of transition zone assembly. Abolishing its centriolar tethering, however, allows CEP162 to stay on the growing end of the axoneme and ectopically assemble transition zone components at cilia tips. This generates extra-long cilia with strikingly swollen tips that actively release ciliary contents into the extracellular environment. CEP162 is thus an axoneme-recognition protein pre-tethered at centriole distal ends before ciliogenesis to promote and restrict transition zone formation specifically at the cilia base.

Centriole distal appendages promote membrane docking, leading to cilia initiation.

The distal appendages (DAPs) of centrioles have been proposed to anchor cilia to the plasma membrane, but their molecular composition, assembly, and exact function in ciliogenesis remain poorly understood. Using quantitative centrosome proteomics and superresolution microscopy, we identified five DAP components, including one previously described (CEP164), one partially characterized (CEP89 [ccdc123]), and three novel (CEP83 [ccdc41], SCLT1, and FBF1) DAP proteins. Analyses of DAP assembly revealed a hierarchy. CEP83 recruits both SCLT1 and CEP89 to centrioles. Subsequent recruitment of FBF1 and CEP164 is independent of CEP89 but mediated by SCLT1. All five DAP components are essential for ciliogenesis; loss of CEP83 specifically blocks centriole-to-membrane docking. Undocked centrioles fail to recruit TTBK2 or release CP110, the two earliest modifications found on centrioles prior to cilia assembly, revealing centriole-to-membrane docking as a temporal and spatial cue promoting cilia initiation.

Imaging the endothelial glycocalyx in vitro by rapid freezing/freeze substitution transmission electron microscopy.

OBJECTIVE: Recent publications questioned the validity of endothelial cell (EC) culture studies of glycocalyx (GCX) function because of findings that GCX in vitro may be substantially thinner than GCX in vivo. The assessment of thickness differences is complicated by GCX collapse during dehydration for traditional electron microscopy. We measured in vitro GCX thickness using rapid freezing/freeze substitution (RF/FS) transmission electron microscopy (TEM), taking advantage of the high spatial resolution provided by TEM and the capability to stably preserve the GCX in its hydrated configuration by RF/FS. METHODS AND RESULTS: Bovine aortic EC (BAEC) and rat fat pad EC were subjected to conventional or RF/FS-TEM. Conventionally preserved BAEC GCX was ≈0.040 µm in thickness. RF/FS-TEM revealed impressively thick BAEC GCX of ≈11 µm and rat fat pad EC GCX of ≈5 µm. RF/FS-TEM also discerned GCX structure and thickness variations due to heparinase III enzyme treatment and extracellular protein removal, respectively. Immunoconfocal studies confirmed that the in vitro GCX is several micrometers thick and is composed of extensive and well-integrated heparan sulfate, hyaluronic acid, and protein layers. CONCLUSIONS: New observations by RF/FS-TEM reveal substantial GCX layers on cultured EC, supporting their continued use for fundamental studies of GCX and its function in the vasculature.