Comprehensive proteome analysis of brush border membrane fraction of ileum of ezrin knockdown mice

BioID2 screening identifies KIAA1671 as an EPS8 proximal factor that marks sites of microvillus growth

Microvilli are defining morphological features of the apical surfaces in diverse epithelial tissues. To develop our understanding of microvillus biogenesis, we used a biotin proximity-labeling approach to uncover new molecules enriched near EPS8, a well-studied marker of the microvillus distal tip compartment. Mass spectrometry of biotinylated hits identified KIAA1671, a large (∼200 kDa), disordered, and previously uncharacterized protein. Based on immunofluorescent staining and expression of fluorescent protein-tagged constructs, we found that KIAA1671 localizes to the base of the brush border in native intestinal tissue and polarized epithelial-cell culture models, as well as dynamic actin-rich structures in unpolarized, nonepithelial cell types. Live imaging also revealed that during the early stages of microvillar growth, KIAA1671 colocalizes with EPS8 in diffraction-limited puncta. However, once elongation of the core bundle begins, these two factors separate, with EPS8 tracking the distal end and KIAA1671 remaining behind at the base of the structure. These results suggest that KIAA1671 cooperates with EPS8 and potentially other assembly factors to initiate growth of microvilli on the apical surface. These findings offer new details on how transporting epithelial cells builds the brush border and may inform our understanding of how apical specializations are assembled in other epithelial contexts.

Optimized extraction and large-scale proteomics of pig jejunum brush border membranes for use in in vitro digestion models

Despite the physiological importance of the hydrolases from the intestinal brush border membrane (BBM), a step simulating the intestinal digestion has not been included yet in the harmonized protocols of in vitro digestion, due to commercial unavailability of these enzymes and lack of consensus for the conditions of use. The proper utilize of BBM requires a detailed investigation of their enzymatic composition. BBM vesicles were purified from specimens of pig jejunum optimizing previously described methods and assayed for aminopeptidase N and dipeptidyl peptidase IV activity. Large-scale proteomics was carried out with a bottom-up shotgun approach, also performing a rough quantification with the iBAQ (intensity Based Absolute Quantification). Overall, 1428 proteins were identified and functionally classified by gene ontology enrichment analysis. The predominant enzyme fraction (220 gene products) was represented by hydrolases, including peptidases, glycosidases, and lipases. Aminopeptidase N and sucrase-isomaltase represented 52.9 % and 50.2 % of the peptidase and glycosidase abundance, respectively. In addition to expected transporters and cytoskeletal actin-binding proteins, purified BBM vesicles also contains a complex array of protease inhibitors, here described for the first time, that may modulate the activity of hydrolases. Considering the similarity with the human counterpart, intestinal porcine BBM are suited for simulating the human small intestinal digestion.

SARS-CoV-2 replication in airway epithelia requires motile cilia and microvillar reprogramming

How SARS-CoV-2 penetrates the airway barrier of mucus and periciliary mucins to infect nasal epithelium remains unclear. Using primary nasal epithelial organoid cultures, we found that the virus attaches to motile cilia via the ACE2 receptor. SARS-CoV-2 traverses the mucus layer, using motile cilia as tracks to access the cell body. Depleting cilia blocks infection for SARS-CoV-2 and other respiratory viruses. SARS-CoV-2 progeny attach to airway microvilli 24 h post-infection and trigger formation of apically extended and highly branched microvilli that organize viral egress from the microvilli back into the mucus layer, supporting a model of virus dispersion throughout airway tissue via mucociliary transport. Phosphoproteomics and kinase inhibition reveal that microvillar remodeling is regulated by p21-activated kinases (PAK). Importantly, Omicron variants bind with higher affinity to motile cilia and show accelerated viral entry. Our work suggests that motile cilia, microvilli, and mucociliary-dependent mucus flow are critical for efficient virus replication in nasal epithelia.

Physical Activity Attenuates the Obesity-Induced Dysregulated Expression of Brown Adipokines in Murine Interscapular Brown Adipose Tissue

In recent years, brown adipose tissue (BAT), which has a high heat-producing capacity, has been confirmed to exist even in adults, and it has become a focal point for the prevention and the improvement of obesity and lifestyle-related diseases. However, the influences of obesity and physical activity (PA) on the fluid factors secreted from BAT (brown adipokines) are not well understood. In this study, therefore, we focused on brown adipokines and investigated the effects of obesity and PA. The abnormal expressions of gene fluid factors such as galectin-3 (Lgals3) and Lgals3 binding protein (Lgals3bp), whose proteins are secreted from HB2 brown adipocytes, were observed in the interscapular BAT of obese mice fed a high-fat diet for 4 months. PA attenuated the abnormalities in the expressions of these genes. Furthermore, although the gene expressions of factors related to brown adipocyte differentiation such as peroxisome proliferator-activated receptor gamma coactivator 1-α were also down-regulated in the BAT of the obese mice, PA suppressed the down-regulation of these factors. On the other hand, lipogenesis was increased more in HB2 cells overexpressing Lgals3 compared with that in control cells, and the overexpression of Lgals3bp decreased the mitochondrial mass. These results indicate that PA attenuates the obesity-induced dysregulated expression of brown adipokines and suggests that Lgals3 and Lgals3bp are involved in brown adipocyte differentiation.

G-strand binding protein 2 is involved in asexual and sexual development of Plasmodium berghei

G-strand binding protein 2 (GBP2) is a Ser/Arg-rich (SR) protein involved in mRNA surveillance and nuclear mRNA quality control in yeast. However, the roles of GBP2 in virulence and sexual development in Plasmodium parasites are unclear, although GBP2 is involved in the asexual development of Plasmodium berghei, the rodent malaria parasite. In this study, we investigated the role of GBP2 in virulence and sexual development of P. berghei using gbp2-deleted P. berghei (Δgbp2 parasites). Then, to identify factors affected by gbp2 deletion, we performed a comparative proteomic analysis of the Δgbp2 parasites. We found that GBP2 was not associated with the development of experimental cerebral malaria during infection with P. berghei, but asexual development of the parasite was delayed with deletion of gbp2. However, the development of P. berghei gametocytes was significantly reduced with deletion of gbp2. Comparative proteomic analysis revealed that the levels of adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP), and hypoxanthine-guanine phosphoribosyltransferase (HGPRT) in Δgbp2 parasites were significantly higher than those in wild-type (WT) parasites, suggesting that biosynthesis of purine nucleotides may be involved in function of GBP2. Therefore, we investigated the effect of purine starvation on the sexual development and proteome. In nt1-deleted P. berghei (Δnt1 parasites), the production of male and female gametocytes was significantly reduced compared to that in WT parasites. Moreover, we found that protein levels of GBP2 in Δnt1 parasites were markedly lower than in WT parasites. These findings suggest that GBP2 is primarily involved in the sexual development of malaria parasites, and its function may be suppressed by purine starvation.

Ezrin Orchestrates Signal Transduction in Airway Cells

Ezrin is a critical structural protein that organizes receptor complexes and orchestrates their signal transduction. In this study, we review the ezrin-meditated regulation of critical receptor complexes, including the epidermal growth factor receptor (EGFR), CD44, vascular cell adhesion molecule (VCAM), and the deleted in colorectal cancer (DCC) receptor. We also analyze the ezrin-meditated regulation of critical pathways associated with asthma, such as the RhoA, Rho-associated protein kinase (ROCK), and protein kinase A (cAMP/PKA) pathways. Mounting evidence suggests that ezrin plays a role in controlling airway cell function and potentially contributes to respiratory diseases. Ezrin can participate in asthma pathogenesis by affecting bronchial epithelium repair, T lymphocyte regulation, and the contraction of the airway smooth muscle cells. These studies provide new insights for the design of novel therapeutic strategies for asthma treatment.

Abnormal Small Intestinal Epithelial Microvilli in Patients With Crohn's Disease

BACKGROUND & AIMS

Crohn disease (CD) presents as chronic and often progressive intestinal inflammation, but the contributing pathogenic mechanisms are unclear. We aimed to identify alterations in intestinal cells that could contribute to the chronic and progressive course of CD.

METHODS

We took an unbiased system-wide approach by performing sequence analysis of RNA extracted from formalin-fixed paraffin-embedded ileal tissue sections from patients with CD (n = 36) and without CD (controls; n = 32). We selected relatively uninflamed samples, based on histology, before gene expression profiling; validation studies were performed using adjacent serial tissue sections. A separate set of samples (3 control and 4 CD samples) was analyzed by transmission electron microscopy. We developed methods to visualize an overlapping modular network of genes dysregulated in the CD samples. We validated our findings using biopsy samples (110 CD samples for gene expression analysis and 54 for histologic analysis) from the UNITI-2 phase 3 trial of ustekinumab for patients with CD and healthy individuals (26 samples used in gene expression analysis).

RESULTS

We identified gene clusters that were altered in nearly all CD samples. One cluster encoded genes associated with the enterocyte brush border, leading us to investigate microvilli. In ileal tissues from patients with CD, the microvilli were of decreased length and had ultrastructural defects compared with tissues from controls. Microvilli length correlated with expression of genes that regulate microvilli structure and function. Network analysis linked the microvilli cluster to several other down-regulated clusters associated with altered intracellular trafficking and cellular metabolism. Enrichment of a core microvilli gene set also was lower in the UNITI-2 trial CD samples compared with controls; expression of microvilli genes was correlated with microvilli length and endoscopy score and was associated with response to treatment.

CONCLUSIONS

In a transcriptome analysis of formalin-fixed and paraffin-embedded ileal tissues from patients with CD and controls, we associated transcriptional alterations with histologic alterations, such as differences in microvilli length. Decreased microvilli length and decreased expression of the microvilli gene set might contribute to epithelial malfunction and the chronic and progressive disease course in patients with CD.

Pathophysiological Roles of Ezrin/Radixin/Moesin Proteins

Ezrin/radixin/moesin (ERM) proteins function as general cross-linkers between plasma membrane proteins and the actin cytoskeleton and are involved in the functional expression of membrane proteins on the cell surface. They also integrate Rho guanosine 5'-triphosphatase (GTPase) signaling to regulate cytoskeletal organization by sequestering Rho-related proteins. They act as protein kinase A (PKA)-anchoring proteins and sequester PKA close to its target proteins for their effective phosphorylation and functional regulation. Therefore, ERM proteins seem to play important roles in the membrane transport of electrolytes by ion channels and transporters. In this review, we focus on the pathophysiological roles of ERM proteins in in vivo studies and introduce the phenotypes of their knockout and knockdown mice.