Role of the microtubules in the electrical activity of the primary cilium of renal epithelial cells.

The primary cilium is a non-motile sensory organelle that transduces environmental cues into cellular responses. It comprises an axoneme, a core of nine doublet microtubules (MTs) coated by a specialized membrane populated by receptors, and a high density of ion channels. Dysfunctional primary cilia generate the pathogenesis of several diseases known as ciliopathies. However, the electrical role of MTs in ciliary signaling remains largely unknown. Herein, we determined by the patch clamp technique the electrical activity of cytoplasmic and axonemal MTs from wild-type LLC-PK1 renal epithelial cells. We observed electrical oscillations with fundamental frequencies at ∼39 Hz and ∼93 Hz in sheets of cytoplasmic MTs. We also studied in situ and isolated, intact and Triton X-permeabilized primary cilia, observing electrical oscillations with peak frequencies at either 29-49 Hz (non-permeabilized) or ∼40-49 Hz (permeabilized) and ∼93 Hz (both). We applied Empirical Mode Decomposition (EMD), Continuous Wavelet Transform (CWT), and Cross-Correlation Analysis (CCA) to assess the differences and the coherence in the Time-Frequency domains of electrical oscillations between cytoplasmic and axonemal MTs. The data indicate that axonemal and cytoplasmic MTs show different patterns of electrical oscillations preserving coherence at specific frequency peaks that may serve as electromagnetic communication between compartments. Further, the electrical behavior of axonemal MTs was modified by siRNA deletion of polycystin-2 (PC2), which lengthens primary cilia, thus linking ciliary channels to the morphological and electrical behavior of cilia in ciliopathies. The encompassed evidence indicates that the primary cilium behaves as an electrical antenna, with an excitable MT structure that produces electrical oscillations whose synchronization and propagation constitute a novel cell signaling mechanism.

Establishment and Comprehensive Molecular Characterization of an Immortalized Glioblastoma Cell Line from a Brazilian Patient.

Glioblastoma (GBM) is the most common and aggressive primary brain tumor in adults, with few effective treatment strategies. The research on the development of new treatments is often constrained by the limitations of preclinical models, which fail to accurately replicate the disease's essential characteristics. Herein, we describe the obtention, molecular, and functional characterization of the GBM33 cell line. This cell line belongs to the GBM class according to the World Health Organization 2021 Classification of Central Nervous System Tumors, identified by methylation profiling. GBM33 expresses the astrocytic marker GFAP, as well as markers of neuronal origin commonly expressed in GBM cells, such as ßIII-tubulin and neurofilament. Functional assays demonstrated an increased growth rate when compared to the U87 commercial cell line and a similar sensitivity to temozolamide. GBM33 cells retained response to serum starvation, with reduced growth and diminished activation of the Akt signaling pathway. Unlike LN-18 and LN-229 commercial cell lines, GBM33 is able to produce primary cilia upon serum starvation. In summary, the successful establishment and comprehensive characterization of this GBM cell line provide researchers with invaluable tools for studying GBM biology, identifying novel therapeutic targets, and evaluating the efficacy of potential treatments.

Activation of Hedgehog signaling by the oncogenic RELA fusion reveals a primary cilia-dependent vulnerability in supratentorial ependymoma.

BACKGROUND: Supratentorial RELA fusion (ST-RELA) ependymomas (EPNs) are resistant tumors without an approved chemotherapeutic treatment. Unfortunately, the molecular mechanisms that lead to chemoresistance traits of ST-RELA remain elusive. The aim of this study was to assess RELA fusion-dependent signaling modules, specifically the role of the Hedgehog (Hh) pathway as a novel targetable vulnerability in ST-RELA. METHODS: Gene expression was analyzed in EPN from patient cohorts, by microarray, RNA-seq, qRT-PCR, and scRNA-seq. Inhibitors against Smoothened (SMO) (Sonidegib) and Aurora kinase A (AURKA) (Alisertib) were evaluated. Protein expression, primary cilia formation, and drug effects were assessed by immunoblot, immunofluorescence, and immunohistochemistry. RESULTS: Hh components were selectively overexpressed in EPNs induced by the RELA fusion. Single-cell analysis showed that the Hh signature was primarily confined to undifferentiated, stem-like cell subpopulations. Sonidegib exhibited potent growth-inhibitory effects on ST-RELA cells, suggesting a key role in active Hh signaling; importantly, the effect of Sonidegib was reversed by primary cilia loss. We, thus, tested the effect of AURKA inhibition by Alisertib, to induce cilia stabilization/reassembly. Strikingly, Alisertib rescued ciliogenesis and synergized with Sonidegib in killing ST-RELA cells. Using a xenograft model, we show that cilia loss is a mechanism for acquiring resistance to the inhibitory effect of Sonidegib. However, Alisertib fails to rescue cilia and highlights the need for other strategies to promote cilia reassembly, for treating ST-RELA tumors. CONCLUSION: Our study reveals a crucial role for the Hh pathway in ST-RELA tumor growth, and suggests that rescue of primary cilia represents a vulnerability of the ST-RELA EPNs.

Polycystin-2 (TRPP2) regulates primary cilium length in LLC-PK1 renal epithelial cells.

Polycystin-2 (PC2, TRPP2) is a Ca2+ permeable nonselective cation channel whose dysfunction generates autosomal dominant polycystic kidney disease (ADPKD). PC2 is present in different cell locations, including the primary cilium of renal epithelial cells. However, little is known as to whether PC2 contributes to the primary cilium structure. Here, we explored the effect(s) of external Ca2+, PC2 channel blockers, and PKD2 gene silencing on the length of primary cilia in wild-type LLC-PK1 renal epithelial cells. Confluent cell monolayers were fixed and immuno-labeled with an anti-acetylated α-tubulin antibody to identify primary cilia and measure their length. Although primary cilia length measurements did not follow a Normal distribution, the data were normalized by Box-Cox transformation rendering statistical differences under all experimental conditions. Cells exposed to high external Ca2+ (6.2 mM) decreased a 13.5% (p < 0.001) primary cilia length as compared to controls (1.2 mM Ca2+). In contrast, the PC2 inhibitors amiloride (200 µM) and LiCl (10 mM), both increased primary ciliary length by 33.2% (p < 0.001), and 17.4% (p < 0.001), respectively. PKD2 gene silencing by siRNA elicited a statistically significant, 10.3% (p < 0.001) increase in primary cilia length compared to their respective scrambled RNA transfected cells. The data indicate that conditions that regulate PC2 function or gene expression modify the length of primary cilia in renal epithelial cells. Blocking of PC2 mitigates the effects of elevated external Ca2+ concentration on primary cilia length. Proper regulation of PC2 function in the primary cilium may be essential in the onset of mechanisms that trigger cyst formation in ADPKD.

Primary cilia formation is diminished in schizophrenia and bipolar disorder: A possible marker for these psychiatric diseases.

Primary cilium (PC) is a microtubule-rich organelle that protrudes from the plasma membrane and acts as a cellular antenna sensing extracellular signals during brain development. DISC1 (Disrupted-in-Schizophrenia-1) is involved in PC formation and is considered a risk factor for neuropsychiatric disorders. We have previously described altered subcellular distribution of DISC1 and an aberrant microtubule organization in olfactory neuronal precursors (ONP) obtained from schizophrenia (SCZ) and bipolar disorder (BD) patients. Herein, we analyzed in vitro PC formation in healthy control subjects, SCZ and BD patients. The results indicated that 66.73±4.33% of ONP from control subjects showed immunostaining for the PC marker, acetylated α-tubulin. By contrast, only a small percentage of cells in culture from paranoid SCZ and BD patients showed PC staining (SCZ, 12.8±4.43%; BD, 12.32±5.86%). However, cells from an affected proband with disorganized SCZ and a subject with BD displayed a higher percentage of cells with cilia (SCZ, 42.20%; BD, 38.59%). Additionally, cilia elongation was observed in lithium-treated ONP derived from all groups, with a more evident response in cells from the BD group. The present study provides novel evidence that the molecular pathways involved in PC formation are defective in SCZ and BD, and impairment in these processes may be involved in the physiopathology of both diseases. Our observations also suggest that ONP is a patient-derived cell model with a potential use for diagnosis and high-throughput drug screening for brain diseases.

Neuron's little helper: The role of primary cilia in neurogenesis.

The generation of new neurons involves a great variety of cell-extrinsic and cell-intrinsic signals. The primary cilium, long regarded as an "evolutionary vestige," has emerged as an essential signaling hub in many cells, including neural progenitors and differentiating neurons. Most progenitors harbor an apically-localized primary cilium, which is assembled and disassembled following the cell cycle, while the presence, position and length of this organelle appears to be even more variable in differentiating neurons. One of the main extracellular cues acting through the cilium is Sonic Hedgehog, which modulates spatial patterning, the progression of the cell cycle and the timing of neurogenesis. Other extracellular signals appear to bind to cilia-localized receptors and affect processes such as dendritogenesis. All the observed dynamics, as well as the many signaling pathways depending on cilia, indicate this organelle as an important structure involved in neurogenesis.