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Estrogen Regulates the Satellite Cell Compartment in Females

Skeletal muscle mass, strength, and regenerative capacity decline with age, with many measures showing greater deterioration in females about the time estrogen levels decrease at menopause. Here we show that maintenance of muscle stem cells, satellite cells, as well as self-renewal and differentiation into muscle fibers, are severely compromised by estrogen deficiency. Mechanistically, by hormone replacement, use of a selective estrogen-receptor modulator (bazedoxifene), and conditional estrogen receptor knockout, we implicate 17{beta}-estradiol and satellite cell expression of estrogen receptor (ER) and show that estrogen signaling through this receptor is necessary to prevent apoptosis of satellite cells. Early data from a biopsy study of women who transitioned from peri-to post-menopause are consistent with the loss of satellite cells coincident with the decline in estradiol in humans. Together, these results demonstrate an important role for estrogen in satellite cell maintenance and muscle regeneration in females.

cell biology↗

Massive osteopetrosis caused by giant, non-functional osteoclasts in R51Q SNX10 mutant mice

The molecular mechanisms that regulate fusion of monocytes into functional osteoclasts are virtually unknown. We describe a knock-in mouse model for the R51Q mutation in sorting nexin 10 (SNX10) that exhibits osteopetrosis and related symptoms of patients of autosomal recessive osteopetrosis linked to this mutation. Osteopetrosis arises in homozygous R51Q SNX10 mice due to a unique combination of reduced numbers of osteoclasts that are non-functional. Fusion of mutant monocytes is deregulated and occurs rapidly and continuously to form giant, non-functional osteoclasts. Mutant osteoclasts mature quickly and survive poorly in vitro, possibly accounting for their scarcity in vivo. These cells also exhibit impaired ruffled borders, which are required for bone resorption, providing an additional basis for the osteopetrotic phenotype. More broadly, we propose that the maximal size of osteoclasts is actively determined by a genetically-regulated, cell-autonomous mechanism that limits precursor cell fusion, and for which SNX10 is required.

cell biology↗

Histological, transcriptomic and in vitro analysis reveal an intrinsic activated state of myogenic precursors in hyperplasic muscle of trout

BackgroundThe dramatic increase in myotomal muscle mass in post-hatching fish is related to their ability to lastingly produce new muscle fibres, a process termed hyperplasia. The molecular and cellular mechanisms underlying fish muscle hyperplasia largely remain unknown. In this study, we aimed to characterize intrinsic properties of myogenic cells originating from fish hyperplasic muscle. For this purpose, we compared in situ proliferation, in vitro cell behavior and transcriptomic profile of myogenic precursors originating from hyperplasic muscle of juvenile trout (JT) and from non-hyperplasic muscle of fasted juvenile trout (FJT) and adult trout (AT).\n\nResultsFor the first time, we showed that myogenic precursors proliferate in hyperplasic muscle from JT as shown by in vivo BrdU labeling. This proliferative rate was very low in AT and FJT muscle. Transcriptiomic analysis revealed that myogenic cells from FJT and AT displayed close expression profiles with only 64 differentially expressed genes (BH corrected p-val < 0.001). In contrast, 2623 differentially expressed genes were found between myogenic cells from JT and from both FJT and AT. Functional categories related to translation, mitochondrial activity, cell cycle, and myogenic differentiation were inferred from genes up regulated in JT compared to AT and FJT myogenic cells. Conversely, Notch signaling pathway, that signs cell quiescence, was inferred from genes down regulated in JT compared to FJT and AT. In line with our transcriptomic data, in vitro JT myogenic precursors displayed higher proliferation and differentiation capacities than FJT and AT myogenic precursors.\n\nConclusionsThe transcriptomic analysis and examination of cell behavior converge to support the view that myogenic cells extracted from hyperplastic muscle of juvenile trout are intrinsically more potent to form myofibres than myogenic cells extracted from non-hyperplasic muscle. The generation of gene expression profiles in myogenic cell extracted from muscle of juvenile trout may yield insights into the molecular and cellular mechanisms controlling hyperplasia and provides a useful list of potential molecular markers of hyperplasia.

cell biology↗

Insulin sensitivity and PIP3 turnover in Drosophila are regulated by phosphatidylinositol 5 phosphate 4-kinase.

Phosphatidylinositol-3,4,5-trisphosphate (PIP3) generation at the plasma membrane is a key event during activation of receptor tyrosine kinases such as the insulin receptor and is critical for normal growth and metabolism. The lipid kinases and phosphatases regulating PIP3 levels are described but mechanisms controlling their activity remain unclear. We report that in Drosophila, phosphatidylinositol 5 phosphate 4-kinase (PIP4K) function at the plasma membrane is required for normal PIP3 levels during insulin receptor activation. Depletion of PIP4K increases PIP3 levels and augments sensitivity to insulin through enhanced Class I phosphoinositide 3-kinase (PI3K) activity. Animals lacking PIP4K show enhanced insulin signalling dependent phenotypes in vivo and are resistant to the metabolic consequences of a high-sugar diet, highlighting the importance of PIP4K in normal metabolism and development. Thus, PIP4KS are key regulators of receptor tyrosine kinase signalling with implications for growth factor dependent processes including tumour growth, T-cell activation and metabolism.

cell biology↗

Unbiased dynamic characterization of RNA-protein interactions by OOPS

Current methods for the identification of RNA-protein interactions require a quantity and quality of sample that hinders their application, especially for dynamic biological systems or when sample material is limiting. Here, we present a new approach to enrich RNA-Binding Proteins (RBPs): Orthogonal Organic Phase Separation (OOPS), which is compatible with downstream proteomics and RNA sequencing. OOPS enables recovery of RBPs and free protein, or protein-bound RNA and free RNA, from a single sample in an unbiased manner. By applying OOPS to human cell lines, we extract the majority of known RBPs, and importantly identify additional novel RBPs, including those from previously under-represented cellular compartments. The high yield and unbiased nature of OOPS facilitates its application in both dynamic and inaccessible systems. Thus, we have identified changes in RNA-protein interactions in mammalian cells following nocodazole cell-cycle arrest, and defined the first bacterial RNA-interactome. Overall, OOPS provides an easy-to-use and flexible technique that opens new opportunities to characterize RNA-protein interactions and explore their dynamic behaviour.

cell biology↗

Prolonged culture of primary human keratinocytes isolated from suction blisters

Keratinocytes are the most abundant cell type in the epidermis. They prevent desiccation and provide immunological and barrier defense against potential pathogens such as Staphylococcus aureus and Candida albicans. The study of this first line of immune defense is hindered by invasive isolation methods and insufficient techniques for long-term passage of primary keratinocytes in vitro. Primary keratinocytes have been successfully isolated from blister roofs induced by negative pressure, which separates the epidermis from the dermis in vivo in human subjects. This method allows collection of pure epidermal cells without dermal contamination in a minimally invasive manner. However, the isolated keratinocytes differentiate and senesce when cultured in vitro beyond five passages. Here, we present evidence that the Rho kinase (ROCK) inhibitor Y-27632 can be used to effectively increase the proliferative capabilities of keratinocytes isolated using the suction blister method, similar to what has been previously reported for primary keratinocytes isolated using alternative methods. We show that the increase in passage number is directly correlated to delayed differentiation, and that cells passaged long term with the inhibitor retain their ability to stratify in organotypic raft cultures and respond to cytokine treatment; additionally, the late passage cells have a heterogeneous mix of differentiated and non-differentiated cells which may be predicted by a ratio of select differentiation markers. The described method presents a minimally invasive procedure for keratinocyte isolation and prolonged culture that allows analysis of keratinocyte function in both healthy volunteers and patients with dermatologic diseases.

cell biology↗

Adaptation of actin dynamics and membrane tension control for yeast endocytosis

During clathrin-mediated endocytosis in eukaryotes, actin assembly is required to overcome large membrane tension and turgor pressure. However, the molecular mechanisms by which the actin machinery adapts to varying membrane tension remain unknown. In addition, how cells reduce their membrane tension when they are challenged by hypotonic shocks remains unclear. We used quantitative microscopy to demonstrate that cells rapidly reduce their membrane tension using three parallel mechanisms. In addition to using their cell wall for mechanical protection, yeast cells disassemble eisosomes to buffer moderate changes in membrane tension on a minute time scale. Meanwhile, a temporary reduction of the rate of endocytosis for 2 to 6 minutes, and an increase in the rate of exocytosis for at least 5 minutes allow cells to add large pools of membrane to the plasma membrane. We built on these results to submit the cells to abrupt increases in membrane tension and determine that the endocytic actin machinery of fission yeast cells rapidly adapts to perform clathrin-mediated endocytosis. Our study sheds light on the tight connection between membrane tension regulation, endocytosis and exocytosis.

cell biology↗

A positive feedback loop drives centrosome maturation in flies

Centrosomes are formed when mother centrioles recruit pericentriolar material (PCM) around themselves. The PCM expands dramatically as cells prepare to enter mitosis (a process termed centrosome maturation), but it is unclear how this expansion is achieved. In flies, Spd-2 and Cnn form an extensive scaffold around the mother centriole that recruits other components of the mitotic PCM, and the Polo-dependent phosphorylation of Cnn at the centrosome is crucial for scaffold assembly. Here we show that, like Cnn, Spd-2 is specifically phosphorylated at centrosomes. This phosphorylation appears to create multiple phosphorylated S-S/T(p) motifs that allow Spd-2 to recruit Polo to the expanding scaffold. If Spd-2 cannot recruit Polo to the expanding scaffold, the scaffold is initially assembled around the mother centriole, but it cannot expand outwards, and centrosome maturation fails. We conclude that Spd-2, Polo and Cnn cooperate to form a positive feedback loop that drives the dramatic expansion of the mitotic centrosome in flies.

cell biology↗

Proteolytic Remodeling of Cargo Receptor Networks by RHBDL4 Tunes Secretory Pathway Flux

Cargo receptors are central organizers of the secretory pathway, yet the mechanisms controlling their abundance remain poorly understood. The endoplasmic reticulum (ER)-resident intramembrane protease RHBDL4 promotes substrate turnover via a non-canonical branch of ER-associated degradation and has recently been implicated in regulating secretory pathway components. We previously identified the p24 cargo receptor TMED7 as an RHBDL4 substrate, suggesting that cargo receptor turnover contributes to secretory pathway regulation. Here, quantitative proteomics identify members of the ER-Golgi intermediate compartment (ERGIC) cargo receptor family as endogenous RHBDL4 substrates, demonstrating that RHBDL4 targets multiple cargo receptor families within the early secretory pathway. Accordingly, RHBDL4 modulates multiple ERGIC-dependent transport pathways. In addition, unbiased secretome analysis reveals increased secretion of lysosomal precursor proteins upon RHBDL4 ablation. Mechanistically, we show that this phenotype is mediated, at least in part, by RHBDL4-dependent cleavage of the lysosomal cargo receptor sortilin/SORT1. Together, these findings identify cargo receptors as a major class of RHBDL4 substrates and establish proteolytic remodeling of cargo receptor networks as a mechanism for regulating secretory pathway flux.

cell biology↗

Red and blue light cues drive contrasting remodeling of lipophilic metabolites and photophysiology in natural benthic diatom biofilms

Intertidal mudflats are low hydrodynamic energy environments hosting microphytobenthic communities that experience strong spatiotemporal variability in light regimes, including changes in spectral quality and light intensity that can lead to cellular photooxidative stress. To cope with these fluctuations, autotrophs exhibit diverse and highly plastic adaptations that are often species-dependent and shaped by their ecological niches. This study investigates photophysiological responses and metabolic remodeling in a diatom assemblage originating from a natural winter microphytobenthic biofilm under contrasting red and blue light intensities. To this end, photosynthetic parameters were monitored alongside changes in lipophilic metabolites, including untargeted lipids and lipophilic pigments. While few metabolites showed temporal remodeling, rapid and contrasting changes were observed within 30 minutes in response to both spectral quality and light intensity. Red light treatments induced broader remodeling of lipophilic metabolites than blue light, whereas blue light appeared to have a greater impact on photosynthetic parameters. Moreover, red light induced xanthophyll-cycle responses comparable to those observed under blue light at equivalent incident intensity. We discuss these metabolic responses in relation to diatom photoadaptive strategies, placing these findings within the intertidal environmental framework. This work further underlines the importance of understanding rapid metabolic plasticity in coping with light fluctuations, providing new insights into the photoregulatory strategies of natural microphytobenthic communities.

cell biology↗

GDF15 contributes to inflammasome-associated excessive mechanoresponses of hyperlipidemic PdL fibroblasts

Orthodontic tooth movement relies on a tightly regulated pro-inflammatory and pro resorptive mechanoresponse of local periodontal ligament fibroblasts (PdLFs). Dysregulation is linked to complications such as root resorption and tooth loss. Hyperlipidemic conditions promote excessive PdL mechanoresponses, with growth differentiation factor 15 (GDF15) acting as potential regulator. This study examined the contribution of the inflammasome/pyroptosis pathway as underlying mechanism for dysregulated mechanoresponses. Human PdLFs were treated with palmitic acid (PA) or oleic acid (OA) for six days before 24 hours of compressive loading. PA increased CASP1, CASP4, and CASP3 activity, secretion of IL-1{beta}, IL-18, and HMGB1, and LDH release. Pharmacological blockade and siRNA-mediated knockdown of inflammasome- and pyroptosis-related targets revealed that NLRP3, CASP1, CASP4, and GSDMD partially contributed to monocyte and osteoclast overactivation. Silencing PA-increased GDF15, partially normalized the phenotype, at least in part by inflammasome/pyroptosis regulation. GDF15 acted through extracellular, and a nuclear signaling route, each accounting partially to this phenotype. Together, GDF15 partially regulates the PA-induced, pyroptosis-associated overactivated mechanoresponse alongside pyroptosis-independent mechanisms suggesting it as an interesting target for potential clinical interventions.

cell biology↗

POU2AF2/OCA-T1 coactivates POU2F2 and defines a lineage-specific dependency in diffuse large B-cell lymphoma

Lineage-restricted transcriptional programs establish cell identity and can create selective dependencies in cancer. Here, we identify POU2AF2, encoding the transcriptional co-activator OCA-T1, as a critical lineage-specific dependency in a subset of diffuse large B-cell lymphoma (DLBCL). Pan-cancer dependency analyses and patient cohorts reveal elevated POU2AF2 expression in genetically aggressive DLBCL, where its depletion markedly suppresses tumor growth in vitro and in vivo. Mechanistically, POU2AF2 cooperates with the B-cell lineage-defining transcription factor POU2F2 (OCT2) to activate lymphocyte activation gene programs through direct chromatin engagement, thereby sustaining malignant transcriptional networks. We further identified a key epigenetic regulatory axis composed of the lineage-specific transcription factor TCF3 and the histone methyltransferase SET1A-COMPASS that drives POU2AF2 expression downstream of B-cell receptor signaling. Single-cell transcriptomic analysis reveals that POU2AF2 marks and sustains an innate-like B1 B-cell population in vivo, a candidate cell of origin for lymphoma. Together, these findings define a lineage-restricted POU2AF2/POU2F2 transcriptional module, controlled by a TCF3/SET1A epigenetic network, that sustains both innate-like B-cell identity and malignant fitness in DLBCL. Our study uncovers a previously unrecognized lineage-specific transcriptional dependency and highlights POU2AF2 and its associated regulatory circuitry as potential therapeutic targets in aggressive B-cell malignancies.

cell biology↗

Glutaminase contributes to MYC-induced cell-autonomous autophagy and to RasV12-dependent non-autonomous autophagy in the Drosophila wing disc epithelium

MYC-driven metabolic reprogramming supports rapid cell growth but also creates metabolic demands that require adaptive mechanisms to maintain cellular homeostasis. Here, combining clonal analysis in Drosophila wing imaginal discs with studies in Schneider S2 cells, we identify glutamine metabolism as a component of Myc-induced autophagy. Myc increased the expression of genes involved in glutamine utilization, including glutaminase (GLS), and enhanced ammonia production, a metabolic by-product of glutaminolysis. Genetic depletion of GLS in clones suppressed the accumulation of Myc-induced Atg8a-positive structures and reduced autophagic flux, demonstrating that glutaminase contributes to the autophagic response elicited by Myc. Exogenous NHCl was sufficient to induce Atg8a-positive structures and partially restored their accumulation following GLS depletion, supporting ammonia as a downstream contributor to this response. Mechanistically, Myc-induced autophagy in clones required the core autophagy factor Atg5 but was not suppressed by depletion of Rheb or Atg1, consistent with an autophagic program that can operate independently of canonical TOR-Atg1 signaling. We further found that Myc activity is required for RasV12-driven epithelial overgrowth and that RasV12 cells induce a pronounced non-cell-autonomous accumulation of Atg8a-positive structures in wild-type cells surrounding RasV12 clones. Depletion of either Myc or GLS in RasV12 cells strongly reduced this neighboring autophagic response, linking Myc-dependent glutamine metabolism in transformed cells to autophagy in the surrounding tissue. Together, our findings identify GLS-dependent glutamine metabolism as a previously unrecognized component of Myc-induced autophagy and extend this relationship to Ras-transformed epithelia, where Myc and Gls contribute to non-cell-autonomous autophagic responses in neighboring cells.

cell biology↗

Arterial Elastin Abundance, Rather Than Orthologue Origin, Modulates Medial Arterial Calcification in Matrix Gla Protein-Deficient Mice

Abstract Calcific deposits in the arterial media have been associated with a number of metabolic and genetic disorders including diabetes, chronic kidney disease and generalized arterial calcification of infancy. While medial calcification and physiologic hard tissue mineralization in the skeleton are both regulated by several common determinants, emerging data suggest that there might be fundamental differences in the mechanisms underlying these two processes. Objective: We previously demonstrated that elastin haploinsufficiency delays medial calcification in MGP-deficient mice. Here, using mice in which a human ELN transgene rescues mouse elastin deficiency, we investigated whether the origin and abundance of arterial elastin differentially affect the initiation and progression of medial calcification. Approach and Results: We pursued a transgenic approach to alter the arterial elastin scaffold in MGP-deficient mice. Our analyses of a humanized MGP-deficient model with 40% reduction of medial elastin content showed a complete absence of the early-stage vascular calcification. Additionally, we showed that mouse and human elastin orthologues affect vascular calcification in a comparable manner. Conclusion: Arterial elastin abundance, rather than orthologue origin, modulates the initiation and progression of medial calcification in MGP-deficient mice. A further reduction in arterial elastin beyond that achieved by elastin haploinsufficiency profoundly delays mineral deposition and maturation, whereas restoration of elastin abundance through transgenic human ELN expression restores arterial calcification.

cell biology↗

Non-invasive forecasting of skin cancer evolution through longitudinal hair sampling

The ability to longitudinally track clonal evolution non-invasively would transform cancer interception strategies, long before late-stage disease when most cancer genomes are analysed. Here, we demonstrate that repeated hair sampling from the same individual followed by exome sequencing enables tracking of somatic evolution in vivo over several months after chemically induced skin carcinogenesis. We found that hair follicles accumulate a higher mutation burden than spatially-matched skin and harbour mutations that spread into surrounding epidermis and persist throughout tumour progression. DNA-damaged follicles enter sustained quiescence that delays replication and repair, creating a reservoir for long-lived mutations. During premalignant progression, carcinogen-associated mutations become enriched as follicular clones expand into adjacent skin. Mutation tracking identified genes that may govern tumour predisposition and initiation, many of which are mutated at high incidence in human cutaneous squamous cell carcinoma cohorts. Hair follicles therefore provide a non-invasive readout to forecast the early development of skin cancer, enabling patient risk stratification.

cell biology↗

Replication stress at centromeres biases the segregation of DNA damage

Replication-associated errors can cause DNA damage to accumulate on the newly synthesized strand over time. In specific cases such as stem cells, retention of the immortal strand used as template preserves one daughter cell into pluripotency while correlating with terminal differentiation of the damage one. In somatic cells, DNA damage distribution after mitosis remains unclear. Here, we uncovered a mechanism of non-random segregation of the DNA damage marker gH2AX occurring during a single cell division cycle. Replication stress using hydroxyurea (HU) upon release into S phase in RPE-1, BJ, hCEC D29 and fibroblasts showed reproducible Non-Random Segregation (NRS) of gH2AX in the ensuing G1, a phenotype not observed in any of the cancer cell lines analyzed. Notably, removal of R-loops led to a reduction of cells with NRS, whether RNaseH1 was over-expressed globally or exclusively targeted to centromeres, indicating that centromeric DNA-RNA hybrids contribute to NRS of the damage. In line with our previous evidence of centromeric chromatin disruption leading to R-loops, rapid removal of the histone H3 variant CENP-A causes damage and NRS, although to a lower extent than HU alone. This implies that additional mechanisms contribute to centromeric R-loops and NRS of damage in the daughter cells upon mitotic exit. Mechanistically, chemical inhibition of the catalytic activity of Rad51 led to a significant drop in NRS without a change in the total amount of damaged cells, implying involvement of the Homologous Recombination (HR) pathway to accumulation of gH2AX to only one chromatid. In turn, this affects the spindle-kinetochore with a measurable length asymmetry, inducing mechanical and/or epigenetic signals that affect the orientation of the sister chromatids on the metaphase plate to bias segregation. Altogether, we found replication-induced asymmetric segregation of DNA damage during mitosis that is influenced by centromeric R-loops, Rad51 activity and spindle dynamics, with implications on cell fate, chromosome and genome stability in the daughter cells.

cell biology↗

Data-driven spectroscopic dictionaries and detector-calibrated inference for photon-limited Raman hyperspectral imaging of living cells

Label-free Raman imaging of living cells is photon limited: at exposures compatible with cellular dynamics, single-pixel spectra carry about one count per channel on a dominant smooth background. We present an unmixing framework in which the decoder of a physics-constrained autoencoder is restricted to a data-driven spectroscopic dictionary: band centers,widths, and pseudo-Voigt shapes are measured from the dataset and fixed, and the network learns only nonnegative band amplitudes, a smooth B-spline background, and a per-pixel gain.First, on slit-scanning images of HeLa cells (532 nm) the dictionary yields spike-free component spectra that read as band tables, including a resonance-enhanced cytochrome-c-associated component matching literature spectra, and the most stable decomposition against the component number. Second, the dictionary and initialization calibrated at 1 s exposure perline transfer to 100 ms per line (12 s sweeps): cytochrome-c spectral identity survives a single sweep (correlation 0.92) while its map remains photon limited; the dictionary provides spectral physicality, and the transferred initialization prevents a structural collapse that global map correlations miss; in a measurement-derived phantom the dictionary estimator holds thecytochrome-c spectrum to 17-19{degrees} spectral angle at 100 ms, where classical factorizations and free decoders lose it (55-64{degrees}). Estimation on the count-equivalent detector output uses a calibrated shifted-Poisson quasi-likelihood. Third, evaluation must be time matched:correlation against a separately acquired reference saturates through slow specimen drift and acquisition mismatch rather than photon noise, and the self-consistency of learned denoisers is inflated by shared bias; time-matched self-consistency and independent cross-checks areproposed.

cell biology↗

Lipogenic gene expression and substrate sensitivity in the bovine mammary gland shape milk fat composition

Milk fat is produced by mammary epithelial cells (MEC) through a conserved mechanism shared among all fat-producing cells across biological kingdoms. Although highly conserved, different tissues and organisms produce distinctive fat compositions. Notably, ruminant milk fat is characterized by enrichment in short and medium chain fatty acids. We hypothesized that this unique profile is driven by MEC-specific metabolic characteristics related to their response to lipogenic substrates. To study this, we compared bovine MEC and udder-derived fibroblasts in terms of their lipogenic capacity and fatty acid composition when exposed to lipogenic building blocks. When exposed to acetate, MEC showed coordinated upregulation of acyl-CoA short-chain synthetase 1 (ACSS1) and diacylglycerol transferase (DGAT), while expression of acyl-CoA synthetase long-chain 1 (ACSL1) decreased. Medium chain fatty acids were also elevated in acetate-treated MEC and not in fibroblasts. The role of ACSS1 in the production of medium chain fatty acids in MEC was confirmed by knockdown experiments. Metabolomics analysis showed that in MEC acetate treatment triggered a broad metabolic response, primarily amino acids catabolism, energy and polar lipid metabolism. Collectively, these findings demonstrate effective utilization of acetate for de novo fatty acid synthesis in MEC with preferred tendency to produce medium chain fatty acids.

cell biology↗