Biology subjects

Sah, N.

Publications and source records attributed to Sah, N..

6 recordsLinked to original sources

bioRxiv2026

Select properties of supramammillary input to adult-born dentate gyrus neurons

The hypothalamic supramammillary nucleus (SUM) projects to the hippocampal dentate gyrus (DG), a brain area crucial for learning, memory, and adult neurogenesis. How SUM inputs regulate adult-born DG (abDG) neurons to support memory processing remains unclear. Here, using monosynaptic tracing in adult mice, we identified a distinct subpopulation of abDG-targeting SUM neurons defined by large somata and low firing rate. Electrophysiological recordings revealed that these SUM neurons co-release glutamate and GABA onto abDGs, and that voluntary running selectively enhances GABAergic transmission. Chemogenetic silencing of SUM-DG GABAergic projections impaired pattern separation, the ability to make fine distinctions between similar stimuli, but not fear conditioning and spatial navigation memory. Altogether, our findings reveal that a distinct SUM subpopulation provides inhibitory modulation to abDG neurons, establishing a novel circuit mechanism for sparse encoding during pattern separation.

neuroscience↗

bioRxiv2026

The miR-221-5p/RAD18/RAD51 axis regulates DNA damage tolerance and homologous recombination to drive platinum resistance in ovarian cancer.

Platinum resistance remains a major barrier in Ovarian cancer (OC) treatment[1]. While hyperactivation of DNA damage response (DDR) is a hallmark of chemoresistance[2], the underlying epigenetic mechanisms driving this adaptation remain poorly understood. Here, we identify a novel post-transcriptional regulatory axis involving miR-221-5p that governs two critical DDR effectors: RAD18, which mediates DNA damage tolerance through trans-lesion synthesis (TLS)[3][4], and RAD51, the central recombinase for homologous recombination (HR)[5][6]. Although the miR-221/222 cluster is traditionally categorized as oncogenic[7][8], we demonstrate that the miR-221-5p arm functions as a potent tumor suppressor in OC. Bioinformatic and luciferase reporter assays confirmed that miR-221-5p directly targets the 3'UTRs of both RAD18 and RAD51. In OC clinical specimens and cell lines, miR-221-5p downregulation inversely correlates with RAD18/RAD51 expression. Functionally, miR-221-5p restoration suppressed platinum-induced PCNA mono-ubiquitination and HR, inducing a "functional BRCAness" that sensitized both established and patient-derived primary OC cells to carboplatin and PARP inhibition. Furthermore, in vivo disseminated xenograft models demonstrated that stable miR-221-5p expression significantly reduced tumor burden. Collectively, our results delineate a novel regulatory mechanism where loss of miR-221-5p drives chemoresistance by derepressing the RAD18/RAD51 axis, identifying this axis as a promising therapeutic target.

cancer biology↗

bioRxiv2026

Creatine kinase regulates energy metabolism and growth of trophoblasts

Study questionDoes the human placenta utilize the creatine phosphagen system for energy homeostasis during development? Summary answerComponents of the creatine (Cr)-creatine kinase (CK)-phosphocreatine (PCr) system are dynamically expressed by the trophoblast and mesenchymal compartments throughout gestation wherein creatine kinase is required for cellular ATP metabolism, cell cycle, and proliferation of trophoblast cells. What is known alreadyThe Cr-CK-PCr system maintains ATP homeostasis in tissues with high energy demand and is required for proliferation, migration, and invasion of tumor cells. The term human placenta can synthesize and transport creatine locally. Early placental development involves trophoblast proliferation, an event requiring ATP, but the role of the creatine phosphagen system during early placental development remains unknown. Study design, size, durationWe performed immunohistochemistry (IHC) and immunofluorescence (IF) for different components (biosynthesis, transport, utilization) of the Cr-Ck-PCr system in human placentae (n=3/group) across gestation including first trimester, second trimester, and term. Using primary human trophoblast stem cells (hTSCs) and trophoblast organoids (TO), we determined the role of the creatine phosphagen system in trophoblast growth by functional inhibition of creatine kinase. Participants/materials, setting, methodsIHC/IF were performed in human placentae across gestation for proteins involved in biosynthesis (AGAT and GAMT), transport (SLC6A8, SLC22A15, and SLC6A13) and utilization (CKB and CKMT1) of creatine to determine the presence of the creatine phosphagen system locally in the placenta. For delineating the functional importance of this system in placental development, cyclocreatine (cCr), a creatine analogue, was used for functional inhibition of CK. Primary hTSCs were culture in medium containing 0 (control), 1, 10, 20 mM cCr for 48 hours followed by analysis of cell growth (cell count), cell cycle (EdU incorporation assay), apoptosis (Annexin V/PI flow cytometry), energy metabolism (Sea horse mito-stress and glycolytic stress tests), and gene expression (qPCR). Primary TO were also treated with 20mM cCr for 6 days in vitro to determine the role of Cr-CK-PCr system in placental development. Main results and the role of chanceAGAT localized to the fetal villous mesenchyme, while GAMT was broadly expressed in the trophoblast and fetal mesenchyme compartments across gestation. CKB localized primarily to fetal mesenchyme with strongest expression at term. CKMT1 was broadly expressed in all trophoblast subtypes. SLC6A8 was abundant in early syncytiotrophoblast but absent at term, where its expression shifted to fetal blood vessels. SLC22A15 was expressed in the endothelial cells of fetal capillaries across gestation. In primary hTSCs, cyclocreatine (20mM) treatment reduced proliferation (P<0.001), decreased expression of trophoblast epithelial marker EGFR (P<0.05), induced G0/G1 and G2/M arrests (P<0.0001), enhanced early and late apoptosis (P<0.0001), and downregulated GPX8 expression (P<0.05). Seahorse analysis revealed marked reductions (P<0.01) in mitochondrial (basal, maximal, and ATP-linked) and glycolytic (rate, capacity, and reserve) function compared to controls. In primary human TO, cyclocreatine treatment reduced the growth of organoids (P<0.05) as well the expression of EGFR (P<0.05). Large scale dataN/A Limitations, reasons for cautionFurther experiments assessing apoptosis, cellular stress and redox imbalance may provide more mechanistic role of the creatine phosphagen system in trophoblast metabolism and function. Since the functional role of the Cr-CK-PCr system was investigated in vitro, findings of this study should be taken with caution for implications of in vivo placental development. Nevertheless, reproducible results of reduced growth of trophoblast cells using both 2D and 3D cultures is highly suggestive of the importance of the creatine phosphagen system in early placental development. Wider implications of the findingsThis study provides foundational knowledge that the placenta contains the creatine phosphagen system, known for ATP homeostasis, and that this system ensures proper cell division, survival and placental development. Dysregulation of components of Cr-CK-PCr system in placenta has been observed in pregnancy disorders such as preeclampsia and fetal growth restriction warranting continued investigation into mechanisms and potential remediation using creatine supplementation. Stem cells share similar metabolic features so findings of this study can be implicated in other stem cells models as well. Study funding/competing interest(s)This work was supported by CIRM EDUC4-12804 Interdisciplinary Stem Cell Training Grant and a Lalor Foundation Postdoctoral Fellowship awarded to NS, and by the California Institute for Regenerative Medicine (DISC0-13757) and the National Institute of Child Health and Human Development (R01-HD096260) award to FS. The authors have no competing interest to declare.

physiology↗

bioRxiv2026

Novel polymeric fluoropyrimidine CF10 demonstrates superior therapeutic index and survival advantage in patient-derived models of 5-fluorouracil-refractory colorectal cancer

BackgroundFluoropyrimidines, specifically 5-fluorouracil (5-FU), remain the cornerstone of colorectal cancer (CRC) therapy. However, intrinsic and acquired resistance, alongside dose-limiting systemic toxicities, often result in treatment failure and disease relapse. There is a pressing clinical need for next-generation fluoropyrimidines that can retain the antitumor activity in 5-FU-refractory CRC models while maintaining a favorable safety profile. MethodsWe evaluated the antitumor efficacy of CF10, a novel polymeric fluoropyrimidine designed for the sustained delivery of FdUMP, against equimolar 5-FU. We utilized a diverse panel of six patient-derived CRC organoid (PDO) models to assess 3D growth inhibition under both normoxic ([~]20% O2) and physioxic (5% O2) conditions. Mechanisms of action were investigated via {gamma}H2AX signaling (DNA damage), Annexin V/PI flow cytometry (death kinetics), and ALDEFLUOR assays (stem-like populations). Functional suppression of metastasis-associated phenotypes was evaluated using 3D Matrigel invasion assays. Finally, the therapeutic index and overall survival were validated in vivo using two independent patient-cell-derived xenograft (PCDX) models (TX-CC-199 and TX-CC-201). ResultsCF10 demonstrated significantly greater suppression of organoid growth compared to equimolar 5-FU across all patient-derived lines, regardless of morphological heterogeneity or oxygen tension. In 3D invasion assays, CF10 achieved superior anti-invasive activity even at a 10-fold lower molar dose than 5-FU. This functional advantage was mirrored by a marked depletion of the ALDH-high stem-like subpopulation, which was largely recalcitrant to 5-FU. Mechanistically, CF10 induced intensified replication stress, DNA damage and repair signaling ({gamma}H2AX, Top1cc/pRPA32, FANCD2), and pushed the CRC to irreversible/terminal, PI-positive death states. In vivo, CF10 treatment resulted in profound tumor growth inhibition and a robust survival advantage in two patient cell-derived xenograft (PCDX) models (Log-rank P<0.01) without inducing systemic weight loss or noticeable toxicity. ConclusionsBy integrating 3D patient-derived modeling with in vivo validation, we demonstrate that CF10 effectively overcomes the biological and pharmacological limitations of 5-FU. CF10 targets the aggressive, invasive, and stem-like subpopulations of CRC that drive clinical relapses. These findings provide a compelling translational rationale for the clinical development of CF10 as a superior alternative to standard fluoropyrimidines in both treatment-naive and refractory CRC. Significance StatementDespite the foundational role of 5-fluorouracil (5-FU) in colorectal cancer (CRC) therapy, resistance and systemic toxicity remain major barriers to curative outcomes. This study identifies CF10, a novel polymeric fluoropyrimidine, as a superior alternative that overcomes 5-FU resistance in biologically diverse patient-derived organoids and xenograft models. Crucially, CF10 demonstrates a unique capacity to suppress the invasive, aldehyde dehydrogenase (ALDH)-high stem-like subpopulations that likely survive standard chemotherapy (5-FU) by maintaining efficacy under physiological oxygen levels and providing a significant survival advantage in vivo with improved tolerability. CF10 represents a promising translational candidate for the treatment of both treatment-naive and refractory CRC.

cancer biology↗

bioRxiv2025

VGLL1 contributes to both the transcriptome and epigenome of the developing trophoblast compartment

The trophectoderm (TE), the first lineage specified during mammalian development, initiates implantation and gives rise to placental trophoblasts. While animal models have elucidated key conserved signaling pathways involved in early TE specification, including BMP, WNT, and HIPPO, species-specific differences during early development emphasize the need for human-specific models. We previously identified VGLL1, a coactivator of TEAD transcription factors, as a human-specific placental marker. In this study, we employed a pluripotent stem cell (PSC)-based model of TE induction by BMP4 to investigate chromatin remodeling and transcriptional dynamics during TE formation. BMP4-induced chromatin accessibility changes promoted a trophoblast gene expression program, while mesoderm lineage markers were only transiently expressed upon canonical WNT activation. We found that VGLL1 was expressed downstream of key TE transcription factors (GATA2/3, TFAP2A/C) but was essential for establishment of full trophoblast identity by up-regulating EGFR and reinforcing GATA3 expression through positive feedback. Notably, VGLL1 enhanced canonical WNT signaling via direct regulation of WNT receptors and effectors. We also identified KDM6B, a histone demethylase that removes H3K27me3 repressive marks, as a direct VGLL1 target. KDM6B facilitated activation of bivalent promoters associated with TE markers, linking epigenetic regulation to lineage identity. Our findings establish a mechanistic framework positioning VGLL1 as a central regulator that integrates HIPPO, BMP, and WNT signaling pathways to drive establishment of human TE. Statement of SignificanceEarly development of the human placenta is essential for pregnancy success, yet the mechanisms that guide placental lineage specification remain poorly defined. Using human stem cells, we show how signaling pathways and chromatin remodeling programs work together to direct formation of the trophectoderm, the earliest placental cell type. We identify VGLL1 as a key regulator linking multiple signaling networks to gene expression and epigenetic control. Our findings reveal a species-specific mechanism of placental initiation with broad implications for understanding reproductive disorders, pregnancy loss, and advancing stem cell-based models to study and potentially treat human placental disease.

developmental biology↗

bioRxiv2024

Single-cell transcriptomics reveal differences between chorionic and basal plate cytotrophoblasts and trophoblast stem cells

Cytotrophoblast (CTB) of the early gestation human placenta are bipotent progenitor epithelial cells, which can differentiate into invasive extravillous trophoblast (EVT) and multinucleated syncytiotrophoblast (STB). Trophoblast stem cells (TSC), derived from early first trimester placentae, have also been shown to be bipotential. In this study, we set out to probe the transcriptional diversity of first trimester CTB and compare TSC to various subgroups of CTB. We performed single-cell RNA sequencing on six normal placentae, four from early (6-8 weeks) and two from late (12-14 weeks) first trimester, of which two of the early first trimester cases were separated into basal (maternal) and chorionic (fetal) fractions prior to sequencing. We also sequenced three TSC lines, derived from 6-8 week placentae, to evaluate similarities and differences between primary CTB and TSC. CTB clusters displayed notable distinctions based on gestational age, with early first trimester placentae showing enrichment for specific CTB subtypes, further influenced by origin from the basal or chorionic plate. Differential expression analysis of CTB from basal versus chorionic plate highlighted pathways associated with proliferation, unfolded protein response, and oxidative phosphorylation. We identified trophoblast states representing initial progenitor CTB, precursor STB, precursor and mature EVT, and multiple CTB subtypes. CTB progenitors were enriched in early first trimester placentae, with basal plate cells biased toward EVT, and chorionic plate cells toward STB, precursors. Clustering and trajectory inference analysis indicated that TSC were most like EVT precursor cells, with only a small percentage of TSC on the pre-STB differentiation trajectory. This was confirmed by flow cytometric analysis of 6 different TSC lines, which showed uniform expression of proximal column markers ITGA2 and ITGA5. Additionally, we found that ITGA5+ CTB could be plated in 2D, forming only EVT upon spontaneous differentiation, but failed to form self-renewing organoids; conversely, ITGA5-CTB could not be plated in 2D, but readily formed organoids. Our findings suggest that distinct CTB states exist in different regions of the placenta as early as six weeks gestation and that current TSC lines most closely resemble ITGA5+ CTB, biased toward the EVT lineage.

developmental biology↗