Hoi-Hung Cheung

Fetal hematopoietic stem and progenitor cells (HSPCs) require active ribosome biogenesis to sustain their rapid proliferation, yet how non-structural ribosomal factors regulate this process remains unclear. Here, we identify the RNA helicase Ddx21 as a critical determinant of fetal hematopoiesis through its epigenetic role in maintaining active ribosomal transcription. Conditional knockout of Ddx21 in murine fetal hematopoietic cells resulted in severe anemia, fetal liver hypoplasia, and depletion of HSPCs, accompanied by erythroid maturation arrest. Mechanistically, Ddx21 deficiency disrupted ribosomal and hematopoietic gene expressions, impaired translational capacity, and activated p53 pathway, triggering cell cycle arrest and apoptosis. While p53 inhibition partially rescued proliferation defects, it failed to restore rRNA transcription, pointing to p53-independent mechanisms. Multi-omics profiling revealed that Ddx21 interacts with the histone demethylase Kdm5a, co-occupying active promoters marked by H3K4me3. Loss of Ddx21 diminished H3K4me3 levels at ribosomal DNA (rDNA) and hematopoietic genes such as cKit and Gata1 , downregulating their transcription. Strikingly, Kdm5a inhibition restored rRNA expression and protein translation in Ddx21-deficient cells, and combined inhibition of Kdm5a and p53 cooperatively rescued HSPC function. These findings demonstrate a paradigm wherein Ddx21 couples ribosome biogenesis to epigenetic regulation by sequestering Kdm5a at active chromatin, thereby preserving transcriptional output essential for fetal hematopoietic expansion.

RecQ helicases are known as “caretakers” of the genome for their conserved helicase activities to resolve different complex DNA structures. Aberrant accumulation of unsolved DNA structures could lead to defects in DNA replication, gene transcription, and unrepaired DNA lesions. Pathogenic mutations on BLM, WRN, and RECQL4 are associated with several pathological conditions, namely Bloom syndrome (BS), Werner syndrome (WS), and Rothmund-Thomson syndrome (RTS). These syndromes are characterized by genomic instability and cancer predisposition. Additionally, some RecQ helicase diseases are linked to developmental defects and premature aging. In this review, we provide an overview of the RecQ helicases, focusing on the molecular functions and mechanisms, as well as the consequences of their dysfunction in cellular processes. We also discuss the significance of RecQ helicases in preventing various genetic disorders (BS, WS, RTS) and the insights obtained from the different animal models developed for studying the pathophysiology of RecQ helicase deficiencies.

Background: Pathogenic or null mutations in WRN helicase is a cause of premature aging disease Werner syndrome (WS). WRN is known to protect somatic cells including adult stem cells from premature senescence. Loss of WRN in mesenchymal stem cells (MSCs) not only drives the cells to premature senescence but also significantly impairs the function of the stem cells in tissue repair or regeneration. Results: In this study, we profiled the signaling pathways altered in WRN-deficient MSC and applied pharmacological method to activate the AKT signaling in these cells and examined their cellular phenotype related to aging. We found that the AKT signaling in WRN-deficient MSCs was significantly suppressed while the AKT upstream phosphatases (SHIP1/2) were upregulated. Knockdown or inhibition of SHIP1/2 could ameliorate premature senescence in WRN-deficient MSCs. Moreover, SHIP inhibition stimulated MSC proliferation and suppressed expression of pro-inflammatory cytokines IL-6 and IL-8. The stemness of WRN-deficient MSC was also improved upon pharmacological treatments with the inhibitors. Conclusions: These results suggested that targeting the SHIP/AKT signaling pathway is beneficial to WRN-deficient stem cells and fibroblasts, which might be applied for improving the trophic function of MSC in, for instance, promoting angiogenesis.

MicroRNAs (miRNAs) are generally evolutionarily conserved, but a small number of them are found exclusively in primates. MiR-1202 is a primate-specific miRNA that was previously revealed as being involved in major depression disorder (MDD). Moreover, the genomic locus where miR-1202 locates (6q25.3) is strongly associated with recurrent early-onset MDD and neurodevelopmental disorder. We hypothesize that miR-1202 plays a unique role in the brain in fine-tuning the transcriptional network that governs neurogenesis. Here, we reported that microdeletion of miR-1202 resulted in retarded organoid growth but enhanced dopaminergic (DA) neuron differentiation in midbrain organoids. Integrated analysis of miRNA-interacting targets and transcriptional changes in miR-1202 knockout cells revealed that APC2, a negative regulator of canonical WNT/β-catenin pathway, was a downstream target of miR-1202. Knockdown of APC2 resulted in attenuated DA neurogenesis, in contrast to the enhanced DA neurogenesis in miR-1202 knockout cells. Treatments of the brain organoids with antidepressants increased miR-1202 expression and simultaneously inhibited APC2 expression. Consistently, APC2 expression was found to increase in MDD patients. Our results suggest that miR-1202 regulates dopamine neurogenesis by inhibiting the APC2/WNT signaling pathway, which plays a distinct role in the midbrain-hindbrain regional patterning during the early development of the central nervous system.

Background: Pathogenic mutations inWRNare a cause of premature aging disease Werner syndrome (WS). Besides accelerated aging phenotypes and cancer predisposition, patients with WS also display underdevelopment in the skeletal system, characterized by short stature, light body weight and unusually thin extremities. The reasons for these developmental defects are not completely understood and the underlying molecular mechanism remains to be elucidated.Results: In this study, WRN was found to modulate transcription ofshort stature homeoboxgeneSHOX. Loss of WRN resulted in insufficient expression of SHOX, the gene dose of which is critical for driving chondrocyte differentiation. WRN could bind the G-quadruplex (G4) structures in theSHOXpromoter and stimulate transcription. Aberrant formation of G4 structures in WRN-deficient cells impeded normal transcription of SHOX, thus resulting in impaired chondrogenesis. Chondrogenesis could be rescued by overexpression of WRN helicase or SHOX, suggesting that SHOX is a downstream target of WRN. Gene editing of the G4 structures in theSHOXpromoter could increase SHOX expression, therefore rescuing the impaired chondrogenesis in WRN-deficient cells.Conclusions: Our data suggest that dysgenesis of the developing bone in WS might be caused by SHOX insufficiency. Aberrant formation of G4 structures inSHOXpromoter suppresses SHOX expression and impairs chondrogenesis. Targeted mutagenesis in the G4 structures enhances SHOX expression and thus providing an opportunity to rescue the chondrogenic defect.

Parkinson disease (PD) is a neurological movement disorder resulting primarily from damage to and degeneration of the nigrostriatal dopaminergic pathway. The pathway consists of neural populations in the substantia nigra that project to the striatum of the brain where they release dopamine. Diagnosis of PD is based on the presence of impaired motor features such as asymmetric or unilateral resting tremor, bradykinesia, and rigidity. Nonmotor features including cognitive impairment, sleep disorders, and autonomic dysfunction are also present. No cure for PD has been discovered, and treatment strategies focus on symptomatic management through restoration of dopaminergic activity. However, proposed cell replacement therapies are promising because midbrain dopaminergic neurons have been shown to restore dopaminergic neurotransmission and functionally rescue the dopamine-depleted striatum. In this review, we summarize our current understanding of the molecular pathogenesis of neurodegeneration in PD and discuss the development of new therapeutic strategies that have led to the initiation of exploratory clinical trials. We focus on the applications of stem cells for the treatment of PD and discuss how stem cell research has contributed to an understanding of PD, predicted the efficacy of novel neuroprotective therapeutics, and highlighted what we believe to be the critical areas for future research.

WRN mutation causes a premature aging disease called Werner syndrome (WS). However, the mechanism by which WRN loss leads to progeroid features evident with impaired tissue repair and regeneration remains unclear. To determine this mechanism, we performed gene editing in reprogrammed induced pluripotent stem cells (iPSCs) derived from WS fibroblasts. Gene correction restored the expression of WRN. WRN^+/+ mesenchymal stem cells (MSCs) exhibited improved pro‐angiogenesis. An analysis of paracrine factors revealed that hepatocyte growth factor (HGF) was downregulated in WRN^−/− MSCs. HGF insufficiency resulted in poor angiogenesis and cutaneous wound healing. Furthermore, HGF was partially regulated by PI3K/AKT signaling, which was desensitized in WRN^−/− MSCs. Consistently, the inhibition of the PI3K/AKT pathway in WRN^+/+ MSC resulted in reduced angiogenesis and poor wound healing. Our findings indicate that the impairment in the pro‐angiogenic function of WS‐MSCs is due to HGF insufficiency and PI3K/AKT dysregulation, suggesting trophic disruption between stromal and epithelial cells as a mechanism for WS pathogenesis.

Mouse embryonic stem cells (ESCs) are isolated from the inner cell mass of blastocysts, and they exist in different states of pluripotency—naïve and primed states. Pten is a well-known tumor suppressor. Here, we generated Pten^−/− mouse ESCs with the CRISPR-Cas9 system and verified that Pten^−/− ESCs maintained naïve pluripotency by blocking Gsk3β activity. Serum/LIF and 2i (MAPK and GSK3 inhibitors) conditions are commonly used for ESC maintenance. We show that the Pten-inhibitor SF1670 contributed to sustaining mouse ESCs and that Pten activation by the S380A, T382A, and T383A mutations (Pten-A3) suppressed the pluripotency of ESCs. The in vivo teratoma formation ability of SF1670-treated ESCs increased, while the Pten-A3 mutations suppressed teratoma formation. Furthermore, the embryoid bodies derived from Pten-deficient ESCs or SF1670-treated wild-type ESCs showed greater expression of ectoderm and pluripotency markers. These results suggest that Pten-mediated Gsk3β modulates the naïve pluripotency of ESCs and that Pten ablation regulates the lineage-specific differentiation.