Loss-of-Function of p21-Activated Kinase 2 Links BMP Signaling to Neural Tube Patterning Defects

Antenatal phenotype associated with PAK2 pathogenic variants: bilateral pleural effusion as a warning sign

Fetal pleural effusions can arise in various contexts with different prognosis. They have been reported in fetuses presenting with hereditary or acquired conditions. One particularly rare genetic disorder, known as Knobloch syndrome, seems to emerge as a potential new cause of fetal pleural effusions, associated with severe outcomes. Knobloch syndrome 1 can be caused by biallelic variants in COL18A1. It is primarily characterized by its ophthalmic features, including severe vitreoretinal degeneration with retinal detachment and macular abnormalities. Neurological defects such as encephalocele and developmental delay, along with skeletal and renal malformations, are also associated with the syndrome. The Knobloch syndrome 2 is caused by monoallelic variants in the kinase domain of PAK2. It is less described and seems to also be associated with cardiac and respiratory damage in addition to the Knobloch syndrome 1 phenotype. PAK2 is a ubiquitous protein with a major implication in regulation and remodeling of the cytoskeleton and numerous other cellular pathways. Knobloch-associated variants seem to cause a loss of the kinase function of the protein. Even if the ophthalmic defects are almost constant, PAK2-associated Knobloch syndrome has slightly different features from Knobloch syndrome 1 in which pulmonary and lymphatic damages are still unseen. In a prenatal trio exome sequencing, we identified a novel de novo PAK2 missense variant, NM_002577.4:c.836 A > C, p.(Gln279Pro), classified as likely pathogenic in a 24 weeks of gestation fetus whose only sign was severe bilateral pleural effusion. From a literature review of patients, we recognize this sign as an important antenatal indicator of Knobloch syndrome 2, as it was the first sign identifiable in 2 out of 5 patients. This adds new evidence for the implication of this gene in fetal pleural effusions, with potentially severe outcomes.

The Critical Role of YAP/BMP/ID1 Axis on Simulated Microgravity-Induced Neural Tube Defects in Human Brain Organoids

Integrated biochemical and biophysical signals regulate embryonic development. Correct neural tube formation is critical for the development of central nervous system. However, the role of microgravity in neurodevelopment and its underlying molecular mechanisms remain unclear. In this study, the effects of stimulated microgravity (SMG) on the development of human brain organoids are investigated. SMG impairs N-cadherin-based adherens junction formation, leading to neural tube defects associated with dysregulated self-renewal capacity and neuroepithelial disorganization in human brain organoids. Bulk gene expression analyses reveal that SMG alters Hippo and BMP signaling in brain organoids. The neuropathological deficits in SMG-treated organoids can be rescued by regulating YAP/BMP/ID1 axis. Furthermore, sing-cell RNA sequencing data show that SMG results in perturbations in the number and function of neural stem and progenitor cell subpopulations. One of these subpopulations senses SMG cues and transmits BMP signals to the subpopulation responsible for tube morphogenesis, ultimately affecting the proliferating cell population. Finally, SMG intervention leads to persistent neurologic damage even after returning to normal gravity conditions. Collectively, this study reveals molecular and cellular abnormalities associated with SMG during human brain development, providing opportunities for countermeasures to maintain normal neurodevelopment in space.

Regulation of Vascular Injury and Repair by P21-Activated Kinase 1 and P21-Activated Kinase 2: Therapeutic Potential and Challenges

The PAK (p21-activated kinases) family is a class of intracellular signal transduction protein kinases that regulate various cellular functions, mainly through their interactions with small GTP enzymes. PAK1 and PAK2 in the PAK kinase family are key signal transduction molecules that play important roles in various biological processes, including morphological changes, migration, proliferation, and apoptosis, and are involved in the progression of many diseases. Abnormal expression or dysregulation of PAK1 and PAK2 may be associated with several diseases, including cancer, neurological diseases, etc. The current research mainly focuses on studying the role of PAK and PAK inhibitors in the regulation of cancer progression, but relatively few reports are available that explore their potential role in cardiovascular diseases. Vascular injury and repair are complex processes involved in many cardiovascular conditions, including atherosclerosis, restenosis, and hypertension. Emerging research suggests that PAK1 and PAK2 have pivotal roles in vascular endothelial cell functions, including migration, proliferation, and angiogenesis. These kinases also modulate vascular smooth muscle relaxation, vascular permeability, and structural alterations, which are critical in the development of atherosclerosis and vascular inflammation. By targeting these activities, PAK proteins are essential for both normal vascular physiology and the pathogenesis of vascular diseases, highlighting their potential as therapeutic targets for vascular health. This review focuses on recent studies that offer experimental insights into the mechanisms by which PAK1 and PAK2 regulate the biological processes of vascular injury and repair and the therapeutic potential of the current existing PAK inhibitors in vascular-related diseases. The limitations of treatment with some PAK inhibitors and the ways that future development can overcome these challenges are also discussed.

New kinase-deficient PAK2 variants associated with Knobloch syndrome type 2

The p21-activated kinase (PAK) family of proteins regulates various processes requiring dynamic cytoskeleton organization such as cell adhesion, migration, proliferation, and apoptosis. Among the six members of the protein family, PAK2 is specifically involved in apoptosis, angiogenesis, or the development of endothelial cells. We report a novel de novo heterozygous missense PAK2 variant, p.(Thr406Met), found in a newborn with clinical manifestations of Knobloch syndrome. In vitro experiments indicated that this and another reported variant, p.(Asp425Asn), result in substantially impaired protein kinase activity. Similar findings were described previously for the PAK2 p.(Glu435Lys) variant found in two siblings with proposed Knobloch syndrome type 2 (KNO2). These new variants support the association of PAK2 kinase deficiency with a second, autosomal dominant form of Knobloch syndrome: KNO2.

Characterizing neuroinflammation and identifying prenatal diagnostic markers for neural tube defects through integrated multi-omics analysis

BACKGROUND

Neural Tube Defects (NTDs) are congenital malformations of the central nervous system resulting from the incomplete closure of the neural tube during early embryonic development. Neuroinflammation refers to the inflammatory response in the nervous system, typically resulting from damage to neural tissue. Immune-related processes have been identified in NTDs, however, the detailed relationship and underlying mechanisms between neuroinflammation and NTDs remain largely unclear. In this study, we utilized integrated multi-omics analysis to explore the role of neuroinflammation in NTDs and identify potential prenatal diagnostic markers using a murine model.

METHODS

Nine public datasets from Gene Expression Omnibus (GEO) and ArrayExpress were mined using integrated multi-omics analysis to characterize the molecular landscape associated with neuroinflammation in NTDs. Special attention was given to the involvement of macrophages in neuroinflammation within amniotic fluid, as well as the dynamics of macrophage polarization and their interactions with neural cells at single-cell resolution. We also used qPCR assay to validate the key TFs and candidate prenatal diagnostic genes identified through the integrated analysis in a retinoic acid-induced NTDs mouse model.

RESULTS

Our analysis indicated that neuroinflammation is a critical pathological feature of NTDs, regulated both transcriptionally and epigenetically within central nervous system tissues. Key alterations in gene expression and pathways highlighted the crucial role of STATs molecules in the JAK-STAT signaling pathway in regulating NTDs-associated neuroinflammation. Furthermore, single-cell resolution analysis revealed significant polarization of macrophages and their interaction with neural cells in amniotic fluid, underscoring their central role in mediating neuroinflammation associated with NTDs. Finally, we identified a set of six potential prenatal diagnostic genes, including FABP7, CRMP1, SCG3, SLC16A10, RNASE6 and RNASE1, which were subsequently validated in a murine NTDs model, indicating their promise as prospective markers for prenatal diagnosis of NTDs.

CONCLUSIONS

Our study emphasizes the pivotal role of neuroinflammation in the progression of NTDs and underlines the potential of specific inflammatory and neural markers as novel prenatal diagnostic tools. These findings provide important clues for further understanding the underlying mechanisms between neuroinflammation and NTDs, and offer valuable insights for the future development of prenatal diagnostics.