Midkine (MDK) is a dynamic molecular rheostat that operates differently depending on tissue context. It is widely induced after injury across multiple systems, including cardiovascular, neural, musculoskeletal, liver, and kidneys, yet its regulation often becomes disrupted with aging. MDK is also linked to fibrosis, immune aging, and tumor development. In this review, we discuss MDK effects in three tissue injury models and emerging therapeutic approaches to leverage MDK’s rheostat function.
The human lens is a transparent, avascular organ essential for focusing light and achieving visual acuity. While animal models have illuminated lens development, direct models of human lens organogenesis remain limited. We present an in vitro platform for lens morphogenesis by combining spatially patterned self-formed ectodermal autonomous multizone (SEAM) differentiation of human induced pluripotent stem cells (hiPSCs), with a lens optimised medium (LOM). Lentoids exhibited zone-specific organisation, upregulation of lens crystallins and connexins, and spatial protein localisation reflective of lens epithelial and fiber cells. LOM-treated cultures exhibited enhanced γ-crystallin expression, cadherin-mediated organisation, and capsule basement membrane deposition, alongside ultrastructural features of a maturing lens, including elongated cortical-like fibers, epithelial layering, and intercellular junctions with ball-and-socket-like interdigitations. Lentoids demonstrated self-renewing, preplacodal and presumptive lens ectodermal PAX6⁺/SIX3⁺/SOX2⁺ epithelial-like populations, which formed secondary lentoids, following activation of lens crystallin differentiation transcription factors—PROX1 and SOX1. These findings advance hiPSC-derived lens models and reveal an epithelial plasticity—offering a platform for studying ectodermal pathways, regenerative biology, and cataractogenesis. Lens differentiation requires the highest translational output to generate lifelong structural proteins, alongside a superior protein quality control system, and hiPSC-derived platforms provide a human model to study the limits of cellular differentiation and protein homeostasis.
Retinal ganglion cell (RGC) degeneration and the limited regenerative capacity of mammalian central nervous system axons result in irreversible vision loss in optic neuropathies. Identifying intrinsic regulators that promote both neuroprotection and axon regeneration is critical for developing effective therapies. This study identified POU domain class 2 transcription factor 2 (Pou2f2) as a previously unrecognized regulator involved in RGC biology. Single-cell RNA sequencing analysis of developing mouse and human retinas showed that Pou2f2 is enriched in RGC clusters and suppressed by an RGC fate suppressor in the mouse retinal progenitor cell culture. Pou2f2 protein was detected in mouse RGCs and optic nerves, where its expression decreased following optic nerve crush (ONC). In primary RGC cultures, AAV2-mediated Pou2f2 overexpression enhanced neurite outgrowth, whereas Pou2f2 knockdown reduced neurite length. In vivo, intravitreal injection of Pou2f2 overexpression AAV2s increased axon regeneration, improved RGC survival, and partially preserved RGC function after ONC. Bulk RNA sequencing data revealed early activation of cytoskeletal growth pathways and later upregulation of DNA repair-associated genes, whereas immunostaining and in vitro analyses suggested activation of AKT/mTOR signaling following Pou2f2 overexpression. Together, these findings identify Pou2f2 as a promising molecular target for gene-based therapies for RGC degenerative diseases, including glaucoma and other optic neuropathies.
Fibroblasts are mesenchymal cells with essential functions for connective tissue homeostasis and repair through the production and organization of the extracellular matrix (ECM). Most reconstructed skin models used in research and skin-related applications rely on fibroblasts to produce ECM. Despite their shared functions, human fibroblasts from different origins exhibit heterogeneity in age, morphotype, and localization. Induced pluripotent stem cells (iPSCs) offer a promising alternative by providing a consistent and scalable source of fibroblasts, overcoming the challenges of availability and variability. Here, we show that iPSC-derived fibroblasts (F-hiPSC) exhibit enhanced proliferative capacity and substantial functional differences compared to primary fibroblasts. Our aim was thus to comprehensively characterize F-hiPSCs in terms of fibroblast marker expression to benchmark their subtype identity, phenotype and ECM production. Secretome analysis also revealed that both Transforming Growth Factor-beta (TGF-β) abundance and activity were strongly increased in F-hiPSC, thereby enhancing ECM production and collagen I biosynthesis and affecting the maturation and assembly of collagen I fibers. By inhibiting the main TGF-β signaling receptor, we also unraveled the potential of modulating TGF-β signaling to normalize F-hiPSC ECM production.
Abstract How Doxorubicin (Dox) mediated damage to stem cells or cardiomyocytes contributes to cardiotoxicity and cardiac regeneration is unclear. Using a human iPSC-based model together with corresponding iPSC-derived cardiomyocytes (iCMs) revealed that iPSCs are much more sensitive against single short pulse-treatments with Dox than iCMs. Major mitochondrial impairments such as increased mitochondrial fragmentation, loss of mitochondrial membrane potential, reduced ATP levels, and altered mitochondrial DNA (mtDNA) organization, yet neither increased ROS formation, nuclear DNA damage response, nor apoptosis were detected in Dox-treated iPSCs. Whole genome transcriptome profiling revealed major differences in the transcriptional response to Dox including downregulation of genes regulating cellular homeostasis and energy metabolism. Dox exposure at the iPSC stage, termed priming here, shifts the global transcriptional landscape of iCMs towards reduced cardiac muscle regeneration, energy metabolism, muscle contraction, and increased fibrosis. Functionally, priming caused iCMs to ‘memorize’ this early Dox treatment resulting in reduced ATP levels, altered mtDNA organization, and in impaired contractility and oscillating Ca 2+ handling. We propose that Dox-induced mitochondrial dysfunction and transcriptional priming in stem cells alters durably cardiac and bioenergetic properties of its progeny which may impair the regenerative capacity after differentiation. This may be of particular relevance for children and teenagers undergoing chemotherapy.
