Filipa Timóteo-Ferreira

Following muscle injury, a series of well-coordinated events ensures proper healing. Among these, inflammatory cells, particularly macrophages (MPs), play a fundamental role by phagocytosing damaged tissue and coordinating the actions of other cells involved in regeneration. Partial depletion of infiltrating MPs has been associated with endothelial cells (ECs) undergoing endothelial-to-mesenchymal transition (EndMT), contributing to extracellular matrix accumulation. However, the specific mechanisms linking MPs to this process, as well as their role in influencing EC fate, remain unclear. Here, we adopt a single-cell transcriptomics approach in mice to define a specific signature of the regenerating muscle niche. We show that perturbing MP recruitment upon injury results in impaired MP polarization, creating an aberrant inflammatory, non-regenerative, and less angiogenic microenvironment, which in turn drives ECs toward EndMT. Furthermore, we highlight complex signalling interactions between MPs and ECs, with SPP1 emerging as one of the critical modulators of these processes.

Embryonic hematopoiesis involves successive waves of progenitors from distinct anatomical sites, but the origins and contributions of early hematopoietic stem and progenitor cells (HSPCs) remain incompletely defined. Here we use genetic fate mapping in mice to temporally label hemogenic endothelium (HE) subsets and track their progeny. We show that a wave of fetal-restricted HSPCs arises from HE in the vitelline and umbilical arteries between embryonic days 8.5 and 9.5, preceding the emergence of definitive hematopoietic stem cells. Lineage tracing, single-cell transcriptomic analyses and functional assays revealed that these progenitors are transient and distinct from erythro-myeloid progenitors, contribute extensively to fetal lympho-myelopoiesis but decline postnatally. Our findings reveal a previously unrecognized early HE wave as a key source of fetal-restricted HSPCs, refining the spatial–temporal understanding of layered hematopoiesis and informing developmental origins of blood cell diversity.

Hemogenic endothelium (HE) is recognized as the origin of all definitive blood cells, including hematopoietic stem cells (HSCs); however, the mechanisms governing the hematopoietic progenitor versus HSC fate choice within the HE remain unknown. Here we combine differentiation assays with full-length single-cell transcriptome data for extra-embryonic yolk sac (YS) and intra-embryonic aorta–gonad–mesonephros (AGM) region HE populations. We identified and localized three differentiation trajectories, each containing a distinct HE subset: erythromyeloid progenitor-primed HE in the YS plexus, lymphomyeloid progenitor-primed HE in large YS arteries and hematopoietic stem and progenitor cell-primed HE in the AGM. Chromatin modifiers and spliceosome components were enriched in AGM HE. This correlated with a higher isoform complexity of the AGM HE transcriptome. Distinct AGM HE-specific isoform expression patterns were observed for a broad range of genes, including stemness-associated factors like Runx1 . Our data form a unique resource for studying cell fate decisions in different HE populations.

Following muscle injury, a series of well-coordinated events ensure proper healing. Among these, inflammatory cells, particularly macrophages (MPs), play a fundamental role by phagocytosing damaged tissue and coordinating the actions of other cells involved in regeneration. Partial depletion of infiltrating MPs has been associated with endothelial cells (ECs) undergoing endothelial-to-mesenchymal transition (EndMT), contributing to extracellular matrix accumulation. However, the specific mechanisms linking MPs to this process, as well as their role in influencing EC fate, remain unclear. Here, we adopt a single cell transcriptomics approach in mice to define a specific signature of the regenerating muscle niche. We show that perturbing MP recruitment upon injury results in impaired MP polarization, creating an aberrant inflammatory, non-regenerative, and less angiogenic microenvironment which in turn drives ECs toward EndMT. Furthermore, we highlight complex signalling interactions between MPs and ECs, with SPP1 emerging as one of the critical modulators of these processes.

Advanced maternal age is associated with higher infertility rates, pregnancy-associated complications, and progeny health issues. The ovary is considered the main responsible for these consequences due to a continuous decay in follicle number and oocyte quality. Intracellular imbalance between oxidant molecules and antioxidant mechanisms, in favour of the former, results in oxidative stress (OS) that is believed to contribute to ovarian ageing. This work is aimed at evaluating whether an age-related increase in ovarian OS, inflammation, and fibrosis may contribute to tissue dysfunction and whether specific antioxidant supplementation with a NADPH oxidase inhibitor (apocynin) could ameliorate them. Mice aged 8–12 weeks (reproductively young) or 38-42 weeks (reproductively aged) were employed. Aged mice were divided into two groups, with one receiving apocynin (5 mM) in the drinking water, for 7 weeks, upon which animals were sacrificed and their ovaries collected. Ovarian structure was similar at both ages, but the ovaries from reproductively aged mice exhibited lipofuscin deposition, enhanced fibrosis, and a significant age-related reduction in primordial and primary follicle number when compared to younger animals. Protein carbonylation and nitration, and markers of OS were significantly increased with age. Moreover, mRNA levels of inflammation markers, collagens, metalloproteinases (MMPs), and tissue inhibitor MMPs (TIMPs) were upregulated. Expression of the antifibrotic miRNA29c-3p was significantly reduced. Apocynin supplementation ameliorated most of the age-related observed changes, sometimes to values similar to those observed in young females. These findings indicate that there is an age-related increase in OS that plays an important role in enhancing inflammation and collagen deposition, contributing to a decline in female fertility. Apocynin supplementation suggests that the imbalance can be ameliorated and thus delay ovarian ageing harmful effects.

For a successful pregnancy to occur, a predecidualized receptive endometrium must be invaded by placental differentiated cells (extravillous trophoblast cells (EVTs)) and, at the same time, continue decidualization. EVT invasion is aimed at anchoring the placenta to the maternal uterus and ensuring local blood supply increase necessary to provide normal placental and foetal development. The first is achieved by migrating through the maternal endometrium and deeper into the myometrium, while the second by transforming uterine spiral arteries into large vessels. This process is a tightly regulated battle comprising interests of both the mother and the foetus. Invading EVTs are required to perform a scope of functions: move, adhere, proliferate, differentiate, interact, and digest the extracellular matrix (ECM); tolerate hypoxia; transform the maternal spiral arteries; and die by apoptosis. All these functions are modulated by their surrounding microenvironment: oxygen, soluble factors (e.g., cytokines, growth factors, and hormones), ECM proteins, and reactive oxygen species. A deeper comprehension of oxidative uterine microenvironment contribution to trophoblast function will be addressed in this review.