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Cardiac fibroblasts play a pivotal role in maintaining heart homeostasis by depositing extracellular matrix (ECM) to provide structural support for the myocardium, vasculature, and neuronal network and by contributing to essential physiological processes. In response to injury such as myocardial infarction or pressure overload, fibroblasts become activated, leading to increased ECM production that can ultimately drive left ventricular remodeling and progress to heart failure. Recently, the American Journal of Physiology-Heart and Circulatory Physiology issued a call for papers on cardiac fibroblasts that yielded articles with topics spanning fibroblast physiology, technical considerations, signaling pathways, and interactions with other cell types. This mini-review summarizes those articles and places the new findings in the context of what is currently known for cardiac fibroblasts and what future directions remain. [ABSTRACT FROM AUTHOR]

This article explores the role of IL4Ra signaling in the development of heart failure following myocardial ischemic injury. The authors conducted studies on mice and found that administering IL4 and IL13 after a heart attack improved cardiac function. They also created a mouse model with a knockout of the IL4Ra receptor and observed that these mice experienced greater deterioration of cardiac function compared to control mice. Additionally, the authors conducted retrospective studies on patients using a drug called dupilumab, which targets the IL4Ra receptor, and found that these patients had a lower risk of developing heart disease, heart failure, or cerebrovascular events. The authors conclude that IL4Ra signaling plays a protective role in preventing the progression to heart failure after an ischemic event. They also discuss the potential cardiac side effects of dupilumab and suggest the need for further research to develop targeted therapies that can mitigate these effects while effectively treating atopic dermatitis. [Extracted from the article]

Paracrine signaling is challenging to study in vitro, as conventional culture tools dilute soluble factors and offer little to no spatiotemporal control over signaling. Microfluidic chips offer potential to address both of these issues. However, few solutions offer both control over onset and duration of cell–cell communication, and high throughput. We have developed a microfluidic chip designed to culture cells in adjacent chambers, separated by valves to selectively allow or prevent exchange of paracrine signals. The chip features 16 fluidic inputs and 128 individually-addressable chambers arranged in 32 sets of 4 chambers. Media can be continuously perfused or delivered by diffusion, which we model under different culture conditions to ensure normal cell viability. Immunocytochemistry assays can be performed in the chip, which we modeled and fine-tuned to reduce total assay time to 1 h. Finally, we validate the use of the chip for co-culture studies by showing that HEK293Ta cells respond to signals secreted by RAW 264.7 immune cells in adjacent chambers, only when the valve between the chambers is opened. [ABSTRACT FROM AUTHOR]

During normal ageing a low rate of division of pre-existing cardiomyocytes, rather than progenitor cells, is responsible for cardiomyocyte genesis; this process is increased fourfold during myocardial infarction. Heart-cell replacement in the adult There is controversy in the cardiovascular field regarding the extent of existing cardiomyocyte turnover versus progenitor cell contributions during mammalian cardiac homeostasis throughout adult life. This study takes a novel approach to settling the debate by using a combination of prospective labelling with the nitrogen-15 isotope and genetic pulse-chase to measure DNA synthesis in the adult mammalian heart. The authors conclude that during normal ageing, preexisting cardiomyocytes are the dominant source of cardiomyocyte replacement in normal mammalian myocardial homeostasis, a process that is increased fivefold during recovery from myocardial infarction. Although recent studies have revealed that heart cells are generated in adult mammals, the frequency of generation and the source of new heart cells are not yet known. Some studies suggest a high rate of stem cell activity with differentiation of progenitors to cardiomyocytes.sup.1. Other studies suggest that new cardiomyocytes are born at a very low rate.sup.2,3,4, and that they may be derived from the division of pre-existing cardiomyocytes. Here we show, by combining two different pulse-chase approaches--genetic fate-mapping with stable isotope labelling, and multi-isotope imaging mass spectrometry--that the genesis of cardiomyocytes occurs at a low rate by the division of pre-existing cardiomyocytes during normal ageing, a process that increases adjacent to areas of myocardial injury. We found that cell cycle activity during normal ageing and after injury led to polyploidy and multinucleation, but also to new diploid, mononucleate cardiomyocytes. These data reveal pre-existing cardiomyocytes as the dominant source of cardiomyocyte replacement in normal mammalian myocardial homeostasis as well as after myocardial injury., Author(s): Samuel E. Senyo [sup.1] , Matthew L. Steinhauser [sup.1] , Christie L. Pizzimenti [sup.1] , Vicky K. Yang [sup.1] , Lei Cai [sup.1] , Mei Wang [sup.4] [sup.5] , [...]

Mass spectrometry with stable isotope labels has been seminal in discovering the dynamic state of living matter (1,2), but is limited to bulk tissues or cells. We developed multi-isotope imaging mass spectrometry (MIMS) that allowed us to view and measure stable isotope incorporation with submicrometre resolution (3,4). Here we apply MIMS to diverse organisms, including Drosophila, mice and humans. We test the 'immortal strand hypothesis', which predicts that during asymmetric stem cell division chromosomes containing older template DNA are segregated to the daughter destined to remain a stem cell, thus insuring lifetime genetic stability. After labelling mice with [sup.15]N-thymidine from gestation until post-natal week 8, we find no [sup.15]N label retention by dividing small intestinal crypt cells after a four-week chase. In adult mice administered [sup.15]N-thymidine pulse-chase, we find that proliferating crypt cells dilute the [sup.15]N label, consistent with random strand segregation. We demonstrate the broad utility of MIMS with proof-of-principle studies of lipid turnover in Drosophila and translation to the human haematopoietic system. These studies show that MIMS provides high-resolution quantification of stable isotope labels that cannot be obtained using other techniques and that is broadly applicable to biological and medical research., MIMS combines ion microscopy with secondary ion mass spectrometry (SIMS), stable isotope reporters and intensive computation (Supplementary Fig. 1). MIMS allows imaging and measuring of stable isotope labels in cell [...]

Loss of cardiomyocytes is a major cause of heart failure, and while the adult heart has a limited capacity for cardiomyogenesis, little is known about what regulates this ability or whether it can be effectively harnessed. Here we show that 8 weeks of running exercise increase birth of new cardiomyocytes in adult mice (~4.6-fold). New cardiomyocytes are identified based on incorporation of 15N-thymidine by multi-isotope imaging mass spectrometry (MIMS) and on being mononucleate/diploid. Furthermore, we demonstrate that exercise after myocardial infarction induces a robust cardiomyogenic response in an extended border zone of the infarcted area. Inhibition of miR-222, a microRNA increased by exercise in both animal models and humans, completely blocks the cardiomyogenic exercise response. These findings demonstrate that cardiomyogenesis can be activated by exercise in the normal and injured adult mouse heart and suggest that stimulation of endogenous cardiomyocyte generation could contribute to the benefits of exercise.

Skull morphogenesis is a complex, dynamic process involving two different germ layers and progressing to the coordinated, directional growth of individual bones. The mechanisms underlying directional growth toward the apex are not completely understood. Here, a microfluidic chip-based approach is utilized to test whether calvarial osteoblast progenitors undergo haptotaxis on a gradient of Fibronectin1 (FN1) via lamellipodia. Mimicking the embryonic cranial mesenchyme's FN1 pattern, FN1 gradients is established in the chip using computer modeling and fluorescent labeling. Primary mouse calvarial osteoblast progenitors are plated in the chip along an array of segmented gradients of adsorbed FN1. The study performs single-cell tracking and measures protrusive activity. Haptotaxis is observed at an intermediate FN1 concentration, with an average directional migration index (yFMI) of 0.07, showing a significant increase compared to the control average yFMI of -0.01. A significant increase in protrusive activity is observed during haptotaxis. Haptotaxis is an Arp2/3-dependent, lamellipodia-mediated process. Calvarial osteoblast progenitors treated with the Arp2/3 (Actin Related Protein 2/3 complex) inhibitor CK666 show significantly diminished haptotaxis, with an average yFMI of 0.01. Together, these results demonstrate haptotaxis on an FN1 gradient as a new mechanism in the apical expansion of calvarial osteoblast progenitors during development and shed light on the etiology of calvarial defects., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

We present a fully-integrated solution for controlling pneumatically-driven microfluidic chips, featuring a pump, one or more pressure regulators and up to 32 solenoid valves, controlled by a microcontroller. The microfluidics control system requires only a power source and a computer or mobile device for its operation. A touchscreen interface communicates with the microcontroller over USB or Bluetooth and allows users to control the system with ease either manually or autonomously, allowing experiments to run with no user intervention. The pressure regulators were purpose-built, enabling integrated pressure sources on-board, rather than relying on external equipment. These regulators can also be used as stand-alone devices in any other application., Competing Interests: Declaration of interest None.