Both space flight and ground simulated microgravity experiments have shown significant structural and functional remodeling of mouse hearts. However, the cellular and molecular mechanisms behind it are difficult to decipher at the overall animal level. Microgravity three-dimensional cell culture technology was used to study various types of cells derived from mouse hearts in vitro by simulating weightlessness environment. The core pathological processes such as myocardial cell activation, fibroblast activation, and endothelial cell dysfunction were successfully revealed, providing experimental basis for understanding space induced cardiac dysfunction and developing protective measures.

1、 Discovery of Whole Animal Experiment: Macroscopic Effects of Microgravity on Mouse Heart

After spaceflight or ground simulation of microgravity (such as hind limb unloading), mouse hearts typically exhibit:

1. Reduction of cardiac mass and WS：Especially the left ventricular mass responsible for pumping blood has decreased.

2. Functional changes: Contraction function and pumping efficiency decrease.

3. Morphological remodeling: Changes in myocardial fiber arrangement and increased deposition of interstitial collagen indicate a risk of fibrosis.

2、 Experimental strategy and core findings of microgravity cell culture

By isolating different cellular components of mouse hearts and studying them in microgravity culture systems such as RWV and maglev, scientists have made groundbreaking discoveries:

1. Effects on myocardial cells

·Phenotype: Reversal from contraction type to fetal type.

·Experimental evidence: Mouse cardiomyocytes cultured in a rotating bioreactor showed downregulation of contractile proteins (such as alpha myosin heavy chain) expression, while fetal proteins (such as beta myosin heavy chain) were upregulated. This is highly consistent with the overall decrease in cardiac function in mice after weightlessness.

·Mechanism exploration: Research has found that the expression profiles of microRNAs (such as miR-1 and miR-133) undergo changes, and these miRNAs regulate the hypertrophy of cardiomyocytesWSThe key switch.

·Phenotype: Enhanced autophagy and apoptosis activity in cells.

·Experimental evidence: In 3D cultured cardiac spheroids, the expression of autophagy marker LC3-II increases and cell survival rate decreases. This indicates that under microgravity conditions, the balance between self-renewal of myocardial cells and clearance of damaged organelles is disrupted, promotingWS process.

2. Effects on cardiac fibroblasts

·Phenotype: Activation and promotion of fibrosis.

·Experimental evidence: This is one of the most important discoveries in microgravity cell culture. Under simulated microgravity, mouse cardiac fibroblasts were abnormally activated and transformed into myofibroblasts (expressing α - smooth muscle actin, α-SMA）。

·Mechanism exploration: Activated fibroblasts synthesize and secrete a large amount of collagen (type I and III), leading to excessive deposition of extracellular matrix. The TGF - β 1/Smad signaling pathway has been confirmed to be the "main switch" of this process. This directly explains the trend of cardiac interstitial fibrosis observed in overall animal experiments.

3. Effects on cardiac endothelial cells

·Phenotype: Impaired angiogenesis and barrier dysfunction.

·Experimental evidence: Mouse cardiac microvascular endothelial cells cultured in microgravity showed a significant decrease in their angiogenic ability, as well as slower cell migration and proliferation rates.

·Mechanism exploration: The receptor expression and signal transduction of angiogenesis related factors (such as VEGF) are obstructed. Meanwhile, the distribution and dysfunction of cell junction proteins (such as VE cadherin) may lead to changes in vascular permeability, affecting the nutrition and oxygen supply of the myocardium.

4. Effects on cardiac stem cells/progenitor cells

·Phenotype: Impaired proliferation and differentiation potential.

·Experimental evidence: Simulating microgravity can inhibit the self-renewal and differentiation of mouse cardiac progenitor cells into cardiomyocytes.

·Impact: This means that in microgravity environments, the inherent repair and regeneration potential of the heart is weakened, which may exacerbate functional loss caused by cell apoptosis and aging.

3、 Experimental advantages of microgravity cell culture

1. Accuracy of mechanism research: It is possible to separately study the response of a certain cell type (such as purified fibroblasts) to microgravity, eliminating interference from factors such as nerves and body fluids in the in vivo environment.

2. Analysis of signaling pathways: facilitates the use of inhibitors, agonists, or gene editing techniques to directly validate the role of specific signaling pathways (such as TGF - β, Hippo) in microgravity response.

3. Platform for drug screening: Based on the above findings, protective drugs can be screened on 3D cultured "heart like" models. For example, testing whether TGF - β inhibitors can prevent the activation of fibroblasts, or testing whether antioxidants can protect cardiomyocytes.

4、 Challenges and Future Directions

·Challenge:

·Model complexity: Current single-cell types or simple co culture models are still unable to simulate the complex cellular network and electro-mechanical coupling of the heart.

·Cultivation period: The period of in vitro simulation is relatively short, making it difficult to correspond to long-term space exposure.

·Future direction:

·Constructing a more complex organoid model: co culturing cardiomyocytes, fibroblasts, and endothelial cells in proportion to form a "miniature heart" with pulsatile function to study the interactions between cells.

·Combining mechanical force stimulation: applying mechanical force simulating heart pulsation after microgravity cultivation, studying the recovery process of "heavy load", and providing strategies for the recovery of heart function after astronauts return to Earth.

·Linkage with space experiments: Compare and verify the results of ground cell culture with in orbit experiments on the International Space Station.

Conclusion

Microgravity cell culture technology is like a high-power microscope, magnifying the specific effects of microgravity on different cellular components of mouse hearts. It clearly indicates that the decline in space heart function is not a single cell functional degradation, but the result of the coordinated disorder of multiple cells such as cardiomyocytes, fibroblasts, endothelial cells, etc. These profound insights from the cellular level not only provide new targets for protecting the cardiovascular health of astronauts, but also greatly enrich our understanding of the pathological mechanisms of diseases such as heart failure and fibrosis on Earth.