Masternak, Michal M

Summary Human spaceflight has historically been led by government agencies, but the emergence of commercial organizations is enabling broader participation and new research opportunities. In this study, we present a comprehensive molecular characterization of early human responses to spaceflight, leveraging multi-omics data across the first three weeks of two commercial missions. Biospecimens from six individuals, four from the Axiom 2 mission (10 days) and two from Axiom 3 (21 days), were analyzed using single-cell and bulk RNA sequencing, alongside proteomic profiling. Individual and integrative analyses of these datasets reveal systemic changes in cell types, transcripts, and proteins related to immune regulation, osteoclast differentiation, NF-κB signaling, and blood homeostasis pathways. Importantly, several of the detected pathways align with physiological patterns observed in longer-duration missions. This work establishes a foundational resource for understanding early adaptation to spaceflight at the cellular and molecular levels, providing insights to reduce future space-travel health risks. Highlights First integrated multi-omics analysis using single-cell, bulk RNA sequencing and proteomic profiling of early human spaceflight responses across two commercial missions (Ax-2 and Ax-3). Distinct PBMC clustering was observed across Ax-2 and Ax-3, and post-flight samples. It showed fewer monocytes, dendritic cells, and megakaryocytes with increased naïve CD4⁺ and cytotoxic T cells. Multi-omics integration identifies shared biological signatures, including osteoclast differentiation, metabolic stress, and coagulation changes. These findings lay the foundation for developing countermeasures to protect immune, skeletal, and vascular health during spaceflight.

Cellular senescence is defined as a state of permanent cell cycle arrest, providing a natural barrier against cancer. However, senescent cells are very metabolically active and secrete a complex mixture of bioactive molecules collectively known as the senescence-associated secretory phenotype (SASP), which play a dual role in cancer biology. While the SASP can suppress tumors by facilitating immunosurveillance, it can also promote tumor progression by fostering a pro-inflammatory milieu, stimulating angiogenesis, enhancing invasiveness, and enabling immune evasion. In Head and Neck Cancers (HNCs), a highly heterogeneous group of malignancies, SASP has emerged as a critical player in disease progression and treatment resistance. Persistent DNA damage response (DDR) signaling drives SASP and thereby contributes to the progression of head and neck cancer by modulating the tumour microenvironment. It influences the tumor microenvironment (TME) by facilitating epithelial-to-mesenchymal transition (EMT), promoting cancer stem cell-like properties, and impairing the efficacy of radiotherapy, chemotherapy, and immune checkpoint inhibitors. These effects underscore the need for targeted interventions to regulate SASP activity. This review presents a comprehensive overview of the molecular mechanisms underlying SASP generation and its effects on HNCs. We discuss the dual roles of SASP in tumor suppression and progression, its contribution to therapy resistance, and emerging therapeutic strategies, including novel senolytic and senomorphic drugs. Finally, we highlight key challenges and future directions for translating SASP-targeted therapies into clinical practice, emphasizing the need for biomarker discovery, and a deeper understanding of SASP heterogeneity. By targeting the SASP, there is potential to enhance therapeutic outcomes and improve the management of HNCs.

Abstract Aging is associated with intestinal dysbiosis, a condition characterized by diminished microbial biodiversity and inflammation. This leads to increased vulnerability to extraintestinal manifestations such as autoimmune, metabolic, and neurodegenerative conditions and accelerates mortality. As such, modulation of the gut microbiome is a promising way to extend healthspan. In this study, we explore the effects of fecal microbiota transplant (FMT) from long-living Ames dwarf donors to their normal littermates, and vice versa, on the recipient gut microbiota and liver transcriptome. Importantly, our previous studies highlight differences between the microbiomes of Ames dwarf relative to their normal siblings, potentially contributing to their extended lifespan and healthspan. Our findings demonstrate that FMT from Ames dwarf mice to normal mice significantly alters the recipient’s gut microbiota, reprograms bacterial metabolic functions related to healthy aging, and changes the liver transcriptome, indicating improved metabolic health. Our liver mRNA sequencing and RT-PCR validation reveals that FMT in normal recipient animals administered dwarf donor stool may contribute to the significant downregulation of p21, Elovl3, and Insig2, genes involved with cellular senescence and liver metabolic pathways. Our data suggest a regulatory axis exists between the gut and liver, highlighting the potential of microbiome-targeted therapies in promoting healthy aging. Future research should validate these findings and study the underlying mechanisms that confer geroprotection.

Abstract Muscle wasting is a significant hurdle in patients due to immobilization, prolonged bed rest, and injury. In particular, the older population develops sarcopenia, characterized by progressive loss of muscle strength due to natural aging. However, there are no FDA-approved drugs for sarcopenia, and it is critical to explore novel therapeutics. Myostatin inhibition is one such strategy that has had varying degrees of success previously, yet the desired levels of muscle strength have not been achieved. Here, we employed a novel vaccine (V13) that generates anti-myostatin antibodies and another (V07) that generates anti-activin A; myostatin and activin A regulate muscle growth negatively. We administered seven doses of V13, V07, and V35 (generates both anti-myostatin and anti-activin A) to long-living, GH-deficient Ames dwarf mice (df/df) and their normal littermate controls (N/df). By week 24 post-first dose, we saw increased forelimb grip strength in V13, V07, and V35 vaccinated df/df mice and V07 and V35 vaccinated N/df mice. Additionally, almost 40% of the vaccinated df/df mice completed the accelerating rotarod trials, compared to the 20% of placebo-treated counterparts. We observed increased lean body mass and reduced fat mass in vaccinated N/df mice, yet surprisingly there were no changes in lean and fat mass in df/df mice. In summary, our results indicate that while myostatin and activin A inhibition play an intimate role in fat metabolism in the presence of GH/IGF-1, this immunization strategy improves muscle motor performance in GH/IGF-1 deficient mice providing promising treatments in older animals regardless age-associated suppression of GH/IGF-1 axis.

AbstractDespite the growing interest by researchers into cellular senescence, a hallmark of cellular aging, its role in human skin remains equivocal. The skin is the largest and most accessible human organ, reacting to the external and internal environment. Hence, it is an organ of choice to investigate cellular senescence and to target root‐cause aging processes using senolytic and senomorphic agents, including naturally occurring plant‐based derivatives. This review presents different aspects of skin cellular senescence, from physiology to pathology and signaling pathways. Cellular senescence can have both beneficial and detrimental effects on the skin, indicating that both prosenescent and antisenescent therapies may be desirable, based on the context. Knowledge of molecular mechanisms involved in skin cellular senescence may provide meaningful insights for developing effective therapeutics for senescence‐related skin disorders, such as wound healing and cosmetic skin aging changes.

Abstract Cellular senescence contributes to age-related disorders including physical dysfunction, disabilities, and mortality caused by tissue inflammation and damage. Senescent cells accumulate in multiple tissues with aging and at etiological sites of multiple chronic disorders. The senolytic drug combination, Dasatinib plus Quercetin (D+Q), is known to reduce senescent cell abundance in aged mice. However, the effects of long-term D+Q treatment on intestinal senescent cell and inflammatory burden and microbiome composition in aged mice remain unknown. Here, we examine the effect of D+Q on senescence (p16Ink4a and p21Cip1) and inflammation (Cxcl1, Il1β, Il6, Mcp1, and Tnfα) markers in small (ileum) and large (caecum and colon) intestine in aged mice (n = 10) compared to age-matched placebo-treated mice (n = 10). Additionally, we examine microbial composition along the intestinal tract in these mice. D+Q-treated mice show significantly lower senescent cell (p16 and p21 expression) and inflammatory (Cxcl1, Il1β, Il6, Mcp1, and Tnfα expression) burden in small and large intestine compared with control mice. Further, we find specific microbial signatures in ileal, cecal, colonic, and fecal regions that are distinctly modulated by D+Q, with modulation being most prominent in small intestine. Further analyses reveal specific correlation of senescence and inflammation markers with specific microbial signatures. Together, these data demonstrate that the senolytic treatment reduces intestinal senescence and inflammation while altering specific microbiota signatures and suggest that the optimized senolytic regimens might improve health via reducing intestinal senescence, inflammation, and microbial dysbiosis in older subjects.

Abstract Aging is the greatest risk factor for most chronic diseases. The somatotropic axis is one of the most conserved biological pathways that regulates aging across species. 17α-Estradiol (17α-E2), a diastereomer of 17β-estradiol (17β-E2), was recently found to elicit health benefits, including improved insulin sensitivity and extend longevity exclusively in male mice. Given that 17β-E2 is known to modulate somatotropic signaling in females through actions in the pituitary and liver, we hypothesized that 17α-E2 may be modulating the somatotropic axis in males, thereby contributing to health benefits. Herein, we demonstrate that 17α-E2 increases hepatic insulin-like growth factor 1 (IGF1) production in male mice without inducing any changes in pulsatile growth hormone (GH) secretion. Using growth hormone receptor knockout (GHRKO) mice, we subsequently determined that the induction of hepatic IGF1 by 17α-E2 is dependent upon GH signaling in male mice, and that 17α-E2 elicits no effects on IGF1 production in female mice. We also determined that 17α-E2 failed to feminize the hepatic transcriptional profile in normal (N) male mice, as evidenced by a clear divergence between the sexes, regardless of treatment. Conversely, significant overlap in transcriptional profiles was observed between sexes in GHRKO mice, and this was unaffected by 17α-E2 treatment. Based on these findings, we propose that 17α-E2 acts as a pleiotropic pathway modulator in male mice by uncoupling IGF1 production from insulin sensitivity. In summary, 17α-E2 treatment upregulates IGF1 production in wild-type (and N) male mice in what appears to be a GH-dependent fashion, while no effects in female IGF1 production are observed following 17α-E2 treatment.

Cellular senescence represents one of the major risk factors for chronic liver disease and contributes to morbidity, mortality, and increased healthcare spending. A relevant strategy for understanding the role of senescent cells in liver pathogenesis is to use genetic or pharmacological strategies to eliminate senescent cells. The combination of the senolytic drugs, Dasatinib and Quercetin (D+Q), effectively reduces senescent cell burden in multiple tissues, extending both healthspan and lifespan in mice, and alliviating obesity and age‐associated hepatic steatosis. The aim of this study was to investigate effects of D+Q treatment on livers of young and old female mice. A total of 40 mice, 20 young females (3‐months) and 20 old females (18‐months), was divided into 4 groups: Young (Y) mice treated with either D+Q or placebo and old (O) mice treated with D+Q or placebo. The treatment was performed for 3 consecutive days every 2 weeks over 10 weeks. Comparative analysis of hepatic miRNAs indicated that D+Q treatment significantly decreased levels of senescence‐specific miR‐126 expression in livers of old mice treated with D+Q compared to vehicle‐treated old mice (p=0.025), As expected, there was no effect of D+Q treatment in young animals. Analysis of miR‐126 target genes indicated that PI3K gene expression was significantly increased in response to D+Q treatment (p=0.003). Additionally, Akt1 and mTOR mRNA levels were increased in D+Q‐treated mice (p=0.008 and p=0.02, respectively). In summary, our data suggest that the mechanism of PI3K signaling pathway activation upon elimination of senescent cells by treatment with D+Q is mediated through downregulation of senescence‐specific miR‐126. Support or Funding Information This work is supported by National Institutes of Health (NIH) (R56AG061414, R15AG059190 and R03AG059846)