Biology subjects

Signer, R. A.

Publications and source records attributed to Signer, R. A..

3 recordsLinked to original sources

bioRxiv2025

Proteostasis Remodeling Across Development Defines Fetal, Neonatal, and Adult Hematopoietic Stem Cell States

Hematopoietic stem cells (HSCs) must preserve protein homeostasis (proteostasis) despite dramatic changes in proliferative and biosynthetic demands during development, yet how proteostasis is regulated across these transitions is poorly understood. Here, we show that fetal and neonatal HSCs operate through distinct, stage-specific proteostasis programs that differ fundamentally from those in adulthood. Using quantitative in vivo assays spanning embryonic through adult stages, we uncover an unanticipated decoupling between protein synthesis and protein quality control during development, revealing that fetal and neonatal HSCs employ specialized mechanisms to safeguard proteome integrity under developmental stress. Developing HSCs experience a distinctive proteostasis landscape characterized by elevated protein synthesis, increased unfolded protein burden, and selective engagement of stress-buffering and protein degradation pathways that are largely dispensable in young adult HSCs. Disruption of these pathways compromises early life HSC function and long-term fitness, establishing proteostasis control as a key regulator of stem cell maturation. These findings define previously unrecognized mechanisms by which HSCs manage the proteome during early life and reveal fundamental principles governing stem cell proteostasis across ontogeny.

developmental biology↗

bioRxiv2025

Proteostasis Stress Drives Stem Cell Aging, Clonal Hematopoiesis and Leukemia

Aging is the primary risk factor for clonal hematopoiesis and the development of hematologic malignancies (1-5), yet the selective pressures that shape stem cell behavior and clonal expansion during aging remain poorly defined. Here, we identify proteostasis stress as a central driver of hematopoietic stem cell (HSC) aging and clonal evolution. We show that Heat shock factor 1 (Hsf1) is activated in aging HSCs to preserve proteostasis and sustain self-renewal. However, this physiological, age-associated adaptive mechanism is co-opted by pre-leukemic Dnmt3a-mutant HSCs to resist proteostasis and inflammatory stress required to fuel clonal expansion during aging. In the context of co-occurring Dnmt3a and Nras mutations, which are frequently observed in human acute myeloid leukemia (AML) (6-13), mutant HSCs and progenitors exhibit heightened dependence on Hsf1 for expansion, malignant transformation and disease progression. Loss of Hsf1, or disruption of proteostasis, impairs expansion of mutant progenitors, delays leukemia onset, and prolongs survival. Together, these findings reveal proteostasis as a key constraint in the aging hematopoietic system that imposes a selective bottleneck. Hsf1 activation enables both physiological adaptation in aging stem cells and pathological clonal outgrowth in pre-leukemic and leukemic states, establishing proteostasis control as a pivotal mechanism linking stem cell aging to clonal hematopoiesis and malignancy.

cancer biology↗

bioRxiv2024

Inhibition of RhoA-mediated secretory autophagy in megakaryocytes mitigates myelofibrosis in mice

Megakaryocytes (MKs) are large, polyploid cells that contribute to bone marrow homeostasis through the secretion of cytokines such as transforming growth factor {beta}1 (TGF{beta}1). During neoplastic transformation, immature MKs accumulate in the bone marrow where they induce fibrotic remodeling ultimately resulting in myelofibrosis. Current treatment strategies aim to prevent MK hyperproliferation, however, little is understood about the potential of targeting dysregulated cytokine secretion from neoplastic MKs as a novel therapeutic avenue. Unconventional secretion of TGF{beta}1 as well as interleukin 1{beta} (IL1{beta}) via secretory autophagy occurs in cells other than MKs, which prompted us to investigate whether similar mechanisms are utilized by MKs. Here, we identified that TGF{beta}1 strongly co-localized with the autophagy marker light chain 3B in native MKs. Disrupting secretory autophagy by inhibiting the small GTPase RhoA or its downstream effector Rho kinase (ROCK) markedly reduced TGF{beta}1 and IL1{beta} secretion in vitro. In vivo, conditional deletion of the essential autophagy gene Atg5 from the hematopoietic system limited megakaryocytosis and aberrant cytokine secretion in an MPLW515L-driven transplant model. Similarly, mice with a selective deletion of Rhoa from the MK and platelet lineage were protected from progressive fibrosis. Finally, disease hallmarks in MPLW515L-transplanted mice were attenuated upon treatment with the autophagy inhibitor hydroxychloroquine or the ROCK inhibitor Y27632, either as monotherapy or in combination with the JAK2 inhibitor ruxolitinib. Overall, our data indicate that aberrant cytokine secretion is dependent on secretory autophagy downstream of RhoA, targeting of which represents a novel therapeutic avenue in the treatment of myelofibrosis. One Sentence SummaryTGF{beta}1 is released from megakaryocytes via RhoA-mediated secretory autophagy, and targeting this process can alleviate fibrosis progression in a preclinical mouse model of myelofibrosis.

cell biology↗