Chaperone-mediated autophagy regulates the pluripotency of embryonic stem cells

Epigenome-Metabolome-Epigenome signaling cascade in cell biological processes

Cell fate determination as a fundamental question in cell biology has been extensively studied at different regulatory levels for many years. However, the mechanisms of multi-level regulation of cell fate determination remain unclear. Recently we have proposed an Epigenome-Metabolome-Epigenome (E-M-E) signaling cascade model to describe the crossover cooperation during mouse somatic cell reprogramming. In this review, we summarize the broad roles of E-M-E signaling cascade in different cell biological processes including cell differentiation and dedifferentiation, cell specialization, cell proliferation and cell pathological processes. Precise E-M-E signaling cascades are critical in these cell biological processes, and it is of worth to explore each step of E-M-E signaling cascade. E-M-E signaling cascade model sheds light on and may open a window to explore the mechanisms of multi-level regulation of cell biological processes.

Role of chaperone-mediated autophagy in the pathophysiology including pulmonary disorders

Autophagy is a highly conserved mechanism of delivering cytoplasmic components for lysosomal degradation. Among the three major autophagic pathways, chaperone-mediated autophagy (CMA) is primarily characterized by its selective nature of protein degradation, which is mediated by heat shock cognate 71 kDa protein (HSC70: also known as HSPA8) recognition of the KFERQ peptide motif in target proteins. Lysosome-associated membrane protein type 2A (LAMP2A) is responsible for substrate binding and internalization to lysosomes, and thus, the lysosomal expression level of LAMP2A is a rate-limiting factor for CMA. Recent advances have uncovered not only physiological but also pathological role of CMA in multiple organs, including neurodegenerative disorders, kidney diseases, liver diseases, heart diseases, and cancers through the accumulation of unwanted proteins or increased degradation of target proteins with concomitant metabolic alterations resulting from CMA malfunction. With respect to pulmonary disorders, the involvement of CMA has been demonstrated in lung cancer and chronic obstructive pulmonary disease (COPD) pathogenesis through regulating apoptosis. Further understanding of CMA machinery may shed light on the molecular mechanisms of refractory disorders and lead to novel treatment modalities through CMA modulation.

Dynamic regulation of mitochondrial-endoplasmic reticulum crosstalk during stem cell homeostasis and aging

Cellular therapy exerts profound therapeutic potential for curing a broad spectrum of diseases. Adult stem cells reside within a specified dynamic niche in vivo, which is essential for continuous tissue homeostatic maintenance through balancing self-renewal with lineage selection. Meanwhile, adult stem cells may be multipotent or unipotent, and are present in both quiescent and actively dividing states in vivo of the mammalians, which may switch to each other state in response to biophysical cues through mitochondria-mediated mechanisms, such as alterations in mitochondrial respiration and metabolism. In general, stem cells facilitate tissue repair after tissue-specific homing through various mechanisms, including immunomodulation of local microenvironment, differentiation into functional cells, cell "empowerment" via paracrine secretion, immunoregulation, and intercellular mitochondrial transfer. Interestingly, cell-source-specific features have been reported between different tissue-derived adult stem cells with distinct functional properties due to the different microenvironments in vivo, as well as differential functional properties in different tissue-derived stem cell-derived extracellular vehicles, mitochondrial metabolism, and mitochondrial transfer capacity. Here, we summarized the current understanding on roles of mitochondrial dynamics during stem cell homeostasis and aging, and lineage-specific differentiation. Also, we proposed potential unique mitochondrial molecular signature features between different source-derived stem cells and potential associations between stem cell aging and mitochondria-endoplasmic reticulum (ER) communication, as well as potential novel strategies for anti-aging intervention and healthy aging.

Auxeticity in biosystems: an exemplification of its effects on the mechanobiology of heterogeneous living cells

Auxeticity (negative Poisson's ratio) is the unique mechanical property found in an extensive variety of materials, such as metals, graphene, composites, polymers, foams, fibers, ceramics, zeolites, silicates and biological tissues. The enhanced mechanical features of the auxetic materials have motivated scientists to design, engineer and manufacture man-made auxetic materials to fully leverage their capabilities in different fields of research applications, including aeronautics, medical, protective equipments, smart sensors, filter cleaning, and so on. Atomic force microscopy (AFM) indentation is one of the most widely used methods for characterizing the mechanical properties and response of the living cells. In this contribution, we highlight main consequences of auxeticity for biosystems and provide a representative example to quantify the effect of nucleus auxeticity on the force response of the embryonic stem cells. A parametric study has been conducted on a heterogeneous stem cell to evaluate the effect of nucleus diameter, nucleus elasticity, indenter's shape and location on the force-indentation curve. The developed model has also been validated with the recently reported experimental studies available in the literature. Our results suggest that the nucleus auxeticity plays a profound role in cell mechanics especially for large size nucleus. We also report the mechanical stresses induced within the hyperelastic cell model under different loading conditions that would be quite useful in decoding the interrelations between mechanical stimuli and cellular behavior of auxetic biosystems. Finally, current and potential areas of applications of our findings for regenerative therapies, tissue engineering, 3 D/4D bioprinting, and the development of meta-biomaterials are discussed.

Characterizing the Low-Dose Effects of Methylmercury on the Early Stages of Embryo Development Using Cultured Human Embryonic Stem Cells

BACKGROUND

Global concerns of methylmercury (MeHg) exposure have been raised, especially on its effects on pregnant women. Recent epidemiological studies have revealed associations between maternal blood/hair MeHg concentrations, adverse pregnancy outcomes, and developmental deficits. However, the underlying mechanisms remain unclear.

OBJECTIVES

In this study, we characterized the effects of MeHg exposure on undifferentiated human embryonic stem cells (hESCs) and extrapolated the effects to human embryonic development.

METHODS

hESCs were exposed to 0, 1, 5, 10, 50, 100 or 200nM MeHg for 24 h or 6 d. Cell adherence and colony formation and expansion were examined under the microscope. Cell attachment, viability/proliferation, apoptosis, stress response, cell cycle, autophagy, and expression of cell lineage marker genes and proteins were measured at the end of exposures.

RESULTS

Our results indicated that exposure to nanomolar concentrations of MeHg was associated with a) higher levels of reactive oxygen species (ROS) and hemeoxygenase-1 (HO-1), suggesting increased stress and adaptive responses; b) lower cellular adhesion, viability/proliferation, and colony formation and expansion; c) higher levels of apoptosis, reflected by higher cleaved caspase-3 expression and Annexin V binding; d) higher levels of cytoskeleton protein α-tubulin expression; e) higher rates of G1/S phase cell cycle arrest; and f) autophagy inhibition, as shown by a lower LC3BII/LC3BI ratio and accumulation of SQSTM1 (p62). These outcomes were accompanied by higher expressions of self-renewal genes or proteins or both, including OCT4, SOX2, NANOG, and cytokine receptor IL6ST, as well as pluripotency and the cell fate regulator cyclin D1.

DISCUSSION

These results revealed that under the selection pressure of exposure to low doses of MeHg, some hESCs underwent apoptosis, whereas others adapted and survived with enhanced self-renewal gene expression and specific morphological phenotypes. Findings from the present study provide in vitro evidence that low doses of MeHg adversely affect hESCs when exposed during a period of time that models embryonic pre-, during, and early postimplantation stages. https://doi.org/10.1289/EHP7349.

Intravenously Infused Stem Cells for Cancer Treatment

Despite the recent influx of immunotherapies and small molecule drugs to treat tumors, cancer remains a leading cause of death in the United States, in large part due to the difficulties of treating metastatic cancer. Stem cells, which are inherently tumoritropic, provide a useful drug delivery vehicle to target both primary and metastatic tumors. Intravenous infusions of stem cells carrying or secreting therapeutic payloads show significant promise in the treatment of cancer. Stem cells may be engineered to secrete cytotoxic products, loaded with oncolytic viruses or nanoparticles containing small molecule drugs, or conjugated with immunotherapies. Herein we describe these preclinical and clinical studies, discuss the distribution and migration of stem cells following intravenous infusion, and examine both the limitations of and the methods to improve the migration and therapeutic efficacy of tumoritropic, therapeutic stem cells.

Induced pluripotent stem cell technology: trends in molecular biology, from genetics to epigenetics

Induced pluripotent stem cell (iPSC) technology, based on autologous cells' reprogramming to the embryonic state, is a new approach in regenerative medicine. Current advances in iPSC technology have opened up new avenues for multiple applications, from basic research to clinical therapy. Thus, conducting iPSC trials have attracted increasing attention and requires an extensive understanding of the molecular basis of iPSCs. Since iPSC reprogramming is based on the methods inducing the expression of specific genes involved in pluripotency states, it can be concluded that iPSC reprogramming is strongly influenced by epigenetics. In this study, we reviewed the molecular basis of reprogramming, including the reprogramming factors (OCT4, SOX2, KLF4, c-MYC, NANOG, ESRRB, LIN28 as well as their regulatory networks), applied vectors (retroviral vectors, adenoviral vectors, Sendaiviral vectors, episomal plasmids, piggyBac, simple vectors, etc.) and epigenetic modifications (miRNAs, histones and DNA methylation states) to provide a comprehensive guide for reprogramming studies.

Gene Regulation and Cellular Metabolism: An Essential Partnership

It is recognized that cell metabolism is tightly connected to other cellular processes such as regulation of gene expression. Metabolic pathways not only provide the precursor molecules necessary for gene expression, but they also provide ATP, the primary fuel driving gene expression. However, metabolic conditions are highly variable since nutrient uptake is not a uniform process. Thus, cells must continually calibrate gene expression to their changing metabolite and energy budgets. This review discusses recent advances in understanding the molecular and biophysical mechanisms that connect metabolism and gene regulation as cells navigate their growth, proliferation, and differentiation. Particular focus is given to these mechanisms in the context of organismal development.

Mechanisms for Modulating Anoikis Resistance in Cancer and the Relevance of Metabolic Reprogramming

The attachment of cells to the extracellular matrix (ECM) is the hallmark of structure–function stability and well-being. ECM detachment in localized tumors precedes abnormal dissemination of tumor cells culminating in metastasis. Programmed cell death (PCD) is activated during tumorigenesis to clear off ECM-detached cells through “anoikis.” However, cancer cells develop several mechanisms for abrogating anoikis, thus promoting their invasiveness and metastasis. Specific factors, such as growth proteins, pH, transcriptional signaling pathways, and oxidative stress, have been reported as drivers of anoikis resistance, thus enhancing cancer proliferation and metastasis. Recent studies highlighted the key contributions of metabolic pathways, enabling the cells to bypass anoikis. Therefore, understanding the mechanisms driving anoikis resistance could help to counteract tumor progression and prevent metastasis. This review elucidates the dynamics employed by cancer cells to impede anoikis, thus promoting proliferation, invasion, and metastasis. In addition, the authors have discussed other metabolic intermediates (especially amino acids and nucleotides) that are less explored, which could be crucial for anoikis resistance and metastasis.

From Autonomy to Integration, From Integration to Dynamically Balanced Integrated Co-existence: Non-aging as the Third Stage of Development

Reversible senescence at the cellular level emerged together with tissue specialization in Metazoans. However, this reversibility (ability to permanently rejuvenate) through recapitulation of early stages of development, was originally a part of ontogenesis, since the pressure of integrativeness was not dominant. The complication of specialization in phylogenesis narrowed this "freedom of maneuver", gradually "truncating" remorphogenesis to local epimorphosis and further up to the complete disappearance of remorphogenesis from the ontogenesis repertoire. This evolutionary trend transformed cellular senescence into organismal aging and any recapitulation of autonomy into carcinogenesis. The crown of specialization, Homo sapiens, completed this post-unicellular stage of development, while in the genome all the potential for the next stage of development, which can be called the stage of balanced coexistence of autonomous and integrative dominants within a single whole. Here, completing the substantiation of the new section of developmental biology, we propose to call it Developmental Biogerontology.

Deciphering the autophagy regulatory network via single-cell transcriptome analysis reveals a requirement for autophagy homeostasis in spermatogenesis

Background: Autophagy has been implicated as a crucial component in spermatogenesis, and autophagy dysfunction can lead to reproductive disorders in animal models, including yeast, C. elegans and mice. However, the sophisticated transcriptional networks of autophagic genes throughout human spermatogenesis and their biological significance remain largely uncharacterized. Methods: We profiled the transcriptional signatures of autophagy-related genes during human spermatogenesis by assessing specimens from nine fertile controls (including two normal persons and seven obstructive azoospermia (OA) patients) and one nonobstructive azoospermia (NOA) patient using single-cell RNA sequencing (scRNA-seq) analysis. Dysregulation of autophagy was confirmed in two additional NOA patients by immunofluorescence staining. Gene knockdown was used to identify the role of Cst3 in autophagy during spermatogenesis. Results: Our data uncovered a unique, global stage-specific enrichment of autophagy-related genes. Human-mouse comparison analysis revealed that the stage-specific expression pattern of autophagy-related genes was highly conserved in mammals. More importantly, dysregulation of some clusters of autophagy-related genes was observed in NOA patients, suggesting the association of autophagy with male infertility. Cst3, a human-mouse conserved and autophagy-related gene that is actively expressed in spermatogonia and early spermatocytes, was found to regulate spermatogonial stem cell (SSC) maintenance and subsequent male germ cell development. Knockdown of Cst3 increased autophagic activity in mouse SSCs and subsequently suppressed the transcription of SSC core factors such as Oct4, Id1, and Nanos3, which could be efficiently rescued by manipulating autophagic activity. Conclusions: Our study provides comprehensive insights into the global transcriptional signatures of autophagy-related genes and confirms the importance of autophagy homeostasis in SSC maintenance and normal spermatogenesis, opening new avenues for further dissecting the significance of the autophagy regulatory network in spermatogenesis as well as male infertility.

Chaperone-mediated autophagy sustains haematopoietic stem-cell function

The activation of mostly quiescent haematopoietic stem cells (HSCs) is a prerequisite for life-long production of blood cells¹. This process requires major molecular adaptations to allow HSCs to meet the regulatory and metabolic requirements for cell division^2-4. The mechanisms that govern cellular reprograming upon stem-cell activation, and the subsequent return of stem cells to quiescence, have not been fully characterized. Here we show that chaperone-mediated autophagy (CMA)⁵, a selective form of lysosomal protein degradation, is involved in sustaining HSC function in adult mice. CMA is required for protein quality control in stem cells and for the upregulation of fatty acid metabolism upon HSC activation. We find that CMA activity in HSCs decreases with age and show that genetic or pharmacological activation of CMA can restore the functionality of old mouse and human HSCs. Together, our findings provide mechanistic insights into a role for CMA in sustaining quality control, appropriate energetics and overall long-term HSC function. Our work suggests that CMA may be a promising therapeutic target for enhancing HSC function in conditions such as ageing or stem-cell transplantation.

Chaperone Mediated Autophagy Substrates and Components in Cancer

Chaperone-mediated autophagy (CMA) represents a specific way of lysosomal protein degradation and contrary to macro and microautophagy is independent of vesicles formation. The role of CMA in different physiopathological processes has been studied for several years. In cancer, alterations of the CMA principal components, Hsc70 and Lamp2A protein and mRNA levels, have been described in malignant cells. However, changes in the expression levels of these CMA components are not always associated with changes in CMA activity and their biological significance must be carefully interpreted case by case. The objective of this review is to discuss whether altering the CMA activity, CMA substrates or CMA components is accurate to avoid cancer progression. In particular, this review will discuss about the evidences in which alterations CMA components Lamp2A and Hsc70 are associated or not with changes in CMA activity in different cancer types. This analysis will help to better understand the role of CMA activity in cancer and to elucidate whether CMA can be considered as target for therapeutics. Further, it will help to define whether the attention of the investigation should be focused on Lamp2A and Hsc70 because they can have an independent role in cancer progression beyond of their participation in altered CMA activity.

The intrinsic proteostasis network of stem cells

The proteostasis network adjusts protein composition and maintains protein integrity, which are essential processes for cell function and viability. Current efforts, given their intrinsic characteristics, regenerative potential and fundamental biological functions, have been directed to define proteostasis of stem cells. These insights demonstrate that embryonic stem cells and induced pluripotent stem cells exhibit an endogenous proteostasis network that not only modulates their pluripotency and differentiation but also provides a striking ability to suppress aggregation of disease-related proteins. Moreover, recent findings establish a central role of enhanced proteostasis to prevent the aging of somatic stem cells in adult organisms. Notably, proteostasis is also required for the biological purpose of adult germline stem cells, that is to be passed from one generation to the next. Beyond these links between proteostasis and stem cell function, we also discuss the implications of these findings for disease, aging, and reproduction.