Biological activity and in vivo half-life of pro-activin A in male rats

Activity-dependent regulation of microglia numbers by pyramidal cells during development shape cortical functions

Beyond their role as immune sentinels, microglia are actively involved in establishing and maintaining cortical circuits. Alteration in microglial numbers has been associated with abnormal behaviors akin to those observed in neurodevelopmental disorders. Consequently, establishing the appropriate microglial numbers during development is crucial for ensuring normal cortical function. Here, we uncovered a dynamic relationship between pyramidal cells and microglia that tunes microglial numbers and development through distinct phases of mouse postnatal development. Changes in pyramidal cell activity during development induce differential release of activity-dependent proteins such as Activin A, which, in turn, adjusts microglial numbers accordingly. Decoupling of this relationship not only changes microglial numbers but has a long-term consequence on their role as synaptic organizers, which ultimately affects cortical function. Our findings reveal that microglia adapt their numbers to changes in pyramidal cell activity during a critical time window in development, consequently adjusting their numbers and function to the demands of the developing local circuits.

Stepwise release of Activin-A from its inhibitory prodomain is modulated by cysteines and requires furin coexpression to promote melanoma growth

The Activin-A precursor dimer can be cleaved by furin, but how this proteolytic maturation is regulated in vivo and how it facilitates access to signaling receptors is unclear. Here, analysis in a syngeneic melanoma grafting model shows that without furin coexpression, Activin-A failed to accelerate tumor growth, correlating with failure of one or both subunits to undergo cleavage in signal-sending cells, even though compensatory processing by host cells nonetheless sustained elevated circulating Activin-A levels. In reporter assays, furin-independent cleavage of one subunit enabled juxtacrine Activin-A signaling, whereas completion of proteolytic maturation by coexpressed furin or by recipient cells stimulated contact-independent activity, crosstalk with BMP receptors, and signal inhibition by follistatin. Mechanistically, Activin-A processing was modulated by allosteric disulfide bonds flanking the furin site. Disruption of these disulfide linkages with the prodomain enabled Activin-A binding to cognate type II receptors independently of proteolytic maturation. Stepwise proteolytic maturation is a novel mechanism to control Activin-A protein interactions and signaling.

Improving Circulation Half-Life of Therapeutic Candidate N-TIMP2 by Unfolded Peptide Extension

Matrix metalloproteinases (MMPs) are significant drivers of many diseases, including cancer, and are established targets for drug development. Tissue inhibitors of metalloproteinases (TIMPs) are endogenous MMP inhibitors and are being pursued for the development of anti-MMP therapeutics. TIMPs possess many attractive properties for drug candidates, such as complete MMP inhibition, low toxicity, low immunogenicity, and high tissue permeability. However, a major challenge with TIMPs is their rapid clearance from the bloodstream due to their small size. This study explores a method for extending the plasma half-life of the N-terminal domain of TIMP2 (N-TIMP2) by appending it with a long, intrinsically unfolded tail containing Pro, Ala, and Thr (PATylation). We designed and produced two PATylated N-TIMP2 constructs with tail lengths of 100 and 200 amino acids (N-TIMP2-PAT100 and N-TIMP2-PAT200). Both constructs demonstrated higher apparent molecular weights and retained high inhibitory activity against MMP-9. N-TIMP2-PAT200 significantly increased plasma half-life in mice compared to the non-PATylated variant, enhancing its therapeutic potential. PATylation offers distinct advantages for half-life extension, such as fully genetic encoding, monodispersion, and biodegradability. It can be easily applied to N-TIMP2 variants engineered for high affinity and selectivity toward individual MMPs, creating promising candidates for drug development against MMP-related diseases.

Mathematical Modeling of Tumor Immune Interactions: The Role of Anti-FGFR and Anti-PD-1 in the Combination Therapy

Bladder cancer poses a significant global health burden with high incidence and recurrence rates. This study addresses the therapeutic challenges in advanced bladder cancer, focusing on the competitive mechanisms of ligand or drug binding to receptors. We developed a refined mathematical model that integrates the dynamics of tumor cells and immune responses, particularly targeting fibroblast growth factor receptor 3 (FGFR3) and immune checkpoint inhibitors (ICIs). This study contributes to understanding combination therapies by elucidating the competitive binding dynamics and quantifying the synergistic effects. The findings highlight the importance of personalized immunotherapeutic strategies, considering factors such as drug dosage, dosing schedules, and patient-specific parameters. Our model further reveals that ligand-independent activated-state receptors are the most essential drivers of tumor proliferation. Moreover, we found that PD-L1 expression rate was more important than PD-1 in driving the dynamic evolution of tumor and immune cells. The proposed mathematical model provides a comprehensive framework for unraveling the complexities of combination therapies in advanced bladder cancer. As research progresses, this multidisciplinary approach contributes valuable insights toward optimizing therapeutic strategies and advancing cancer treatment paradigms.

Improving Circulation Half-Life of Therapeutic Candidate N-TIMP2 by Unfolded Peptide Extension

Matrix Metalloproteinases (MMPs) are drivers of many diseases including cancer and are established targets for drug development. Tissue inhibitors of metalloproteinases (TIMPs) are human proteins that inhibit MMPs and are being pursued for the development of anti-MMP therapeutics. TIMPs possess many attractive properties of a drug candidate, such as complete MMP inhibition, low toxicity and immunogenicity, high tissue permeability and others. A major challenge with TIMPs, however, is their formulation and delivery, as these proteins are quickly cleared from the bloodstream due to their small size. In this study, we explore a new method for plasma half-life extension for the N-terminal domain of TIMP2 (N-TIMP2) through appending it with a long intrinsically unfolded tail containing a random combination of Pro, Ala, and Thr (PATylation). We design, produce and explore two PATylated N-TIMP2 constructs with a tail length of 100- and 200-amino acids (N-TIMP2-PAT100 and N-TIMP2-PAT200, respectively). We demonstrate that both PATylated N-TIMP2 constructs possess apparent higher molecular weights compared to the wild-type protein and retain high inhibitory activity against MMP-9. Furthermore, when injected into mice, N-TIMP2-PAT200 exhibited a significant increase in plasma half-life compared to the non-PATylated variant, enhancing the therapeutic potential of the protein. Thus, we establish that PATylation could be successfully applied to TIMP-based therapeutics and offers distinct advantages as an approach for half-life extension, such as fully genetic encoding of the gene construct, mono-dispersion, and biodegradability. Furthermore, PATylation could be easily applied to N-TIMP2 variants engineered to possess high affinity and selectivity toward individual MMP family members, thus creating attractive candidates for drug development against MMP-related diseases.

Endogenous repair theory enriches construction strategies for orthopaedic biomaterials: a narrative review

The development of tissue engineering has led to new strategies for mitigating clinical problems; however, the design of the tissue engineering materials remains a challenge. The limited sources and inadequate function, potential risk of microbial or pathogen contamination, and high cost of cell expansion impair the efficacy and limit the application of exogenous cells in tissue engineering. However, endogenous cells in native tissues have been reported to be capable of spontaneous repair of the damaged tissue. These cells exhibit remarkable plasticity, and thus can differentiate or be reprogrammed to alter their phenotype and function after stimulation. After a comprehensive review, we found that the plasticity of these cells plays a major role in establishing the cell source in the mechanism involved in tissue regeneration. Tissue engineering materials that focus on assisting and promoting the natural self-repair function of endogenous cells may break through the limitations of exogenous seed cells and further expand the applications of tissue engineering materials in tissue repair. This review discusses the effects of endogenous cells, especially stem cells, on injured tissue repairing, and highlights the potential utilisation of endogenous repair in orthopaedic biomaterial constructions for bone, cartilage, and intervertebral disc regeneration.

Differentiation of Human Pluripotent Stem Cells Into Definitive Endoderm Cells in Various Flexible Three-Dimensional Cell Culture Systems: Possibilities and Limitations

The generation of human stem cell-derived spheroids and organoids represents a major step in solving numerous medical, pharmacological, and biological challenges. Due to the advantages of three-dimensional (3D) cell culture systems and the diverse applications of human pluripotent stem cell (iPSC)-derived definitive endoderm (DE), we studied the influence of spheroid size and 3D cell culture systems on spheroid morphology and the effectiveness of DE differentiation as assessed by quantitative PCR (qPCR), flow cytometry, immunofluorescence, and computational modeling. Among the tested hydrogel-based 3D systems, we found that basement membrane extract (BME) hydrogel could not retain spheroid morphology due to dominant cell-matrix interactions. On the other hand, we found that nanofibrillar cellulose (NFC) hydrogel could maintain spheroid morphology but impeded growth factor diffusion, thereby negatively affecting cell differentiation. In contrast, suspension culture provided sufficient mass transfer and was demonstrated by protein expression assays, morphological analyses, and mathematical modeling to be superior to the hydrogel-based systems. In addition, we found that spheroid size was reversely correlated with the effectiveness of DE formation. However, spheroids of insufficient sizes failed to retain 3D morphology during differentiation in all the studied culture conditions. We hereby demonstrate how the properties of a chosen biomaterial influence the differentiation process and the importance of spheroid size control for successful human iPSC differentiation. Our study provides critical parametric information for the generation of human DE-derived, tissue-specific organoids in future studies.

Activin A Modulates Inflammation in Acute Pancreatitis and Strongly Predicts Severe Disease Independent of Body Mass Index

Acute pancreatitis (AP) is a healthcare challenge with considerable mortality. Treatment is limited to supportive care, highlighting the need to investigate disease drivers and prognostic markers. Activin A is an established mediator of inflammatory responses, and its serum levels correlate with AP severity. We hypothesized that activin A is independent of body mass index (BMI) and is a targetable promoter of the AP inflammatory response.

Leveraging Quantitative Systems Pharmacology Approach into Development of Human Recombinant Follistatin Fusion Protein for Duchenne Muscular Dystrophy

Quantitative understanding about the dynamics of drug-target interactions in biological systems is essential, especially in rare disease programs with small patient populations. Follistatin, by antagonism of myostatin and activin, which are negative regulators of skeletal muscle and inflammatory response, is a promising therapeutic target for Duchenne Muscular Dystrophy. In this study, we constructed a quantitative systems pharmacology model for FS-EEE-Fc, a follistatin recombinant protein to investigate its efficacy from dual target binding, and, subsequently, to project its human efficacious dose. Based on model simulations, with an assumed efficacy threshold of 7-10% muscle volume increase, 3-5 mg/kg weekly dosing of FS-EEE-Fc is predicted to achieve meaningful clinical outcome. In conclusion, the study demonstrated an application of mechanism driven approach at early stage of a rare disease drug development to support lead compound optimization, enable human dose, pharmacokinetics, and efficacy predictions.

Structural biology of the TGFβ family

The transforming growth factor beta (TGFβ) signaling pathway orchestrates a wide breadth of biological processes, ranging from bone development to reproduction. Given this, there has been a surge of interest from the drug development industry to modulate the pathway – at several points. This review discusses and provides additional context for several layers of the TGFβ signaling pathway from a structural biology viewpoint. The combination of structural techniques coupled with biophysical studies has provided a foundational knowledge of the molecular mechanisms governing this high impact, ubiquitous pathway, underlying many of the current therapeutic pursuits. This work seeks to consolidate TGFβ-related structural knowledge and educate other researchers of the apparent gaps that still prove elusive. We aim to highlight the importance of these structures and provide the contextual information to understand the contribution to the field, with the hope of advancing the discussion and exploration of the TGFβ signaling pathway.

Impact statement

The transforming growth factor beta (TGFβ) signaling pathway is a multifacetted and highly regulated pathway, forming the underpinnings of a large range of biological processes. Here, we review and consolidate the key steps in TGFβ signaling using literature rooted in structural and biophysical techniques, with a focus on molecular mechanisms and gaps in knowledge. From extracellular regulation to ligand–receptor interactions and intracellular activation cascades, we hope to provide an introductory base for understanding the TGFβ pathway as a whole.

Identification and characterization of a novel heparan sulfate-binding domain in Activin A longest variants and implications for function

Activins regulate numerous processes including inflammation and are synthesized as precursors consisting of a long N-terminal pro-region and a mature protein. Genomic human databases currently list three activin A (Act A) variants termed X1, X2 and X3. The X3 variant is the shortest, lacks N-terminal segments present in X1 and X2, and has been the focus of most past literature. Here, we asked whether these variants are expressed by human cells and tissues and what structural features are contained within their pro-regions. Human monocytic-like cells THP1 and U937 expressed X1 and X2 variants after exposure to phorbol ester or granulocyte-macrophage colony-stimulating factor, while X2 transcripts were present in placenta. Expression vectors encoding full length X2 or X3 variants resulted in production and secretion of biologically active Act A from cultured cells. Previous studies reported a putative HS-binding domain (HBD) in the X3 pro-region. Here, we identified a novel HBD with consensus HS-binding motifs near the N-terminal end of X1 and X2 pro-regions. Peptides encompassing this new domain interacted with substrate-bound HS with nanomolar affinity, while peptides from putative X3 HBD did not. In good agreement, full length X2 pro-region interacted with heparin-agarose, while the X3 pro-region did not. In sum, our study reveals that Act A variants are expressed by inflammatory cells and placenta and yield biological activity. The high affinity HBD in X1 and X2 pro-region and its absence in X3 could greatly influence overall Act A distribution, availability and activity in physiological and pathological circumstances.

Activin A improves retinal pigment epithelial cell survival on stiff but not soft substrates

In several retinal degenerative disease pathologies, such as dry age-related macular degeneration (AMD), the retinal pigment epithelium (RPE) cell monolayer becomes dysfunctional. Promising tissue engineering treatment approaches implant RPE cells on scaffolds into the subretinal space. However, these approaches are not without challenges. Two major challenges that must be addressed are RPE dedifferentiation and the inflammatory response to cell/scaffold implantation. Design and optimization of scaffold cues for the purpose of RPE transplantation remain relatively unexplored, specifically the mechanical properties of the scaffolds. Prior work from our group indicated that by varying substrate moduli significant differences could be induced in cell cytoskeleton structure, cellular activity, and expression of inflammatory markers. We hypothesized that Activin A would provide rescue effects for cells demonstrating dedifferentiated characteristics. Results demonstrated that for cells on low modulus scaffolds, the mechanical environment was the dominating factor and Activin A was unable to rescue these cells. However, Activin A did demonstrate rescue effects for cells on high modulus scaffolds. This finding indicates that when cultured on scaffolds with an appropriate modulus, exogenous factors, such as Activin A, can improve RPE cell expression, morphology, and activity, while an inappropriate scaffold modulus can have devastating effects on RPE survival regardless of chemical stimulation. These findings have broad implications for the design and optimization of scaffolds for long-term successful RPE transplantation. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2871-2880, 2018.

Effect of T-2 toxin-injected shrimp muscle extracts on mouse macrophage cells (RAW264.7)

Following intramuscular injections of 0.1 mL, 3 mg kg^-1BW^-1(1/10 LD₅₀) T-2 toxin (T-2), the tissue concentration of T-2 in shrimp was quantitatively detected using LC-MS/MS. The biological half-time (t_1/2) of T-2 in blood was 40.47 ± 0.24 min. The highest number of intramuscular T-2 shrimp could tolerate when given at blood t_1/2 intervals was 4. The shrimps which were injected 5 T-2 died. The T-2 toxin highest accumulation was 0.471 ± 0.012 ng g^-1BW^-1. The effect of toxic shrimp muscle subjected to different processing conditions (high pressure, trifluoroacetic acid, acid and alkali digestions, artificial digestive juice [to simulate exposure to gastric and intestinal juices]) on mouse macrophage cells (RAW267.4) were evaluated by the MTT assay. The inhibition ratio of 2% muscle extract on RAW267.4 was 85.70 ± 2.63%. The immunocytotoxicity of muscle extracts to RAW264.7 was highest in muscle extracts subjected to physical and chemical digestion (high pressure > NaOH > trifluoroacetic acid > 0.02 M HCl > 0.2 M HCl > controls), and also artificial digestion (artificial intestinal juice > artificial gastric juice > N type intestinal juice > N type gastric liquid > controls). Results showed that high-pressure and artificial intestinal juice were most effective in the release of modified T-2 to free T-2 thus enhancing toxicity. These results can be interpreted as measurement of T-2 in food being of little value because of enhanced toxicity of T-2-contaminated food as they pass through the gastrointestinal tract.

The Use of Gene Ontology Term and KEGG Pathway Enrichment for Analysis of Drug Half-Life

A drug's biological half-life is defined as the time required for the human body to metabolize or eliminate 50% of the initial drug dosage. Correctly measuring the half-life of a given drug is helpful for the safe and accurate usage of the drug. In this study, we investigated which gene ontology (GO) terms and biological pathways were highly related to the determination of drug half-life. The investigated drugs, with known half-lives, were analyzed based on their enrichment scores for associated GO terms and KEGG pathways. These scores indicate which GO terms or KEGG pathways the drug targets. The feature selection method, minimum redundancy maximum relevance, was used to analyze these GO terms and KEGG pathways and to identify important GO terms and pathways, such as sodium-independent organic anion transmembrane transporter activity (GO:0015347), monoamine transmembrane transporter activity (GO:0008504), negative regulation of synaptic transmission (GO:0050805), neuroactive ligand-receptor interaction (hsa04080), serotonergic synapse (hsa04726), and linoleic acid metabolism (hsa00591), among others. This analysis confirmed our results and may show evidence for a new method in studying drug half-lives and building effective computational methods for the prediction of drug half-lives.

Structure and activation of pro-activin A

Activins are growth factors with multiple roles in the development and homeostasis. Like all TGF-β family of growth factors, activins are synthesized as large precursors from which mature dimeric growth factors are released proteolytically. Here we have studied the activation of activin A and determined crystal structures of the unprocessed precursor and of the cleaved pro-mature complex. Replacing the natural furin cleavage site with a HRV 3C protease site, we show how the protein gains its bioactivity after proteolysis and is as active as the isolated mature domain. The complex remains associated in conditions used for biochemical analysis with a dissociation constant of 5 nM, but the pro-domain can be actively displaced from the complex by follistatin. Our high-resolution structures of pro-activin A share features seen in the pro-TGF-β1 and pro-BMP-9 structures, but reveal a new oligomeric arrangement, with a domain-swapped, cross-armed conformation for the protomers in the dimeric protein.

Activins are members of the TGF-β family of growth factors that are processed from precursors into the mature proteins. Here, the authors use structural biology and biochemistry to examine the protein domain organisation and gain insights into the activation of pro-activin A.