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DiIorio SE, Young B, Parker JB, Griffin MF, Longaker MT. Understanding Tendon Fibroblast Biology and Heterogeneity. Biomedicines 2024; 12:859. [PMID: 38672213 PMCID: PMC11048404 DOI: 10.3390/biomedicines12040859] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2024] [Revised: 04/06/2024] [Accepted: 04/08/2024] [Indexed: 04/28/2024] Open
Abstract
Tendon regeneration has emerged as an area of interest due to the challenging healing process of avascular tendon tissue. During tendon healing after injury, the formation of a fibrous scar can limit tendon strength and lead to subsequent complications. The specific biological mechanisms that cause fibrosis across different cellular subtypes within the tendon and across different tendons in the body continue to remain unknown. Herein, we review the current understanding of tendon healing, fibrosis mechanisms, and future directions for treatments. We summarize recent research on the role of fibroblasts throughout tendon healing and describe the functional and cellular heterogeneity of fibroblasts and tendons. The review notes gaps in tendon fibrosis research, with a focus on characterizing distinct fibroblast subpopulations in the tendon. We highlight new techniques in the field that can be used to enhance our understanding of complex tendon pathologies such as fibrosis. Finally, we explore bioengineering tools for tendon regeneration and discuss future areas for innovation. Exploring the heterogeneity of tendon fibroblasts on the cellular level can inform therapeutic strategies for addressing tendon fibrosis and ultimately reduce its clinical burden.
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Affiliation(s)
- Sarah E. DiIorio
- Hagey Laboratory for Pediatric Regenerative Medicine, Division of Plastic and Reconstructive Surgery, Department of Surgery, Stanford University School of Medicine, Stanford, CA 94305, USA; (S.E.D.); (B.Y.); (J.B.P.); (M.F.G.)
- Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Bill Young
- Hagey Laboratory for Pediatric Regenerative Medicine, Division of Plastic and Reconstructive Surgery, Department of Surgery, Stanford University School of Medicine, Stanford, CA 94305, USA; (S.E.D.); (B.Y.); (J.B.P.); (M.F.G.)
| | - Jennifer B. Parker
- Hagey Laboratory for Pediatric Regenerative Medicine, Division of Plastic and Reconstructive Surgery, Department of Surgery, Stanford University School of Medicine, Stanford, CA 94305, USA; (S.E.D.); (B.Y.); (J.B.P.); (M.F.G.)
- Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Michelle F. Griffin
- Hagey Laboratory for Pediatric Regenerative Medicine, Division of Plastic and Reconstructive Surgery, Department of Surgery, Stanford University School of Medicine, Stanford, CA 94305, USA; (S.E.D.); (B.Y.); (J.B.P.); (M.F.G.)
| | - Michael T. Longaker
- Hagey Laboratory for Pediatric Regenerative Medicine, Division of Plastic and Reconstructive Surgery, Department of Surgery, Stanford University School of Medicine, Stanford, CA 94305, USA; (S.E.D.); (B.Y.); (J.B.P.); (M.F.G.)
- Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA
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Avey AM, Valdez O, Baar K. Characterization of an in vitro engineered ligament model. Matrix Biol Plus 2024; 21:100140. [PMID: 38235356 PMCID: PMC10792631 DOI: 10.1016/j.mbplus.2023.100140] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Revised: 12/10/2023] [Accepted: 12/20/2023] [Indexed: 01/19/2024] Open
Abstract
In vivo tendon and ligament research can be limited by the difficultly of obtaining tissue samples that can be biochemically analyzed. In this study, we characterize the most widely used in vitro engineered ligament model. Despite previous works suggesting multiple passages change gene expression in 2D primary tenocytes, we found no relationship between passage number and expression of classical tendon fibroblast markers across different biological donors. When engineered into 3D ligaments, there was an increase in maximal tensile load between 7 and 14 days in culture, that corresponded with an increase in collagen content. By contrast, percent collagen increased logarithmically from Day 7 to Day 14, and this was similar to the increase in the modulus of the tissue. Importantly, there was no relationship between passage number and mechanical function or collagen content in the two independent donors tested. These results suggest that the model develops quickly and is reliable across differing passage numbers. This provides the field with the ability to 1) consistently determine functional changes of interventions out to passage number 10; and 2) to time interventions to the appropriate developmental stage: developing/regenerating (Day 7) or mature (Day 14) tissue.
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Affiliation(s)
- Alec M. Avey
- Department of Neurobiology, Physiology and Behavior, University of California Davis, Davis, CA 95616, United States
| | - Omar Valdez
- Department of Neurobiology, Physiology and Behavior, University of California Davis, Davis, CA 95616, United States
| | - Keith Baar
- Department of Neurobiology, Physiology and Behavior, University of California Davis, Davis, CA 95616, United States
- Department of Physiology and Membrane Biology, University of California Davis, Davis, CA 95616, United States
- VA Northern California Health Care System, Mather, CA 95655, USA
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Avey AM, Devos F, Roberts AG, Essawy ESE, Baar K. Inhibiting JAK1, not NF-κB, reverses the effect of pro-inflammatory cytokines on engineered human ligament function. Matrix Biol 2024; 125:100-112. [PMID: 38151137 DOI: 10.1016/j.matbio.2023.12.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Revised: 12/23/2023] [Accepted: 12/23/2023] [Indexed: 12/29/2023]
Abstract
The role of inflammation in chronic tendon/ligament injury is hotly debated. There is less debate about inflammation following acute injury. To better understand the effect of acute inflammation, in this study we developed a multi-cytokine model of inflammatory tendinitis. The combined treatment with TNF-α, IL-1β, and IL-6, at dosages well below what are routinely used in vitro, decreased the mechanical properties and collagen content of engineered human ligaments. Treatment with this cytokine mixture resulted in an increase in phospho-NF-κB and MMP-1, did not affect procollagen production, and decreased STAT3 phosphorylation relative to controls. Using this more physiologically relevant model of acute inflammation, we inhibited NF-κB or JAK1 signaling in an attempt to reverse the negative effects of the cytokine mixture. Surprisingly, NF-κB inhibition led to an even greater decrease in mechanical function and collagen content. By contrast, inhibiting JAK1 led to an increase in mechanical properties, collagen content and thermal stability concomitant with a decrease in MMP-1. Our results suggest that inhibition of JAK1, not NF-κB, reverses the negative effects of pro-inflammatory cytokines on collagen content and mechanics in engineered human ligaments.
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Affiliation(s)
- Alec M Avey
- Department of Neurobiology, Physiology and Behavior, University of California Davis, Davis, CA 95616, United States
| | - Florence Devos
- Department of Neurobiology, Physiology and Behavior, University of California Davis, Davis, CA 95616, United States
| | - Albany G Roberts
- Department of Neurobiology, Physiology and Behavior, University of California Davis, Davis, CA 95616, United States
| | - El Sayed El Essawy
- Department of Neurobiology, Physiology and Behavior, University of California Davis, Davis, CA 95616, United States; Department of Sport Psychology, Mansoura University, Dakahlia Governorate 35516, Egypt
| | - Keith Baar
- Department of Neurobiology, Physiology and Behavior, University of California Davis, Davis, CA 95616, United States; Department of Physiology and Membrane Biology, University of California Davis, Davis, CA 95616, United States; VA Northern California Health Care System, Mather, CA 95655, United States.
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Steffen D, Mienaltowski M, Baar K. Spatial gene expression in the adult rat patellar tendon. Matrix Biol Plus 2023; 19-20:100138. [PMID: 38124714 PMCID: PMC10731370 DOI: 10.1016/j.mbplus.2023.100138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Revised: 11/08/2023] [Accepted: 11/15/2023] [Indexed: 12/23/2023] Open
Abstract
Tendons are dense connective tissues with relatively few cells which makes studying the molecular profile of the tissue challenging. There is not a consensus on the spatial location of various cell types within a tendon, nor the accompanying transcriptional profile. In the present study, we used two male rat patellar tendon samples for sequencing-based spatial transcriptomics to determine the gene expression profile. We integrated our data with a mouse Achilles single cell dataset to predict the cell type composition of the patellar tendon as a function of location within the tissue. The spatial location of the predicated cell types suggested that there were two populations of tendon fibroblasts, one located in the tendon midsubstance, while the other localized with red blood cells, pericytes, and immune cells to the tendon peripheral connective tissue. Of the highest expressed spatially variable genes, there were multiple genes with known function in tendon: Col1a1, Col1a2, Dcn, Fmod, Sparc, and Comp. Further, a novel spatially regulated gene (AABR07000398.1) with no known function was identified. The spatial gene expression of tendon associated genes (Scx, Thbs4, Tnmd, Can, Bgn, Lum, Adamts2, Lox, Ppib, Col2a1, Col3a1, Col6a2) was also visualized. Both patellar tendon samples had similar expression patterns for all these genes. This dataset provides new spatial insights into gene expression in a healthy tendon.
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Affiliation(s)
- Danielle Steffen
- Department of Neurobiology, Physiology & Behavior, University of California Davis, Davis, CA, United States
| | - Michael Mienaltowski
- Department of Animal Science, University of California Davis, Davis, CA, United States
| | - Keith Baar
- Department of Neurobiology, Physiology & Behavior, University of California Davis, Davis, CA, United States
- Physiology and Membrane Biology, University of California Davis, Davis, CA, United States
- VA Northern California Health Care System, Mather, CA 95655, United States
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