Macrophage Induced Senescence in Osteoprogenitor Cells: Pro- and Anti-inflammatory Effects on Bone Regeneration
Location
LSUHSC Center for Advanced Learning and Simulation (CALS)
Document Type
Presentation
Start Date
22-6-2024 10:30 AM
End Date
22-6-2024 11:25 AM
Publication Date
2024-06-22
Description
Introduction: Macrophages are essential to coordinating mammalian tissue regeneration1. In the dynamic bone microenvironment, macrophages exist as dual-natured entities, adopting pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes in response to specific conditions. M1 macrophages, activated by IFNγ and LPS, release cytokines and ROS that induce cellular senescence, hindering the regenerative function of osteoprogenitor cells (OPs)2. In contrast, macrophages, induced by IL-13, can play a reparative role, suggesting their protective effect against tissue damage due to inflammation2,3. The distinction between these phenotypes is crucial in the context of healing and regeneration across the entire human body. Mice, mirroring human regenerative abilities, offer an applicable model to study these effects and are able to regenerate the distal half of the digit tip, known as the third phalangeal element (P3). This regenerative capability contrasts with the response to amputations proximal to this point (P2), where regeneration fails, resulting in a cartilaginous callus without bone growth beyond the amputation plane and subsequent dermal scar formation4. The underlying reasons for this disparity in healing outcomes between amputations mice, or union or non-union fractures in humans, raise questions about whether the differences are attributable to intrinsic qualities of OPs or to the environmental factors influencing the healing process. This study aims to explore how OPs respond to the senescence-inducing effects of macrophage-derived factors, considering the potential influence of macrophage phenotypes on the regenerative process. If differences in P2 and P3 cell regeneration capabilities are caused by their intrinsic characteristics, we hypothesize that P2 cells will demonstrate increased senescence in response to stimulation with macrophage-conditioned media. Methods: OPs were isolated from P2 and P3 mouse digits and cultured. To measure stress resistance, P3 and P2 cells were placed in 24 well plates with different variations of macrophage conditioned media. To make macrophage conditioned media bone marrow macrophages are treated with different stimulants, IFN/LPS (M1), IL-13 (M2), or no treatment (M0) for 24 hours. The media was washed off and OPs were collected 24 hours later for SA-βGal senescent staining. Results: P3 OPs exhibited significantly increased senescence when exposed to the untreated macrophages (M0) and IFN/LPS treated (M1) conditions, compared to P2 cells, which showed no significant change in senescence levels. M2-conditioned media exerted a seemingly protective effect, with no observed difference in senescence between P2 and P3 cells. Discussion: Our findings contradict our hypothesis and suggest that extrinsic factors are what affect the regenerative properties of P2 and P3 cells. P3 cells showing increased senescence convey the complexity of the bone microenvironment, particularly in how macrophage-derived factors modulate cellular senescence differently in OPs derived from different locations of mouse digits. M2-conditioned media, which did not differentiate between P2 and P3 cells in terms of senescence, highlights the potential of anti-inflammatory macrophages in mitigating regeneration and promoting tissue repair. Overall, these findings indicate that certain OPs exhibit resistance or vulnerability to inflammatory environments. Furthermore, they suggest that in vivo injuries capable of regenerating these inflammatory conditions may vary across different regions, potentially due to differences in secretory factors and other regional characteristics. Significance/Clinical relevance: This study could provide valuable insights into the optimization of bone repair and regeneration strategies by modulating the macrophage microenvironment.
Recommended Citation
Culpepper, Sylvia, "Macrophage Induced Senescence in Osteoprogenitor Cells: Pro- and Anti-inflammatory Effects on Bone Regeneration" (2024). Dept. of Orthopaedics: Robert D. D’Ambrosia Lectureship & Research Day. 15.
https://digitalscholar.lsuhsc.edu/ortho_rd/2024/presentation2/15
Macrophage Induced Senescence in Osteoprogenitor Cells: Pro- and Anti-inflammatory Effects on Bone Regeneration
LSUHSC Center for Advanced Learning and Simulation (CALS)
Introduction: Macrophages are essential to coordinating mammalian tissue regeneration1. In the dynamic bone microenvironment, macrophages exist as dual-natured entities, adopting pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes in response to specific conditions. M1 macrophages, activated by IFNγ and LPS, release cytokines and ROS that induce cellular senescence, hindering the regenerative function of osteoprogenitor cells (OPs)2. In contrast, macrophages, induced by IL-13, can play a reparative role, suggesting their protective effect against tissue damage due to inflammation2,3. The distinction between these phenotypes is crucial in the context of healing and regeneration across the entire human body. Mice, mirroring human regenerative abilities, offer an applicable model to study these effects and are able to regenerate the distal half of the digit tip, known as the third phalangeal element (P3). This regenerative capability contrasts with the response to amputations proximal to this point (P2), where regeneration fails, resulting in a cartilaginous callus without bone growth beyond the amputation plane and subsequent dermal scar formation4. The underlying reasons for this disparity in healing outcomes between amputations mice, or union or non-union fractures in humans, raise questions about whether the differences are attributable to intrinsic qualities of OPs or to the environmental factors influencing the healing process. This study aims to explore how OPs respond to the senescence-inducing effects of macrophage-derived factors, considering the potential influence of macrophage phenotypes on the regenerative process. If differences in P2 and P3 cell regeneration capabilities are caused by their intrinsic characteristics, we hypothesize that P2 cells will demonstrate increased senescence in response to stimulation with macrophage-conditioned media. Methods: OPs were isolated from P2 and P3 mouse digits and cultured. To measure stress resistance, P3 and P2 cells were placed in 24 well plates with different variations of macrophage conditioned media. To make macrophage conditioned media bone marrow macrophages are treated with different stimulants, IFN/LPS (M1), IL-13 (M2), or no treatment (M0) for 24 hours. The media was washed off and OPs were collected 24 hours later for SA-βGal senescent staining. Results: P3 OPs exhibited significantly increased senescence when exposed to the untreated macrophages (M0) and IFN/LPS treated (M1) conditions, compared to P2 cells, which showed no significant change in senescence levels. M2-conditioned media exerted a seemingly protective effect, with no observed difference in senescence between P2 and P3 cells. Discussion: Our findings contradict our hypothesis and suggest that extrinsic factors are what affect the regenerative properties of P2 and P3 cells. P3 cells showing increased senescence convey the complexity of the bone microenvironment, particularly in how macrophage-derived factors modulate cellular senescence differently in OPs derived from different locations of mouse digits. M2-conditioned media, which did not differentiate between P2 and P3 cells in terms of senescence, highlights the potential of anti-inflammatory macrophages in mitigating regeneration and promoting tissue repair. Overall, these findings indicate that certain OPs exhibit resistance or vulnerability to inflammatory environments. Furthermore, they suggest that in vivo injuries capable of regenerating these inflammatory conditions may vary across different regions, potentially due to differences in secretory factors and other regional characteristics. Significance/Clinical relevance: This study could provide valuable insights into the optimization of bone repair and regeneration strategies by modulating the macrophage microenvironment.