In Vivo Imaging of Newt Lens Regeneration: Novel Insights Into the Regeneration Process

Macrophages modulate fibrosis during newt lens regeneration

BACKGROUND

Previous studies have suggested that macrophages are present during lens regeneration in newts, but their role in the process is yet to be elucidated.

METHODS

Here we generated a transgenic reporter line using the newt, Pleurodeles waltl, that traces macrophages during lens regeneration. Furthermore, we assessed early changes in gene expression during lens regeneration using two newt species, Notophthalmus viridescens and Pleurodeles waltl. Finally, we used clodronate liposomes to deplete macrophages during lens regeneration in both species and tested the effect of a subsequent secondary injury after macrophage recovery.

RESULTS

Macrophage depletion abrogated lens regeneration, induced the formation of scar-like tissue, led to inflammation, decreased iris pigment epithelial cell (iPEC) proliferation, and increased rates of apoptosis in the eye. Some of these phenotypes persisted throughout the last observation period of 100 days and could be attenuated by exogenous FGF2 administration. A distinct transcript profile encoding acute inflammatory effectors was established for the dorsal iris. Reinjury of the newt eye alleviated the effects of macrophage depletion, including the resolution of scar-like tissue, and re-initiated the regeneration process.

CONCLUSIONS

Together, our findings highlight the importance of macrophages for facilitating a pro-regenerative environment in the newt eye by regulating fibrotic responses, modulating the overall inflammatory landscape, and maintaining the proper balance of early proliferation and late apoptosis of the iPECs.

Neural dependency in wound healing and regeneration

In response to injury, humans and many other mammals form a fibrous scar that lacks the structure and function of the original tissue, whereas other vertebrate species can spontaneously regenerate damaged tissues and structures. Peripheral nerves have been identified as essential mediators of wound healing and regeneration in both mammalian and nonmammalian systems, interacting with the milieu of cells and biochemical signals present in the post-injury microenvironment. This review examines the diverse functions of peripheral nerves in tissue repair and regeneration, specifically during the processes of wound healing, blastema formation, and organ repair. We compare available evidence in mammalian and nonmammalian models, identifying critical nerve-mediated mechanisms for regeneration and providing future perspectives toward integrating these mechanisms into a therapeutic framework to promote regeneration.

Macrophages modulate fibrosis during newt lens regeneration

Background

Previous studies indicated that macrophages play a role during lens regeneration in newts, but their function has not been tested experimentally.

Methods

Here we generated a transgenic newt reporter line in which macrophages can be visualized in vivo. Using this new tool, we analyzed the location of macrophages during lens regeneration. We uncovered early gene expression changes using bulk RNAseq in two newt species, Notophthalmus viridescens and Pleurodeles waltl. Next, we used clodronate liposomes to deplete macrophages, which inhibited lens regeneration in both newt species.

Results

Macrophage depletion induced the formation of scar-like tissue, an increased and sustained inflammatory response, an early decrease in iris pigment epithelial cell (iPEC) proliferation and a late increase in apoptosis. Some of these phenotypes persisted for at least 100 days and could be rescued by exogenous FGF2. Re-injury alleviated the effects of macrophage depletion and re-started the regeneration process.

Conclusions

Together, our findings highlight the importance of macrophages in facilitating a pro-regenerative environment in the newt eye, helping to resolve fibrosis, modulating the overall inflammatory landscape and maintaining the proper balance of early proliferation and late apoptosis.

OCTSharp: an open-source and real-time OCT imaging software based on C

Optical coherence tomography (OCT) demands massive data processing and real-time displaying during high-speed imaging. Current OCT imaging software is predominantly based on C++, aiming to maximize performance through low-level hardware management. However, the steep learning curve of C++ hinders agile prototyping, particularly for research purposes. Moreover, manual memory management poses challenges for novice developers and may lead to potential security issues. To address these limitations, OCTSharp is developed as an open-source OCT software based on the memory-safe language C#. Within the managed C# environment, OCTSharp offers synchronized hardware control, minimal memory management, and GPU-based parallel processing. The software has been thoroughly tested and proven capable of supporting real-time image acquisition, processing, and visualization with spectral-domain OCT systems equipped with the latest advanced hardware. With these enhancements, OCTSharp is positioned to serve as an open-source platform tailored for various applications.

Characterizing the lens regeneration process in Pleurodeles waltl

BACKGROUND

Aging and regeneration are heavily linked processes. While it is generally accepted that regenerative capacity declines with age, some vertebrates, such as newts, can bypass the deleterious effects of aging and successfully regenerate a lens throughout their lifetime.

RESULTS

Here, we used Spectral-Domain Optical Coherence Tomography (SD-OCT) to monitor the lens regeneration process of larvae, juvenile, and adult newts. While all three life stages were able to regenerate a lens through transdifferentiation of the dorsal iris pigment epithelial cells (iPECs), an age-related change in the kinetics of the regeneration process was observed. Consistent with these findings, iPECs from older animals exhibited a delay in cell cycle re-entry. Furthermore, it was observed that clearance of the extracellular matrix (ECM) was delayed in older organisms.

CONCLUSIONS

Collectively, our results suggest that although lens regeneration capacity does not decline throughout the lifespan of newts, the intrinsic and extrinsic cellular changes associated with aging alter the kinetics of this process. By understanding how these changes affect lens regeneration in newts, we can gain important insights for restoring the age-related regeneration decline observed in most vertebrates.

Macrophages modulate fibrosis during newt lens regeneration

Previous studies indicated that macrophages play a role during lens regeneration in newts, but their function has not been tested experimentally. Here we generated a transgenic newt reporter line in which macrophages can be visualized in vivo. Using this new tool, we analyzed the location of macrophages during lens regeneration. We uncovered early gene expression changes using bulk RNAseq in two newt species, Notophthalmus viridescens and Pleurodeles waltl. Next, we used clodronate liposomes to deplete macrophages, which inhibited lens regeneration in both newt species. Macrophage depletion induced the formation of scar-like tissue, an increased and sustained inflammatory response, an early decrease in iris pigment epithelial cell (iPEC) proliferation and a late increase in apoptosis. Some of these phenotypes persisted for at least 100 days and could be rescued by exogenous FGF2. Re-injury alleviated the effects of macrophage depletion and re-started the regeneration process. Together, our findings highlight the importance of macrophages in facilitating a pro-regenerative environment in the newt eye, helping to resolve fibrosis, modulating the overall inflammatory landscape and maintaining the proper balance of early proliferation and late apoptosis.

Two is not necessarily better than one: A double lens in a pre-metamorphic adult axolotl (Ambystoma mexicanum)

An 8-year-old female pre-metamorphic axolotl (Ambystoma mexicanum) was examined for a suspected anterior lens luxation. Slit-lamp biomicroscopy revealed two lens-like structures in the anterior chamber of the right eye (OD), each with cataractous change. Ultrasound biomicroscopy and optical coherence tomography (OCT) were performed without sedation, and revealed small lenticular structures each with distinct nuclei and cortices. Although a distinct connection of the two lenticular structures could not be definitively ruled out, the structures appeared separate. Each of the lenticular structures was closely associated with its respective iris leaflet. This report demonstrates application of advanced imaging for diagnostic use in axolotl ophthalmology, showing that imaging of the lens can be performed without sedation, topical anesthetic, nor contact gel with high diagnostic quality. Although two distinct lenses were diagnosed with no historical evidence of trauma, the small sizes of each lenticular structure, with no detectable connection between them, are suggestive of a possible regenerative abnormality. This report opens discussion for the regenerative capabilities of the pre-metamorphic adult axolotl and possible implementations of their use in regenerative medicine research for the development of future therapies.

In Vivo and Ex Vivo View of Newt Lens Regeneration

Lens regeneration in the adult newt illustrates a unique example of naturally occurring cell transdifferentiation. During this process, iris pigmented epithelial cells (iPECs) reprogram into a lens, a tissue that is derived from a different embryonic source. Several methodologies both in vivo and in culture have been utilized over the years to observe this phenomenon. Most recently, Optical Coherence Tomography (OCT) has been identified as an effective tool to study the lens regeneration process in continuity through noninvasive, real-time imaging of the same animal. Described in this chapter are three different methodologies that can be used to observe the newt lens regeneration process both in vivo and ex vivo.