Porous Precision-Templated 40 μm Pore Scaffolds Promote Healing through Synergy in Macrophage Receptor with Collagenous Structure and Toll-Like Receptor Signaling

Porous precision-templated scaffolds (PTS) with uniform, interconnected, 40 μm pores have shown favorable healing outcomes and a reduced foreign body reaction (FBR). Macrophage receptor with collagenous structure (MARCO) and toll-like receptors (TLRs) have been identified as key surface receptors in the initial inflammatory phase of wound healing. However, the role of MARCO and TLRs in modulating monocyte and macrophage phenotypes within PTS remains uncharacterized. In this study, we demonstrate a synergetic relationship between MARCO and TLR signaling in cells inhabiting PTS, where induction with TLR3 or TLR4 agonists to 40 μm scaffold-resident cells upregulates the transcription of MARCO. Upon deletion of MARCO, the prohealing phenotype within 40 μm PTS polarizes to a proinflammatory and profibrotic phenotype. Analysis of downstream TLR signaling shows that MARCO is required to attenuate nuclear factor kappa B (NF-κB) inflammation in 40 μm PTS by regulating the transcription of inhibitory NFKB inhibitor alpha (NFKBIA) and interleukin-1 receptor-associated kinase 3 (IRAK-M), primarily through a MyD88-dependent signaling pathway. Investigation of implant outcome in the absence of MARCO demonstrates an increase in collagen deposition within the scaffold and the development of tissue fibrosis. Overall, these results further our understanding of the molecular mechanisms underlying MARCO and TLR signaling within PTS. Impact statement Monocyte and macrophage phenotypes in the foreign body reaction (FBR) are essential for the development of a proinflammatory, prohealing, or profibrotic response to implanted biomaterials. Identification of key surface receptors and signaling mechanisms that give rise to these phenotypes remain to be elucidated. In this study, we report a synergistic relationship between macrophage receptor with collagenous structure (MARCO) and toll-like receptor (TLR) signaling in scaffold-resident cells inhabiting porous precision-templated 40 μm pore scaffolds through a MyD88-dependent pathway that promotes healing. These findings advance our understanding of the FBR and provide further evidence that suggests MARCO, TLRs, and fibrosis may be interconnected.

Novel HALO® image analysis to determine cell phenotype in porous precision-templated scaffolds

Image analysis platforms have gained increasing popularity in the last decade for the ability to automate and conduct high-throughput, multiplex, and quantitative analyses of a broad range of pathological tissues. However, imaging tissues with unique morphology or tissues containing implanted biomaterial scaffolds remain a challenge. Using HALO®, an image analysis platform specialized in quantitative tissue analysis, we have developed a novel method to determine multiple cell phenotypes in porous precision-templated scaffolds (PTS). PTS with uniform spherical pores between 30 and 40 μm in diameter have previously exhibited a specific immunomodulation of macrophages toward a pro-healing phenotype and an overall diminished foreign body response (FBR) compared to PTS with larger or smaller pore sizes. However, signaling pathways orchestrating this pro-healing in 40 μm PTS remain unclear. Here, we use HALO® to phenotype PTS resident cells and found a decrease in pro-inflammatory CD86 and an increase in pro-healing CD206 expression in 40 μm PTS compared to 100 μm PTS. To understand the mechanisms that drive these outcomes, we investigated the role of myeloid-differentiation-primary-response gene 88 (MyD88) in regulating the pro-healing phenomenon observed only in 40 μm PTS. When subcutaneously implanted in MyD88KO mice, 40 μm PTS reduced the expression of CD206, and the scaffold resident cells displayed an average larger nuclear size compared to 40 μm PTS implanted in mice expressing MyD88. Overall, this study demonstrates a novel image analysis method for phenotyping cells within PTS and identifies MyD88 as a critical mediator in the pore-size-dependent regenerative healing and host immune response to PTS.

Monocytes contribute to a pro-healing response in 40 μm diameter uniform-pore, precision-templated scaffolds

Porous precision-templated scaffolds (PTS) with uniformly distributed 40 μm spherical pores have shown a remarkable ability in immunomodulating resident cells for tissue regeneration. While the pore size mediated pro-healing response observed only in 40 μm pore PTS has been attributed to selective macrophage polarization, monocyte recruitment and phenotype have largely been uncharacterized in regulating implant outcome. Here, we employ a double transgenic mouse model for myeloid characterization and a multifaceted phenotyping approach to quantify monocyte dynamics within subcutaneously implanted PTS. Within 40 μm PTS, myeloid cells were found to preferentially infiltrate into the scaffold. Additionally, macrophage receptor with collagenous structure (MARCO), an innate activation marker, was significantly upregulated within 40 μm PTS. When 40 μm PTS were implanted in monocyte-depleted mice, the transcription of MARCO was significantly decreased and an increase in pro-inflammatory inducible nitric oxide synthase (iNOS) and tumor necrosis factor alpha (TNFα) were observed. Typical of a foreign body response (FBR), 100 μm PTS significantly upregulated pro-inflammatory iNOS, secreted higher amounts of TNFα, and displayed a pore size dependent morphology compared to 40 μm PTS. Overall, these results identify a pore size dependent modulation of circulating monocytes and implicates MARCO expression as a defining subset of monocytes that appears to be responsible for regulating a pro-healing host response.

Indocyanine green staining and removal of internal limiting membrane in macular hole surgery: histology and outcome

PURPOSE

To report the surgical technique, outcome, and histologic findings involving indocyanine green staining and removal of internal limiting membrane in primary macular hole surgery.

METHODS

Prospectively, consecutive patients with idiopathic macular hole or myopic macular hole with retinal detachment were recruited. After pars plana vitrectomy and epiretinal membrane removal, the internal limiting membrane was stained and removed. The specimens were stained using hematoxylin and eosin and periodic acid-Schiff. Immunohistochemical staining was also performed for glial fibrillary acidic protein, vimentin, type I and type IV collagen, and actin.

RESULTS

Among 10 patients (10 eyes) in the study, nine eyes had stage 3 or 4 macular hole. Four of them had chronic macular hole. The tenth patient had retinal detachment resulting from a myopic macular hole. Postoperatively, all cases had closure of macular hole without an elevated edge and the retina was attached. Seven patients had improvement of 2 or more Snellen lines, whereas visual acuity remained the same for the other three patients. In six eyes in which complete histologic examinations were feasible, internal limiting membrane was confirmed and two eyes also had a small amount of epiretinal membrane. Myofibrocytes in internal limiting membrane, either scattered or as a single layer, were found in three cases.

CONCLUSIONS

Removal of indocyanine green--stained internal limiting membrane around idiopathic macular hole or myopic macular hole with retinal detachment is confirmed with histology and may contribute to macular hole closure and retinal reattachment.

Ocular histopathologic and biochemical studies of the cerebrohepatorenal syndrome (Zellweger's syndrome) and its relationship to neonatal adrenoleukodystrophy

The eyes of three infants with cerebrohepatorenal disease (Zellweger's syndrome) who died demonstrated ganglion cell loss, gliosis of the nerve fiber layer and optic nerve, optic atrophy, and changes resembling those of retinitis pigmentosa in the retina and pigment epithelium. Ultrastructural examination showed bileaflet inclusions identical to those seen in neonatal adrenoleukodystrophy in the pigment epithelium and in pigmented macrophages, but these were absent in the cornea. Biochemical analysis of tissues demonstrated an excessive amount of very-long-chain fatty acids in the ocular tissues, an abnormality also found in adrenoleukodystrophy. These histopathologic and biochemical results demonstrated that the cerebrohepatorenal syndrome and neonatal adrenoleukodystrophy are similar in regard to ocular abnormalities and the presence of saturated very-long-chain fatty acids.