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Photoreceptor precursor cell integration into rodent retina after treatment with novel glycopeptide

Cell replacement therapy is emerging as an important approach in novel treatments for neurodegenerative diseases. Many problems remain, in particular, improvements are needed in the survival of transplanted cells and increasing functional integration into host tissue. These problems arise because of immune rejection, suboptimal precursor cell type, trauma during cell transplantation, toxic compounds released by dying tissues, and nutritional deficiencies. They recently developed an ex vivo system to facilitate the identification of factors contributing to the death of transplanted neuronal (photoreceptor) and showed 2.8‐fold improvement in transplant cell survival after pre‐treatment with a novel glycopeptide (PKX‐001). In this study theyextended these studies to look at cell survival, maturation, and functional integration in an in vivo rat model of rhodopsin‐mutant retinitis pigmentosa causing blindness. They found that only when human photoreceptor precursor cells (PPCs) were pre‐incubated with PKX‐001 prior to transplantation, did the cells integrate and mature into cone photoreceptors expressing S‐opsin or L/M opsin. In addition, ribbon synapses were observed in the transplanted cells suggesting they were making synaptic connections with the host tissue. Furthermore, optokinetic tracking and electroretinography responses in vivo were significantly improved compared to cell transplants without PKX‐001 pre‐treatment. These data demonstrate that PKX‐001 promotes significant long‐term stem cell survival in vivo, providing a platform for further investigation towards the clinical application to repair damaged or diseased retina.


Cell transplantation is emerging as an important innovation in future treatments of many neurological diseases such as stroke and the many subtypes of neurodegeneration (such as Alzheimer’s disease). A key feature of cell transplantation is the possibility of recovery of function in such diseases. Recently, photoreceptor precursor cells (PPCs) have been studied as possible treatments for retinal diseases such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP). An important issue in this work is the low survival rate of retinal precursor cells after transplantation in vivo. Many factors could be responsible for this including immune rejection, suboptimal cell types being used for transplantation, trauma during cell delivery, nutritional deficits in the target tissue, and toxic compounds secreted from the target tissue. Recently they highlighted the possible role of the necrotic release of prostaglandins from degenerating host tissue, and the secondary triggering of inflammation as possible contributory factors in limiting the lifespan of cells transplanted into retinal tissue. Previously they showed that PPC survival can be significantly improved when cells are pretreated with PKX-001 (previously known as anti-aging glycoprotein AAGP) in an ex-vivo model of human retinal dystrophy.


In this study, they extend the work into studies of cell survival, maturation, and functional integration into rodent retina exhibiting retinal dystrophy due to rhodopsin gene mutation1.



PPCs of human origin integrate into treated retina at 6 months.

Representative sagittal cryosection through the retina showing PPCs labelled with Cell Trace Far Red DDAO-SE. The STEM121 immunolabeling in green identifies cells of human origin. Nuclei counterstained with DAPI. RPE, retinal pigment epithelium; ONL, outer nuclear layer; INL, inner nuclear layer; GCL, ganglion cell layer. Size bar = 25 µm. In the merged image two PPCs are identified by dotted lines. Inset shows higher magnification of one cell extending a projection towards the RPE.


Characterization of PPCs.

(A) Immunohistochemical labelling of PPCs with antibodies to CRX, S-Opsin, L/M-Opsin and Recoverin. (B) Quantification of real-time RT-PCR expression data for pluripotency markers (NANOG and SOX2) and photoreceptor markers (CRX, NRL, SW-opsin (SWO), Recoverin (REC), and rhodopsin (RHO) in iPSCs and in differentiated PPCs. Data presented as mean ± SEM. *P<0.001; **P<0.01 (N=9).

Maturation of PPCs in treated host retina at 6 months.

(A) Expression of Cell Trace Far Red DDAO-SE in PPCs in the host retina. Nuclei stained with DAPI. Inset, higher magnification of a maturing PPC that has become elongated suggestive of an emerging inner segment (arrow). (B) Expression of Ribeye (CTBP2) in PPCs (arrows). Inset, higher magnification showing two characteristic green dots identifying the connection between the PPC and a second order INL neuron. (C) Confocal image of a cell expressing Cell Trace Far Red DDAO-SE (red) and immunolabeling for S-opsin (green). Nuclei stained with DAPI. Inset, higher magnification of a mature cone photoreceptor that has an inner segment (IS) labeled with Far Red and localization of S-opsin in the photoreceptor outer segment (OS). (D) Confocal image of cells expressing Cell Trace Far Red DDAO-SE (red) and immunolabeling for L/M-opsin (green). Inset, higher magnification showing a mature photoreceptor that has an inner segment (IS) labeled with Far ed and the outer segment (OS) localization of L/M-opsin. RPE, retinal pigment epithelium;

ONL, outer nuclear layer; INL, inner nuclear layer; GCL, ganglion cell layer. Size bar = 25 µm.


  1. Viringipurampeer, I.A., Yanai, A., Nizamudheen, V.S., Gregory‐Evans, C.Y. and Gregory‐Evans, K. (2021), Photoreceptor precursor cell integration into rodent retina after treatment with novel glycopeptide PKX‐001. J Tissue Eng Regen Med. Accepted Author Manuscript. https://doi.org/10.1002/term.3193