A New Approach to Treating Chronic Kidney Disease: Replenishing Your Nephrons

As some of you may know, I have chronic kidney disease (CKD). Thanks to my wife and the scare put into me by my nephrologist, that I would soon have to begin dialysis, I have managed to get my CKD  in remission, or at least under control. My GFR number (that indicates when you must start dialysis) has held steady, or actually gotten better since my wife put me on a strict diet and I have lost about 15 pounds – and my nephrologist took me off of lisinopril (for blood pressure control), which seemed to raise my GFR by about three points. So, it appears I won’t have to go on dialysis any time soon.

All that being said, and with my strong interest in the use of stem cells and gene therapy in treating retinal diseases in ophthalmology, I have been searching the web for research on the use of stem cells to treat kidney disease or to produce new nephrons, the kidney cells that filter the blood as it passes through the kidney – and that go bad or die causing CKD. I think I have found very early research of that possibility.

Earlier this week, I saw a news  release from the University of Queensland in Australia that said that Dr. Melissa Little and her research group at the Institute of Molecular Bioscience (IMB) have found a set of six genes that can prompt some types of adult kidney cells to regress to an earlier stage of development (stem cells) and act like the precursors to the cells of the nephron. Since it is death or damage of nephrons that causes chronic kidney disease, by forcing adult cells to act like early nephrons, they may have potentially found a way to trigger the growth of new filters in the kidney.

All of your nephron cells are formed before birth and people with fewer nephrons are at higher risk of kidney disease.

Note: Dr. Little is one of sources that I had found in my web search as she had published a paper on “Stem Cell Options for Kidney Disease” in 2008, and we had corresponded at the beginning of this year when I began my search for a stem cell answer.

"This discovery is the first of its kind and offers hope to patients with chronic kidney disease. If we can find a way to provide new nephrons to an adult or increase nephron numbers in babies at birth, we could potentially reduce the risk of disease progression," said Professor Little.

This landmark paper, “Direct Transcriptional Reprogramming of Adult Cells to Embryonic Nephron Progenitors”, by Caroline E. Hendry, Jessica M. Vanslambrouck, Jessica Ineson, Norseha Suhaimi, Minoru Takasato, under the supervision of Professors Fiona Rae and Melissa H. Little, was published June 14th in the Journal of the American Society of Nephrology, the world's leading nephrology journal.

Professor Little said, “There was still more work to be done to encourage these reprogrammed early nephron cells to function and integrate. While this is a beginning, we hope it will inspire industry leaders and researchers around the world to invest further in cellular and bioengineering approaches to kidney repair and regeneration."

Stem Cells Australia Program Leader and Chair of Stem Cell Science at The University of Melbourne, Professor Martin Pera welcomed the research findings. "This innovative study provides evidence that adult cells can be reprogrammed to resemble the cells in the embryo that give rise to the kidney. The results pave the way for future studies that will enable researchers to produce human kidney cells in the laboratory, for use in studies of renal disorders, and for testing new drugs. Eventually this technology might help to make cells for transplantation to treat kidney disease," said Professor Pera.

The Technology

I have attempted to read Dr. Little’s paper on reprogramming kidney cells, and with her assistance, this is what I understand she and her colleagues have done, which is a very early step in the long road to someday being able to replenish nephron cells in an adult kidney.

In an earlier paper written by Caroline Hendry and Dr. Little, “Reprogramming the kidney: a novel approach for regeneration”, they discussed the various approaches that might be taken to re-create viable cells within a diseased kidney, including using  induced pluripotent stem cells (iPSCs) derived from skin cells or other sites, or even the use of embryonic stem cells (ESCs) that would be introduced into the kidney to form new nephrons (?), if they could – as shown in the accompanying figure (but how would you control the formation of the new cells?). But they concluded that the best approach would be reprogramming existing kidney cells to the progenitor stage, with the hope that these would develop into the needed new cells, or in this case, nephrons, the approach they ultimately used in this new research.

Figure1 | The application of reprogramming to the kidney, indicating the feasible starting cells and target phenotypes.

(i) Reprogramming may involve the directed differentiation of human embryonic stem cells (hESCs)/induced pluripotent stem cells (iPSCs) to a renal lineage. The iPSCs may be recipient-derived and may be derived from adult kidney cells or any other available adult cell type using the same factors. Directed differentiation is likely to recapitulate development; hence, it is likely to require differentiation through a nephron progenitor intermediate (induced nephron progenitor cell; iNP) but may continue on to more specific mature renal cell types.

(ii) A specific renal lineage may also be achieved via lineage-instructive reprogramming directly to that state from an adult cell type. Again, this may be the renal epithelium, renal stroma, or any other available differentiated adult cell type; however, this is likely to be more successful if the attractor states of the starting and target cell type are as close as possible. Reprogramming may be to the iNP state or directly to a more mature renal cell fate.

(iii) Finally, reprogramming may use the classical Yamanaka factors until the cells pass the point of no return, after which a renal lineage may be reached via the application of the appropriate environmental cues. Such cues may once again target the iNP state or aim to directly induce a more mature renal cell type.

As previously stated, the nephron progenitor population of the embryonic kidney gives rise to all of the nephron cells that will be present in the adult kidney, prior to birth. So, currently, what you’ve got at birth is what you live with.

Using a screening technique, the researchers were able to identify a group of six genes, that activate a network of genes that can reprogram adult proximal tubule cells back to the nephron progenitor stage – which in turn can form adult nephron cells. Although the researchers believe that other factors are required, they concluded that these results suggest that re-initiation of kidney development (nephron cells) from a population of adult cells (proximal tubule cells) by generating embryonic progenitors may be feasible, opening the way for additional cellular and bioengineering approaches to renal repair and regeneration.

In their literature search, they could not find any previous reports of kidney cells being reprogrammed back to a progenitor cell type. Their hope is that this discovery will lead others to follow their lead and begin further work in the possible reprogramming of adult kidney cells for the repair and rejuvenation of diseased kidneys.

Sources:

News Releases:

Research reprograms future of kidney health, Institute for Molecular Bioscience and Stem Cells Australia, June 14, 2013

Papers:

Direct Transcriptional Reprogramming of Adult Cells to Embryonic Nephron Progenitors, Hendry et al, Jnl Am Soc. Nephrology, June 11, 2013

Reprogramming the kidney: a novel approach for regeneration, Hendry and Little, Kidney International, March 21, 2012

Stem Cell Options for Kidney Disease, Hopkins et al, Jnl of Pathology, October 20, 2008


Resource:

Healthline.com recently launched a free, interactive "Human Body Maps" tool. One of the “maps” is of the kidney, showing and explaining how the kidney works to cleanse the body of waste material carried by the blood. To see a "map" of the kidney, and read how it functions, please follow this link.

Gene Therapy in Ophthalmology Update 19: A New Virus Vector for Safer Delivery of Gene Therapies

Researchers at the University of California at Berkeley, along with some assistance from the Flaum Eye Institute and Center for Visual Science at the University of Rochester, have come up with a new version of an adeno-associated virus (AAV) vector that can deliver genes deep into the retina using an intravitreal injection of the vector into the vitreous, a less-invasive technique, instead of an intraretinal injection below the surface of the retina, which is the usual way gene therapy is currently delivered.

The study was authored by postdoctoral fellows Deniz Dalkaral (then with Helen Wills Neuroscience Institute of UCal Berkeley, but now with Institut de la Vision in Paris) and Leah C. Byrne (Helen Wills), and graduate students Ryan R. Klimczak and Meike Visel (UCal Berkeley’s Dept. of Molecular and Cell Biology), and Lu Yin and William H. Merigan (Flaum Eye Institute and Center for Visual Science at the Univ. of Rochester), under the direction of Professors John G. Flannery, and David V. Schaffer of UCal Berkeley. The paper, “In Vivo–Directed Evolution of a New Adeno-Associated Virus for Therapeutic Outer Retinal Gene Delivery from the Vitreous”, was published online on June 12th in Science Tranlational Medicine.

As explained by Dr. Jean Bennett, a professor of ophthalmology at the University of Pennsylvania in Philadelphia, who was not involved in the study, but who has done extensive work with gene therapy in the treatment of Leber’s congenital amaurosis, “It shows the results of a very clever system to evolve AAV to target cells in the retina efficiently from an intravitreal injection.”

“Intravitreal injection, whereby a needle is pushed into the eye’s vitreous, or gel-like core, is a common drug delivery procedure performed under local anesthetic in a doctor’s office”, explained Bennett. “But using this routine injection technique in trials of gene therapy for retinal degeneration has thus far proven impossible.”

The problem, as explained by Dr. David Schaffer, a professor of chemical and biomolecular engineering, bioengineering, and neuroscience at the University of California, Berkeley, who led the research, is that current AAV vectors are incapable of penetrating deep into the retina where the target cells for retinal diseases are located. “AAV is a respiratory virus and so it evolved to infect lung epithelial cells,” explained Schaffer, “It never evolved to penetrate deep into tissue.”

Patients receiving gene therapy have theretofore undergone a vitrectomy (removal of the vitreous) and a direct intraretinal injection, which requires hospitalization and general anesthetic, and can sometimes even damage the retina. “If it were possible to inject AAV into the vitreous instead of the retina and still get gene delivery to the target cells, said Bennett, “one could envision the [doctor saying], ‘Ok, well just come into the office and get your gene therapy, tomorrow afternoon at two.’”

With that aim, Schaffer and colleagues used a process called “directed evolution” to randomly create millions of variations of the AAV virus to determine which ones were better at tissue penetration. They injected regular AAV into the vitreous of mouse eyes and one week later collected photoreceptor cells from deep within the retina. The tiny percentage of AAV vectors that made it into those cells were then amplified, repackaged into virus particles and injected into the vitreous again. They repeated the injection, recovery, and amplification a total of six times, finally isolating 48 AAV variants for sequencing. Two thirds of those isolates turned out to be the same variant, and Schaffer and colleagues named it 7m8.

Lastly, to determine whether the 7m8 vector would be likely to show similar deep penetration in the human retina, Schaffer had the vector carrying a gene-encoding fluorescent protein injected into the vitreous of macaque eyes. Primate retinas are considerably thicker than those of mice, and the vector did not consistently reach the deep cell layers – showing a spotty penetration pattern rather than the wide and even pan-retinal penetration that had been seen in the mice. However, 7m8 did effectively target photoreceptor cells of the fovea – a thinner part of the primate retina that is essential for the sharp detailed vision humans use when reading and driving. “That’s a really important region to protect,” said Schaffer. “For the quality of life of patients who are going blind, if you can at least protect the fovea that would be a huge improvement.”

Eye cells labeled with green fluorescent protein have successfully taken up the virus, showing that the ‘evolved’ virus (right) is more effective than the virus currently used for gene therapy (left). The new virus is particularly good at targeting the critical photoreceptors (top layer). (Source: University of California, Berkeley)

Note: All of the “directed evolution” work with mice to discover the 7m8 AAV vector was done at UCal Berkeley, while the confirmatory primate injection and imaging was done at the Univ. of Rochester.

Schaffer and colleagues don’t yet know what makes the 7m8 vector so much better at tissue penetration than its AAV ancestor, but they plan to find out and use that knowledge to further improve its penetration in the primate retina.

"Building upon 14 years of research, we have now created a virus that you just inject into the liquid vitreous humor inside the eye, and it delivers genes to a very difficult-to-reach population of delicate cells in a way that is surgically non-invasive and safe. "It's a 15-minute procedure, and you can likely go home that day."

The engineered virus works far better than current therapies when administered from the vitreous of the eye in rodent models of two human degenerative eye diseases (X-linked retinoschisis and Leber’s), and can penetrate photoreceptor cells in monkeys' eyes, which are similar to those of humans.

Schaffer said he and his team are now collaborating with other investigators to identify the patients most likely to benefit from this gene delivery technique and, after some preclinical development, hope soon to head into clinical trials.

Schaffer predicts that the viruses can be used not only to insert genes that restore function to non-working genes, but can knock out genes or halt processes that are actively killing retinal cells, which may be the case in age-related macular degeneration.

As noted by  Dr. Stephen Rose, Ph.D., chief research officer, Foundation Fighting Blindness, one of the co-funders of the research, “This is a critical next step in the development of retinal gene therapies. The enhanced AAV holds potential for treating more of the retina and doing so more safely. Incremental advancements like this are essential to getting the best treatments out to the patients.”

The investigators showed efficacy for the 7m8 AAV in a large animal as well as mouse models of retinoschisis and Leber congenital amaurosis, or LCA (RPE65 mutations). In the mouse studies, the virus was able to penetrate the retina and deliver a corrective gene to enable the retina to function normally.

While the large animal did not have a retinal disease, the virus transduced many regions of its retina. Ultimately, in both types of animals, the AAV was able to deliver genetic cargo to a variety of retinal cells, including: photoreceptors, the cells that provide vision; the retinal pigment epithelium, a layer of cells providing nutrients and waste disposal; and ganglion cells, which are a target for emerging, vision-restoring optogenetic therapies. (Editor’s Note: See, for example, my writeup of the “Nirenberg Technique”, an optogenetic approach to restore near normal vision to the blind.)

Most notably, the intravitreally administered AAV was able to penetrate the fovea, a small pit in the center of the retina rich in cones, which provides the vision most critical to daily living, but is often made fragile by degenerative diseases. Researchers have been concerned that injections underneath the fovea could cause permanent damage and vision loss in patients with advanced degeneration in their central retina.

AAVs are currently used for gene delivery in several retinal gene therapy clinical trials, including those that have restored vision in children and young adults with LCA (RPE65). AAVs are attractive for gene delivery because of their natural ability to penetrate a variety of cells. In addition, humans are exposed to the virus in nature and, therefore, tolerate it well.

To identify the optimal AAV for intravitreal gene delivery, the scientists used a process called “directed evolution” to randomly create millions of variations of the virus. The variants were then screened in mice to identify the top candidates for gene delivery to the retina. In addition to looking for an AAV that could penetrate retinal cells well, the researchers searched for a variant that could pass through a formidable barrier in the eye known as the inner limiting membrane, or ILM, which separates the vitreous from the retina.

The scientists from UC Berkeley plan to work with others to perform additional toxicology and efficacy studies to ready the 7m8 AAV for study in humans.

Sources:

In Vivo–Directed Evolution of a New Adeno-Associated Virus for Therapeutic Outer Retinal Gene Delivery from the Vitreous, Deniz Dalkara1 et al, Science Translational Medicine, June 12, 2013

Genes Get in Your Eye: Directed evolution of a gene therapy virus vector improves its penetration into the retina, Ruth Williams, The Scientist, June 12, 2013

Easy and Effective Therapy to Restore Sight: Engineered Virus Will Improve Gene Therapy for Blinding Eye Diseases, Robert Sanders, University of California - Berkeley, June 12, 2013

Researchers Identify Better Virus for Retinal Gene Delivery, Foundation Fighting Blindness, June 12, 2013