SOX9

Investigators have discovered why some injured kidneys heal while others develop scarring that can lead to kidney failure. Their findings could lead to the development of noninvasive tests to detect kidney scarring and, eventually, new therapies to reverse the condition. Cedars-Sinai investigators have discovered why some injured kidneys heal while others develop scarring that can lead to kidney failure. Their findings, detailed in a paper published in the peer-reviewed journal Science, could lead to the development of noninvasive tests to detect kidney scarring and, eventually, new therapies to reverse the condition. "The key to this discovery was our ability to directly compare injured kidney cells that successfully regenerated with those that did not," said Sanjeev Kumar, MD, PhD, a nephrologist-scientist in the Board of Governors Regenerative Medicine Institute and the Department of Medicine at Cedars-Sinai and senior author of the study. "Injured cells activate a protein called SOX9 to regenerate themselves. When they have healed, the cells silence this protein. Cells that aren't able to regenerate leave SOX9 active, and this leads to a type of scarring called fibrosis. But when we deactivate SOX9 in a timely fashion, the scarring literally goes away." The kidneys, two fist-sized organs that filter waste from the blood, can be injured by diabetes and high blood pressure, serious infections such as COVID-19, and overuse of antibiotics and non-steroidal anti-inflammatory pain medications, said Kumar, who is also part of the Department of Biomedical Sciences at Cedars-Sinai. The SOX9 protein plays a major role in organ development but is not active in healthy adult kidneys. In previous work at another institution, Kumar and team found that when kidneys are injured, the surviving cells reactivate SOX9 as part of the healing process. In this study, Kumar and fellow investigators studied kidney damage in laboratory mice. They labeled individual cells at the point of injury, then followed how the cells' progeny evolved over time. "At Day 10, some cells' descendants were fully healed while others were not," Kumar said. "The cell lineage that healed had switched off SOX9 expression, while the unhealed lineage, in a continuing attempt to fully regenerate, maintained SOX9 activity. It's like a sensor that switches on when cells want to regenerate, and off when they are restored, and we are the first to identify this." Further, investigators discovered that cells that were unable to regenerate began recruiting proteins called Wnts, another key player in organ development. Over time, this accumulation of Wnts triggered scarring. And they found that deactivating SOX9 a week after injury promoted kidney recovery. Investigators observed the same process in patient databases from collaborating institutions in Switzerland and Belgium. "We could see that by Day 7, human patients with transplanted kidneys that were slow to begin working also activated SOX9," Kumar said. "And in our collaborators' database, we were able to distinguish that patients who had sustained SOX9 activation had lower kidney function and more scarring than those who did not. Human kidneys with cells that maintained SOX9 were also enriched with Wnts and showed increased fibrosis." These discoveries provide targets for drug development, as well as for noninvasive biomarker discovery permitting diagnosis of kidney fibrosis through the urine, Kumar said. Currently, the only available test for kidney fibrosis is a biopsy, which carries many risks. "Elucidating the mechanisms of scarless healing versus fibrosis has eluded investigators for decades and has implications beyond the kidney, including for certain cancers," said Paul Noble, MD, chair of the Department of Medicine and director of the Women's Guild Lung Institute at Cedars-Sinai and a co-author of the study. The findings could also lead to new treatment options for patients, said Clive Svendsen, PhD, executive director of the Board of Governors Regenerative Medicine Institute at Cedars-Sinai and a co-author of the study. "These findings help us understand for the first time how the kidney's response to injury sometimes leads to fibrosis," Svendsen said. "Future work along these lines could also advance our understanding of fibrosis in the heart, lungs and liver."

A research team has recently made a significant advancement in spinal cord injury treatment by using genetically modified human neural stem cells (hNSCs). They found that specifically modulating a gene expression to a certain level in hNSCs can effectively promote the reconstruction of damaged neural circuits and restore locomotor functions, offering great potential for new therapeutic opportunities for patients with spinal cord injury. A research team co-led by City University of Hong Kong (CityU) and The University of Hong Kong (HKU) has recently made a significant advancement in spinal cord injury treatment by using genetically modified human neural stem cells (hNSCs). They found that specifically modulating a gene expression to a certain level in hNSCs can effectively promote the reconstruction of damaged neural circuits and restore locomotor functions, offering great potential for new therapeutic opportunities for patients with spinal cord injury. Traumatic spinal cord injury is a devastating condition that commonly results from accidents such as falls, car crashes or sport-related injuries. Spinal neurons with long axons play critical roles in transmitting signals between the brain and the rest of the body, controlling our movement and sensory perception. Spinal cord injury causes irreversible damage to neurons and axons, which significantly interrupts signal transmission, hence leading to defective locomotion and somatosensory functions. "Currently, there are no effective clinical management or treatment regimens for patients with spinal cord injury, often leaving them with lifelong disabilities," explained Professor Jessica Liu Aijia, Assistant Professor in the Department of Neuroscience at CityU and the co-leader of the research. "While recent progress has been made in promoting spinal cord regeneration through transplantation of hNSCs derived from human induced pluripotent stem cells, the degree of functional recovery obtained has been modest. This is largely due to the hostile micro-environment around the lesion site, such as the formation of barrier-like structures called astroglial scars and the lack of neurotrophic factors in adults for neuronal differentiation. These factors hinder functional neuronal regeneration, resulting in prolonged repairing and limited functional recovery." A gene -- SOX9 was reported with a high-level expression at the injury site in previous studies, and the gene itself is the leading cause of the glial scars' formation and the hindrance of neuronal survival and differentiation. To overcome the adverse effects of the post-injury micro-environment, the joint-research team engineered the transplanted neural stem cells with a graded reduction of SOX9 by approximately 50%. The genetically modified hNSCs expressing half-dose of SOX9 resulted in robust neuronal differentiation and maturation (a process by which immature cells in the nervous system become specialised nerve cells) after transplantation in a hostile microenvironment, promoting neural circuits reconstruction in the spinal cord within a shorter period of time. It also remarkably reduced glial scar accumulation, facilitating long-distance axon outgrowth. The team recorded a large number of axons extending more than 35mm at 3 months post-graft, while relatively less in number with shorter extensions to 25mm with non-modified neural stem cells. To further explore the therapeutic effects of the modified hNSCs in treating spinal cord injury, the research team used a severe spinal cord injury rat model to evaluate the locomotion recovery after transplantation, including grid walking and consecutive walk. The former recorded limb coordination, such as the capability to grasp a grid rung with correct placement, and the latter recorded stepping patterns to demonstrate their gait and fingertip motor ability. Compared to rats' graft with non-modified hNSCs, rats' graft with SOX9 gene-modified hNSCs performed much better in placing their affected hind paws on the grid, with fewer misdirected steps after 10 weeks post-injury. In addition, these treated rats demonstrated a good gait with clear paw position and toe movement when walking across a metre-long narrow corridor. "Our findings reveal a new treatment direction by using a genetically modified strategy to alter the grafts' response to the deleterious microenvironment in vivo after injury, improving cell tolerance to the niche and self-differentiation potential. This brings a new treatment direction for repairing damaged spinal cord," said Professor Liu. "This genetic modification of hNSCs, particularly those derived from patient-specific human-induced pluripotent stem cells, which can be generated from a patient's skin or blood cells, eliminates ethical concerns in using embryonic stem cells and minimises the risk of rejection by the immune system. It provides a more effective autologous stem cell therapy for severe traumatic spinal cord injury," she added.

In skin, some aberrant adult epidermal stem cells turn on SOX9, kickstarting a process that ultimately activates cancer genes. Early on, every stem cell faces a fateful choice. During skin development, for instance, the embryonic epidermis begins as a single layer of epidermal progenitor cells. Their choice is to become a mature epidermal cell or switch to becoming a hair follicle cell. This so-called fate switch is governed by the transcription factor SOX9. If the progenitor cell expresses SOX9, hair follicle cells develop. If it doesn't, epidermal cells do. But there is a dark side to SOX9, as it's implicated in many of the deadliest cancers worldwide, including lung, skin, head and neck, and bone cancer. In skin, some aberrant adult epidermal stem cells later turn on SOX9 despite their chosen path -- and never turn it off, kickstarting a process that ultimately activates cancer genes. Scientists have never fully understood how this doomed outcome ensues at a molecular level. But now Rockefeller researchers have revealed the mechanisms behind this malignant turn of events. SOX9, it turns out, belongs to a special class of proteins that govern the transfer of genetic information from DNA to mRNA. That means it has the ability to pry open sealed pockets of genetic material, bind to previously silent genes within, and activate them. They published their results in Nature Cell Biology. "Our discovery provides new insights into how cancer derails a stem cell's carefully tuned decision-making process, thereafter making it impossible for it to make normal tissue," says Elaine Fuchs, head of the Robin Chemers Neustein Laboratory of Mammalian Cell Biology and Development. "It also illuminates new SOX9-activated genes as potential therapeutic targets." Rare keys to gene expression Our genome is not an open book. In fact, it's more like a library filled with a few billion books that are mostly under lock-and-key -- the majority of genetic material actually lies silent within non-coding and tightly bound packets of DNA cordoned off by histone proteins in a closed state. Together the DNA and histones form what's called closed chromatin. The genes that are packaged into this cloistered material is inaccessible to the transcription proteins, or factors, that would help it to express the genes within. But there are a few rare keys that aren't simply transcription factors. These "pioneer factors" can unlock those genetic packets. They possess the superpower to peer inside the closed chromatin and recognize binding sites within. They then recruit other transcription factors to help them pry open the closed chromatin and bind to receptor sites on the nucleosome, which reprograms the chromatin and activates new genes. This normally happens during early stages of development, when a stem cell's fate is yet to be determined. In adult skin, SOX9 is normally associated with maintaining the identity of adult hair follicle stem cells. It's normally suppressed in adult epidermal stem cells. But that's not the case when it comes to basal cell and squamous cell carcinomas. "In the disease context, SOX9 gets reactivated in adult epidermal stem cells," says Yihao Yang, first author of the study. How this process might unfold step by step has been unknown, Yang says. "Reprogramming in vitro happens really fast -- within 48 hours. With such a short time window, it's hard to get a good resolution on the sequence of events." The SOX9 swap To find out, the researchers engineered mice that contained a copy of SOX9 that could be activated in their adult epidermal stem cells when the mice were fed doxycycline, a drug that induced the transgenic SOX9. "In adult tissues, choices that were easily made in embryogenesis are tightly suppressed so that adult stem cells stick to their dedicated task," explains Fuchs. Unleashing SOX9, however, turned out to be a potent influencer, progressively reprogramming the epidermal stem cells to new fates. "By only expressing this single SOX9 transcription factor," Yang says, "we were able to induce basal cell carcinoma-like structures by week six. By week 12, we started to see lesions that resembled human basal cell carcinoma." Simultaneously, they tracked the epigenetic process going on behind the scenes. In the first two weeks, SOX9 turned off the epidermal stem cell genes. Reversing their normal state, they began to turn on hair follicle stem cell genes. Seeking the mechanism, the researchers discovered that to achieve this fate switch, SOX9 hijacked the nuclear machinery from the active epidermal genes and brought this stolen equipment to the silent hair follicle genes. It then enlisted other transcription factors to pry open the closed chromatin bind to the silent genes within, turning them on. "When SOX9 could not be regulated, the stem cells failed to make hair but instead just kept proliferating and activating several new transcription factors, eventually leading to a basal cell carcinoma state," Fuchs says. This complicated, identity-shifting back-and-forth was only possible because SOX9 is a pioneer factor, Yang says. "Only a pioneer factor has the ability to access closed chromatin," he points out. Because SOX9 is overly active in many of the deadliest cancers worldwide, the researchers aim to look for ways to intervene in its role in proliferating these cells. "By identifying how SOX9's interacting proteins and its target genes change during malignancy, we hope to make inroads into unearthing new drug targets for these cancers," Fuchs says.