Optogenetics, a biological technique that uses light to control and manipulate cell behavior, has steadily grown into one of the most promising methods over the past decade. The technique uses light to turn particular genes on or off, triggering certain biological functions.
Researchers at Texas A&M University are exploring ways to use optogenetics to control the flow of calcium ions into cells. Their work could have important implications for regenerative medicine and the treatment of various diseases and disorders.
Calcium is a crucial element in many biological functions. When calcium ions enter the cell or are released from stores within the cell, they act as second messengers that regulate important activities within the cell, including cell growth, gene expression, metabolism and homeostasis.
Accordingly, abnormal calcium influx can result in serious health consequences.
“Dysregulation of calcium signaling leads to a series of diseases including cancer, cardiovascular disorders and neurodegenerative diseases,” said Yubin Zhou, an associate professor at the Texas A&M Institute of Biosciences and Technology and the leader of the research.
By developing a method to turn calcium influx on and off using light, Zhou and his team may have found a novel approach to treating such diseases.
Optogenetics, Zhou explained, “confers high spatiotemporal resolution, reversibility, and photo-tunability to control cellular events.” In other words, it enables control of cellular functions with a high degree of precision.
As a result, it serves as a unique and effective method of controlling cellular calcium influx.
Controlling gene expression through calcium inflow
The researchers developed what they call the CaRROT system (calcium-responsive transcriptional reprogramming tool), a method of using both chemicals and light to control genome editing and transcriptional reprogramming.
CaRROT uses a pulse of light or chemicals to trigger the flow of calcium ions into cells. The researchers then used Opto-CRAC, another technology developed by Zhou’s team, to photo-activate calcium signals. CaRROT hijacks these signals and delivers a genome-engineering tool into the cell that manipulates gene expression, ultimately changing the function of the cell.
“When the light is switched on, the gates controlling calcium ions open to allow the flow of calcium from the external space into the cytoplasm of the cell,” Nhung Nguyen, a doctoral student at Texas A&M who led this research, said in a statement. “This process ultimately turns on the expression of specific genes.”
The researchers believe that CaRROT could have a wide range of uses in regenerative medicine and treating diseases.
“CaRROT can be targeted to endogenous genes to turn on or off gene expression with tailored function,” Zhou said. “For example, the constitutive expression of several oncogenes in cancer cells such as Her2, K-Ras, c-Myc, etc. are involved in the initiation and progression of cancer. CaRROT can be repurposed to shut down the expression of these genes to intervene cancer progression. In addition, when coupled with base editing tools, CaRROT can be used to correct mutations in the genome to reverse disease.”
The technology may one day be utilized to reprogram cells in damaged organs, enabling doctors to heal wounds and accelerate tissue regeneration, all by exposing the tissue to light, Yun Huang, assistant professor in the Center for Epigenetics and Disease Prevention at Texas A&M and collaborative senior author of the study, suggested in a statement.
Blocking calcium inflow with optoRGK
The scientists also developed a tool, named optoRGK, that uses light to stop the inflow of calcium ions into cells.
optoRGK is a novel class of genetically-encoded inhibitors, which can be triggered by light to turn off voltage-gated calcium channels in the membrane of cells.
The dysfunction of such voltage-gated calcium channels, and the overflow of calcium into cells, is associated with a wide variety of diseases, including some neuropsychiatric disorders and a number of cardiovascular disorders, including high blood pressure, arrhythmia and coronary artery disease.
These diseases have long been treated with traditional calcium-channel blockers that perform the same function as optoRGK but are generally less precise and can be toxic to cells, creating a host of side effects.
“Because of these side effects, generating new interventional approaches to complement the traditional calcium-channel blockers is much needed in the clinic,” Zhou said in a statement. “Our new optogenetic tool provides a non-conventional method to interrogate physiological and pathophysiological processes medicated by these voltage-gated calcium channels.”
The researchers tested optoRGK in cardiac muscle cells. With the light turned off, calcium ions oscillate in and out of the cell to the rhythm of the heart’s beat. When a blue light is turned on, the movement of the calcium ions is visibly reduced, even terminated, noted Zhou in a statement. When the light is turned back off, the calcium ions once more begin oscillating, demonstrating that the process is entirely reversible.
Further research
Moving forward, Zhou and his team will continue to examine how CaRROT and optoRGK can be applied to the treatment of diseases.
“We are aiming to move the optogenetic devices into animal models with cardiovascular diseases to explore the therapeutic potentials,” said Zhou. “For instance, proof of concept experiments have already demonstrated the potential of using RGK to treat heart disease. To test potential in vivo applications, it is our immediate future plan to express optoRGK in the atrioventricular node of rodent models with atrial fibrillation disease, and examine whether photostimulation could suppress aberrant atrioventricular nodal conduction to intervene atrial fibrillation.”
