CRISPR Epigenome Editing Reduces Sensitization in Cultured Rat Sensory Neurons Exposed to an Osteoarthritis Environment
Reducing neuronal hyperresponsiveness in an osteoarthritis environment
CRISPR epigenome editing targeting interleukin-1 receptor type 1 (IL1R1) reduced sensitization in cultured rat sensory neurons exposed to an osteoarthritis environment. Sensitization is a state in which nerves respond more sensitively to stimulation. In knee-related dorsal root ganglion (DRG) neurons, responses returned to the level seen under healthy cartilage conditions, whereas some sensitization remained in temporomandibular-joint-related trigeminal ganglion (TG) neurons. The outcome assessed was the intracellular calcium response to heat stimulation; this should be distinguished from evidence of reduced joint pain or restored sensation in patients.
In osteoarthritis (OA), inflammatory cytokines can make nerves supplying joints hypersensitive and contribute to pain. The researchers focused on IL1R1, an inflammation-related receptor. In culture experiments, they examined whether epigenome editing that selectively suppresses expression of this receptor could lower neuronal responses, and whether the effect was the same in DRG and TG neurons.
Experiments combining human cartilage and rat neurons
The team compared osteoarthritic cartilage obtained from patients undergoing knee replacement with healthy cadaveric cartilage. Rat DRG and TG neurons were cultured on tissue-culture plastic or cartilage slices, and their responses following exposure to interleukin-1β (IL-1β) and osteoarthritic cartilage were assessed. Although human cartilage was used, the cells edited and measured were cultured rat neurons.
The neurons received a lentiviral CRISPR-dCas9-KRAB vector targeting IL1R1 or a nontargeting control vector. A calcium indicator was used to measure transient calcium signals evoked by heat. The main outcomes were the proportion of cells responding to heat and the peak calcium response.
Exposure to IL-1β and exposure to osteoarthritic cartilage each increased the proportion of cells showing heat-evoked calcium responses relative to control conditions in both DRG and TG neurons. After IL1R1-targeted editing, sensitization disappeared in DRG neurons, and responses returned to the level seen under healthy cartilage conditions. In TG neurons, by contrast, the peak calcium response fell to baseline, but the proportion of sensitized cells did not fully normalize. A reduction in response magnitude therefore did not coincide with normalization of the proportion of responding cells.
Differences between ganglia offer a lead for further research
The researchers proposed that osteoarthritis-related factors other than IL1R1 might contribute to the sensitization remaining in TG neurons. However, the supplied abstract alone does not allow those factors to be identified or support a conclusion that multi-target treatment is necessarily required. The observation that targeting the same receptor had different effects in the two ganglia offers a lead for studying differences in joint-related neuronal sensitization.
These findings support a potential strategy for modulating sensory-neuron responses in an osteoarthritis environment. However, the available abstract does not report sample size, effect sizes, statistical values, or response duration, making it difficult to assess the magnitude and durability of the effect. The supplied information also does not establish pain relief in people or long-term safety. Whether reduced cellular responses lead to actual pain control remains to be tested in further research.
The study subjects and findings are described in the Annals of Biomedical Engineering article abstract.
PURPOSE: Osteoarthritis (OA) pain can arise from inflammatory cytokines sensitizing neurons that innervate the temporomandibular joint (TMJ) and knee. Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-based epigenome editing enables targeted repression of inflammatory receptors and offers a promising strategy to modify disease mechanisms. This study tested whether CRISPR epigenome editing of interleukin-1 receptor type 1 (IL1R1) in trigeminal ganglia (TG; TMJ-innervating) and dorsal root ganglia (DRG; knee-innervating) neurons could reduce OA-associated sensitization. METHODS: OA cartilage was collected from knee replacement patients and compared with healthy cadaveric cartilage. Rat TG and DRG neurons were cultured with IL-1β on tissue culture plastic or cartilage explants, loaded with calcium dye, and subjected to thermal stimulation. Neurons were transduced with lentiviral CRISPR-dCas9-KRAB vectors targeting IL1R1 or with nontargeting controls, and heat-evoked calcium transients were measured. RESULTS: Exposure to IL-1β and OA cartilage both increased the proportion of TG and DRG neurons exhibiting heat-induced calcium transients compared with controls. CRISPR epigenome editing of IL1R1 abolished sensitization in DRG neurons, restoring responses to healthy cartilage levels. In TG neurons, editing reduced maximum calcium responses to baseline but did not fully normalize the percentage of sensitized cells, suggesting additional OA factors contribute to TMJ pain. CONCLUSION: CRISPR epigenome editing of IL1R1 in joint-innervating neurons reduces OA cartilage-induced sensitization. These results highlight differential mechanisms underlying OA cartilage driven DRG and TG neuron sensitization and establish epigenome editing as a potential therapeutic strategy to target OA-associated sensitization in the knee and TMJ.
This study can inform the selection of targets and outcome measures for follow-up experiments on osteoarthritis-related neuronal sensitization. For example, when comparing IL1R1 suppression strategies, measuring only peak calcium responses could miss the finding that the proportion of sensitized cells in TG neurons did not fully normalize. One practical use is to design experiments that assess response magnitude and the proportion of responding cells separately, and distinguish DRG results from TG results. Investigating the causes of the sensitization that remains in TG neurons is another possible direction. These are proposed research applications derived from the observations, not conclusions demonstrating reduced pain or treatment safety in patients. Further work must test the connection between changes in cultured cells and actual pain before clinical applicability can be assessed.