Human cortical interneurons show local co-expression of GLP1R and insulin mRNA

This study investigated whether specific human cortical interneuron subtypes locally express glucagon-like peptide-1 receptor (GLP1R) and insulin (INS), hypothesizing this molecular feature might be relevant for intracortical metabolic signaling. Researchers analyzed single layer 1 GABAergic interneurons microdissected from human cortical tissue using laser capture microdissection. Transcriptomic subtype identification was performed using digital PCR preamplification of LAMP5, SV2C, and PRSS12 markers. GLP1R and INS mRNA copy numbers were quantified using single-cell digital PCR, and spatial expression patterns were validated using RNAscope Hi-Plex in situ hybridization. Results showed neurogliaform cells (LAMP5+, SV2C+, PRSS12–) and rosehip cells (LAMP5+, SV2C+, PRSS12+) exhibited significantly higher GLP1R and INS expression than other LAMP5 interneurons. Specifically, GLP1R mRNA was found in 44 out of 72 neurogliaform cells and 18 out of 36 rosehip cells. INS mRNA was detected in 29 out of 72 neurogliaform cells and 11 out of 36 rosehip cells. No INS expression was detected in other LAMP5 interneurons. Co-expression analysis revealed a significant statistical dependency between GLP1R and INS expression, with a mutual information value of 0.244 (p<0.001). The study demonstrates local co-expression of GLP1R and INS in specific human cortical interneuron populations, suggesting a potential molecular substrate for intracortical metabolic signaling.

We think of insulin as something made by the pancreas to control blood sugar. But what if your brain made its own? New research in human brain tissue reveals a surprising local connection. Scientists looked at specific types of calming brain cells, called interneurons, in the outer layer of the brain's cortex. They found that two particular subtypes—called neurogliaform and rosehip cells—were special. These cells not only carried the receptor for a common diabetes drug (GLP-1, like in Ozempic), but they also actively produced insulin messenger molecules right there in the brain. In the cells studied, the receptor was found in 44 out of 72 neurogliaform cells and 18 out of 36 rosehip cells. Insulin production was found in 29 and 11 of those same cell groups, respectively. Other similar calming cells showed no insulin production at all. The analysis showed these two molecules—the drug receptor and insulin—were often made together in the same cells, suggesting a coordinated local system. This discovery points to a potential 'intracortical metabolic signaling' network, meaning the brain's outer layer might have its own way of managing energy and signals using these molecules, completely separate from the body's main insulin supply. It's a clue that could help us understand why drugs that target blood sugar sometimes have powerful effects on the brain.