Over time, memory retrieval is thought to transfer from the hippocampus to a distributed network of neocortical sites. Of these sites, the retrosplenial cortex (RSC) is robustly activated during retrieval of remotely acquired, emotionally-valenced memories. It is unclear, however, whether RSC is specifically involved in memory storage or retrieval, and which neurotransmitter receptor mechanisms serve its function. We addressed these questions by inhibiting N-methyl-d-aspartate receptors (NMDAR) in RSC via infusions of APV prior to tests for context fear in male mice. Anterior cingulate cortex (ACC) and dorsal hippocampus (DH), which have been implicated in the retrieval of remote and recent memory, respectively, served as neuroanatomical controls. Surprisingly, infusion of APV only into RSC, but not ACC or DH, abolished retrieval of remote memory, as revealed by lack of freezing to the conditioning context. APV infused into RSC also impaired retrieval of recent memory, but had no effect on conditioning or memory storage. Within-subject experiments confirmed that the role of RSC in memory retrieval is not time-limited. RSC-dependent context fear memory retrieval was mediated by NR2A, but not NR2B, subunit-containing NMDAR. Collectively, these data are the first demonstration that NMDAR in RSC are necessary for the retrieval of remote and recent memories of fear-evoking contexts. Dysfunction of RSC may thereby contribute significantly to the re-experiencing of traumatic memories in patients with post-traumatic stress disorder (PTSD).

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Background DNA variants in APOL1 associate with kidney disease, but the pathophysiologic mechanisms remain incompletely understood. Model organisms lack the APOL1 gene, limiting the degree to which disease states can be recapitulated. Here we present single-cell RNA sequencing (scRNA-seq) of genome-edited human kidney organoids as a platform for profiling effects of APOL1 risk variants in diverse nephron cell types. Methods We performed footprint-free CRISPR-Cas9 genome editing of human induced pluripotent stem cells (iPSCs) to knock in APOL1 high-risk G1 variants at the native genomic locus. iPSCs were differentiated into kidney organoids, treated with vehicle, IFN-g, or the combination of IFN-g and tunicamycin, and analyzed with scRNA-seq to profile cell-specific changes in differential gene expression patterns, compared with isogenic G0 controls. Results Both G0 and G1 iPSCs differentiated into kidney organoids containing nephron-like structures with glomerular epithelial cells, proximal tubules, distal tubules, and endothelial cells. Organoids expressed detectable APOL1 only after exposure to IFN-g. scRNA-seq revealed cell type-specific differences in G1 organoid response to APOL1 induction. Additional stress of tunicamycin exposure led to increased glomerular epithelial cell dedifferentiation in G1 organoids. Conclusions Single-cell transcriptomic profiling of human genome-edited kidney organoids expressing APOL1 risk variants provides a novel platform for studying the pathophysiology of APOL1-mediated kidney disease.