Discovery of autism/intellectual disability somatic mutations in Alzheimer's brains: mutated ADNP cytoskeletal impairments and repair as a case study

Abstract

With Alzheimer's disease (AD) exhibiting reduced ability of neural stem cell renewal, we hypothesized that de novo mutations controlling embryonic development, in the form of brain somatic mutations instigate the disease. A leading gene presenting heterozygous dominant de novo autism-intellectual disabilities (ID) causing mutations is activity-dependent neuroprotective protein (ADNP), with intact ADNP protecting against AD-tauopathy. We discovered a genomic autism ADNP mutation (c.2188C>T) in postmortem AD olfactory bulbs and hippocampi. RNA-Seq of olfactory bulbs also identified a novel ADNP hotspot mutation, c.2187_2188insA. Altogether, 665 mutations in 596 genes with 441 mutations in AD patients (389 genes, 38% AD-exclusive mutations) and 104 genes presenting disease-causing mutations (OMIM) were discovered. OMIM AD mutated genes converged on cytoskeletal mechanisms, autism and ID causing mutations (about 40% each). The number and average frequencies of AD-related mutations per subject were higher in AD subjects compared to controls. RNA-seq datamining (hippocampus, dorsolateral prefrontal cortex, fusiform gyrus and superior frontal gyrus-583 subjects) yielded similar results. Overlapping all tested brain areas identified unique and shared mutations, with ADNP singled out as a gene associated with autism/ID/AD and presenting several unique aging/AD mutations. The large fusiform gyrus library (117 subjects) with high sequencing coverage correlated the c.2187_2188insA ADNP mutation frequency to Braak stage (tauopathy) and showed more ADNP mutations in AD specimens. In cell cultures, the ADNP-derived snippet NAP inhibited mutated-ADNP-microtubule (MT) toxicity and enhanced Tau-MT association. We propose a paradigm-shifting concept in the perception of AD whereby accumulating mosaic somatic mutations promote brain pathology.

14-3-3 shuttles Activity-dependent neuroprotective protein to the cytoplasm to promote appropriate neuronal morphogenesis, cortical connectivity and calcium signaling

“…It is likely that control and Adnp shRNA neurons begin neurite formation simultaneously, but Adnp deficient neurons extend neurites that slowly and stably continue to elongate due to a lack of retraction, whereas control neurons rapidly form and retract many different neurites. This is in agreement with Adnp’s direct involvement in microtubule dynamics (25, 63). However, a direct investigation of how loss of Adnp effects the microtubule network during this developmental process will be crucial to understanding the cellular etiology of ADNP syndrome.…”

“…Furthermore, deficits in ADNP have also been associated with neurodegeneration and Tau pathology. A recent paper identified somatic mutations in ADNP driving Tau-microtubule dissociation and increased tauopathy (25), in line with early discoveries of tauopathy in an animal model of ADNP deficiency (29).…”

“…However, when a secondary neurite did emerge it was almost always stabilized, 83% of the time never retracting and re-emerging as is common in control neurons which had a 50% stabilization rate. This result can be attributed to microtubule stabilization and invasion (8, 11–13, 53), in which Adnp has a known role in both the axon growth cone and in developing dendritic spines (25, 63), and we propose that Adnp also fulfills this role during neurite initiation. Taken together the steady growth rate, lack of neurite retraction, and increased neurite stabilization in Adnp deficient neurons are mechanisms that could contribute to the increased basal dendrite number and increased axon length seen in mature Adnp deficient cortical neurons.…”

“…ADNP heterozygous deficiency has been well modeled in the Adnp +/- mouse, which has both behavioral and anatomical defects akin to ADNP syndrome (34). Similarly, somatic mutations in ADNP are linked to neurodegeneration in Alzheimer’s disease (25). We performed a cell-type and developmental timing specific analysis of how loss of Adnp affects a specific subpopulation of neurons, layer 2/3 pyramidal neurons, in the developing mouse somatosensory cortex.…”

Microbiota changes associated with ADNP deficiencies: rapid indicators for NAP (CP201) treatment of the ADNP syndrome and beyond

“…Additionally, in humans, blood borne concentrations of ADNP correlate with intelligence (Malishkevich et al 2016) and decrease in AD (Yang et al 2012). Finally, somatic ADNP brain mutations in AD correlate with disease-specific tau pathology (Ivashko-Pachima et al 2019). The most distinctive alterations in the gut microbiome composition observed in AD is the decreasing abundance of anti-inflammatory bacterial species such as Bifidobacterium breve strain A1 and increasing abundance of pro-inflammatory bacterial species such as Firmicutes and Bacteroidetes (Bostanciklioglu 2019), with both Bifidobacterium regulated by the Adnp genotype and by NAP (above and (Escher et al 2018)) and also dysregulated in ASD (Xu et al 2019).…”