Shank3 deletion in PV neurons is associated with abnormal behaviors and neuronal functions that are rescued by increasing GABAergic signaling

BACKGROUND

Phelan-McDermid syndrome (PMS) is a neurodevelopmental disorder characterized by developmental delay, intellectual disability, and autistic-like behaviors and is primarily caused by haploinsufficiency of SHANK3 gene. Currently, there is no specific treatment for PMS, highlighting the need for a better understanding of SHANK3 functions and the underlying pathophysiological mechanisms in the brain. We hypothesize that SHANK3 haploinsufficiency may lead to alterations in the inhibitory system, which could be linked to the excitatory/inhibitory imbalance observed in models of autism spectrum disorder (ASD). Investigation of these neuropathological features may shed light on the pathogenesis of PMS and potential therapeutic interventions.

METHODS

We recorded local field potentials and visual evoked responses in the visual cortex of Shank3∆11-/- mice. Then, to understand the impact of Shank3 in inhibitory neurons, we generated Pv-cre+/- Shank3Fl/Wt conditional mice, in which Shank3 was deleted in parvalbumin-positive neurons. We characterized the phenotype of this murine model and we compared this phenotype before and after ganaxolone administration.

RESULTS

We found, in the primary visual cortex, an alteration of the gain control of Shank3 KO compared with Wt mice, indicating a deficit of inhibition on pyramidal neurons. This alteration was rescued after the potentiation of GABAA receptor activity by Midazolam. Behavioral analysis showed an impairment in grooming, memory, and motor coordination of Pv-cre+/- Shank3Fl/Wt compared with Pv-cre+/- Shank3Wt/Wt mice. These deficits were rescued with ganaxolone, a positive modulator of GABAA receptors. Furthermore, we demonstrated that treatment with ganaxolone also ameliorated evocative memory deficits and repetitive behavior of Shank3 KO mice.

LIMITATIONS

Despite the significant findings of our study, some limitations remain. Firstly, the neurobiological mechanisms underlying the link between Shank3 deletion in PV neurons and behavioral alterations need further investigation. Additionally, the impact of Shank3 on other classes of inhibitory neurons requires further exploration. Finally, the pharmacological activity of ganaxolone needs further characterization to improve our understanding of its potential therapeutic effects.

CONCLUSIONS

Our study provides evidence that Shank3 deletion leads to an alteration in inhibitory feedback on cortical pyramidal neurons, resulting in cortical hyperexcitability and ASD-like behavioral problems. Specifically, cell type-specific deletion of Shank3 in PV neurons was associated with these behavioral deficits. Our findings suggest that ganaxolone may be a potential pharmacological approach for treating PMS, as it was able to rescue the behavioral deficits in Shank3 KO mice. Overall, our study highlights the importance of investigating the role of inhibitory neurons and potential therapeutic interventions in neurodevelopmental disorders such as PMS.

Shank3 Transgenic and Prenatal Zinc-Deficient Autism Mouse Models Show Convergent and Individual Alterations of Brain Structures in MRI

Research efforts over the past decades have unraveled both genetic and environmental factors, which contribute to the development of autism spectrum disorders (ASD). It is, to date, largely unknown how different underlying causes result in a common phenotype. However, the individual course of development and the different comorbidities might reflect the heterogeneous genetic and non-genetic contributions. Therefore, it is reasonable to identify commonalities and differences in models of these disorders at the different hierarchical levels of brain function, including genetics/environment, cellular/synaptic functions, brain regions, connectivity, and behavior. To that end, we investigated Shank3 transgenic mouse lines and compared them with a prenatal zinc-deficient (PZD) mouse model of ASD at the level of brain structural alterations in an 11,7 T small animal magnetic resonance imaging (MRI). Animals were measured at 4 and 9 weeks of age. We identified a decreased total brain volume (TBV) and hippocampal size of Shank3^−/− mice but a convergent increase of basal ganglia (striatum and globus pallidus) in most mouse lines. Moreover, Shank3 transgenic mice had smaller thalami, whereas PZD mice had this region enlarged. Intriguingly, Shank3 heterozygous knockout mice mostly showed minor abnormalities to full knockouts, which might reflect the importance of proper Shank3 dosage in neuronal cells. Most reported volume changes seemed to be more pronounced at younger age. Our results indicate both convergent and divergent brain region abnormalities in genetic and non-genetic models of ASD. These alterations of brain structures might be mirrored in the reported behavior of both models, which have not been assessed in this study.

Unbalanced chromosomal rearrangements in a metastasizing salivary gland tumor with benign histology

Benign metastasizing pleomorphic adenoma (BMPA) is a rare tumor of the salivary glands. Despite benign histopathologic features, it can metastasize and is sometimes lethal. No chromosomal data have been reported for this tumor type. We have by chromosome banding and fluorescence in situ hybridization analysis examined the short-term cultures of three skeletal metastases from a BMPA and identified two related hypodiploid clones: 44,XX,dic(3;22)(p11;q13) or der(3)t(3;22)(p11;q?) add(22)(q?),der(9;21)(q10;q10),der(13)t(1;13)(q11;p13)/45,XX,-3,der(9;21 ) (q10;q10),der(13)t(1;13)(q11; p13),?der(22)t(3;22)(q22;q13), +mar. The karyotypic features of this BMPA thus differ from the characteristic cytogenetic findings in pleomorphic adenomas and carcinomas ex pleomorphic adenoma.

Genomic PCR detects tumor cells in peripheral blood from patients with myxoid liposarcoma

Myxoid liposarcoma (MLS) is the most common subtype of liposarcoma. The cytogenetic hallmark of MLS is the pathognomonic t(12;16)(q13;p11), present in more than 85% of cases. The translocation leads to the fusion of the CHOP and FUS genes at 12q13 and 16p11, respectively, and the generation of a FUS/CHOP hybrid protein. The presence of a tumor-specific chimeric gene makes it possible to identify MLS cells by polymerase chain reaction (PCR). We have analyzed peripheral blood samples obtained during a 10-year period at diagnosis of primary and/or recurrent disease in 19 MLS patients with t(12;16) and in one MLS patient with t(12;22;20), resulting in the fusion of the CHOP and EWS genes. Nested PCR on genomic DNA from blood samples amplified FUS/CHOP hybrid fragments in three patients and EWS/CHOP in the patient with t(12;22;20). There was no obvious association between PCR findings and clinical outcome, but larger series are needed to draw any firm conclusions.

MR imaging of skeletal muscle hemangiomas. A report of 16 cases

PURPOSE

Our purpose was to evaluate how MR imaging depicts the vascular fibrofatty structure of hemangiomas.

MATERIAL AND METHODS

MR images of 16 histologically proven skeletal muscle hemangiomas were reviewed retrospectively in a nonblinded manner. One patient was examined at 0.5 T, 9 at 1.0 T, and 6 at 1.5 T, and the imaging protocols varied.

RESULTS

All lesions were lobulated/tubular. Signal characteristics of fat were seen in 13 lesions as lace-like thin septa within or around the tumor. All 16 studies exhibited a hyperintense signal on T2-weighted spin-echo (SE) (n=15) or T1-weighted fast fat suppressed inversion recovery SE images (n=1). Postcontrast images showed marked signal enhancement in parts of the areas, both of high and low T2-weighted signal. Surgical staging based on MR images was correct in all lesions.

CONCLUSION

MR images display the characteristic vascular fibrofatty structure of hemangiomas and may allow correct diagnosis.

Cytogenetic findings in malignant peripheral nerve sheath tumors

Clonal chromosome aberrations were detected in 8 short-term cultured malignant peripheral nerve sheath tumors (MPNST). Seven had a near-triploid chromosome number and I was in the hyperhaploid-hypodiploid range. No recurrent structural rearrangements were found; the bands most frequently involved (3 tumors) were 7p11, 12p13 and 14q11. The most common numerical changes were loss of a sex chromosome (all tumors) and loss of at least 1 copy of chromosomes 8, 16 and 22 (4 tumors). Pooling our data with those on the 20 previously published MPNST with abnormal karyotypes, we found that the chromosome number has often been in the triploid range (12 tumors), with stem line variation between 34 and 270. All chromosome arms, except 22p and the Y chromosome, were involved in recombinations. The most frequently rearranged bands were 7p22 (6 tumors) and 1p21, 7p11 and 14q11 (5 tumors each). Most numerical and unbalanced structural aberrations have led to loss of genetic material, in particular from Xq26-qter (13 tumors); 11q22-qter and 13p (12 tumors); 9p22-pter, 11p13-pter, 17p and 17q11-21 (11 tumors); 1p22-32 and 1p34-pter (10 tumors) and 6q25-qter and chromosome 16 (9 tumors).

Chromosome aberrations in tenosynovial giant cell tumors and nontumorous synovial tissue

Five tenosynovial giant cell tumors--4 pigmented villonodular synovitis (PVNS) and 1 nodular tenosynovitis (NTS)--were investigated cytogenetically. Clonal chromosome aberrations were detected in 3 of them. One PVNS had t(7;16)(q22;q24) as the sole anomaly, whereas 1 PVNS and the NTS displayed aberrations suggesting clonal evolution: t(1;19)(p11;p12)/t(1;19), +12 and ins(5;1)(q31p34)/ins(5;1),t(2;4)(p23;q21), respectively. Including our 3 cases, a total of 6 tenosynovial giant cell tumors with karyotypic changes have been reported. Apart from 2 PVNS with trisomies 5 and 7, and 2 NTS with rearrangement of chromosome band 1p13, no recurrent chromosome change has been detected. Although the detection of clonal, acquired chromosome abnormalities has formerly generally been accepted as sufficient to conclude that a lesion is neoplastic, the interpretation of the pathogenetic significance of the karyotypic aberrations in synovial tumors is obscured by the fact that we have also detected comparable aberrations in obviously nonneoplastic synovial tissue. One of 2 lesions from patients with hemorrhagic synovitis carried a clonal del(13)(q12q21), and 2 of 4 synovectomy samples from patients with rheumatoid arthritis displayed -Y and -Y together with +7. The available cytogenetic data therefore cannot be used to resolve the controversy as to whether tenosynovial giant cell tumors are truly neoplastic or only reactive, inflammatory proliferations.