Aminopeptidase O Protein mediates the association between Lachnospiraceae and appendicular lean mass

Objective

Investigating the causal relationship between Lachnospiraceae and Appendicular lean mass (ALM) and identifying and quantifying the role of Aminopeptidase O Protein (AOPEP) as a potential mediator.

Methods

The summary statistics data of gut microbiota composition from the largest available genome-wide association study (GWAS) meta-analysis conducted by the MiBioGen Consortium (n = 13,266). Appendicular lean mass data were obtained from the UK-Biobank (n = 450,243). We conducted bidirectional two-sample Mendelian randomization (MR) analysis using summary-level data from GWAS to investigate the causal relationship between Lachnospiraceae and ALM. Additionally, we employed a drug-targeted MR approach to assess the causal relationship between AOPEP and ALM. Finally, a two-step MR was employed to quantitatively estimate the proportion of the effect of Lachnospiraceae on ALM that is mediated by AOPEP. Cochran's Q statistic was used to quantify heterogeneity among instrumental variable estimates.

Results

In the MR analysis, it was found that an increase in genetically predicted Lachnospiraceae [OR = 1.031, 95% CI (1.011-1.051), P = 0.002] is associated with an increase in ALM. There is no strong evidence to suggest that genetically predicted ALM has an impact on Lachnospiraceae genus [OR = 1.437, 95% CI (0.785-2.269), P = 0.239]. The proportion of genetically predicted Lachnospiraceae mediated by AOPEP was 34.2% [95% CI (1.3%-67.1%)].

Conclusion

Our research reveals that increasing Lachnospiraceae abundance in the gut can directly enhance limb muscle mass and concurrently suppress AOPEP, consequently mitigating limb muscle loss. This supports the potential therapeutic modulation of gut microbiota for sarcopenia. Interventions such as drug treatments or microbiota transplantation, aimed at elevating Lachnospiraceae abundance and AOPEP inhibition, synergistically improve sarcopenia in the elderly, thereby enhancing the overall quality of life for older individuals.

Mutation screening of AOPEP variants in a large dystonia cohort

STUDY OBJECTIVES

Recently, AOPEP has been identified to be a novel causative gene of autosomal-recessive dystonia. However, no large cohort study has been conducted to confirm the association. We aimed to systematically evaluate the genetic associations of AOPEP with dystonia in a large Chinese dystonia cohort.

METHODS

We analyzed rare variants of AOPEP in 878 dystonia patients with whole-exome sequencing. The over-representation of rare variants in patients was examined with Fisher's exact test at allele and gene levels.

RESULTS

Among the 878 patients with dystonia, we found two patients with biallelic likely pathogenic variants in the AOPEP gene. One patient carried putative compound heterozygous variants (p.A212D and p.G216R) and presented with childhood-onset segmental dystonia involving the upper limbs and craniocervical muscles accompanied by myoclonus of the dystonia affected areas. One patient carried homozygote of p.M291Nfs*68 and presented with adult-onset isolated cervical dystonia. Another 15 patients were identified to carry heterozygous rare variants in AOPEP, including 2 loss-of-function variants (p.M291Nfs*68 and p.R493X) and 6 missense variants. One loss-of-function variant (p.R493X) was the same as previously reported. Nearly, all of the 15 patients carrying heterozygous variants in AOPEP presented with isolated dystonia with only craniocervical muscles affected, except for one patient who carried the p.R493X variant presented with segmental dystonia affecting the neck and right upper limb combined with parkinsonism. Gene-based burden analysis detected enrichment of rare variants and rare damaging variants of AOPEP in dystonia.

CONCLUSIONS

Our study supplemented the evidence on the role of AOPEP in autosomal-recessive dystonia in Chinese population, and expanded the genotypic and phenotypic spectrum of AOPEP.

Biallelic AOPEP Loss-of-Function Variants Cause Progressive Dystonia with Prominent Limb Involvement

BACKGROUND

Monogenic causes of isolated dystonia are heterogeneous. Assembling cohorts of affected individuals sufficiently large to establish new gene-disease relationships can be challenging.

OBJECTIVE

We sought to expand the catalogue of monogenic etiologies for isolated dystonia.

METHODS

After the discovery of a candidate variant in a multicenter exome-sequenced cohort of affected individuals with dystonia, we queried online platforms and genomic data repositories worldwide to identify subjects with matching genotypic profiles.

RESULTS

Seven different biallelic loss-of-function variants in AOPEP were detected in five probands from four unrelated families with strongly overlapping phenotypes. In one proband, we observed a homozygous nonsense variant (c.1477C>T [p.Arg493*]). A second proband harbored compound heterozygous nonsense variants (c.763C>T [p.Arg255*]; c.777G>A [p.Trp259*]), whereas a third proband possessed a frameshift variant (c.696_697delAG [p.Ala234Serfs*5]) in trans with a splice-disrupting alteration (c.2041-1G>A). Two probands (siblings) from a fourth family shared compound heterozygous frameshift alleles (c.1215delT [p.Val406Cysfs*14]; c.1744delA [p.Met582Cysfs*6]). All variants were rare and expected to result in truncated proteins devoid of functionally important amino acid sequence. AOPEP, widely expressed in developing and adult human brain, encodes a zinc-dependent aminopeptidase, a member of a class of proteolytic enzymes implicated in synaptogenesis and neural maintenance. The probands presented with disabling progressive dystonia predominantly affecting upper and lower extremities, with variable involvement of craniocervical muscles. Dystonia was unaccompanied by any additional symptoms in three families, whereas the fourth family presented co-occurring late-onset parkinsonism.

CONCLUSIONS

Our findings suggest a likely causative role of predicted inactivating biallelic AOPEP variants in cases of autosomal recessive dystonia. Additional studies are warranted to understand the pathophysiology associated with loss-of-function variation in AOPEP. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.