Osteoclast-specific Plastin 3 knockout in mice fail to develop osteoporosis despite dramatic increased osteoclast resorption activity.

PLS3 loss-of-function mutations in humans and mice cause X-linked primary osteoporosis. However, it remains largely unknown how PLS3 mutations cause osteoporosis and which function PLS3 plays in bone homeostasis. A recent study showed that ubiquitous Pls3 KO in mice results in osteoporosis. Mainly osteoclasts were impacted in their function However, it has not been proven if osteoclasts are the major cell type affected and responsible for osteoporosis development in ubiquitous Pls3 KO mice. Here, we generated osteoclast-specific Pls3 KO mice. Additionally, we developed a novel polyclonal PLS3 antibody that showed specific PLS3 loss in immunofluorescence staining of osteoclasts in contrast to previously available antibodies against PLS3, which failed to show PLS3 specificity in mouse cells. Moreover, we demonstrate that osteoclast-specific Pls3 KO causes dramatic increase in resorptive activity of osteoclasts in vitro. Despite these findings, osteoclast-specific Pls3 KO in vivo failed to cause any osteoporotic phenotype in mice as proven by micro-CT and three-point bending test. This demonstrates that the pathomechanism of PLS3-associated osteoporosis is highly complex and cannot be reproduced in a system singularly focused on one cell type. Thus, the loss of PLS3 in alternative bone cell types might contributes to the osteoporosis phenotype in ubiquitous Pls3 KO mice.

De Novo and Inherited Variants in GBF1 are Associated with Axonal Neuropathy Caused by Golgi Fragmentation.

Distal hereditary motor neuropathies (HMNs) and axonal Charcot-Marie-Tooth neuropathy (CMT2) are clinically and genetically heterogeneous diseases characterized primarily by motor neuron degeneration and distal weakness. The genetic cause for about half of the individuals affected by HMN/CMT2 remains unknown. Here, we report the identification of pathogenic variants in GBF1 (Golgi brefeldin A-resistant guanine nucleotide exchange factor 1) in four unrelated families with individuals affected by sporadic or dominant HMN/CMT2. Genomic sequencing analyses in seven affected individuals uncovered four distinct heterozygous GBF1 variants, two of which occurred de novo. Other known HMN/CMT2-implicated genes were excluded. Affected individuals show HMN/CMT2 with slowly progressive distal muscle weakness and musculoskeletal deformities. Electrophysiological studies confirmed axonal damage with chronic neurogenic changes. Three individuals had additional distal sensory loss. GBF1 encodes a guanine-nucleotide exchange factor that facilitates the activation of members of the ARF (ADP-ribosylation factor) family of small GTPases. GBF1 is mainly involved in the formation of coatomer protein complex (COPI) vesicles, maintenance and function of the Golgi apparatus, and mitochondria migration and positioning. We demonstrate that GBF1 is present in mouse spinal cord and muscle tissues and is particularly abundant in neuropathologically relevant sites, such as the motor neuron and the growth cone. Consistent with the described role of GBF1 in Golgi function and maintenance, we observed marked increase in Golgi fragmentation in primary fibroblasts derived from all affected individuals in this study. Our results not only reinforce the existing link between Golgi fragmentation and neurodegeneration but also demonstrate that pathogenic variants in GBF1 are associated with HMN/CMT2.