Effects of prelamin A processing inhibitors on the differentiation and activity of human osteoclasts

Osteoclast differentiation is a complex process involving cytoskeleton and nuclear reorganization. Osteoclasts regulate bone homeostasis and have a key role in bone degenerative processes. Osteolysis and osteoporosis characterize a subset of laminopathies, inherited disorders due to defects in lamin A/C. Laminopathies featuring bone resorption are characterized, at the molecular level, by anomalous accumulation of the unprocessed lamin A precursor, called prelamin A. To obtain a suitable cell model to study prelamin A effects on osteoclasts, prelamin A processing inhibitors FTI-277 or AFCMe were applied to peripheral blood monocytes induced to differentiate towards the osteoclastic lineage. Previous studies have shown that treatment with FTI-277 causes accumulation of non-farnesylated prelamin A, while AFCMe inhibition of prelamin A maturation causes accumulation of a farnesylated form. We demonstrate that monocytes subjected to FTI-277 treatment and mostly those subjected to AFCMe administration, differentiate towards the osteoclastic lineage more efficiently than untreated monocytes, in terms of number of multinucleated giant cells, mRNA expression of osteoclast-related genes and TRACP 5b activity. On the other hand, the bone resorption activity of osteoclasts obtained in the presence of high prelamin A levels is lower with respect to control osteoclasts. This finding may help the understanding of the osteolytic and osteoporotic processes that characterize progeroid laminopathies.