Microtubules form important cytoskeletal structures that play a role in establishing and maintaining neuronal polarity, regulating neuronal morphology, transporting cargo, and scaffolding signaling molecules to form signaling hubs. Within a neuronal cell, microtubules are found to have variable lengths and can be both stable and dynamic. Microtubule associated proteins, post-translational modifications of tubulin subunits, microtubule severing enzymes, and signaling molecules are all known to influence both stable and dynamic pools of microtubules. Microtubule dynamics, the process of interconversion between stable and dynamic pools, and the proportions of these two pools have the potential to influence a wide variety of cellular processes. Reduced microtubule stability has been observed in several neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic Lateral Sclerosis (ALS), and tauopathies like Progressive Supranuclear Palsy. Hyperstable microtubules, as seen in Hereditary Spastic Paraplegia (HSP), also lead to neurodegeneration. Therefore, the ratio of stable and dynamic microtubules is likely to be important for neuronal function and perturbation in microtubule dynamics might contribute to disease progression.

We studied the effect of metal mixture (MM), comprising As, Cd, and Pb, in developing female rat skeleton from gestation day 5 until postnatal day 60 (P-60). MM resulted in synergistic inhibition in viability and differentiation of osteoblasts in vitro, likely induced by reactive oxygen species. MM, administered at their most frequently occurring concentrations present in the groundwater of India, i.e., As: 0.38 ppm, Pb: 0.22 ppm, and Cd: 0.098 ppm or 10× of the ratio to developing rats, exhibited a synergistic decrease in ex vivo mineralization of bone marrow stromal (osteoprogenitor) cells. MM group showed a dose-dependent attenuation in weight and axial lengths and shortening of tibias at P-60. Furthermore, the growth plate was shortened, which was associated with shorter proliferative and hypertrophic zones, decreased parathyroid hormone-related protein and Indian hedgehog expression in the chondrocytes, reduced primary and secondary spongiosa, and hypomineralized osteoids-a major characteristic of osteomalacia. In addition, compared with the control, MM-treated rats were clearly osteopenic based on bone mineral density, microarchitecture, biomechanical strength, and particularly the biochemical profile, that suggested high turnover bone loss. Finally, in comparison to the control, the fracture-healing ability of MM group was delayed and accompanied by inferior quality of the healed bone. Together, these data demonstrated that the mixture of As, Cd, and Pb induced synergistic toxicity to developing skeleton, thereby diminishing modeling-directed bone accrual, inducing osteopenia and dampening fracture healing.