Disruption of Dhcr7 and Insig1/2 in cholesterol metabolism causes defects in bone formation and homeostasis through primary cilium formation

Abstract

Human linkage studies suggest that craniofacial deformities result from either genetic mutations related to cholesterol metabolism or high-cholesterol maternal diets. However, little is known about the precise roles of intracellular cholesterol metabolism in the development of craniofacial bones, the majority of which are formed through intramembranous ossification. Here, we show that an altered cholesterol metabolic status results in abnormal osteogenesis through dysregulation of primary cilium formation during bone formation. We found that cholesterol metabolic aberrations, induced through disruption of either Dhcr7 (which encodes an enzyme involved in cholesterol synthesis) or Insig1 and Insig2 (which provide a negative feedback mechanism for cholesterol biosynthesis), result in osteoblast differentiation abnormalities. Notably, the primary cilia responsible for sensing extracellular cues were altered in number and length through dysregulated ciliary vesicle fusion in Dhcr7 and Insig1/2 mutant osteoblasts. As a consequence, WNT/β-catenin and hedgehog signaling activities were altered through dysregulated primary cilium formation. Strikingly, the normalization of defective cholesterol metabolism by simvastatin, a drug used in the treatment of cholesterol metabolic aberrations, rescued the abnormalities in both ciliogenesis and osteogenesis in vitro and in vivo. Thus, our results indicate that proper intracellular cholesterol status is crucial for primary cilium formation during skull formation and homeostasis.Bone Research (2020) 8:1; https://doi.

Renal Ciliopathies: Sorting Out Therapeutic Approaches for Nephronophthisis

“…In addition to its classical well-established functions, cholesterol is enriched in the ciliary membrane and was revealed to play an important role in ciliogenesis ( Maerz et al, 2019 ) as well as in Hh signaling as a direct modulator of SMO activity ( Kong et al, 2019 ). Interestingly, and in agreement with those observations, mutations in genes encoding actors of the cholesterol biosynthesis pathway were associated with skeletal disorders ( Suzuki et al, 2020 ) resembling those associated with mutations in IFT-A subunit encoding genes (see introduction). Statins were shown to improve CKD in various animal models ( Ecder, 2016 ) and were also shown to improve renal function in the Cy/Anks6/Nphp16 rat model, likely through an effect on the renin-angiotensin system ( Gile et al, 1995 ; Zafar et al, 2007 ).…”

Inhibition of the Growth of Breast Cancer-Associated Brain Tumors by the Osteocyte-Derived Conditioned Medium

“…CM was prepared from MLO-A5 osteocytes and astrocytes at ~80% confluence after 24 h incubation and an Amicon filter unit with a cutoff mass at 3 kDa (Sigma-Aldrich, St. Louis, MO, USA) was used to remove microparticles and condense it by 10-fold. Cellular proliferation was examined using an MTT assay, and a wound-healing scratch assay and a Transwell invasion assay were conducted to evaluate cell motility and invasion capability, respectively, using the procedure previously described [ 48 ].…”

Targeting mitochondrial dysfunction with small molecules in intervertebral disc aging and degeneration

“…Conversely, either cyclosporine A (CsA), a mitophagy inhibitor, or parkin knockdown blunts the protective effects of melatonin [ 115 ]. Melatonin also showed the ability to prevent NLRP3 inflammasome priming and activation and inhibited IL-1β secretion [ 116 ]. In vitro IL-1β stimulation of NP cells increased the expression of NLRP3 and P20 and the level of mtROS and upregulated NF-κB signaling while the expression of SOD 2 decreased.…”

“…Melatonin treatment, on the other hand, reduced the NP cells’ inflammatory response via disturbing NLRP3/IL-1β-positive loop, downregulation of NF-κB, and enhancing the anti-oxidant activity of mitochondria. In in vivo evaluations on AF-punctured rat models, melatonin treatment demonstrated the upper expression of collagen II and aggrecan and lower level of NLRP3, P20, and IL-1β in comparison to melatonin+ LPS (NLRP3 inflammasome activator) injection, indicating the anti-degenerative and anti-inflammatory response of melatonin against NLRP3 inflammasome priming and activation [ 116 ].…”