Regulation of intracellular Ca2+/CaMKII signaling by TRPV4 membrane translocation during osteoblastic differentiation

TRPV4 Activator-Containing CMT-Hy Hydrogel Enhances Bone Tissue Regeneration In Vivo by Enhancing Mitochondrial Health

Treating different types of bone defects is difficult, complicated, time-consuming, and expensive. Here, we demonstrate that transient receptor potential cation channel subfamily V member 4 (TRPV4), a mechanosensitive, thermogated, and nonselective cation channel, is endogenously present in the mesenchymal stem cells (MSCs). TRPV4 regulates both cytosolic Ca2+ levels and mitochondrial health. Accordingly, the hydrogel made from a natural modified biopolymer carboxymethyl tamarind CMT-Hy and encapsulated with TRPV4-modulatory agents affects different parameters of MSCs, such as cell morphology, focal adhesion points, intracellular Ca2+, and reactive oxygen species- and NO-levels. TRPV4 also regulates cell differentiation and biomineralization in vitro. We demonstrate that 4α-10-CMT-Hy and 4α-50-CMT-Hy (the hydrogel encapsulated with 4αPDD, 10 and 50 nM, TRPV4 activator) surfaces upregulate mitochondrial health, i.e., an increase in ATP- and cardiolipin-levels, and improve the mitochondrial membrane potential. The same scaffold turned out to be nontoxic in vivo. 4α-50-CMT-Hy enhances the repair of the bone-drill hole in rat femur, both qualitatively and quantitatively in vivo. We conclude that 4α-50-CMT-Hy as a scaffold is suitable for treating large-scale bone defects at low cost and can be tested for clinical trials.

TRPV4 regulates osteoblast differentiation and mitochondrial function that are relevant for channelopathy

Different ion channels present in the osteoblast regulate the cellular functions including bio-mineralization, a process that is a highly stochastic event. Cellular events and molecular signaling involved in such process is poorly understood. Here we demonstrate that TRPV4, a mechanosensitive ion channel is endogenously present in an osteoblast cell line (MC3T3-E1) and in primary osteoblasts. Pharmacological activation of TRPV4 enhanced intracellular Ca²⁺-level, expression of osteoblast-specific genes and caused increased bio-mineralization. TRPV4 activation also affects mitochondrial Ca²⁺-levels and mitochondrial metabolisms. We further demonstrate that different point mutants of TRPV4 induce different mitochondrial morphology and have different levels of mitochondrial translocation, collectively suggesting that TRPV4-mutation-induced bone disorders and other channelopathies are mostly due to mitochondrial abnormalities. These findings may have broad biomedical implications.

Hydrogel cultures reveal Transient Receptor Potential Vanilloid 4 regulation of myofibroblast activation and proliferation in valvular interstitial cells

As aortic valve stenosis develops, valve tissue becomes stiffer. In response to this change in environmental mechanical stiffness, valvular interstitial cells (VICs) activate into myofibroblasts. We aimed to investigate the role of mechanosensitive calcium channel Transient Receptor Potential Vanilloid type 4 (TRPV4) in stiffness induced myofibroblast activation. We verified TRPV4 functionality in VICs using live calcium imaging during application of small molecule modulators of TRPV4 activity. We designed hydrogel biomaterials that mimic mechanical features of healthy or diseased valve tissue microenvironments, respectively, to investigate the role of TRPV4 in myofibroblast activation and proliferation. Our results show that TRPV4 regulates VIC proliferation in a microenvironment stiffness-independent manner. While there was a trend toward inhibiting myofibroblast activation on soft microenvironments during TRPV4 inhibition, we observed near complete deactivation of myofibroblasts on stiff microenvironments. We further identified Yes-activated protein (YAP) as a downstream target for TRPV4 activity on stiff microenvironments. Mechanosensitive TRPV4 channels regulate VIC myofibroblast activation, whereas proliferation regulation is independent of the microenvironmental stiffness. Collectively, the data suggests differential regulation of stiffness-induced proliferation and myofibroblast activation. Our data further suggest a regulatory role for TRPV4 regarding YAP nuclear localization. TRPV4 is an important regulator for VIC myofibroblast activation, which is linked to the initiation of valve fibrosis. Although more validation studies are necessary, we suggest TRPV4 as a promising pharmaceutical target to slow aortic valve stenosis progression.