Biology of Exosomes

Transfer of biologically active molecules between cells can be mediated by exosomes that are small membrane bound vesicles that are secreted by all cells. Exosomes, part of a class of extracellular vesicles, carry in their membranes and central core, immuno-relevant cargo. Here we explore the transfer of transmembrane ion channels via exosomes to lung immune cells lacking a class of ion channels that are important in fighting infection.

Macrophages and Innate Immunity

Macrophages stand as the sentinels in the lung, fighting bacterial infections as are present in the CF lung.  They facilitate the efficient killing of invading bacterial pathogens and remove cells that have undergone programmed cell death.  In carrying out these essential functions, phagocytes, including lung macrophages, utilize a select population of ion transport proteins that are expressed in intracellular organelles.  Organellar transport proteins control the microbicidal ionic composition of the phagosomes which hold the ingested captured bacteria inside the cell. A critical transport protein which is defective in CF, the chloride ion channel CFTR, renders the lung macrophage unable to carry out its task in killing internalized bacteria.

Mechanism of Bone formation

Live bone differs from other connective tissues, including cartilage, in that it is bounded by an active osteoblast layer allowing the bone to create dense lamellar type I collagen, regulate pH and mineral deposition, and regulate water content for an extremely compact and strong structure. Many features of the osteoblast environment are not well described and are only becoming appreciated with high resolution microscopy on bone explants and osteoblasts differentiated in culture. Only osteoblasts make bone. Osteoblasts deposit matrix proteins composed of ~ 99% type I collagen.  Into this organic matrix, mineral is deposited with removal of protons produced by hydroxyapatite production; the matrix matures from amorphous to crystalline hydroxyapatite. A major barrier to progress in bone biology, especially treatment of bone loss due to aging in traumatic injury to bone, is the lack of understanding of the key mechanisms for the formation and mineralization of bone matrix. This is critical to maintenance of bone mass and for the prevention of osteoporosis. Mineral deposition yields acid, and occurs in an isolated compartment. Thus, osteoblasts must remove the acid created by mineral deposition.  -Our work supports this premise strongly and includes demonstration that bone matrix pH varies independently of extracellular fluid pH, although gaps in understanding persist.  We study osteoblast membrane preparations and living bone explants using two photon microscopy to identify the transport proteins and ion channels in the maintenance of bone mass and the healing of traumatic bone injury.