COL6A3 and chronic obstructive pulmonary disease: COPD patients with osteoporosis display a higher expression of COL6A3 and a lower bronchial epithelial expression of PHEX. Collagen Type VI Alpha 3 Chain (COL6A3), one of three alpha-chains that together form the Collagen VI monomer, is an important extracellular matrix protein [10–12].