High-density Lipoprotein Metabolism (3) In addition, apolipoproteins are shuttled between HDL and the triglyceride-rich lipoproteins in response to metabolic needs. Thus, the nascent triglyceride-rich lipoproteins acquire apo CII from HDL to form mature triglyceride-rich lipoproteins. Following LPL-mediated hydrolysis of triglycerides, apo CII, which is no longer required by the remnant lipoprotein, transfers back to HDL, which then donates the apo E required for hepatic remnant uptake (Fig. 6.9).