Characteristics of PPT1 and TPP1 enzymes in neuronal ceroid lipofuscinosis (NCL) 1 and 2 by dried blood spots (DBS) and leukocytes and their application to newborn screening

Mol Genet Metab. 2018 May;124(1):64-70. doi: 10.1016/j.ymgme.2018.03.007. Epub 2018 Mar 19.

Abstract

We first characterized PPT1 and TPP1 enzymes in dried blood spots (DBS), plasma/serum, and leukocytes/lymphocytes using neuronal ceroid lipofuscinosis (NCL) 1 and 2 patients and control subjects. PPT1 enzyme had only one acid form in control DBS, plasma/serum, and leukocytes/lymphocytes and showed deficient activities in these samples from NCL 1 patients. Conversely, TPP1 enzymes in control DBS and leukocytes/lymphocytes consisted of two forms, an acidic form and a neutral form, whereas serum TPP1 enzyme had only a neutral form. In control subjects, the optimal pH of PPT1 enzyme in DBS, plasma/serum, and leukocytes/lymphocytes was 4.5 to 5.0 in the acidic form, whereas TPP1 enzyme in control DBS and leukocytes/lymphocytes was pH 4.5 and 6.5, respectively. In NCL 1 and 2, both PPT1 and TPP1 enzyme activities in DBS, plasma, and leukocytes/lymphocytes were markedly reduced in acidic pH, whereas heterozygotes of NCL 1 and 2 in the acidic form showed intermediate activities between patients and control subjects. In neutral conditions, pH 6.0, the PPT1 enzyme activities in NCL 1 patients showed rather higher residual activities and intermediate activities in heterozygotes in NCL 1, which was probably caused by mutated proteins in three cases with NCL 1 patients. TPP1 enzyme activities at neutral pH 6.5 to 7.0 in DBS and leukocytes/lymphocytes showed higher enzyme activities in NCL 2 patients and heterozygotes. The reason for the increases of neutral TPP1 enzyme activities at pH 6.5 to 7.0 in NCL 2 DBS and leukocytes/lymphocytes, is obscure, but possibly caused by secondary activation of neutral TPP1 enzyme due to the absence of the acidic form. Interestingly, TPP1 activity in serum only consisted of a neutral form, no acidic form, and was not deficient in any NCL 2 patient. Therefore, we can diagnose NCL 1 patients by plasma/serum enzyme assay of PPT1, but not diagnose NCL 2 by serum TPP1 enzyme assay. A pilot study of newborn screening of NCL 1 and 2 has been established by more than 1000 newborn DBS assays. Using this assay system, we will be able to perform newborn screening of NCL 1 and 2 by DBS.

Keywords: NCL1; NCL2; Newborn screening; PPT1; TPP1; pH optimum.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aminopeptidases / blood*
  • Child
  • Child, Preschool
  • Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / blood*
  • Dried Blood Spot Testing / methods
  • Female
  • Humans
  • Hydrogen-Ion Concentration
  • Infant, Newborn
  • Leukocytes / chemistry*
  • Male
  • Membrane Proteins / blood*
  • Mutation
  • Neonatal Screening / methods*
  • Neuronal Ceroid-Lipofuscinoses / diagnosis*
  • Pilot Projects
  • Serine Proteases / blood*
  • Thiolester Hydrolases / blood*
  • Tripeptidyl-Peptidase 1

Substances

  • Membrane Proteins
  • Tripeptidyl-Peptidase 1
  • Thiolester Hydrolases
  • PPT1 protein, human
  • Serine Proteases
  • Aminopeptidases
  • Dipeptidyl-Peptidases and Tripeptidyl-Peptidases
  • TPP1 protein, human

Supplementary concepts

  • Ceroid Lipofuscinosis, Neuronal, 1
  • Ceroid Lipofuscinosis, Neuronal, 2