Genetic analysis of Pycr1 and Pycr2 in mice.

Area of Science:

• Biochemistry and Genetics
• Molecular Biology
• Metabolic Disorders

Background:

• Proline biosynthesis is crucial, catalyzed by pyrroline-5-carboxylate reductases (PYCR1, PYCR2, PYCR3).
• Mutations in human PYCR1 and ALDH18A1 cause Cutis Laxa (CL); PYCR2 mutations cause hypomyelinating leukodystrophy 10 (HLD10).
• Understanding the in vivo function and redundancy of PYCR1 and PYCR2 is essential for disease modeling.

Purpose of the Study:

• To investigate the genetic basis and in vivo function of Pycr1 and Pycr2 in mice.
• To characterize the phenotypes associated with loss-of-function mutations in Pycr1 and Pycr2.
• To assess the functional redundancy between Pycr1 and Pycr2 in proline biosynthesis.

Main Methods:

• Generated and analyzed mice with a null allele of Pycr1 and a chemically-induced mutation in Pycr2.
• Phenotypic characterization of single and Pycr1; Pycr2 double mutant mice, including neurological, metabolic, and integumentary assessments.
• In vitro enzymatic assays using yeast complementation and analysis of proline levels in mutant mice and cell cultures.

Main Results:

• Pycr1 null mice showed no CL-related phenotypes.
• Pycr2 loss-of-function mutants exhibited neurological and neuromuscular defects, including weight loss and kyphosis, with altered lipid metabolism and reduced white blood cell counts.
• Pycr1; Pycr2 double mutants were sub-viable, indicating significant functional redundancy; proline deficiency exacerbated phenotypes, suggesting proline becomes semi-essential.

Conclusions:

• Pycr1 and Pycr2 exhibit functional redundancy in proline biosynthesis in mice.
• Loss of Pycr2 leads to severe metabolic and neurological disorders, partially mimicking CL and HLD10.
• These findings provide a valuable mouse model for studying CL and HLD10 and highlight proline's semi-essential nature upon PYCR loss.