Expression and activity of l-isoaspartyl methyltransferase decrease in stage progression of human astrocytic tumors

Area of Science:

• Biochemistry
• Neuro-oncology
• Molecular Biology

Background:

• Protein repair enzyme PIMT (protein l-isoaspartyl methyltransferase) activity is reduced in epilepsy.
• Astrocytic tumors are the most common primary brain tumors.
• Understanding PIMT regulation in brain tumors is crucial for therapeutic strategies.

Purpose of the Study:

• To investigate the regulation and expression of PIMT in human astrocytic tumors.
• To correlate PIMT levels with tumor grade and neuronal markers.
• To explore PIMT's role in brain tumor progression.

Main Methods:

• Quantitative analysis of PIMT expression and enzyme activity in human astrocytic tumors across all grades.
• RT-PCR to analyze PIMT mRNA variants (Type I and Type II).
• Measurement of neuron-specific enolase (NSE) to assess neuronal cell numbers.
• Orthotopic rat brain tumor model for in vivo validation.

Main Results:

• PIMT expression and activity were significantly decreased in all grades of astrocytic tumors compared to normal brain tissue.
• PIMT levels showed a marked reduction, ranging from 46% to 80%, correlating with increasing tumor grade.
• Down-regulation of type II PIMT mRNA and accumulation of abnormal aspartyl residues were observed in glioblastomas.

Conclusions:

• PIMT expression and activity are significantly reduced during the progression of human astrocytic tumors.
• Reduced PIMT levels correlate with decreased neuronal cell numbers in these tumors.
• These findings highlight PIMT as a potential biomarker and therapeutic target in astrocytic brain tumors.